Originally Posted by ah-kay

Graplr - what I meant is that some projects are difficult to justify except the feel good factor. I think Solar Hot Water ( convection type ) has the best return and short payback period ( your friend's system ). Very little mainenance and abundant amount of hot water. I had one on my roof until the tank leaked. The water was so hot and abundant that I can 'sell' it to my neighbors. As for Solar cells to generate electricity, the capital investment is huge and the payback period is long. You may get a tax credit for solar cells. Same goes for hybrid cars as you only save, may be $40, of gas per month but the premium is $5000+. Even project like this post is not really worth it except for the inverter. After you added the head, a governer, wiring, switch panel, plumbing, bypass radiator etc it would come to a considerable amount of money plus your sweat equity.