The photo below is of a passive solar hot water system on the roof of a house about a block away from my house. That one is a double system, I wouldn't need that capacity.

It is used as an auxiliary to pre-heat the water before it goes into the propane hot water heater. The vendor says that in the warm months my hot water propane expense will drop to zero, and that I can expect water temperatures up to 80 degrees C. Even in the "cold" months our weather rarely drops down into the 60's (F) and I have an absolutely unobstructed Southern exposure so it should be effective even then.

At the price quoted for the heater and installation, and the promised savings (65% reduction of my total annual propane bill) it would amortize in four years, and after that would be pure savings. It has an 80 year warranty, meaning I will be about 150 years old when it finally wears out.

Does anyone have experience/knowledge of this style of passive solar hot water heater, and/or recommendations where to look for unbiased information?

tanstaafl.