re: Solar thread (yes, energy from the sun)

I've looked into the idea, and if I build a new house, it will probably be seriously considered. But I don't see the 25% annual return on investment. If I put $20k into a system, and my average elctricity bill is $120, the system would have to cover 100% of my electrical needs for over 13 years to pay for itself. Where does this ROI come from?