It doesn't give you 25% a year, because you don't have your investment anymore (or most of it, if there is a second-hand market.) After the first year you'd have a -75% return, after the 5th you'd be at an effective annual 4.5%, after the 10th at an effective 9.5%.

It goes up from there, but it takes a while to become an investment better than alternatives. Inverters start failing after 10 years, too, and they're half the cost of a $400 setup, I believe.