OK, I'm gonna try to get this thread flowing. I've been doing a lot of research into small scale steam power in my spare time over the last several years. I am convinced that it's viable. However, the big problem is practicality.
For anyone who is considering building a small scale steam power plant for home power, I recommend that you adopt several design criteria that are rooted in the principle of making the most of steam power's inherent strengths, and minimizing the effects of its weaknesses. The strengths include: (1) clean combustion, (2) can be very quiet if properly designed, (3) multi-fuel capacity, (4) long life. Weaknesses include (1) low thermal efficiency, (2) expensive unconventional components, (3) potentially dangerous.
In my opinion, a small scale steam power plant for powering a small off grid home should adopt the following:
1. Use a piston engine, and a monotube steam generator. At low power levels suitable for powering a home a piston engine will be more efficient than a turbine. A monotube steam generator (as opposed to a boiler) is both the safest and most efficient option.
2. Operate the system at a constant low power (one the order of 1 KW or less) for long periods. This makes for a simpler system, but it also makes for a smaller system. Use the engine to drive a small efficient permanent magnet alternator for battery charging. Use an inverter on the battery to provide electricity, or you could go with a DC system.
3. Put the heat in the exhaust steam to work for you. If this energy is not put to use, then the net efficiency of the system will be too low to be practical. But if it is put to full use the system can be more efficient than any other option (even grid power). The latent heat in the steam exhaust can (a) provide space heating, (b) heat water (including pasteurization or distillation if desired), (c) provide air conditioning with absorption/adsorption cooling, (d) dry food, (e) can food, and many other applications (drying clothes, drying wood fuel, etc). The largest electrical loads in the home are electric heating elements and air conditioning compressor motors. If these can be displaced, then there is little need for a high powered system. What IS desired is a system that operates reliably at a reasonably high efficiency for long periods at a low output, and is easy and inexpensive to repair.
This is just an intro to start a discussion. Please reply if you're interested in exploring this topic further. I honestly believe small scale steam power can make a comeback, and hopefully in a big way.
ADDENDUM: I suggested absorption/adsorption cooling as an option for cooling with heat. Other possibilities include steam jet cooling, refrigerant jet cooling, ammonia absorption, and various absorption cooling systems that operate at a high vacuum and use water as the refrigerant. Each have various advantages and disadvantages. If the efficiency of a small scale steam engine system can be sufficiently high, then a refrigerant compressor could be driven directly to support a ductless a/c unit. This would avoid the many energy conversion losses in generating electricity and using the electricity to power a compressor motor.
