Well first, if it takes you 20-30 years to break even, you’re getting ripped off, or your loan’s interest rate is terrible and you’re making minimum payments. Solar panels have warranties that basically match the life of a roof these days, so ideally, you’ll replace that roof at the same time as putting up new panels. Solar panel tech has come a long way in 25 years, the optimist in me says 25 years from now they’ll be cheaper, more efficient, and more reliable than they are today.