Oops, the previous message went out unfinished and uncut. Wrong key. 
Sorry. Here is the sequel:

Water requires about 2.2 MJ/kg to boil. There is no way around that. If you 
think of the engine in terms of mass flow, it takes about 0.05 kg of fuel to 
boil a kg of water in an unspecified amount of time. It also takes a 1 meter 
mirror in full sun (1kW) about 37 minutes to boil the same amount of water 
(assuming no losses in either case).

So 1 sq. meter of mirror used for an hour will equal ~0.03 kg of fuel (about 1 
oz). You can take this as a base for cost calculations I think. I don't think 
that mirror life can be counted on to be longer than 2 years. With 200 days of 
sun/year and 8 hours of usable sun/day = 3200 mirror hours (not so bad). The 
fuel equivalent is 96 kg (~36 gallons at density 0.7). At $2.6/gal ~= 
$94. Say $100. The equivalent in heating costs is probably half that. 
This does not take into account system losses for the sun system, which 
are going to be huge.

So assuming the solar system efficiency is 50% (a good figure imho) the 
equivalent gas price equivalent of a 1 sq. meter mirror for 200 sun 
days/year, 2 years, and 8 hours/day is about $50 over 2 years. If I read 
heating costs correctly for USA the bills are about $150/month per 
(small) house so $150/month in mirrors would be at least 81 square 
meters of sun collectors (about half floor surface of the liveable part 
of the house ?) not counting the storage arrangements.

> How much is it going to cost?
> How much electricity can I get out of it?

I don't think that a 10% efficient (with heat recovery and very high 
temperature steam) steam engine is practicable in garage build mode, 
even if using a burner with fossil fuel.

I also think that using solar for heating makes a lot of sense but using 
it for making electricity (at least via steam) is not a good 
proposition.

I would think in terms of sun heat + heat storage for heating and 
cooling (adsorbtion process) and co-generation for electricity, with the 
extra heat from co-generation supplied to the sun system. The fuel for 
co-generation will have to be fossil but may be supplemented with 
vegetable oil, biogas etc.

I think that efficient electricity generation is reserved for large 
plants whoch can afford the hardware to maximize efficiency (I heard 
60+% is possible using diesel + steam turbine or gas turbine + steam 
turbine).

Peter
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