# Lifestyles & Discussion > Freedom Living >  Alternative Energy Projects

## buenijo

I found a great site that links to many different alternative energy projects: http://www.builditsolar.com/Projects/Projects.htm. 

If you come across sites similar to this, then please post links. It would be nice to consolidate such information here. I'll post links to other sites as I find them.

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## buenijo

www.aquaflector.com (from the link on the previous post) - This is very similar to an idea I had a while back. Inexpensive reflectors are configured such that a single cable under tension will move them over the operating range. This allows simple counterweights to track the system automatically. Here is how the operation is described on the site: "At the end of each row is a floating counterweight which is suspended in a liquid in a container. Each container is plumbed together, so that all the containers maintain identical liquid levels. The last control system is connected to a computer controlled pump. This pump sets the liquid level for all the floats, and thus every floating counter weight will be at exactly the same height. By doing this, large reflective areas can be controlled very economically. It's unbelievably simple. 1 pump could conceivably control 1000's of mirrors and gravity keeps everything aligned with just simple plumbing. Just basic physics!" 

MY IDEA: Get rid of the computer controlled pump. It's possible to drain water from an elevated tank into the float vessel... or, operate a small pump at a constant flow rate. Try to visualize the following to understand a way to precisely control the tracking of the system mechanically. Imagine that water flows into the vessels at a constant rate. Now, the smaller the cross section of the float vessel, the faster the water level rises (for a constant water flow rate which would be the case for a highly elevated water tank). We can progressively change the effective cross section of the float vessel (and the rate at which the fluid level rises) by adding a separate vessel (let's call it the "calibration vessel"). Objects of a proper size and shape are placed within the calibration vessel to do this (only because this is simpler than using a vessel with a complicated conical shape). The system can be calibrated by a combination of mechanical leverage on the linkage, water flow rate into each vessel, and by properly sizing the calibration vessel and placing objects of an appropriate size and shape within. Furthermore, it is possible to connect one such "calibration vessel" to multiple independent but identical systems to vary the tracking rate in a controlled manner. This will be useful for more precise tracking when using a simple lever to rotate the reflectors. Basically, since the length of the lever arm varies slightly over the tracking angle, the calibration vessel can assure a constant angular tracking rate, and do so for a very large number of concentrators. Just use a timer to pump the water back to a storage tank at the end of each day, then start the pump at the same time each day.

Another approach is an active tracking system using either mechanical or electro-mechanical controls (like a soleoid valve) to control water flow to the vessels. This system would not use a calibration vessel. A mechanical approach could place a tube filled with oil at the leading edge of the concentrator target. When the concentrated sunlight hits it, it would expand the oil and force the oil through a capillary tube to a small hydraulic actuator to throttle open a water valve. A small PV panel used to actuate a relay switch for a solenoid valve would work too. Bottom line is I hate the idea of using computer controls when it's not necessary.

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## buenijo

Here's a site for purchasing industrial forklift batteries. http://gbindustrialbattery.com/Forkl...ns_Zone15.html I have heard from many independent sources that forklift batteries are the best choice for off grid batteries. Make sure to review the link on the battery capacity ratings. They are based on 80% depth of discharge, which is excessive. This should be at least cut in half to greatly extend the life of the battery. Still, that single large 12 volt battery at 1182 amp hours will provide 7 kwh of at 40% depth of discharge (pretty damn good if you ask me). Yeah, but it costs $1745 (but includes delivery)! Batteries are expensive, period. This is a primary reason why I believe a small back up generator for battery charging is superior to purchasing an enormous battery system designed to take a home through several days of inclimate weather.

http://gbindustrialbattery.com/Forkl...ns_Zone15.html

Accounts of using a forklift battery w/off grid home:

http://www.power-talk.net/forklift-batteries.html

"Forklift batteries used in solar setups or similar applications where the depth of discharge is not as severe can last 25 years or more."
http://www.forklift-battery-charger....t-charging.php

ADDENDUM: I contacted the company listed above. The prices they list includes delivery, and they will also pick up a discarded battery without additional charge. So, one could power a system with a battery until it's just about dead, then purchase a new battery with free delivery and with the crapped out battery carried away. That seems very convenient.

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## buenijo

Interesting site: www.greenoptimistic.com

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## bwlibertyman

Bump

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## noxagol

> Here's a site for purchasing industrial forklift batteries. http://gbindustrialbattery.com/Forkl...ns_Zone15.html I have heard from many independent sources that forklift batteries are the best choice for off grid batteries. Make sure to review the link on the battery capacity ratings. They are based on 80% depth of discharge, which is excessive. This should be at least cut in half to greatly extend the life of the battery. Still, that single large 12 volt battery at 1182 amp hours will provide 7 kwh of at 40% depth of discharge (pretty damn good if you ask me). Yeah, but it costs $1745! Batteries are expensive, period. This is a primary reason why I believe a small back up generator for battery charging is superior to purchasing an enormous battery system designed to take a home through several days of inclimate weather.
> 
> http://gbindustrialbattery.com/Forkl...ns_Zone15.html


For that price, you may as well get lithium ion car batteries.

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## buenijo

> For that price, you may as well get lithium ion car batteries.


The only source I found for lithium ion battery systems large enough for this application is here: http://www.genasun.com/Genasun-Lithium-2011-03.pdf... $14,000 for a lithium ion battery system of 8.6 kwh capacity. If you know where to get them cheaper, then please let everyone know.

ADDENDUM: I checked several online sources for more traditional batteries designed for solar applications and golf carts. For the same voltage ratings and amp-hour capacities, these "solar" batteries are about 30% more expensive than the forklift battery! It doesn't seem to make any sense to me to not go with a forklift battery for an off grid solar application (unless the system is very small).

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## buenijo

I just found what appears to be a good resource. I have argued in the past for using an engine system to drive a dc generator for battery charging while simulteneously using the engine to drive a refrigerant compressor for air conditioning. The numbers look quite good under these conditions. Storing energy with a battery system, storing cold water and/or ice for air conditioning, and heating water by tapping into engine waste heat (for a/c, space heating, and water heating) reduces engine run time for greater longevity... and reduces fuel consumption. Well, I found a Diesel engine that is configured for this: 
http://www.polarpowerinc.com/product...cogen_lomb.htm. 

Home page: www.polarpowerinc.com

FYI, a Diesel can be operated on wood gas without modification by using just enough Diesel fuel to provide ignition (generally, this is about 10% the Diesel normally required). In fact, the research shows that wood gas ignition on Diesel fuel is more reliable than with spark ignition. Also, running a Diesel on wood gas actually increases its efficiency (neglecting the thermal losses from the gasifier).

http://taylor.ifas.ufl.edu/documents...ne_Systems.pdf (see page 111)

ADDENDUM: The coefficient of performance of this compressor (it appears to be a conventional automotive compressor) is listed at between 1.5 and 2.0 (http://sanden.com/originals/images/S...erformance.pdf), meaning that the cooling provided by the compressor equals this factor multiplied times the mechanical energy delivered to the compressor. That's quite low. In fact, it's about half the mechanical efficiency of the enclosed scroll compressors used in conventional a/c units. However, driving the compressor directly does avoid the energy conversion losses in the generator and a/c compressor motor (and possibly battery/inverter depending on how the system is set up). So, this configuration still requires roughly the same mechanical energy for cooling, and providing a/c in this manner would consume about the same amount of fuel. Still, this configuration could provide a/c at a lower cost and greater reliability in an off grid setting... and it would be fairly easy to configure something like this.

ADDENDUM: It seems my previous addendum to this post should be disregarded. I thought something didn't seem right at the time, but I was just taking the data at face value (this is often dangerous). The coefficient of performance of the automotive compressor I linked is not primarily a function of the mechanical characteristics of the compressor, but the standard test conditions that are used for automotive compressors (generally those conditions seen in actual automotive compressor systems). Well, these tend to use small heat exchangers (because it has to be a compact system for automotive use), and the temperature at the condenser tends to be high (because there's not an abundance of cool air behind the fire wall of an automobile). In other words, there is A LOT of room for improvement. I see no reason why the COP of an a/c system using this compressor cannot be on the order of 3. When considering the energy conversion losses associated with going from engine output shaft, to ac generator, to compressor motor, then to a/c compressor, then a purely mechanical a/c system based on the automotive compressor should double the cooling capacity for the same fuel consumption (assuming the heat exchangers are optimized- meaning, really big with condenser well cooled, and evaporator temperature limited). In fact, it seems to me that the efficiency might be high enough to justify powering one of these compressors with a DC motor powered directly by photovoltaic panels. If this can be made to work without batteries, controllers, and inverters, then perhaps it can be worth it. Although, a small battery system and charge controller would solve a lot of problems.

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## buenijo

Here's an idea for providing a/c in an off grid setting. Excessive output from a large PV array during hot and sunny summer months is used to power window units used to cool a thermal mass such as a large store of water in a highly insulated space. The home is cooled by circulating air through the space, and placing the fan on a thermostat. I'm thinking that a good configuration would be to set up window units on inverters as opportunity loads using battery diversion charge regulators. Here is a description of such a unit: http://www.hydrogenappliances.com/batteryregulator.html. The idea is to have the solar system charge the battery until a certain voltage setpoint is reached, then the regulator would start an a/c unit to cool the water (I'm thinking each window unit should have it's own regulator, and if a different setpoint can be configured for each one, then this would be best). This configuration should avoid a lot of battery losses. Also, during the end of the day when output from the panels drop, then the differing setpoints would shut off the window units sequentially. _A big advantage here is that the size of the battery system need not be enlarged to provide a/c._

NOTE: Using a wood gasifier to power an ac generator at its most efficient output, then using the generator head to power multiple window units too cool a large thermal mass is an efficient way to provide a/c with a wood gasifier, or any generator. The engine is operated at its most efficient output, and the generator run time is greatly diminished. Better results would be had by driving the compressor directly with the engine (i.e. automotive compressor), and using the evaporator to cool the water directly.

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## buenijo

I heard about this technology a few years back. Looks like there are plans in the works for actually building one of these in Arizona. This illustrates well that "efficiency" is not what matters with solar energy... it's net costs/kwh. Personally, I love the idea. Interestingly, a prospective source of revenue from this project is charging admission to view from the top of the tower... at least, I recall reading that suggestion. 2.5 times the height of the Empire State Bldg... that might be worth a gander for a few bucks.

http://www.gizmag.com/enviromission-...newable/19287/

Prototype in Spain: http://www.youtube.com/watch?v=XCGVT...eature=related

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## buenijo

Good article: Insolation, and a Solar Panel’s True Power Output: http://lightbucket.wordpress.com/200...-power-output/

NREL Solar Maps: http://www.nrel.gov/gis/solar.html

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## Kelly.

keep the links and info coming, just because people are replying, doesnt me we arent reading/learning

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## buenijo

> keep the links and info coming, just because people are replying, doesnt me we arent reading/learning


Thanks Kelly.  I figured I might as well share what I find while I'm looking into things. I'll be posting stuff here as I find it, at least until classes start in late August. After that I'm sure I'll be too busy studying.

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## buenijo

Damn good discussion on PV panels: http://itacanet.org/eng/elec/solar/pv.pdf. Note in particular the section "PV Panel Arrays and Wiring".

Main page (plus links to other sites): http://itacanet.org/eng/elec.htm#2

Battery discussion: http://windsun.com/Batteries/Battery_FAQ.htm

Battery charge controller discussion: http://windsun.com/ChargeControls/MPPT.htm

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## buenijo

DEVELOPMENT OF A LOW-COST ROOF-MOUNTED SOLAR SYSTEM USING FLAT-PLANE REFLECTORS
http://itee.uq.edu.au/~aupec/aupec04...PaperID218.pdf

EXPERIMENTAL EVALUATAION OF V-TROUGH (2 SUNS) PV CONCENTRATOR SYSTEM USING COMMERCIAL PV MODULES
http://www.physics.arizona.edu/~cron...ough/SAS06.pdf

I had been searching for information to support my thoughts on building a reflecting system for a pv panel. The ideas expressed in the links are very close to what I was considering, even as far as using stepper motors to control the positions of the reflectors. However, I think I have a much simpler configuration. I see myself buying a panel for testing some time in the near future as this would not be terribly expensive like some of my other proposed projects. I'm interested to know how such a system will increase the actual net electricity generation of a pv array over an entire year, particularly during periods of low solar insolation such as during winter months, early mornings, and late afternoons. It seems that there is potential to increase the real world gain from PV panels using this general approach.

ADDENDUM: The rapidly falling price for PV panels really makes this idea a nonstarter. Rather than make such modifications to an array to increase output, it makes more economic sense to just buy more panels.

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## TonySutton

Visit this website if you want to radically change the way you think about housing.

http://earthship.com/

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## youngbuck

Yes, many thanks for all the information and insight buenijo!  Keep them coming, as I'm (and others are) always interested!

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## Kelly.

> Visit this website if you want to radically change the way you think about housing.
> 
> http://earthship.com/


great idea, but these types of houses can be built with a lot less labor then they use.

i think passive solar, thermal mass housing is a HUGE step towards an energy efficient home, but pounding tires for weeks on end isnt for everyone.

imo, a passive solar, thermal mass home, built with ~18in rammed earth walls, is a good "middle ground" between earthships and a conventional home. rammed earth walls are completely owner/builder doable, and also allow the aid of modern equipment (whacker/bucket loader). combine this house with a in floor solar hot water heater, wood stove for backup heat and you can really get you total amount of power down.

there are a few communities of earthships and i have been inside a few locally. all seem to operate as advertised, cool in the summer, warm in the winter. 

if i had enough money i would love to find a way to produce these homes in a more efficient way. it would be a huge step towards personal freedom for anyone wanting it.

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## Ninja Homer

> great idea, but these types of houses can be built with a lot less labor then they use.
> 
> i think passive solar, thermal mass housing is a HUGE step towards an energy efficient home, but pounding tires for weeks on end isnt for everyone.
> 
> imo, a passive solar, thermal mass home, built with ~18in rammed earth walls, is a good "middle ground" between earthships and a conventional home. rammed earth walls are completely owner/builder doable, and also allow the aid of modern equipment (whacker/bucket loader). combine this house with a in floor solar hot water heater, wood stove for backup heat and you can really get you total amount of power down.
> 
> there are a few communities of earthships and i have been inside a few locally. all seem to operate as advertised, cool in the summer, warm in the winter. 
> 
> if i had enough money i would love to find a way to produce these homes in a more efficient way. it would be a huge step towards personal freedom for anyone wanting it.


I agree with you.  Check this out: http://www.undergroundhousing.com/

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## buenijo

Article: "Nissan unveils system to provide household electricity from all-electric LEAF": http://www.gizmag.com/nissan-leaf-pr...d-power/19411/. 

It seems the price of PV and EV technology has to go down quite a bit more to make this configuration viable for an off grid home. For someone living in a region of high solar insolation, and with driving habits well within the range of a low cost EV, it could be a winner.

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## buenijo

Check out pics of steam engines by Cyclone Power Technologies:

Solar Steam Engine - http://www.facebook.com/media/set/?s...12306672134739. This particular engine puts out 5 hp. It is being designed to be placed on a lightweight parabolic dish. The benefit of this engine is its compact light weight, low cost, and water lubrication. 

Waste Heat Engine - http://www.facebook.com/media/set/?s...12306672134739. This engine is designed for waste heat recovery. It is also being used in a system fueled by biomass. The thermal efficiency of the system is not particularly high at around 12% (not including boiler losses). The benefit of the engine is its simplicity, very broad multi-fuel capacity, waste heat recovery at fairly low temperatures, water lubrication, zero compression, and self-starting ability.  

Automotive Engine - http://www.facebook.com/media/set/?s...type=1&theater. This engine is designed to power full size passenger cars. The thermal efficiency of the system is slightly higher than conventional gasoline automotive engines, but lower than Diesels. However, the efficiency of the engine is highest at part load where automobiles spend most of their time, and there are fewer losses in power transmission (for example, there is no transmission or torque converter required; rather, the engine couples to a gear box directly). Other benefits of the engine in this setting is very broad multi-fuel capacity, water lubrication, clean emissions without any emissions controls equipment, light weight (330 pounds complete), and low noise without noise suppression equipment. Another advantage is no idling of the engine (the engine stops when the car stops, and there is no steam consumed when coasting). This last feature presents a problem in powering auxiliaries. A proposed solution is to use a separate small Cyclone engine for auxiliary power, and/or using a battery system combined with regenerative braking.

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## buenijo

The Bourque Steam Engine: www.newsteamengine.com (excellent discussion on web site)

I am familiar with this system having corresponded with Dr. Bourque a couple of years back. This basic design is the best I've seen for achieving optimal thermal efficiency in a small to medium steam system. The basic configuration is a multi-cylinder compound piston engine with reheat stages between each cylinder. The steam is exhausted at very high temperatures, and this steam is used to preheat the air sent to the furnace for combustion. Therefore, the heat added to the steam in the reheat stages boosts the pressure in the engine for more work, but this heat is not lost because it's recycled back into the system. Peak temperatures are limited to 1000F. This relatively low temperature means the system does not require exotic alloys (a clear advantage). Also, the condenser for the system is maintained at a positive pressure corresponding to a steam saturation temperature of 275F. This high temperature makes for a smaller condenser (great for the automotive setting). Also, this high condenser temperature would make it a lot simpler to put the waste heat to use in a stationary setting.

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## buenijo

Interesting site: www.solarsteamtrain.com. 

In particular, see this page: http://solarsteamtrain.com/cms/content/view/29/28/. The thermal storage abilities of the materials discussed are quite impressive. One kilogram of this new thermal storage material stores twice the energy as the same mass of the best lithium ion battery. Even more impressive is the energy density of these materials. One liter of these new thermal storage materials provides 3 times the energy as the best lithium ion battery of the same volume. Of course, they store only heat energy.

It seems a potential application for these thermal storage materials is in storing solar energy for powering absorption air conditioning units and heating applications. This would displace the most electricity. One configuration that might be practical would be to use a lightweight solar concentrator to generate superheated steam at high pressures for transferring heat to the thermal battery. This configuration could use more traditional fuels (or even biomass) to generate steam for the same purpose when solar is insufficient. 

The article discusses the use of these materials for powering fireless steam locomotives. I must admit that I find that application to be fascinating, but the logistics seem overwhelming. It's possible to use this approach to power automobiles as well, and there is some precedent. See the following discussion of an experimental solar powered steam car: http://www.reocities.com/MotorCity/s.../solarcar.html. It's all very interesting, but personal automobiles powered in this manner would be totally impractical in my opinion.

NOTE: See Peter Brow's main web site as well for interesting links and discussions: http://www.reocities.com/MotorCity/shop/3589/index.html

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## DamianTV

Cold Fusion is getting Hot again...

http://www.ronpaulforums.com/showthr...ews-60-Minutes)

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## buenijo

> Cold Fusion is getting Hot again...
> 
> http://www.ronpaulforums.com/showthr...ews-60-Minutes)


I've been aware of this controversy for a while now. Consider that if this "cold fusion" works out, then new heat engine technologies might benefit. After all, the fusion process generates heat directly, and a system that uses this heat directly would likely be the most cost effective configuration. Imagine a steam car that has to be fueled only every few years or so... or micro cogen steam power plant for a home with the same fueling requirements. I only hope there's a way to purify the deuterium with a process simple enough to allow the individual to avoid the inevitable taxes the goobermint would attach to this source of energy.

NOTE: Check out Andrea Rossi's claims as well that he is achieving "cold fusion" of nickel and hydrogen. It's interesting, but I am highly skeptical of the claims. Supposedly, there are 10 KW units designed to generate steam for residential heating applications to be sold later this year. _I'll believe it when I see it._

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## Simple

The solar chimneys are interesting as far as cost per unit of power, but the prototype in Spain caused some cyclones due to all the hot air rising. I love the idea of a natural wind machine to drive a wind turbine, but the cyclone issue might prevent residential scale applications. I think vertical wind turbines are going to pick up. Cal Tech found a tenfold increase in power output when vertical turbines are spaced four diameters apart and a company called MagLev is going to attempt to advance the wind industry with frictionless industrial sized vertical turbines hovering on rare earth magnets. 

And as far as solar goes, the best thing going now is molten salts that store energy and produce power after the sun has set. On a residential scale, I see a lot of room for advancement of the use of stirling engines to produce power. Sunpower, Infinia, and Stirling Engine systems are selling reflective dishes that focus heat on one end of the stirling engine. They run off heat so a stirling engine could run off your biofuel being burnt for heat, but I've yet to see a good commercial product developed.

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## DamianTV

I cant find the link, but I saw a news bit on some high school student doing the math on the most efficient way to arrange solar panels.  Guess what it looked like?  It looked like Leaves on a Tree!  Maybe mother nature isnt so dumb after all?

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## buenijo

> The solar chimneys are interesting as far as cost per unit of power, but the prototype in Spain caused some cyclones due to all the hot air rising. I love the idea of a natural wind machine to drive a wind turbine, but the cyclone issue might prevent residential scale applications. I think vertical wind turbines are going to pick up. Cal Tech found a tenfold increase in power output when vertical turbines are spaced four diameters apart and a company called MagLev is going to attempt to advance the wind industry with frictionless industrial sized vertical turbines hovering on rare earth magnets.


In my opinion, the net costs of the energy produced by a solar power technology projected over the life of the system is the primary consideration. However, I don't see a solar chimney system as ever being practical for a residential scale unit. As far as the "cyclones" go... well, I don't know the details, but I can't help but suspect that "cyclone" is a misnomer. Besides, these units are best placed in very remote regions where solar insolation is high and lands costs low... who cares about a few minor wind disturbances. 




> And as far as solar goes, the best thing going now is molten salts that store energy and produce power after the sun has set. On a residential scale, I see a lot of room for advancement of the use of stirling engines to produce power. Sunpower, Infinia, and Stirling Engine systems are selling reflective dishes that focus heat on one end of the stirling engine. They run off heat so a stirling engine could run off your biofuel being burnt for heat, but I've yet to see a good commercial product developed.


Again, with solar energy the primary concern is cost. However, I emphasize that whatever system is less capital intensive should be preferred all else equal. In fact, I put a premium on the value of such a system beyond what the projected costs would suggest due to economic arguments. Namely, any "projected" costs are based on prices that can change dramatically in short order. The simpler system that is less capital intensive will be more insulated from these dynamics.

Now, as far as using Stirling engines with reflective dishes, a prospect that I believe might be better is to use modern piston steam engines. These can produce the same power as a Stirling engine that is many times the weight and likely many times the cost (yet to be determined, but the lower mass and greater simplicity provides a good argument). For example, Cyclone Power Technologies is developing a radial steam engine capable of 5 hp that weighs only 20 pounds. These are capable of a thermal efficiency of 30%. Sure, the best Stirling engine can see a higher efficiency, but if the fuel is free then who cares? Also, a small scale solar steam system has other advantages including great ease in cogeneration (steam exhausted from the engine can be used easily in heating applications), and a separate steam generator can be easily configured to drive the engine using a fuel.

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## buenijo

I'm revisiting the idea of using a diversion load battery charge controller (i.e. a shunt regulator) to minimize the size of a battery for an off-grid air conditioning system. The basic idea is to use a conventional vapor compression a/c unit to cool a thermal mass. I have never seen these shunt regulators used in conjunction with anything other than heating elements where some of the output from a PV array (or other source) is shunted to a secondary circuit to protect a battery from overcharging. These are generally used for water heating or for space heating, but what an inefficient way to use electricity in an off grid setting! 

There must be a way to configure the system to allow putting an a/c compressor motor in the secondary circuit. Perhaps this can be accomplished with a solenoid switch. I have no formal electrical training (although, I have been electrocuted a few times!), but it seems to me that the current shunted from the controller can be used to energize the solenoid. The main contacts of the solenoid switch could then be used to close the motor circuit. Operating the compressor motor should draw down the battery until the battery overcharge condition no longer exists whereupon the controller would de-energize the solenoid and open the motor circuit. A large PV array could power multiple window a/c units in this manner, a number of small a/c units should minimize the number of cycles (which is good for longevity). It might also allow for using a single inverter for all a/c units because a single large a/c unit may draw too much current on start up. It seems the best configuration would be to energize the separate a/c units sequentially as required by manipulating the set points accordingly. This might be accomplished by using a separate controller and solenoid for each unit... or perhaps the same controller could be used in combination with separate solenoid switches on each a/c unit by placing a rheostat in the separate control circuits (i.e. the solenoid sides of each switch). Adjusting the rheostats could effectively allow for modulating the set points for each unit. The latter configuration is best (if it works) because solenoid switches and rheostats are a lot cheaper than the controllers.

This idea is half-baked... any electricians out there please chime in.

ADDENDUM: There's what appears to be a good resource for information on solar PV at www.solarpaneltalk.com. I made a few posts to solicit advice on this idea. It's clear that the engineers at that site think powering a/c units with a PV system is not practical, so they wouldn't consider the details. I can't get any advice from them except not to try it. Still, I'm convinced it's viable for a very small well-insulated home where solar insolation is high AND where grid power is not an option. Again, the purpose of the thermal mass is to minimize battery size and maximize battery life (effectively minimizing the single greatest long term cost of an off grid PV system - batteries), but it can't magically increase cooling capacity. This shouldn't be used for anything larger than what might be called a "cabin"... and a well insulated one.

ADDENDUM: I've since learned that quite a few off grid folks are running a/c units. A popular system is to use split ductless a/c units as these are highly efficient, and they do not show high peak starting amperage on the compressor motor. Running these units as opportunity loads is a fairly common strategy in the off grid setting. So, it seems the engineers at solarpaneltalk.com provided bad advice at that time.

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## buenijo

48 volt DC, 18,000 btu/hour a/c unit for off grid solar applications: http://www.sunvoltenergy.net/index.a...ils&Item=13195

This unit is expensive. However, it makes sense because the purchase of a inverter can be avoided. Also, fewer panels need be purchased for the same cooling capacity... not only is the unit highly efficient (based on the specs), but there are a lot of losses avoided when the inverter is not used. Direct DC a/c seems like a winner.

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## buenijo

Options for Solar Air Conditioning:

http://www.machine-history.com/Solar...20Conditioning

Note in particular the use of a dessicant to provide cooling in a region of high humidity. The idea is to circulate air in the home through a bed of silica gel. The moisture in the air is adsorbed in the internal structure of the silica gel. The silica gel must be kept cool during this process. Therefore, perhaps this should be done at night. Solar heat is used to recharge the silica gel as the water is driven out of the silica gel upon heating. The best configuration I've considered for this is to force solar heated air through a desiccant bed taking care to size the silica gel properly to not restrict air flow (as this would consume more electricity in the fan motor). At night the air in the home is circulated through the bed after it has cooled down. I wonder if this would be sufficient to cool a home in a very humid environment like east Texas? Perhaps the air circulated at night can be drawn through a wet pad (as used in swamp coolers)? A huge side benefit is that the same system used to heat the air can be used during the winter for space heating.

See the following study:

Reactivation of a Silica Gel Moist Air Dehumidifier Using Solar Heat
http://www.lged-rein.org/archive_file/01059.pdf
This is a rather technical discussion. The most relevant information I found is that solar heated air at 158F is able to drive out 1 pound of water from 5 pounds of silica gel. Clearly a home would require a helluvalotta silica gel. However, it's not terribly expensive... and it will never have to be replaced. 

As for heating the air consider this idea: http://www.youtube.com/watch?feature...&v=6llEo9VZ-K0, http://www.youtube.com/watch?v=qWK4I...eature=related Here aluminum cans are joined to form a space through which air flows for heating. The cans are painted black and placed in an enclosure for solar heating. See this also: http://www.youtube.com/watch?v=-u7mstBFbrE.

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## buenijo

Just sharing something I found. 

http://www.hydrogenappliances.com/batteryregulator.html

This controller can be used for the solar a/c idea (see comment #29 in this thread).

NOTE: I've seen many bad reviews of this site, so consider the link only as an example of this kind of device.

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## buenijo

THOUGHTS ON OFF GRID AIR CONDITIONING (desiccant bed evaporative cooling)

Here is a prospect for providing cooling from low temperature heat sources such as steam. Solar heated air is a possibility. Best results could be had by using a furnace directly(*). It's not a new idea (see desiccant wheels) - I'm only considering a practical way for an individual to build one. Most of you are likely familiar with a "swamp" cooler (i.e. evaporative cooling). Unfortunately, these are useful only in very dry climates. However, it's possible to use a desiccant to dry the air, send the dry air through an evaporative cooler, then use heat to "regenerate" the desiccant to provide a continual cooling effect. In this configuration hot and humid outside air is forced through a desiccant bed. The adsorption process generates heat as the water vapor condenses on the internal structure of the desiccant and releases latent heat. The dry hot air leaves the desiccant bed and passes through a heat exchanger that precools the air with the cool air exhausted from the home. The now cool dry air is forced through a wet pad that cools the air through evaporation. The desiccant (such as silica gel) is completely nontoxic and will last indefinitely. The only moving parts include blower fans. The blower fans would consume quite a bit of power. However, this would be required during the summer months when solar insolation is greater. A PV array can earn its keep here. 

(*) A small furnace would more completely and more rapidly dry the desiccant bed. I think this idea has merit. However, the toxic gases have to be flushed from the bed before air for the home can be introduced. It turns out this is very easy to do. For example, a wood gas engine system might be operated for several hours daily for battery charging, and the engine cylinder cooling blower fan could be directs to a desiccant bed along with the engine exhaust gases for drying. Once the system is flushed and cooled, then it can be used for cooling.

ADDENDUM: Not that a dry desiccant bed can and is being used in space heating applications. Since the adsorption process generates heat, then humid air moved through the bed will heat the air. One pilot application in Germany is getting air to 200F using zeolite desiccant.

As always, I'm just trying to stimulate thinking on the subject of alternative energy in the off grid setting. Although, I don't know whether or not this would be practical.

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## jmdrake

Cold fusion and other suppressed technology that actually works.  http://jnaudin.free.fr/

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## azxd

> THOUGHTS ON OFF GRID AIR CONDITIONING


Research geothermal heating and cooling.

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## buenijo

> Research geothermal heating and cooling.


Yes, I have. All commercial geothermal units I've researched draw more electricity than a modest off grid power plant can service, and they are costly. Also, I'm more interested in systems that are simpler, and can be installed and serviced by individuals without specialized training (I'm thinking way off grid here, and a system that can move with the homeowner). Still, if you know of a low cost geothermal system rated at below two ton cooling capacity, then I would be very interested to know its specifications. NOTE: I do believe geothermal to be the best option among all commercially available systems (at least for most regions). However, I'll be settling near Houston, TX. My research shows geothermal cooling is not quite so good in that region.

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## azxd

> Yes, I have. All commercial geothermal units I've researched draw more electricity than a modest off grid power plant can service, and they are costly. Also, I'm more interested in systems that are simpler, and can be installed and serviced by individuals without specialized training (I'm thinking way off grid here, and a system that can move with the homeowner). Still, if you know of a low cost geothermal system rated at below two ton cooling capacity, then I would be very interested to know its specifications. NOTE: I do believe geothermal to be the best option among all commercially available systems (at least for most regions). However, I'll be settling near Houston, TX. My research shows geothermal cooling is not quite so good in that region.


Gotta talk to a freind who was telling me of a system that is DIY, and cheap to operate ... Give me a few days to gather some info.

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## buenijo

THOUGHTS ON GEOTHERMAL COOLING

I reviewed geothermal cooling systems. Most of these systems use a vapor compression cycle. They achieve high efficiencies by lowering the discharge pressure on the compressor thereby saving electricity. This is accomplished by using a heat sink in the form of water cooled by the earth. I recall a man in one of the hottest parts of Australia who recounted the results of cooling the condenser of his window a/c unit by placing it in a water storage tank. He claimed the power consumed by the unit went down 40% due to a combination of removing the fan motor load and reducing the discharge pressure on the compressor. This is basically what a geothermal system does, but it works even better because the water used to cool the compressor is at a lower temperature (due to the fairly constant cool temps in the ground). 

My research suggests that geothermal systems often do not work well in the Houston, TX area where I plan to relocate. First, the winters there are very mild, and the summers are brutal (it’s basically a sun-baked swamp). Second, the soil in that region is high in clay which tends to insulate. So, what I’ve heard from independent accounts is that a geothermal system in Houston starts to perform poorly after a few years of dumping all that heat into the ground. At that point the temperature of the heat sink rises, and the discharge pressure on the compressor goes up. 

Finally, a good geothermal cooling system consumes about ½ the electricity of a good conventional central a/c system. For the off grid setting, I consider this electricity consumption to still be way too high. To understand my perspective here, try to imagine powering a small modern home in the Houston area without using grid electricity and having no access to fossil fuels. There is only solar insolation and biomass. That’s real off grid living.

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## buenijo

I'm wondering about the prospect for a person to actually build their own small scale geothermal cooling system from existing mass produced components. Why not retrofit a window unit? This would require disabling or removing the condenser fan on the back of the unit, then enclosing the condenser coil so that water can be used to cool it. Of course, this water would be circulated through a heat exchanger buried in the ground, or the water could be pumped from a nearby body of water. Such a configuration should reduce electricity consumption on the order of 50%, and this might make it worthwhile in an off grid setting.

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## buenijo

I'm surprised I didn't post a link to this site earlier as I first checked it out several years ago: www.backwoodshome.com. In particular, check out the articles under the energy section here: http://www.backwoodshome.com/article_index.html#en.

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## buenijo

I'm surprised I haven't shared this idea yet (or maybe I did and forgot)... you all might be interested. I considered independently this basic design a long while back, but I did see a similar working prototype a few years ago built by a small company in Australia. Unfortunately, I can't find it. A liquid refrigerant is injected into a vessel filled with hot oil. The refrigerant vaporizes, pressurizes the vessel, and expands at the top of the vessel forcing the oil column down through a hydraulic motor. A flywheel driven by the system can be used to drive an alternator and to drive a pump that returns oil to the vessel at the same time a valve opens to send the refrigerant vapor to a condenser (this is done after the pressure drops in the vessel... if properly configured, a large flywheel will store the energy required to return the oil to the vessel and send the refrigerant vapor to the condenser... of course, this could be done with electric motors, but I like the mechanical approach). It's really just a Rankine cycle engine. The advantage is that hydraulics are very reliable and powerful... a hydraulic motor can deliver some serious power in a small package. Plus, you get excellent heat transfer to the working fluid by this method. Finally, potentially it can be a low cost system because the system can be assembled from existing components. Solar heat is really the only viable candidate here because of the temperature limitations of the system that would greatly limit the efficiency. Any other source of heat would consume too much fuel. However, like I've argued before, when it comes to solar energy, efficiency is a four letter word: COST.

ADDENDUM: There is an approach here that will increase efficiency, possibly to the point where using a fuel would be viable. Imagine that the oil in the vessel is heated by a compact coil of copper tubing placed in the very top of the vessel. Heated fluid flows through this copper coil. Baffles will encourage natural circulation within the vessel to efficiently heat the oil and do so quickly. Once the temperature of the oil reaches a set point, a fixed mass of liquid refrigerant is quickly pumped into the vessel. The refrigerant accumulates at the top of the vessel and expands there. Since that's where the heat source is located, the refrigerant vapor will continue to be heated as it expands. This allows for more work to be produced. However, when the refrigerant vapor is finally discharged, this extra heat added must be regenerated into the system by preheating liquid refrigerant before it's injected into the vessel... otherwise, there will be little net gain.

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## Working Poor

here is a blog that I started a few days ago 
http://powerwithsun.blogspot.com/

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## Kelly.

buenijo - have you looked into any large sterling type engines?
being in houston, i would think that a ambient temperature engine would be ideal. if you can produce mechanical power you might use that to power a cooling system.

i have seen a book on a 5 hp sterling, but i havent ever seen one working...
i also know of a site in portugal that has a sterling type motor that runs on hot oil (solar heated). there isnt much info on the motor that i can find, although here is a page with some info: http://www.tamera.org/index.php?id=51&L=0

also, if you are planning to live in houston, you may look into a living roof and a home that is partially underground. cooling tubes and sunroofs can help keep air moving through the house to help cool it also.

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## buenijo

Hi Kelly. I have looked into Stirling engines, and I understand them well. I don't believe I can build one to be cost effective (especially one designed for solar heat). Any solar heat engine designed for a residential market is going to need a lot of money poured into its development. If we ever see one, then I am convinced it will be a piston steam engine like the solar engine being developed by Cyclone Power.

A partially underground home does make sense for cooling. I like the idea, but my wife prefers a more conventional home (and she has made that clear to me on more than one occasion). I'm not in Houston yet, but I'll be locating there sometime late next year. In all honesty, I doubt I'll be able to make the full transition to off grid living for a long while... but I can quickly get a PV array installed and set up a battery charging system fueled by a wood gasifier (and dual fuel an automobile off the gasifier), and that will be the core of the system. That will also give me back up power from the grid. I can work on the more esoteric stuff as I go. Right now I'm considering all things. Other systems I'm considering for off grid living that can be adopted fairly easily include biomass digesters for producing methane and compost, solar air heaters for space heating, raised bed gardening for fruits and vegetables, laying hens for eggs, rain water collection, and water pasteurization and distillation using a small biomass furnace.

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## buenijo

Just more thoughts on small scale solar heat engines for power generation. I like to consider them because it's interesting. However, I am convinced that it can't be cost-effective for a small scale system until highly efficient heat engines suitable for the project are mass-produced to get that major cost down. The only technologies that seem cost effective right now for individual off grid power generation include solar PV (if you have good sun), wind turbines (if you have really good wind), small scale hydro (if you're really lucky), and wood gas engine systems (if you have this fuel source readily available). A large digester can produce enough gas for some power generation, but most people don't have access to enough suitable biomass for this to be a practical option. I say keep a small digester around only for cooking gas and compost.

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## buenijo

Sorry for the deletion here, but this idea is currently under closer scrutiny. If anyone is interested, then contact me directly. Sorry.

ADDENDUM: See post #53

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## The Northbreather

Heres a guide/archive to solar cookers. One has a solar tracker based on a simple diode setup that pretty handy. There's also a few rocket stoves 

http://solarcooking.org/plans/

http://solarcooking.wikia.com/wiki/C...r_cooker_plans

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## buenijo

Hundreds of downloads describing self-reliant technologies:

http://practicalaction.org/browse-and-download-answers

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## roho76

Hey buenijo.

Have you seen this?

http://www.youtube.com/watch?v=xEdQRVQtffw&noredirect=1

While I'm not fond of hydrogen bombs in my back yard but if they're far enough away from the house I guess it doesn't matter. I do like the idea of storing energy in hydrogen instead of batteries that are costly and will need constant replacement. This guy just stores hydrogen in propane tanks and runs his house on it.

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## buenijo

> Hey buenijo.
> 
> Have you seen this?
> 
> http://www.youtube.com/watch?v=xEdQRVQtffw&noredirect=1
> 
> While I'm not fond of hydrogen bombs in my back yard but if they're far enough away from the house I guess it doesn't matter. I do like the idea of storing energy in hydrogen instead of batteries that are costly and will need constant replacement. This guy just stores hydrogen in propane tanks and runs his house on it.


Hi rojo76! Yes, I did see that video several years ago. That's funny... I mentioned that system to a friend of mine a few weeks ago who was wondering about hydrogen fuel cells. You're absolutely right to compare the system to a battery. 

Just my opinions here of course, but I don't see the system as practical even though it is interesting and has some advantages. It's definitely a lot less efficient than chemical batteries. While I don't have references available, I expect the net efficiency of this system to be about half that of a lead acid battery. I think this video shows what happens when engineers have too much money and too much spare time.

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## buenijo

Good discussion on why 15% efficiency for PV panels should be considered very good (I agree!). http://physics.ucsd.edu/do-the-math/...ficiency-snob/. 

Of course, the problem with solar PV is not the efficiency, it's the cost... and not merely the cost of the panels, but everything else that goes along with them. The off gridders are particularly hampered due to battery costs. I'm convinced that the best solution for off gridders is to minimize electricity consumption as much as practical, and focus on battery management to minimize that long term cost. I think solar thermal is a great idea for space heating and water heating (direct solar air heating when possible, and thermal storage with water - or another suitable thermal mass). However, I'm convinced that solar concentrating technologies are not practical for small scale power generation (solar thermal or concentrating PV) except possibly in regions with particularly high direct solar insolation (like high desert regions that see little cloud cover).

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## buenijo

Excellent blog: "Do the Math" by physics professor Tom Murphy: http://physics.ucsd.edu/do-the-math/

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## buenijo

I'm sharing an idea for building a heat engine using existing mass produced components. The heat source that I propose for this system is a small biomass furnace operated at a constant low rate. Ideally, the system should operate at a low speed and low output to increase longevity and allow optimal waste heat recovery. If reasonably high efficiency can be achieved, then using the system to generate a small amount of electricity might be practical. However, the best use I have considered for the system is to drive a blower fan through a belt drive, then use the waste heat from the system in the desiccant evaporative cooling system described in post #33. It might be used for direct space heating applications as well, but there is likely to be a small amount of lube oil contaminating the exhaust air that should be filtered (or use a heat exchanger). Ok, here's the system in an nutshell...

There are four major components: 
(1) compressor - A standard small piston air compressor pump
(2) furnace - A small updraft biomass gasifier furnace
(3) heat exchanger - A large coil of steel tubing placed in the furnace to heat compressed air, or perhaps a small steel tank could be used... or both
(4) expander - A small gas engine converted to run on compressed air 

... other components required for good results include: 
(a) thermal insulation on (2), (4), and the line connecting (3) to (4). 
(b) recuperator on the the furnace exhaust to preheat combustion air

The basic configuration is simple. Connect the expander to the compressor with a belt drive taking care to find the ideal gear ratio. If the displacement of the expander is about twice that of the compressor, then the gear ratio should be roughly 1:1 (just a starting point, but the ratio should be determined by trial and error). Now, connect the discharge of the compressor to one end of the heat exchanger, connect the other side of the heat exchanger to the inlet of the expander. Of course, there is additional tubing required to make these connections.  

Starting the engine: First, start the furnace and let it warm up. Pull the starting cord on the expander several times to charge the system with some compressed air. The compressed air in the line will start to drive the engine at a very low speed, but may stall a few times until the pressure builds. Just keep pumping. Once it starts running the pressure will build to a steady state that is determined by how the system is configured. As long as the compressed air sent through the system achieves a sufficient temperature, then it will expand to supply an increased volume of very hot compressed air sufficient to drive the expander itself and the compressor through all the losses involved. If the insulation is good, the friction low, air expansion in the expander high enough, etc. (that is, if you've done a good job in building the thing), then there will be enough work left over from the engine to power a blower fan or even an alternator. A key feature to this configuration is that the vast majority of the waste heat from the system is available at the expander exhaust in the form of hot air. This can be used directly to regenerate a desiccant in a desiccant evaporative cooling system while the engine powers the large blower fan required of the system. This fan can send air from the home through the dry desiccant, the cooling ductwork, then through a wet pad, and back into the home... all while consuming no electricity (with the possible exception of a very small gear motor use to automatically shift the air flow intermittently between desiccant beds, but this would consume almost negligible electricity). I like the idea of using this engine with the cooling system because low thermal efficiency and a constant low power will still achieve good results (it just has to power the blower fan, and extreme energy conversion losses are avoided by powering the fan directly with the engine).

NOTE: In a region where solar insolation is high and clear (i.e. desert regions in the southwest U.S. for example), a solar concentrator might be used as the heat source. In this case the system is well suited because the bulk and weight of the engine does not have to be mounted on the concentrator. Rather, only the heat exchanger need be mounted.

VIDEO: How to convert a small gas engine to run on compressed air: http://www.youtube.com/watch?v=xmapdIx3vWA. NOTE: This conversion used a specially fabricated cam shaft to change the valve timing. It is also possible to do this by grinding off the lobes on the shaft, and then threading round head machine screws into the shaft to actuate the valve push rods. Use larger screws for the exhaust valves. I spoke with a man who did this to convert a gas engine to operate on steam, and he claimed it worked very well. I'm only speculating here, but it may possible to select a short length of steel pipe at the proper diameter to serve as the cam. The pipe would be drilled and tapped as before with the screws to lift the valves, but the pipe is attached to the face of the gear used to drive the cam. Of course, the stock cam would have to be cut off from the gear. Perhaps a bolt could be used to attach this short pipe section to the gear. If it works, then this approach is good because it would facilitate trial and error, and it would allow for more precise valve timing. Also, note that the conversion in the video shimmed the intake valve spring to keep it shut against air pressure. I suspect a new and stronger spring will be required to use higher pressures, and a suitable spring can likely be found at McMaster.

ADDENDUM: The more astute readers might recognize this engine configuration as an Ericsson cycle or Brayton cycle (personally, I just call it a heat engine). The best way to understand it is to consider how a conventional four stroke gas engine works. The compressor takes care of the intake and compression strokes, the furnace and heat exchanger replaces fuel combustion in the cylinder, and the compressed air expander takes care of the power and exhaust strokes. There are serious limitations to getting high efficiency with this approach. The main problem is that gas engines are designed to radiate heat, and this system has to retain heat for good results. So, the expander has to be well insulated. Also, thermal losses from the furnace should be minimized by using a recuperator (i.e. a heat exchanger that preheats the combustion air with the hot furnace exhaust gases). Also, valve timing is critical. You have to get good expansion of the air in the engine for high efficiency. Finally, getting high pressure is very important for high efficiency, otherwise the losses from friction will be very high. Still, the use I have planned doesn't require high efficiency. In fact, 5% is enough! As far as I'm concerned, the production of electricity in the off grid setting should be done with PV panels and a wood gas engine system for back up power (well, I prefer a good small steam system, but where to get one?). However, if a thermal efficiency of 10% or more can be achieved, then I would consider this system as a viable alternative to a wood gas engine system for stationary power generation because of the other advantages (superior waste heat recovery, fewer losses in energy conversion due to operating at a very low output for extended periods, and not being limited to using wood fuel).

ADDENDUM: The best way to optimize efficiency from something like this is to first minimize the energy consumed in compression. This is done by using the best compressor possible (lowest friction). However, it is particularly important to approach as much as possible isothermal compression. A compressor that is aggressively cooled such that the compressed air leaving the compressor is as cool as possible will have minimized the work consumed in compressing the air. Also, since this compressed air is to be heated, then the lower the temperature the greater the heat that can be accepted in the furnace without exceeding the temperature limitations of the expander. There are other ways to optimize efficiency, but they're all difficult and costly to implement. For example, cooling the compressor would be easier to do in stages. So, the compressor might be a multi-stage piston compressor with each cylinder well cooled, but with intercoolers between the stages. Similarly, the expander might be multi-stage with reheaters placed between each stage. In this manner the compressed air is reheated before proceeding to provide more more work before proceeding to the next cylinder. In this configuration the final exhaust air from the last cylinder will be at very high temperatures, and as much of this heat as possible should be returned to the cycle. The only place that seems reasonable is heating the air sent to the furnace (using a heat exchanger). Forgoing a reheater on the final stage or two would reduce this final exhaust temperature, and can allow for all the heat in the exhaust to be recycled back into the system. In this way the only heat rejected during the cycle is the heat of compression. Theoretically the efficiency of this configuration can be extremely high, but like all such ideas the devils are in the details. Building such a thing would be a nightmare.

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## buenijo

"A Study of Lead-Acid Battery Efficiency Near Top-of-Charge and the Impact on PV System Design":

http://www.localenergy.org/pdfs/Docu...Efficiency.pdf NOTE: This is an excellent discussion. It seems too large a battery is just as bad as too small a battery, but for different reasons. 
(1) A larger battery has higher up front costs, but should allow the battery to last longer by minimizing depth and frequency of discharge. However, battery charge efficiency drops dramatically at higher states of charge, and this could require more panels to be purchased. 
(2) A smaller battery costs less and should raise the average battery charge efficiency. However, it may result in greater and more frequent discharges on the battery which can lower the life of the battery. 

QUOTE: "These tests indicate that from zero SOC to 84% SOC the average overall battery charging efficiency is 91%, and that the incremental battery charging efficiency from 79% to 84% is only 55%." (SOC = State of Charge).
QUOTE: "Charge efficiencies at 90% SOC and greater were measured at less than 50% for the battery tested here,..."

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## buenijo

I don't believe I posted a discussion of adding a thermal mass to a refrigeration system on this thread. So, here it is. I believe a good approach here is to use only a chest freezer. A "refrigerator" can be had by using a small very highly insulated container in an "ice box" approach. A more sophisticated approach could be had by connecting this insulated container to the freezer and letting it cool through natural convection. If this seems like too much trouble, then I suppose it's all a matter of perspective (it seems pretty straightforward to me). Anyway, the thermal mass is added to the chest freezer in the form of bottles of salt water. Adding salt to water will lower the freezing point to as low as -6F. A freezer should not be operated above about 15F. I suggest adding salt to the bottles to get the freezing point down to 5-10F. Now, lower the thermostat setting on the freezer to the lowest setting. The freezer is put on a timer so that it operates only during the day when solar insolation is available. When the timer permits, the low setpoint on the freezer thermostat will cause the compressor motor to start, and it will stay on until the entire mass of water is frozen and the temperature drops further to the thermostat setting (or the timer shuts it off). If properly sized, then this mass of frozen water will carry the freezer to the next day (or longer if desired). The benefits include: (1) the compressor motor does not operate intermittently, which should enhance longevity of the unit, (2) the battery is prevented from discharging at night, which should reduce depth and frequency of discharge and enhance the longevity of the battery, and (3) a lot of battery losses can be avoided here because much of the current produced by the panels is effectively bypassing the battery at this time (the battery is serving partly as a voltage regulator here rather than an energy storage device). If properly configured the compressor will stop early in the afternoon to allow the PV array to carry the battery through a full charge cycle and end the day with a float charge on the battery just in time to support the minimal electrical consumption during the evening hours. Of course, it's fine if you don't get a full charge every day, but the system should be configured so that it occurs regularly. NOTE: Roughly one cubic foot of salt water ice provides the same cooling capacity as 1 KWh of electricity consumed by the compressor of a chest freezer (just a very rough thumb rule).

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## Simple

> In my opinion, the net costs of the energy produced by a solar power technology projected over the life of the system is the primary consideration. However, I don't see a solar chimney system as ever being practical for a residential scale unit. As far as the "cyclones" go... well, I don't know the details, but I can't help but suspect that "cyclone" is a misnomer. Besides, these units are best placed in very remote regions where solar insolation is high and lands costs low... who cares about a few minor wind disturbances.


Cyclones as in heat induced tornados. The solution is to build a really tall tower for greater thermal efficiency and colder exhaust temps. The one they are building in AZ is twice the height of the Empire State Building. I was just saying I'd love to see these scaled down because all they are is a pipe and some plastic, but I'm thinking the weather effects might cause problems. Here is a drawing of the AZ project:






> Again, with solar energy the primary concern is cost. However, I emphasize that whatever system is less capital intensive should be preferred all else equal. In fact, I put a premium on the value of such a system beyond what the projected costs would suggest due to economic arguments. Namely, any "projected" costs are based on prices that can change dramatically in short order. The simpler system that is less capital intensive will be more insulated from these dynamics.
> 
> Now, as far as using Stirling engines with reflective dishes, a prospect that I believe might be better is to use modern piston steam engines. These can produce the same power as a Stirling engine that is many times the weight and likely many times the cost (yet to be determined, but the lower mass and greater simplicity provides a good argument). For example, Cyclone Power Technologies is developing a radial steam engine capable of 5 hp that weighs only 20 pounds. These are capable of a thermal efficiency of 30%. Sure, the best Stirling engine can see a higher efficiency, but if the fuel is free then who cares? Also, a small scale solar steam system has other advantages including great ease in cogeneration (steam exhausted from the engine can be used easily in heating applications), and a separate steam generator can be easily configured to drive the engine using a fuel.


I can't disagree, but the Stirling could potentially work with no water. A stirling generator could also produce power off any heat source. I do like steam and think it does have plenty of good applications, but why use steam directly if T-Hot is 700 degrees? That's why I said I like molten salts- they have a higher boiling point and the ability to store enough thermal energy to keep the steam generators running all night.

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## buenijo

> Cyclones as in heat induced tornados. The solution is to build a really tall tower for greater thermal efficiency and colder exhaust temps. The one they are building in AZ is twice the height of the Empire State Building. I was just saying I'd love to see these scaled down because all they are is a pipe and some plastic, but I'm thinking the weather effects might cause problems. Here is a drawing of the AZ project:


I know what you mean. Unfortunately, this particular system doesn't scale down. It sure is simple, and that's why I like it.




> I can't disagree, but the Stirling could potentially work with no water.


A modern piston engine would operate as a closed system. There would be almost negligible water loss. By contrast, all the highly efficient Stirling engines I've seen use either hydrogen or helium under pressure as the working fluid. That's a lot more exotic than water.




> A stirling generator could also produce power off any heat source.


A steam engine can also produce power off any heat source (although, very low temperatures should use a refrigerant). My only argument here is that a modern piston steam engine can be built at a fraction of the cost, weight, and bulk as a Stirling engine of similar peformance. I'm suggesting only that anyone who considers a Stirling engine for an application should look at the potential for a modern piston steam engine to be a better candidate. Of course, we don't have modern piston steam engines available for purchase either.




> I do like steam and think it does have plenty of good applications, but why use steam directly if T-Hot is 700 degrees? That's why I said I like molten salts- they have a higher boiling point and the ability to store enough thermal energy to keep the steam generators running all night.


Sure, sounds great. There's nothing wrong with thermal storage (especially latent heat in phase change materials).

NOTE: The solar "chimney" idea also achieves thermal storage by heating the ground, and this allows the system to operate for several hours into the night. Of course, the output steadily declines during this period. However, a thermal mass can be added under the collector area to enhance this effect if desired, even allowing for continual operation.

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## buenijo

Listen to these interviews of Steven Harris. 

This man has genuine knowledge, experience, and common sense about alternative energy:

http://www.thesurvivalpodcast.com/tag/steven-harris (NOTE: scroll down to the bottom of the page to access the first of the series of interviews)

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## buenijo

VIDEO: "How It's Made" episode featuring Cyclone Power Technologies (developer of modern piston steam engines):

http://www.youtube.com/watch?v=6NPpelLCIkk

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## buenijo

I was not aware this is being seriously researched until just now. Apparently, solar concentrators are being used to heat air directly for use in large engines. In (A) air is used as a heat transfer medium to make steam. Fuel may be burned to heat the air when solar energy is insufficient. In (B) pressurized air is heated and allowed to expand in a turbine just as I described in a previous post. Again, fuel may be burned to boost the output if desired. Also, the hot air exhaust from the turbine is used to make steam for a combined cycle power plant. This makes so much sense to me... I think it's a great idea. An important point here is that the system is capable of operating on 100% solar, 100% fuel, or anywhere in between... and at very high thermal efficiencies. http://www.volker-quaschning.de/arti...als2/index.php

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## buenijo

A very nice rocket mass heater/stove: www.zaugstoves.com

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## buenijo

Study measuring the performance of a wood furnace with thermal mass (a masonry wood stove). This system works on the same fundamental principle as a "rocket mass heater". http://pages.uoregon.edu/hof/W09HOF/...Heater_ppr.pdf 

The performance is impressive. An average wood fuel consumption of 35 pounds per day over a week is used to maintain a temperature difference between inside and out of roughly 20F. Outside temperatures averaged in the mid-high 40's F during the period. The home is 1700 square feet. Total fuel consumption represented about 8700 btu/hour. However, it is estimated that 80% of this heat was retained in the home, so that's about 7000 btu/hour provided by the furnace. 

I find this study to be interesting because it confirms some research I had done before on the average heat loss from homes. I was considering cooling at the time, but the same principles apply. This study suggests that cooling the same home by 20F lower than average outside temperatures will require about 7000 btu/hour averaged over a 24 hour period. I realize this is only an estimate, and certain heat gains (especially solar gain through windows and attics) should be minimized when cooling. Anyway, let's consider an average outside temperature of 85F during summer. This is about right for many hot regions in the south. It might be 95 during the day, then drop to 75 at night for an overall average in the mid-80's. Now, an average of 75F in the home is good enough. So, this suggests that the cooling rate might be as low as 3500 btu/hour averaged over a 24 hour period. Well, this would consume only about 9 KWh of electricity for standard window a/c units. This suggests that perhaps the idea I mentioned elsewhere in using a large solar array to power window units as the loads for battery diversion charge controllers might work rather well. Remember, the Achilles heel of off grid power systems is the BATTERY. This cooling system does not require much of a battery system, and it can avoid a lot of battery losses.

This low cooling load also suggests a modest desiccant evaporative cooling system can be effective when operated 24/7. So, a system devised for space heating during the winter months to provide a continual heat on the order of 10,000-15,000 btu/hour (which should be plenty where winters are modest as suggested by this study) can also provide enough cooling for the same home during a hot summer. In that case a desiccant evaporative cooling system should provide on the order of 5000-7500 btu/hour cooling when such a heat source is provided. Please note that I realize these are estimates, and they are for illustrative purpose only. However, when considering a more modest off grid home on the order of 1000 square feet and well designed, then this does suggest impressive performance is possible for the cooling systems I had proposed earlier.

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## buenijo

Great site, check it out: http://www.frugal-living-freedom.com/

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## buenijo

Thoughts on water purification: There are many different methods. I prefer the one that is cost effective, efficient, simple, does not require specialized equipment, and that can process a large volume of water quickly and efficiently. Therefore, I prefer pasteurization. Any controllable source of heat at a high enough temperature will work well. Steam would be ideal, but a small furnace operated at a constant low output would be fine. Make sure to use the heated (pasteurized) water to preheat the cool (unpasteurized) water before it moves to the heater. A copper heat exchanger has fantastic heat transfer properties, so go with copper tubing. For the final pass take the water through a filter of sterilized sand followed by charcoal. Everyone says "activated" charcoal, and yeah this is best, but plain crushed charcoal is a lot simpler to make and works well enough. You're just wanting to remove nasties that will make it taste bad and be a bit more susceptible to re-establishing a culture of pathogens. The heat regeneration provided by preheating the water will increase the efficiency many fold because most of the heat placed into the water when the system first starts to heat up can be transferred to the cool water before it reaches the heater (*). This means you need a lot less heat for the same flow rate, or you can have a much higher flow rate for the same heat input rate. I say go with the higher flow rate. So, in this case you just admit water slowly during start up to get really hot water leaving the heater, then you can speed things up to a constant level once you have the preheated water moving through the system. A thermostatic valve would be awesome here. Make sure to flush the lines with super hot water on first start up.

(*) Note that the efficiency gains possible by preheating the water in this manner is not trivial. Expect to increase the yield on the order of 5 fold using this process. More is possible.

ADDENDUM: I realized recently after talking with a friend of mine that pasteurizing water using heat regeneration may not be so easily understood by many. So, consider the following scenario. Water can be pasteurized by heating to 160F for 15 seconds. If the temperature is higher, then it can be held at this higher temperature for less time. So, let's say you put a pot of water on a burner and heat the water to 200F. It is now well pasteurized. The harmful microorganisms in the water are dead or neutralized. So, you don't need the heat in the water anymore. Rather than wasting this heat, use it to preheat the next batch of water to be heated. Of course, the most efficient process would be the one that sends water through continually. Consider the two scenarios:
(1) You send 50F water at 1 gallon per minute through a heater to take the temperature to 200F. It is well pasteurized.
(2) Before the 50F water gets to the heater it first passes through a heat exchanger to be heated by the 200F water leaving the heater. The 50F water gets heated to 170F, and the 200F water is cooled down to 80F (actually, it's a little cooler due to thermal losses). Therefore, without increasing the output of the heater, you can now increase the water flow rate to 5 gallons per minute and get the 170F heated to 200F. The water is heated to greater than 160F for what is likely a lot longer than 15 seconds, and it reaches 200F. It is well pasteurized.

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## buenijo

I was just wondering that it may be practical to heat a water pasteurizing system with solar energy using photovoltaics by using the heat regeneration scheme discussed in the previous post. Before one rejects this notion completely (and I might have done just that in the past), consider the details. Sure, there is a lot of energy in the available sunlight that is not accessed with photovoltaics vs. using the solar energy for direct heating. However, it's not so easy to catch and hold most of this energy, particularly when higher temperatures required for water pasteurization is desired. Conversely, with photovoltaics the energy can be delivered to a very compact water heating vessel that can be easily highly insulated. Furthermore, the system can be tightly controlled.

If we assume that the cold unpasteurized water is preheated by the hot water leaving the heating element to within 10F of the peak temperature, and neglecting thermal losses and the pump load, then one KWh of electricity should be able to pasteurize on the order of 40 gallons of water. This is not trivial. Most areas in the U.S. provide at least 2.5 sun hours each day even during winter days. A 1 KW array should process more than 100 gallons of water under these conditions. In principle, it's possible to control flow through the system with feedback from a thermostat that can be used to operate a small pump. In my opinion, with the high reliability of PV panels, this option should not be discounted.

ADDENDUM: I checked out the specs on a commercial solar water heating panel (not evacuated tube design, but flat plate). It turns out that heating the water to a level sufficient for pasteurization results in substantial thermal losses. More important, these losses rise with decreasing solar irradiance. Considering the losses here, it turns out that the actual mass of water that can be pasteurized by this water heating panel is LESS than what's possible from a PV array of the same price. Very interesting results indeed. Of course, one could just go with a small furnace fueled by wood chips and call it a day. However, it sure is an interesting prospect to have a fully automated water processing system that consumes no fuel.

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## buenijo

Another wacky idea for air conditioning in the off grid setting. Drive an automotive ac compressor with a dc motor powered by a solar array. This seemed a bad idea when I first considered it, but these compressors are durable and efficient despite the poor performance of automotive a/c systems. The reason for this is not the compressor, but the small heat exchangers and higher air temperatures available for the condenser. A system could be optimized for efficiency by using large heat exchangers and providing good cooling. Performance could be further enhanced by reducing the evaporator temperature, and this can yield good results with dry air (I am considering air dried with a desiccant, of course).

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## buenijo

Here is an interesting approach to space cooling for those who desire a simpler system and suitable for a modest dwelling. I was considering a system specifically to minimize electricity requirements. Use a small biomass furnace to regenerate a calcium chloride desiccant solution to high concentrations. This solution must be cooled and pumped to the air dryer. This might be a vessel with packing material (can't obstruct air flow much) over which the concentrated calcium chloride solution continually flows and must be distributed evenly over the packing material (I speculate here, but one might use rocks or maybe even large wood chips). A large insulated duct is connected to the top of this vessel that extends vertically over a good distance. Since the calcium chloride solution increases in temperature as it absorbs water vapor, this air moving through the vessel will be heated. I speculate that retaining this heat with insulation on the vertical ducting, then transferring the dry hot air through a long uninsulated horizontal section of duct for cooling to return to the home might induce enough differential pressure through natural convection to dry the air in a small home efficiently.

As long as the air is dry, then an evaporative cooler can work well. A small portable commercial unit might be used for spot cooling as these use low power fans. It may be possible to provide an evaporative cooling effect by using a low volume, high pressure water pump to send water through atomizing nozzles, and this would consume the least electricity.

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## buenijo

I'm expanding a bit on the the idea of using a small wood gas engine system to power an automotive a/c compressor for air conditioning. I considered the idea a couple years back (well, actually longer ago than that), but I didn't really consider it seriously until more recently. First of all, let me emphasize that the desiccant system is particularly promising for humid regions, and it should be used at least in tandem with a vapor compression system. If this is not done, then the vapor compression system will have to work harder harder. The good news is that some heat from the wood gas engine system can be used to regenerate the desiccant. Furthermore, it is possible to devise the system to freeze a large store of water that can be drawn upon over the following 24 hour period. All in all, I think this configuration has merit. I will summarize here:


1. Operate a small wood gas engine system at a constant output at roughly 5 hp to drive an automotive a/c compressor (or whatever minimal output can be reliably and efficiently maintained, and this is often about 5 hp for a wood gas engine system). How long you operate the system depends on the cooling load and how much fuel you want to burn.

2. Use the evaporator coil to freeze water contained in an insulated vessel. This latter configuration might work well particularly if the water were never fully frozen (just nearly so - make a slush) because ice tends to insulate. Sizing the water vessel properly would make this simple. Use this cold water for air cooling in a mini chilled water system. Note that it may be possible to cool a heat transfer fluid like a water/glycol contained in the insulated vessel, then place smaller water vessels inside the vessel. This will prevent ice formation on the evaporator tube while also freezing water. The water/glycol can be used directly in fan coil units for cooling.

3. Use the engine cylinder cooling blower along with engine exhaust to regenerate a desiccant. This desiccant can be used for both space cooling (see desiccant cooling) and space heating (see desiccant heating).

5. Use heat from the gasifier fuel gas cooler to dry the next batch of wood chip fuel.

5. Use the steam emitted from the heated desiccant to heat  a store of water - waste not want not!

6. Operate the system during evening or morning when the outside temps are lower. Anything that gets the condenser temps down with increase efficiency.

7. May also drive an alternator with the engine for battery charging at this time.

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## buenijo

Good YouTube channel for solar thermal projects. http://www.youtube.com/watch?v=WP8H5IOTwYU 
Videos show very simple designs for water and air heating systems using solar energy including a hot water storage tank and hydronics heating system used to heat the floor above the basement. This is about as simple as it gets, but very effective. 

There is a lot of potential in solar thermal and photovoltaics at the residential scale. I've become increasingly interested in making use of direct solar energy over the last year or so in order to minimize fuel consumption. I can think of several principles that can dramatically increase efficiency in these systems. With solar thermal, optimizing efficiency is all about increasing solar capture and minimizing thermal losses. Certainly if someone desired to provide most of their space heating and water heating with solar, then a large thermal mass is necessary. An ideal system would store heat in a phase change material contained in an insulated enclosure, then tap this heat for all space heating and water heating needs. However, good old fashioned water is really the only practical and cost effective thermal mass for this particular application. You know, 1000 gallons of water is not too imposing, and yet it weighs more than 8000 lbs. Take the temp of that up by 50F with solar heat, and you'd be storing 400,000 btu of heat energy. A modest well insulated home can get by on this, and a simple wood furnace can heat this water via thermosiphon when solar is insufficient.

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## buenijo

See how easy it is to convert a small window a/c unit for water heating using the condenser: http://www.youtube.com/watch?v=GBlrewwpt8M. Note the energy recovered at 7500 btu/hour! This represents the energy removed from the air at the evaporator and most of the energy consumed by the compressor motor. That's a lot of energy at more than 2 KWh per hour (i.e. 2 KW for a roughly 500 watt compressor motor). Operating this unit over one summer could fully pay for itself with the electricity savings alone. Kinda seems absurd to consume energy in operating an a/c system while consuming additional energy to heat water, doesn't it? 

Imagine placing a small pulley on the shaft from which the condenser fan is removed, then using this shaft to drive a small water pump. This water could then be used to water cool the condenser.  If geared properly, then it should provide optimal heating with a single pass of the water provided the temperature of the supply is within a certain range. What I'm thinking here is replacing the cover on the unit, but placing the condenser in an insulated vessel that is secured to the outside of the unit. The hoses connected to the pump would penetrate the cover of the unit. This should restore the convenience of the unit and make it compact and attractive. Plus, water cooling the unit would provide a lot of versatility with respect to placing the unit as it would no longer have to be placed in a window for cooling. Perhaps this latter advantage would make this retrofit worthwhile even if the heat is not put to use. For example, perhaps the heated water could be distributed to a heat exchanger (or large water tank) placed outside to cool the water, then the water would return to the pump in a closed circuit. Being able to place a small a/c unit precisely for spot cooling would allow for consuming a lot less energy (why cool an entire room if you don't have to?). Also, this approach might conceivably be used to circulate water through a heat exchanger buried in the ground (a mini geothermal heat pump). On that note, perhaps a unit could be retrofitted to cool the evaporator with the evaporator fan removed and the shaft used to drive the pump. Then, a geothermal heating system could be had. Seriously, if one were living in a very small and well insulated cabin, then something like this might be effective for heating and cooling.

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## buenijo

Excellent discussion on an experimental off grid home with a series of short articles discussing the system:

http://howtousesolar.com/our-off-gri...-it-all-began/

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## buenijo

I found a 5 ton ammonia absorption chiller designed for residential applications. I'm looking into it, but here it is: http://www.firechill.com/products/ac500/ Too big and too much electricity for off grid use, but interesting nonetheless.

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## buenijo

My opinions on a suitable battery system for an off grid power system:

I consider overall (long term) costs to be the single most important factor. Getting the best value for the battery is paramount. I write "value", not price. What kills a battery is excessive discharge and temperature extremes. Overcharge is also a killer, but it's not so much a problem as the other two. I say go with a new forklift battery. Size the battery such that a full charge on the battery will provide you with all the electricity you need over a 24 hour period without dropping the state of charge below 60%. You never want to drop below 50% state of charge. The bigger the battery, the longer it will last all else equal. The charging efficiency of a battery is very low while it's at a high state of charge. However, with the price of solar panels down so much I consider it preferable to choose a larger battery that stays at a high state of charge and buy extra panels. The overall efficiency can be improved dramatically by using most of your electricity while the panels are producing as this effectively bypasses the battery charging. One example would be placing a thermal mass in freezers and refrigerators and putting them on timers to operate during the day while the panels are producing. Another example is using any high power electrical appliance only when the panels are producing. 

Forklift batteries are hands down the best value I've seen in an off grid battery system. You're looking at about $130-$150 per kilowatt hour of rated storage capacity (80% discharge at 20 hour rate). So, a 1050 pound 24 volt forklift battery will cost you about $2500 delivered in the 48 States (see www.giantbatteryco.com), and will provide 19 KWh electricity at rated capacity. In practice, if you limit discharge to no lower than 60% state of charge and considering inverter losses, then a fully charged battery will provide about 8 KWh of AC electricity, and this is more than most off grid home need each day. Keep a wood gas engine system around for backup charging, and keep a large solar array to minimize wood fuel consumption for this purpose.

As far as the solar array goes, I recommend using two parallel arrays each with a separate controller. These can feed a common battery. I've not found any 48 volt forklift batteries that are not truly massive (way overkill for most off grid set ups). Unfortunately, most solar charge controllers are limited to about 80 amps. At 24 volts this limits the array to no more than 2000 watts. If you're good with what a 2 KW array provides, then fine. If not, then I recommend two parallel arrays, but you'll have to get two controllers. This isn't so bad as it provides redundancy. In my particular case, I'm planning on a 3 KW array to provide a net 6-8 KWh per day in east Texas. I'll get a wood gas engine system at about 2500 watts bulk charging rate for the battery for use only when required to prevent excessive discharge on the battery (bulk charge during early morning, then let the solar array take the battery the rest of the way. Personally, I wouldn't break out the gasifier until the battery voltage drops to under 50% state of charge. 

Well, that's enough ranting for now. Later!

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## klamath

> My opinions on a suitable battery system for an off grid power system:
> 
> I consider overall (long term) costs to be the single most important factor. Getting the best value for the battery is paramount. I write "value", not price. What kills a battery is excessive discharge and temperature extremes. Overcharge is also a killer, but it's not so much a problem as the other two. I say go with a new forklift battery. Size the battery such that a full charge on the battery will provide you with all the electricity you need over a 24 hour period without dropping the state of charge below 60%. You never want to drop below 50% state of charge. The bigger the battery, the longer it will last all else equal. The charging efficiency of a battery is very low while it's at a high state of charge. However, with the price of solar panels down so much I consider it preferable to choose a larger battery that stays at a high state of charge and buy extra panels. The overall efficiency can be improved dramatically by using most of your electricity while the panels are producing as this effectively bypasses the battery charging. One example would be placing a thermal mass in freezers and refrigerators and putting them on timers to operate during the day while the panels are producing. Another example is using any high power electrical appliance only when the panels are producing. 
> 
> Forklift batteries are hands down the best value I've seen in an off grid battery system. You're looking at about $130-$150 per kilowatt hour of rated storage capacity (80% discharge at 20 hour rate). So, a 1050 pound 24 volt forklift battery will cost you about $2500 delivered in the 48 States (see www.giantbatteryco.com), and will provide 19 KWh electricity at rated capacity. In practice, if you limit discharge to no lower than 60% state of charge and considering inverter losses, then a fully charged battery will provide about 8 KWh of AC electricity, and this is more than most off grid home need each day. Keep a wood gas engine system around for backup charging, and keep a large solar array to minimize wood fuel consumption for this purpose.


What is the expected lifespan of those batteries?

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## buenijo

> What is the expected lifespan of those batteries?


It depends on how they're used. In their designed application (i.e. forklift duty) they are often near fully discharged during a work day, and fully charged before the next duty cycle. Often they see at least one full duty cycle each work day. You'll have to verify, but I recall a typical life time of roughly 6-8 years under this heavy industrial usage. However, they are not discarded at this point. Rather, they are often sold second hand (used). The cells at this point might not be able to take a forklift through a full work cycle, but they often work very well in light duty applications (like off grid). In the off grid application, they last 15-20 years by most accounts I've seen. I know of one individual who claimed 10 years on a USED forklift battery, several claimed 15-20 years for a new battery, and one claimed 33+ years for a new battery. Note that this represents information I've mined over the last 5 years or so. NOTE: Personally, I don't recommend that anyone consider a used battery.

http://www.sustainablepreparedness.c...newable-energy

NOTE: See post #3 in this thread.

ADDENDUM: BTW, the much lauded Rolls-Surrette battery has a 6 volt, 400 amp hour, 127 pound battery that I've seen for sale at a good price of $340 (see www.wholesalesolar.com). This price is on par with the price I've seen for forklift batteries. However, there is likely to be a hefty additional charge for delivery. The main advantage here is that the 127 pound battery is much easier to handle than a single massive forklift battery. This seems a value worth the extra cost. By all accounts I've seen, the Rolls-Surrette is among the best battery one can choose for off grid use.

ADDENDUM: The company that I linked provides forklift batteries at the listed prices without delivery charge. Also, they pick up a discarded battery with no charge. This is interesting as one common complaint on forklift batteries is their massive size. Well, if you can have a new battery delivered with the old battery carried off, and all with no charge beyond the cost of the new battery, then that seems quite a deal.

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## buenijo

I started a project recently to develop a micro absorption chiller. I don't yet have anything worthwhile to share, but I'll share what I can when I can. The system is to use lithium bromide as the absorbent. I've acquired the lithium bromide as well as vacuum equipment, but I have yet to get suitable fluid pumps. Note that one must take time to prevent going through precious capital too quickly. 

FYI, while I am doing only basic testing for now, if the results of my testing is positive, then I will assemble a complete test unit. The system I have in mind is to operate at a cooling capacity of 1 refrigeration ton (or 12,000 btu/hour), and I believe this is sufficient for a modest off grid home - even a fairly large home provided the unit is designed for continual operation at this rate and the cooling is split. A small wood gasifier is the desired heat source, but there should also be a provision for using natural gas. The idea for now is to design the system to run at a constant output with chilled water distributed to small fan coil units placed in the home. It's possible to vary the output over a  limited range while keeping high efficiency, but one of the best means to reduce fuel consumption would be to split the cooling (for example, send chilled water to the fan coil unit in the main living area of the home during the day only, then send chilled water to small fan coil units in sleeping quarters at night - of course, a proper off grid cabin could use a single fan coil unit). This is being designed specifically with off grid living in mind. There will also be a provision for heating water with the condenser of the system. It's also possible in principle to configure the system to pump heated water to the fan coil units for space heating. It's also possible to configure the system as a heat pump for space heating, but this requires a source of heat at a moderate temperature such as geothermal or a body of water at least 50F. Right now I'm taking things one step at a time. This is a long term project that will be slow going.

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## buenijo

I performed an interesting experiment today. I was able to draw a high vacuum within a vacuum chamber with a poor vacuum pump by using water vapor to displace the air. I placed hot concentrated lithium bromide solution on the bottom of the vessel, then placed hot water in an insulated container above the solution. I then drew on the chamber with the vacuum pump with a suction line that extended down into the vessel just above the solution. The vacuum pump was able to draw down the vacuum enough to boil the hot water down to about 70F. The idea here is that the water vapor that is less dense than air will displace virtually all the air in the vessel and force it out the vacuum pump suction since this suction is placed at a low point in the system. Once the vacuum pump could no longer boil water to a lower temperature, I then shut the valve and disconnected the pump. I then placed the vessel in a shallow water bath to cool the lithium bromide solution at the bottom of the vessel. Shortly after placing the vessel in the water bath the water within the vessel began to boil and the vacuum gage showed a reducing pressure and the water thermometer showed decreasing temperature. The rate of temperature drop was not fast, but was steady. A gentle swirling of the vessel increased the rate of water evaporation as expected. The temperature fell at a steady rate to an indicated temperature of -1.1C... let's just call it freezing. However, the water showed no obvious signs of actually freezing, it's just really freakin cold. I haven't broke vacuum yet, but once I do I'll check for any signs of ice. Note that the main purpose of this test was to verify that a combination of crappy vacuum pump and water vapor displacement of air can get all the air out of a vacuum vessel. Test is successful.

ADDENDUM: I broke vacuum. No ice, just ice cold water at 33F.

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## buenijo

The latest on my chiller project (beyond being very slow going AND expensive) is that I've sourced and tested the pumps I need, and they work perfectly. I am very pleased. This was one of my major concerns. So, I have everything in place for the next phase of testing which will be the most important: absorber design. I'll post more when I have it.

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## buenijo

I had an independent thought a few days ago on how to go about building a flat plate solar collector while also keeping the interior under a high vacuum for insulation. The purpose is to generate high temperature water and/or steam without resorting to concentration or tracking, and to minimize thermal losses because most flat plate collectors designed for water heating see very poor efficiency at high temperatures. Well, just a few google clicks showed this to have been done before. I believe I can build a unit for about $100 per square meter, and I don't know what the commercial units cost (not yet). Here is one example I stumbled on: http://www.srbenergy.com/pages/carac...s-del-colector . This unit and others are characterized by achieving high temperatures without concentration and with minimal thermal losses to ambient air as expected. This kind of system seems ideal for generating high temperature saturated water under pressure for driving an absorption chiller efficiently. I'm liking the idea of tapping solar heat when its available for space heating, water heating, and space cooling... but then using a biomass gasifying furnace when solar is not available. Use photovoltaics with battery storage for the relatively small amount of electricity required, and one may also use a small wood gas engine system for battery charging on rare occasions when solar is insufficient (may even use the same furnace). Lots of possibilities come to mind.

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## klamath

> I started a project recently to develop a micro absorption chiller. I don't yet have anything worthwhile to share, but I'll share what I can when I can. The system is to use lithium bromide as the absorbent. I've acquired the lithium bromide as well as vacuum equipment, but I have yet to get suitable fluid pumps. Note that one must take time to prevent going through precious capital too quickly. 
> 
> FYI, while I am doing only basic testing for now, if the results of my testing is positive, then I will assemble a complete test unit. The system I have in mind is to operate at a cooling capacity of 1-2 refrigeration tons. A small 
> wood gasifier is the desired heat source, but there should also be a provision for using natural gas. The idea for now is to design the system to run at a constant output with chilled water distributed to small fan coil units placed in the home. It's possible to vary the output over a  limited range while keeping high efficiency, but one of the best means to reduce fuel consumption would be to split the cooling (for example, send chilled water to the fan coil unit in the main living area of the home during the day only, then send chilled water to small fan coil units in sleeping quarters at night - of course, a proper off grid cabin could use a single fan coil unit). This is being designed specifically with off grid living in mind. A first test unit will be single effect. If the results are good, then a double effect system will be configured. There will also be a provision for heating water with the condenser of the system. It's also possible in principle to configure the system to pump heated water to the fan coil units for space heating. It's also possible to configure the system as a heat pump for space heating, but this requires a source of heat at a moderate temperature such as geothermal or a body of water at least 50F. Right now I'm taking things one step at a time. This is a long term project that will be slow going.


I am working on an off grid walk in freezer. If you have an interest I have a thread going here. http://hvac-talk.com/vbb/showthread....ment-questions

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## buenijo

> I am working on an off grid walk in freezer. If you have an interest I have a thread going here. http://hvac-talk.com/vbb/showthread....ment-questions


I checked out the link briefly. There is some good advice there. Using two or three small inits for redundancy is a good idea. Going with urethane insulation and being generous with its application is good. If you can go with water cooling the condenser then definitely do it as this will increase efficiency. One comment on the link suggested that water cooling is not a benefit if the water is not much cooler than the air, but that's wrong. It takes a lot less enegy to flow water over a condenser than air, so water cooling will reduce energy required even if the condenser temperature is constant... but in practice water cooling often reduces the compressor load significantly as well. If your goal is to reduce electricity consumption, then an ammonia absorption system would be ideal. Unfortunately, this would require a lot of development work. If you have the gumption, then I'll discuss it further. However, vapor compression does seem more practical in this particular case mainly because it's possible to charge the freezer and let the insulation and thermal hold the temps until the following day. I believe photovoltaics will be useful here. If you can find a suitable compressor that ismechanically driven as opposed to a hermetic electric motor drive unit, then consider driving such a compressor with a solar array and modest battery system used to power a dc motor. Yeah, it's a big job but it does seem an ideal configuration. What I'm thinking is to configure the system to run only when the solar array is producing as this will not require any significant battery discharge. This would also avoid inverter losses and it would be a lot simpler to get this to handle the motor starting current.

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## klamath

> I checked out the link briefly. There is some good advice there. Using two or three small inits for redundancy is a good idea. Going with urethane insulation and being generous with its application is good. If you can go with water cooling the condenser then definitely do it as this will increase efficiency. One comment on the link suggested that water cooling is not a benefit if the water is not much cooler than the air, but that's wrong. It takes a lot less enegy to flow water over a condenser than air, so water cooling will reduce energy required even if the condenser temperature is constant... but in practice water cooling often reduces the compressor load significantly as well. If your goal is to reduce electricity consumption, then an ammonia absorption system would be ideal. Unfortunately, this would require a lot of development work. If you have the gumption, then I'll discuss it further. However, vapor compression does seem more practical in this particular case mainly because it's possible to charge the freezer and let the insulation and thermal hold the temps until the following day. I believe photovoltaics will be useful here. If you can find a suitable compressor that ismechanically driven as opposed to a hermetic electric motor drive unit, then consider driving such a compressor with a solar array and modest battery system used to power a dc motor. Yeah, it's a big job but it does seem an ideal configuration. What I'm thinking is to configure the system to run only when the solar array is producing as this will not require any significant battery discharge. This would also avoid inverter losses and it would be a lot simpler to get this to handle the motor starting current.


All good points. Solar is still out of my budget as far a costs but it is getting closer. The EPA regs restrict a lot of experimenting on refrigeration systems. Without a license I don't even believe it is possible to buy refrigerant.

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## buenijo

> All good points. Solar is still out of my budget as far a costs but it is getting closer. The EPA regs restrict a lot of experimenting on refrigeration systems. Without a license I don't even believe it is possible to buy refrigerant.


I didn't read the link well at all. If you have 6 KW from a hydro turbine, then you can make this work. Sorry for recommending solar as you simply have no use for it with a hydro resource like that. You're in a great position with that resource. 

I think the heat influx will be significantly less than 12,000 btu/hour based on the size of the freezer and the insulation you discussed in the link. With that kind of insulation I expect a value roughly half this figure at about 6,000 btu/hour and possibly less. Here is my reasoning: an 8 cf deep freezer will consume roughly 1 KWh of electricity over a 24 hour period. If it were super insulated like your freezer, then this would easily drop to about 1/2 KWh per day. This is confirmed by looking at the specs on super insulated "solar" freezers with 4" urethane. The surface area of an 8' by 8' by 8' freezer is about 16 times that of an 8 cf freezer (assuming 2' by 2' by 2'), so the larger freezer would see a heat influx of roughly 16 times that of the smaller freezer, and therefore consume roughly 16 times the electricity, or 8 KWh per day. Yes, a very rough estimate. I do KNOW that superinsulating a freezer with several inches of urethane will dramatically reduce heat influx as I've read accounts of this being done to augment the insulation on existing large units with a resulting dramatic reduction in electricity consumption. This suggests a compressor at only 333 watts could cool the unit (assuming a continual operation). The compressors for large chest freezers might actually work here if running continually of course. If possible, then securing several such systems could be done for both redundancy and operating two in tandem if required. Furthermore, this approach would allow for reducing the starting load, and such a small compressor would not present any problems. It seems a big job to engineer this right, but I don't think it needs a large compressor.

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## klamath

> I didn't read the link well at all. If you have 6 KW from a hydro turbine, then you can make this work. Sorry for recommending solar as you simply have no use for it with a hydro resource like that. You're in a great position with that resource. 
> 
> I think the heat influx will be significantly less than 12,000 btu/hour based on the size of the freezer and the insulation you discussed in the link. With that kind of insulation I expect a value roughly half this figure at about 6,000 btu/hour and possibly less. Here is my reasoning: an 8 cf deep freezer will consume roughly 1 KWh of electricity over a 24 hour period. If it were super insulated like your freezer, then this would easily drop to about 1/2 KWh per day. This is confirmed by looking at the specs on super insulated "solar" freezers with 4" urethane. The surface area of an 8' by 8' by 8' freezer is about 16 times that of an 8 cf freezer (assuming 2' by 2' by 2'), so the larger freezer would see a heat influx of roughly 16 times that of the smaller freezer, and therefore consume roughly 16 times the electricity, or 8 KWh per day. Yes, a very rough estimate. I do KNOW that superinsulating a freezer with several inches of urethane will dramatically reduce heat influx as I've read accounts of this being done to augment the insulation on existing large units with a resulting dramatic reduction in electricity consumption. This suggests a compressor at only 333 watts could cool the unit (assuming a continual operation). The compressors for large chest freezer might actually work here if running continually of course. If possible, then securing several such systems could be done for both redundancy and operating two in tandem if required. Furthermore, this approach would allow for reducing the starting load, and such a small compressor would not present any problems. It seems a big job to engineer this right, but I don't think it needs a large compressor.


I have been researching the cold plates the one guy mentioned. So far I can only find cold plates the hold the box at 0 degrees. I am pretty set on the -15 temperature. For really preserving food the colder the better. My family did canning for years but I love freezing as almost everything is better about freezing. 
As far as load calculation you can download a free program here. http://www.keepriterefrigeration.com/node/213 It is a Good program and it shows about what you said as far a BTU's per hour. All the variables can be figured in from the type of food to the light wattage.

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## buenijo

> I have been researching the cold plates the one guy mentioned. So far I can only find cold plates the hold the box at 0 degrees. I am pretty set on the -15 temperature. For really preserving food the colder the better. My family did canning for years but I love freezing as almost everything is better about freezing. 
> As far as load calculation you can download a free program here. http://www.keepriterefrigeration.com/node/213 It is a Good program and it shows about what you said as far a BTU's per hour. All the variables can be figured in from the type of food to the light wattage.


Thanks for the resource, I will bookmark it. If my figures are close, then it's a testament to the value of estimation when it has a solid foundation. I've found it very useful to check my estimates against the claims of others, even professionals... after all, everyone can be wrong at times.

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## buenijo

I recently became aware of the Xantrex XW inverters. These are very sophisticated inverters designed for integrating multiple power sources with a battery system in the off grid setting. One system I am aware of uses a 6 KW solar array, 7 KW wind turbines, and a generator to power an off grid all electric home (along with a 7000 pound battery system). The inverter can be programmed to automatically start the generator on low battery voltage or high inverter load. It's the latter feature that I find particularly interesting. Since the efficiency of a constant speed generator varies widely over its power range with the optimal efficiency near the highest rated power, then the system is ideally designed such that the generator is always loaded to its optimal output. Well, that's precisely what this inverter can do! So, let's say the inverter is rated for 40 amps continuous, but the demand load climbs above this value. It's possible to program the inverter such that the generator starts, warms up, and then goes online. Now, let's say the generator is most efficient at 30 amps output, and let's say the demand load is 50 amps. Well, the system is designed to allow the generator to provide 30 amps, then let the solar/wind/battery system to provide the balance of 20 amps. Also, if the battery is not full charged, then any excess electricity provided by solar/wind is diverted to the battery for charging. Also note that the inverter stays in phase with the generator at all times. Folks, this performance is quite extraordinary. The system makes it possible to power an off grid home as if it were grid tied. As long as the solar/wind system can provide the bulk of the energy consumed, and as long as the loads are managed reasonably well and energy is conserved, then fuel consumption can be minimal - especially when considering the ability to operate the generator where thermal efficiency is optimal. A Diesel engine can provide ac electricity at an overall efficiency well over 20%, and this corresponds to 8-10 KWh of ac electricity per gallon of fuel consumed (around 40 cents per kwh not including cost of hardware). I don't suggest a Diesel or other generator be used as a primary source of electricity in the off grid setting, but it can be very useful to buffer the solar/wind system along with protecting a battery from excessive discharge. Put the heat from the generator to use in water heating, and the value of the fuel can be further leveraged. Consider that catching half the heat otherwise wasted will triple the energy harvested from the generator system.

All of this hardware is expensive. However, I'm now thinking that a modest and well designed off grid home can be powered reliably and efficiently with a solar/generator hybrid system. If the home is very well insulated, then I believe a more or less conventional electric motor driven vapor compression a/c system is a viable candidate for space cooling mainly because of how this inverter can manage the loads. People are doing it today... although, not without a hefty price tag along with dependence on refined fuels. However, it seems the most practical off grid solution. In particular, I think it's a practical configuration for powering a small home in a remote site where grid power is not available.

I continue to put a premium on configurations that minimize both the battery size and discharge, and that minimize the consumption of refined fuels. Under these conditions a/c would have to be provided almost exclusively during the day when the solar array is producing, and electricity should not be used for any heating applications (unless it were a dump load to prevent excessive battery charge rates). It makes sense to me to use a small biomass furnace for all heating applications. I still consider a micro absorption chiller with heat recovery and fueled by biomass as an ideal solution for all but electricity generation, but these are not available.

http://www.youtube.com/watch?v=KMBdaukbahE

NOTE: This individual who posted the video owns the system I described earlier (6 KW solar and 7 KW wind). Hot summer months require the use of his small Diesel generator to provide sufficient cooling, but the system dramatically reduces fuel consumption that would otherwise be required. He says his system would cost about 70K if installed today, but much of that cost is the wind turbines.

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## buenijo

I was killing time recently doing research to figure what the average household electricity consumption is in Texas for providing a/c. I can't come up with anything other than estimates as the data is limited, but the figures are pretty much what I expected. A typical apartment from 750-1000 s.f. and modern construction will see an average of 500 KWh electricity per month for air conditioning alone in east Texas. The numbers vary widely depending on many factors, but this is a good round figure. 

Personally, I consider this square footage to be suitable for a modest off grid home. With good insulation, radiant barriers, shading, etc. I expect this figure to apply for such a modest home. A typical vapor compression a/c system consumes about 1 KWh for every 10,000 btu of cooling provided. Therefore, this home should require about 500/30 = 16.7 KWh of electricity for air conditioning to provide 167,000 btu of cooling. 

A typical single effect absorption chiller will see a COP of 2/3. This corresponds to about 250,000 btu of heat required to provide the aforementioned cooling capacity, or roughly 31 pounds of commercial wood pellets (assuming 8000 btu/pound). If purchased in bulk, then this quantity of wood pellets will cost about $4 for a total monthly fuel cost of $120 for air conditioning (along with all the heating applications provided at the condenser). The system can also be configured for space heating during winter months, and the same fuel consumption can support space heating and all other heating applications where winters are mild (as in east Texas). Now, one need not rely on commercial pellets, but I'm considering it only for sake of interest. If one were harvesting their wood, then know that green wood has roughly 4300 btu/pound, so one would need to harvest and process about 58 pounds of green wood for a day of operating such a system. The electricity consumed by such a system would be right at 1/4 that of a typical vapor compression system with the same cooling capacity, and this can be supported by a 1.2 KW solar array. 

The reason I'm going over this line of reasoning again is to reinforce my argument that a micro absorption chiller fueled by biomass could be one of the most useful off grid tools ever devised. Most important: it need not exceed a one ton capacity. You get space cooling, space heating, and heat for all manner of applications (with essentially free heat while in cooling mode) for water heating, potable water processing (pasteurization and/or distillation), and even biomass fuel drying for those who wish to process their own fuel. Also, the system is fundamentally simple. Therefore, if properly designed, then it can be made easy to service by the end user. The value of such a system has to be considered in light of this holistic perspective.

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## buenijo

I believe a modest and very well insulated off grid home can be cooled efficiently and effectively by powering a properly sized inverter air conditioner with a photovoltaic array. These units are a lot more efficient than conventional units. The compressor motor is a variable frequency ac motor with permanent magnet rotor. This reduces electricity consumption for two main reasons: (1) there is no electricity consumed in the rotor as is required in conventional motors, and (2) the system can adjust the frequency of the drive (and the speed of the motor) to match cooling demand. This feature makes the size of the heat exchangers for the unit relatively large during part load operation. The result is very efficient cooling of the heat exchangers at these lower outputs which drives down the differential pressure across the compressor which in turn reduces the load on the motor. The performance based on my limited research is an overall COP of 4.0 in many models at part load operation, and even higher in some cases (up to 5.0 in some models). This is ideal for a PV array since the cooling capacity needs to be highest during the day when the solar array is producing, and this will avoid many battery losses by diverting more electricity directly to the compressor motor. However, at other times the cooling demand is likely to be lower, and the unit will operate most efficiently at part load during this time to minimize battery discharge. I've seen units that are programmable with timers that allow for adjusting the thermostat setting automatically at set times throughout the day. A low thermostat setting might be used during the day when the solar array is producing to cool the home rapidly as a thermal mass while also minimizing battery charge rate (and resulting battery losses), then raise the thermostat setting at other times to reduce the output of the unit for optimal efficiency and minimal battery discharge. The unit can also be programmed to shut off at a certain time and restart automatically (at least the unit I reviewed had this feature) - or a timer might be used. This seems a practical solution. Also, I understand that these compressor motors see much lower starting current than conventional units since they increase frequency to the motor incrementally on initial start up (and this is great for powering these units with power inverters off a battery system). While these units are sophisticated and more expensive, they have been mass produced for a long time now. For example, I understand that most if not all a/c units in Japan are the inverter type.

This approach does seem a practical way to achieve air conditioning in the off grid setting. A large PV array and large battery system would be required. Let's say a modest off grid home uses an inverter a/c system rated at 1.5 ton. This system would draw about 1750 watts of electricity when operated at full load (operate at full load by lowering thermostat setting), and this full load would be maintained whenever the large solar array is producing. At other times the unit is operated at a low part load of roughly 1/2 ton, and here it would draw only about 400 watts of electricity for a total electricity consumption of only 18 KWh over a 24 hour period. Most important is only about 7.2 KWh of this is taken from the battery, so a modest battery can handle this without excessive discharge (modest by off grid standards). How big does the solar array have to be? Well, let's consider average solar insolation of 6 KWh per square meter per day (summer time in east Texas). According to my estimates and calculations, a solar array rated at 4670 watts would be required to support this unit, this includes all losses. Of course, one would require additional solar panels to support other electrical loads. A solar array on the order of 6000 watts would be required here. Good news is that the unit cost of solar panels is remarkably low when purchased in bulk. 

By comparison, a micro absorption chiller that provides the same cooling capacity would consume 3-4 KWh of DC electricity (no large inverter required). The battery could be much smaller and still see less discharge. However, the fuel consumed each day would be equal to 43 pounds of wood pellets. Of course, all water heating needs are easily met (and other heating applications can be had like clothes drying, water distillation, biomass fuel drying, etc.). The chiller can also be configured for space heating. However, note also that the inverter a/c unit is generally configured to operate as a heat pump, so it will also provide heating during the winter months. If the winters are mild, then this is where these heat pumps do particularly well. There would be only about 3.5 KWh per square meter per day of solar insolation during the winter months in east Texas, but the large solar array used to provide a/c will provide quite a bit of space heating as well that should equal a bit more than half the cooling capacity during the summer months (so roughly 125,000 btu/day... equal to about 20 pounds of wood pellets, or about $1.50 of natural gas when on considers 80% furnace efficiency). 

In short, a modest off grid home with excellent thermal characteristics, a large PV array, a modest battery with excellent battery management, good inverter, and a few strategies to optimize things should make it possible to provide all the modern comforts in a totally off grid home. Gonna need a small biomass furnace to supplement heating applications, and a back up generator is necessary as well. 

So, which is better: (1) large PV supplemented with small  biomass furnace, or (2) biomass fueled micro absorption chiller supplement with small PV? I guess it depends mainly on whether or not biomass fuel is inexpensive and readily available, and the average solar insolation in one's region. Of course, one could always do both (large PV supplemented with biomass fueled micro absorption chiller). I kinda like this latter idea for disconnecting a typical suburban home from the grid (no bills!... well, you still have the property extortion, err "taxes"). Actually, this kind of system is suitable mainly for a remote/off-grid location.

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## buenijo

My chiller project has required me to work with vacuum equipment, and it's quite easy to work with a high vacuum when the size of the vessels are not large. I've considered different applications for vacuum including water distillation, and also ETHANOL distillation at reduced temperatures. I haven't yet done any serious research into the latter, but here is a site I stumbled on: http://homedistiller.org/equip/designs/vacuum . 

According to the claim, it's possible to achieve near 100% ethanol in a vacuum distillation apparatus. More important, the temperatures required for this distillation are so low that many sources of heat such as solar energy can be used efficiently. If someone is interested in fuel ethanol production, then this prospect should be researched. Getting high alcohol percentage (over 90%) with a single pass from a simple still would be very interesting. Of course, the main problem here is finding an inexpensive source of fermentable sugars. There is also the problem of optimizing an engine for ethanol (one possible solution is to vaporize ethanol and admit the vapors with the intake air to a Diesel engine - ethanol can tolerate very high compression). Also, I sure like the idea of placing the condenser of such a unit inside the home during winter months - may as well get some free heat if you're doing something like this.

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## buenijo

I've been seeing real world practical difficulties in my absorption chiller project, but it's nothing that I had not expected. Developing something like this from scratch is a real pain in the ass. It's one thing to understand clearly the physics of a process, and another thing entirely to build a working system... especially with a limited budget of time and money, and few fabrication skills. I'm shifting gears as I have a new idea on how to go about building the absorber and evaporator. I can't discuss specifics, but the design makes fabrication simpler, and it's modular to allow for easily enlarging capacity. I'll share meaningful results as they come. Right now my hope is to test a very small version of the system and get data to support a conclusion that scaling the system up can achieve the desired capacity of 12,000 btu/hour. So, let's say I can show a low cooling rate with a small system that should scale to provide the desired higher output without becoming too large or expensive to fabricate. I would consider that sufficient reason to build a larger test unit. Until that time I am keeping things small.

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## buenijo

Research suggests that the electricity consumption of a micro absorption chiller can be lower than I previously expected. The pumps I have selected are small 12 or 24 volt DC magnetic drive pumps that draw less than 43 watts electricity (20 watt model is also available). These small pumps will not support a chiller at a high cooling rate, but they should achieve a 1/2 to one ton rating. A typical rotating fan on high draws about 40 watts, but this assumes a very small ac motor... small DC motors are a lot more efficient. I believe I can get the total electricity consumption well under 200 watts for a chiller that is 12,000 btu/hour, and this includes a cooling fan for the absorbent cooler. A thermostatic fan may be the best solution as the fan can operate only when needed as when air temperatures rise during particularly hot days. This way the system does not require the fan load at night and additional battery discharge is avoided. This should take the electricity consumption down below 150 watts. 

Note that modern homes are often recommended for one ton of cooling for as much as 1200 s.f. A modest off grid home (imagine a 500-700 s.f. open cabin with excellent insulation and shading) can be cooled very well by the system I'm working on.

ADDENDUM: I stopped this project (see post #100).

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## buenijo

Large biomass fueled Brayton Cycle engine. http://www.proepowersystems.com/Engine.htm

This is exactly the approach I described in previous post (#53) with the only difference being that the air exhaust from this engine is sent directly to a biomass furnace to support combustion. In my system I was using that hot air to dry a desiccant. This animation makes the system clear. I've always understood since considering that approach that a good compressor, high temperature, and a good expander can result in an efficient system. I can't find any efficiency figures on this particular system, but the temperatures they cite suggest high efficiency. 

This particular configuration is good in my opinion. Sending the hot exhaust to the furnace will increase furnace temperatures all else equal, and most important it seems to me that a very simple furnace can be used here to generate the high temperature exhaust flue gases. A simple insulated fire box with a grate and rough cut firewood stacked inside could be used here. Finally, the heat from the system is available at the furnace exhaust for heating applications, and it's at a high temperature that could even be used to drive an absorption chiller. 

A low power and slow moving system might be worthwhile for a small off grid power plant fueled by biomass. Note that getting high efficiency with the modest pressures they are using hear (3.3 atmospheres) would require a large slow moving engine.

ADDENDUM: I looked at the patent, and they are claiming a net efficiency of 36-40% assuming a 1500F compressed air temperature. The higher efficiency figure assumes a higher air pressure of 10 bar. The lower efficiency figure assumes 3 bar. This is what my estimates would have shown... but 1500F doesn't seem practical for a long lasting system using conventional components. Those temperatures will require some special provisions. Still, a small stationary system that can achieve only 20% net efficiency would be a game changer in remote off grid combined heat and power. Imagine such an engine that can maintain a constant low power for long periods at very slow speeds. You've got all that heat at the final exhaust (and some at the compressor cylinder) for space heating, water heating, water processing, fuel drying, even absorption cooling, or a refrigerant compressor could be driven off the engine at low output to provide a highly efficient vapor compression a/c system (no energy conversion losses in alternator, battery, inverter, compressor motor and a low constant cooling with large heat exchangers would be highly efficient... looking at a coefficient of performance of about 5 here). May also throw up some solar panels to augment electricity generation during the day and run the a/c system described in post #88 in tandem with the heat engine. If the engine is dedicated to electricity generation, then 1 hp will provide about 12 KWh of ac electricity per day.

ADDENDUM: Note that in post #53 I noted that this configuration makes sense for use as a solar heat engine since the air heater can be placed on a solar concentrator with the bulk of the engine on the ground. It's instructive to consider this configuration as a rankine cycle (steam engine) without a phase change. In this case the mechanical work required of the compressor replaces the addition of latent heat and work of the feed pump in the rankine cycle.

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## Natural Citizen

Free Energy, kiddies. Oh yes. It do exist. For the time being it requires a jolt to get it started but...you know...work in progress.

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## buenijo

"Free" energy?

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## buenijo

Good personal account of using a forklift battery in an off grid solar system (see comments by SCharles):

http://www.wind-sun.com/ForumVB/show...m-ideas-please

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## buenijo

Check out interviews of Steven Harris at www.battery1234.com. I've long believed that the most practical backup system for a grid failure is a battery system. Steven makes a thorough discussion of various ways to go about this. A good battery kept on a float charge with grid power can be ready for use (with an inverter) whenever a grid failure occurs. A small generator can be kept on hand for battery charging should the power be lost for an extended period. If natural gas is available, then this is best fuel source. However, many small gas engines can be tri-fueled (gasoline, propane, or natural gas). This is a very practical configuration.

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## Kelly.

> Check out interviews of Steven Harris at battery1234.com. I've long believed that the most practical backup system for a grid failure is a battery system. Steven makes a thorough discussion of various ways to go about this. A good battery kept on a float charge with grid power can be ready for use (with an inverter) whenever a grid failure occurs. A small generator can be kept on hand for battery charging should the power be long for an extended period. If natural gas is available, then this is best fuel source. However, many small gas engines can be tri-fueled (gasoline, propane, or natural gas). This is a very practical configuration.


i agree with this, especially if you buy an inverter that can take PV input as well as a generator input. that way you can buy panels and add to your generating capacity as time goes on.

to me, the idea situation would be to have a large enough battery backup for the necessary loads (freezers/fridges, furnace, etc) and plan to shut down all circuits not needed/used during an outage.then a normal 5k (ish) generator, converted to propane, with 100lb bottle of propane stored.
should give you enough stored energy to keep the batteries charged and food cold/house warm for a while.
if you can back feed the grid and use that money to add to your system, even better.

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## buenijo

> i agree with this, especially if you buy an inverter that can take PV input as well as a generator input. that way you can buy panels and add to your generating capacity as time goes on.
> 
> to me, the idea situation would be to have a large enough battery backup for the necessary loads (freezers/fridges, furnace, etc) and plan to shut down all circuits not needed/used during an outage.then a normal 5k (ish) generator, converted to propane, with 100lb bottle of propane stored.
> should give you enough stored energy to keep the batteries charged and food cold/house warm for a while.
> if you can back feed the grid and use that money to add to your system, even better.


Mr. Harris discusses what he considers to be the ideal configuration, and I agree with him. His advice is to keep the generator loaded down whenever it is used to charge the battery. This can be done by powering the battery charger along with all systems in the home with AC directly from the generator. When the generator is shut down, then the loads in the home can be switched to the inverter powered by the battery. Ideally, get as much work done while the generator is running to minimize battery discharge after the generator is shut down. Also, generators operate most efficiently when loaded down.

Interestingly, he can't say enough good things about the small Honda and Yamaha inverter generators. I had mentioned the Honda EU2000i last year on these forums after I witnessed one in action and got a spectacular review from the owner. The reviews on Amazon are also outstanding. These are pricey, but efficient, very quiet, and highly reliable. They also have tri-fuel retrofits available. Natural gas is the best fuel. Mr. Harris points out that the natural gas system is extremely reliable. Generally, during a loss of grid power the natural gas supply is not affected. There is an exception he points out in earthquake country (i.e. California generally) where natural gas is shut down in the event of an earthquake in case natural gas supply lines are compromised. I see nothing better than these small generators for this purpose (backup power generation during grid failures of limited duration). Now, for an off grid situation, I would do something different. The main differences in an off grid system is having to use a much larger battery and the use of solar panels.

Mr. Harris also discusses what I consider to be a good idea for some settings. An inverter can be powered from the battery of one's car and used for essential functions during a loss of power (like cooling the fridge/freezer). A deep cycle battery might even be charged from the car during a loss of power, and this battery can be used to power modest loads while the car is not running. Yeah, this is not an efficient set up, but it's practical for a loss of power of short duration. He also discusses and provides a video on how to install a battery bank in a vehicle that is charged by the alternator, and can be used with an inverter during a loss of grid power or for powering equipment in remote settings. This is a great system for disaster preparedness... or camping. There are lots of other cool ideas like charging all manner of small electronic appliances directly from a small 12 volt deep cycle battery.

On back feeding the grid, a solar array can be used in a grid-tie configuration, but reconfigured for off-grid during a loss of power. There are even systems that do this automatically. This approach allows the solar array to reduce the electric bill while also providing electricity during loss of power. Personally, I don't like this idea unless grid power happens to be very expensive.

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## buenijo

I'm not sure if this post is appropriate for this thread, but perhaps. There appears to be some momentum behind a new automobile that could be available next year. Check it out here: www.eliomotors.com.

Personally, I love the idea.

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## buenijo

Well, I had been reporting on the progress of a micro absorption chiller project of mine. I hate to disappoint anyone who might have had some interest in this, but I have decided to stop the project. The main reason is that I don't see such a system competing effectively with highly efficient split ductless a/c and heat pump systems that can be powered from photovoltaics. The fact that PV hardware continues to fall in price and increase in quality also led me to this decision. I've also come to appreciate the costs involved with this project. Basically, I can't justify the costs required to design a functional unit only to scrap it for a system powered by PV. Finally, considering the amount of biomass that must be gathered and processed for use in the chiller pretty much wrapped things up for me. It seems I am now fully behind photovoltaics for off grid power generation. If one desires total energy independence (no fossil fuels), then a wood gas engine system can be used for backup power generation (bulk battery charging) when solar insolation is insufficient for any reason (like during inclement weather). A wood gas engine system can also be used to power an automobile if desired, and the gasifier can be used for heating applications as well (like water heating and space heating). However, note also that most split ductless a/c systems also operate in heat pump mode, so a large PV array could contribute to space heating during cold weather to eliminate a small amount of fuel that would otherwise be consumed.

In summary, if one desires total energy independence while maintaining a modern household, then go with photovoltaics and wood gasification.

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## buenijo

Man recently installs 12.5 KW grid tie solar system at $1.72/watt before subsidies. He saved money by doing the install himself. It doesn't look difficult at all.

http://ecorenovator.org/forum/solar-...lar-array.html

Off grid systems are going to be higher because of the battery. My research shows I could get the hardware for a 6 KW off grid system for about $13,000 (panels, 3 midnite classic MPPT controllers, racking, wiring, 24 volt 804 amp hour forklift battery, 3 KW pure sine inverter).

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## r123

UKIP energy spokesman Roger Helmer interviewed on atomic energy (video): http://www.youtube.com/watch?v=S1hlLjxYsKk&feature=youtu.be

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## buenijo

> UKIP energy spokesman Roger Helmer interviewed on atomic energy (video): http://www.youtube.com/watch?v=S1hlLjxYsKk&feature=youtu.be


It seems Roger Helmer is a proponent of Nuclear power plants. There is good reason for this in my opinion. The safety record of nuclear power is exemplary. The main problem I have with nuclear power is the extreme government interventions. It's impossible to know the real costs involved under these conditions. Yeah, this pretty much applies to all energy technologies, but my impression is that things are even more contorted in nuclear power. I expect controls (and costs) to rise further due to Fukushima. 

Personally, for central power, I prefer coal and natural gas. Note that I don't buy the "climate change"/"global warming" line one bit. I'm all for coal as long as the emissions are clean (I do NOT consider CO2 as a "pollutant" to be scrubbed, I consider it as plant food). Let's crank out combined cycle power plants fueled by natural gas (50%+ efficiency in converting btu's to electricity delivered to the home), and large coal-fired supercritical steam plants (40%+ efficiency in converting btu's to electricity delivered to the home, and with fuel costs lower than natural gas!). 

As far as photovoltaics goes, this is a great tool in the hands of the individual for opening up options to reside in remote regions where utility lines either are not available, or would be too expensive to establish. In other words, it is ideal for off grid/remote homes. However, it is also a useful tool for combating a monopolistic energy utility that likes to raise rates willy nilly, or one that provides poor and/or intermittent service. The prices for photovoltaic hardware continues to fall, and we are approaching the point in a few years when the cost of electricity generated by distributed photovoltaic systems reaches grid parity for many regions in the U.S. Already, it is cost competitive to traditional electricity sources in many international markets.

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## Natural Citizen

> I'm all for coal as long as the emissions are clean (I do NOT consider CO2 as a "pollutant" to be scrubbed, I consider it as plant food).


Right. Except all of the trees are being chopped down. One example off of the top of my head would be agribusiness giants like Monsanto (for one) chopping down the rainforests for Monoculture GMO Crops and Biofuels and whatnot.

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## buenijo

> Right. Except all of the trees are being chopped down. One example off of the top of my head would be agribusiness giants like Monsanto (for one) chopping down the rainforests for Monoculture GMO Crops and Biofuels and whatnot.



Yeah, that sucks. There are other sources of biomass that will take up CO2, but the concentration of CO2 will certainly go up either way. I'm not convinced this is so bad. After all, the Earth supported it in the past. I know, but we're changing it too fast! Can we be sure that this will be detrimental? If so, then by what standard? Call me skeptical, but I haven't seen any worthwhile evidence that our increasing CO2 levels is harmful on net balance. I _have_ seen a lot of hype and bull$#@! shoveling (a la Al Gore).

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## r123

Tokyo's Daily Radiation Readings Underscore the Fallacy of the Fukushima Radiation Hysteria: http://educate-yourself.org/cn/tokyo...r03dec12.shtml  Are wind farms saving or killing us? A provocative investigation claims  thousands of people are falling sick because they live near them The  symptoms they claim to have suffered may vary – including dizziness;  increased blood pressure and depression – but the theme remains the  same. Read more: http://www.dailymail.co.uk/home/mosl...#ixzz2XRwvjbYc    Marijuana: Hemp Made Cars Running on Hemp, Supressed Oppertunities .  I’ll guess the oil and steel industry didn’t want this world to be  green. Nor to be a bit more peaceful either. With that much hemp around  needed to fuel all our engines and to replace many of the metals and  plastics, the temptation of that first marijuana sigaret would be too  close around the corner for the masses. The powers that be like the  people more to consume stupifying and aggressifying alcohol products so  they’ll stay in their matrix: http://www.youtube.com/watch?v=DKEubbn_2oA 
In Praise of Tokyo Electric Power Company TEPCO: http://educate-yourself.org/zsl/toky...r03oct13.shtml

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## r123

The Myth of Nuclear ‘Waste’ by Marjorie Mazel Hecht. There’s no such  thing as nuclear waste! This nasty term was invented just to stop the  development of civilian nuclear power.The spent fuel from nuclear power  plants is actually a precious resource: About 96% of it can be recycled  into new nuclear fuel. No other fuel source can make this claim—wood,  coal, oil, or gas. Once these fuels are burned, all that’s left is some  ash or airborne pollutant by-products, which nuclear energy does not  produce.Thus, nuclear is a truly renewable resource. Furthermore, unlike  wind, solar, and other so-called alternative energy sources, a nuclear  fission reactor (the fast reactor or breeder reactor) can actually  create more fuel than it uses up: http://larouchepac.com/node/14724 

We hear a lot about “green jobs” in the renewables industry. The reality is rather
different. A recent report called “Worth The Candle?” by Verso Economics
demonstrates that for every job created in the renewable sector, four jobs are
destroyed elsewhere in the economy. How? By driving up energy costs, reducing
competitiveness and deterring investment. A Spanish study entitled  “Effects on employment of public aid to renewable energy sources” by  Professor Gabriel Calzada Alvarez at King Juan Carlos University  questions whether “green jobs” are worth the public investment.  According to this document renewables have received €28.7 billion in  subsidies. This is nearly €600,000 for each of the 50,200 jobs created.  Meanwhile renewables businesses are collapsing. In the US, President  Obama touted solar-PV company Solyndra as a text-book  example of renewables and green jobs: it soon went belly-up. A study by  The Washington Post shows that of the approximately $19 billion loaned  so far, a total of just 3,545 jobs have been created.That comes to over  $5 million per job.
In China, solar PV manufacturers are facing a crisis as demand fails to  match projections and prices slip below costs. Renewables are not about  “green jobs”.
They’re about green unemployment. In the UK, the world’s largest wind  turbine manufacturer, a Danish company called Vestas, has scrapped plans  to build an offshore wind factory in Kent. The 70 hectare site would  have housed a facility designed to build the Danish company’s 7MW V164  offshore wind turbines but a lack of confirmed orders led to the project  being cancelled. This decision is the second time that Vestas has opted  out of the UK market; in 2009 it closed down a plant making onshore  turbines on the Isle of Wight. Contrary to the claims of the green  lobby, the renewable industry is unsustainable. It needs massive ongoing  public subsidy. Such levels of subsidy are unaffordable,especially in  current economic times. These subsidies are also profoundly regressive.  They take money from poor consumers, including pensioners, and give it  to rich landowners and corporations.

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## buenijo

> In Praise of Tokyo Electric Power Company TEPCO: http://educate-yourself.org/zsl/toky...r03oct13.shtml


Do you endorse this? What evidence is available?

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## buenijo

The best source of information that I've yet discovered for learning about modern photovoltaic systems (off grid OR grid tied) is the discussion forums at www.windsun.com. I highly recommend this resource for anyone interested in learning about these systems, especially those who are doing serious research before purchasing a system. 

I actually stumbled onto the forum while researching the split ductless a/c systems I mentioned earlier in the forum. There are a few people active on the forum who have been using these systems to cool their home (off grid homes powered by a/c) with amazing results. You can check out that particular thread here: http://www.wind-sun.com/ForumVB/show...split+ductless . This thread and others have me totally convinced that a modest and modern home (superior insulation, etc.) can be cooled very effectively with a good vapor compression a/c unit powered by photovoltaics.

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## buenijo

See this thread on induction cookers: http://www.wind-sun.com/ForumVB/show...n-cooker/page1

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## buenijo

I'm discussing the intermittent ammonia absorption refrigeration system. I've posted on this before. Here are a couple of relevant examples:

http://knowledgeableideas.blogspot.c...-icemaker.html

http://crosleyautoclub.com/IcyBall/crosley_icyball.html

I'm presenting these systems again as I believe a system similar to an icy ball would be very useful in the off grid setting (really, it's suitable more for an extreme setting). Also, it's something that can be devised without breaking the bank. However, the unit must see outstanding insulation to reduce the size of the system. If anyone is interested in this prospect for food refrigeration, then I recommend that you first look into extreme insulation. Thick polyurethane is a good prospect. Another prospect I've considered should interest the reader. I understand that some cryogenic storage tanks use crushed perlite under vacuum as insulation. The basic idea here is to have a vessel within a vessel, fill the annular space between the two vessels with dry crushed perlite, then seal the space and draw a vacuum. This might prove difficult to do... so, I think a worthwhile project might be to vacuum seal the perlite in modules (like durable plastic bags - maybe even vacuum equipment designed for food storage) that can be used as insulation. 

It takes some imagination to consider possibilities. What I'm considering is a small super insulated vessel with an integrated micro intermittent ammonia absorption system. A furnace similar to a wood gas camp stove the size of a large soup can burns less than a half pound of dry sticks to recharge the unit daily. A few cubic feet of storage capacity would make for a very useful unit that would be easily transported.

NOTE: Anhydrous ammonia (i.e. pure ammonia) is a controlled substance. However, it can be acquired in the form of industrial cleaning products up to 29% ammonia in water. This concentration is almost sufficient to be used directly in this application (assuming water used as the absorbent as in the icy ball). It would be easy to adjust the concentration since the ammonia is separated during heating (just drain some water out from the absorber after heating until the proportion is right). It's also possible to distill the ammonia out by connecting a vessel of the ammonia/water to a condenser placed in a freezer, evacuating air, then gently heating the vessel to slowly evaporate the ammonia (a long steel tube in the freezer connected to the condensing vessel can catch some water vapor by freezing on the tube). The problem with this set up is that the system is under some positive pressure (but not very high, so it should be reasonable to do this). This problem can be solved by using calcium chloride to absorb the ammonia vapor from the solution. I'll discuss this here: the boiling point of the ammonia/water solution is lower than water. If one connects a calcium chloride vessel to a vessel containing the ammonia/water solution, then pulls vacuum briefly to evacuate air (to speed the absorption process), then ammonia vapor will evaporate quickly from the solution causing it to boil. Some water will leave with the ammonia vapor, and it's desirable to minimize this. This can be done by (1) putting the ammonia/water vessel in an ice bath, (2) placing the calcium chloride vessel in a freezer, and (3) connecting a long steel tube to the calcium chloride vessel (tube is also in freezer). (1) keeps the ammonia water solution cold to inhibit water evaporation, and also prevents the solution from freezing by adding heat during the absorption process. (2) removes the heat of absorption allowing the calcium chloride to increase absorption rate, and lowering the temperature allows the calcium chloride to hold more ammonia. (3) will keep water out of the calcium chloride by freezing the water vapor on the cold tubing wall as described before. I like the idea of using calcium chloride in an "icy ball" set up (modified) as it provides pure ammonia to the evaporator. Also, since it is a solid, then it may do better at absorption without providing check valves as is required with water (although, the calcium chloride will liquify after absorbing sufficient ammonia - better results will probably be had with a check valve, but if it works well enough without, then it seems best to do without the check valves). DANGER: Do not cap the calcium chloride vessel after it absorbs ammonia at low temperature as pressure will build as temperature increases (use a cork or provide a means of relief). As long as the vessel is kept in a freezer, then the ammonia will not vent.

Continuous Operation: Considering the icy ball gives me hope for a continuous ammonia absorption system for air conditioning. Consider that absorption is achieved in the unit with a single small tube extending down into the absorbent solution, with no active cooling to the absorbent, and with the evaporator maintained at low temperatures. A system that provides a large evaporator maintained at a higher temperature, providing excellent cooling of the absorber, and bubbling the ammonia vapor into the solution with a perforated plate similar to a shower head might just work exceptionally well. The main problem I saw with the absorber in my lithium bromide/water system was the extremely low pressures made the flow of water vapor easily disrupted - and the only solutions I considered proved too expensive to be practical. Having much higher pressures and lower evaporator temperatures makes many things possible (and potentially a lot less expensive). Consider that a rise in evaporator temperature from 19F to 20F increases the pressure of ammonia by roughly 1 psi, whereas a rise in evaporator temperature from 39F to 40F increases the pressure of water vapor by only 1/200 psi. So, you see the problem. For mere mortals with very limited funds, ammonia is way to go. 

A configuration I consider is to fuel a system by a small wood gasifier where the hot fuel gases are sent to a combustion chamber to heat the system. The evaporator could be used to freeze water while the condenser heats water. The system can operate at a high rate during the day (perhaps 2 tons) when a PV array is producing thereby powering the pumps and fans required of the system without discharge on a battery system. When shut down, then the cold store provides chilled water for a fan coil unit, and the heated water is available for use as required - the operation of the fan coil unit is done while the absorption unit is shut down (small mag pump for chilled water plus fan consumes only about 50 watts dc for the small unit I'm considering - about 1/2 ton). The system can also be configured to heat and distribute hot water to the fan coil unit for space heating, and it can be configured in heat pump mode to provide heat in excess to that provided by the furnace (done by tapping the heat from the absorber). 

For water freezing you don't want to just put the evaporator into water directly as ice formation will occur on the tube and lower heat transfer (and lower evaporator temperature, pressure, and affect the performance of the system). A better solution is to cool a water/glycol solution contained in an insulated vessel. Containers of water can be added to the system. The allows the evaporator to be heated by a liquid for good heat transfer, and the heat is derived from the multiple water containers surrounded by the cold solution. The water in the containers will freeze, and they will keep the solution cool. The water/glycol solution can be used directly as chilled water by pumping it to the fan coil unit with the small mag pump. A great benefit of this set up is ease in controlling the cooling rate of the system. A fan on the fan coil unit (and one might use more than one fan coil unit - imagine one for central cooling a cabin, and another for spot cooling while sleeping) can use a thermostat or the speed of the fan can be controlled to adjust the cooling demand. A store of chilled water makes this far more practical than trying to control the output of the absorption system. This way the absorption system operates at a fixed rate for simplicity. Note that the continuous system is inherently safer than an icy ball since the heat is applied to a compact steel tubing coil, the vessels are smaller, pressure is limited with a relief valve on the solution pump discharge, and the high pressure vapor side is connected to a large condenser. The only pressure vessels in the system (that is not small diameter tubing) is the absorber vessel and separator vessel that may be thick steel piping. The absorber is at a modest pressure (well under 100 psig), but the separator may approach 400 psig - and the separator is the smaller vessel, so I see the system as inherently safe with a rational design.

NOTE: The continuous system requires an ammonia/water solution pump, and a high output system will require active cooling with a cooling water pump and with heat exchanger and fan (outside fan coil unit). Therefore, the system is operated during the day to allow a PV array to provide the required dc electricity which would be roughly 1/5 that of a conventional a/c unit of equal cooling capacity. In principle, the same could be done with a conventional a/c unit operated as an opportunity load on a PV array. However, one big problem here is the cold storage. The performance of a vapor compression system depends on the temperature difference between the evaporator and condensor. Well, the evaporator temperature must be very low to freeze water, and the condenser temperature will be higher when operated during a summer day (and a great deal higher if one tries to use it for water heating to a sufficiently high temperature to be useful). So, the vapor compression system will require significantly more than 4 times the electricity consumed by the absorption system (assuming the same kind of set up). Of course, one can simply power a/c as an opportunity load on a large PV array. However, this prospect is more interesting and versatile.

NOTE: I suggest a HyPro piston pump with stainless steel internals and teflon seals for the ammonia solution pump. It's also possible to build a plunger pump fairly simply using a small threaded pipe section with two check valves on the end - a length of smooth steel shaft is used as the plunger - the plunger reciprocates in the pipe to draw in and discharge fluid through the check valves - just have to seal the plunger - this can be done by providing a washer on the pipe end with same outside diameter as the pipe and with an inner hole just large enough for the plunger, cut a hole in the pipe end cap just large enough for the plunger, then pack the space between the washer and end cap with teflon compression packing, then tighten the end cap to seal. Note that teflon works very well with ammonia, so teflon tape on all threaded points is also good practice. A prospect for a pump motor is a 24 volt dc gear motor used for electric scooter applications (cheap and reasonably efficient).

ZERO ELECTRICITY: I just considered a way to drive a plunger pump for the ammonia/water solution using the differential pressure between the regenerator and condenser. The pump is hermetically sealed, self-starting, and cycles at a rate directly proportional to the rate the system is heated. This configuration has advantages over traditional 100% heat powered ammonia absorption refrigeration systems that operate at a constant pressure. The pump makes it possible to force the fluid through compact heat exchangers that can reduce thermal losses and regenerate heat back into the system. By contrast, the traditional systems rely on thermosiphon which cannot tolerate restrictions to flow. This new system can be more compact and more efficient.

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