Several years ago, I actually thought about installing solar panels on our house. I asked a friend of mine (who is a builder) and he laughed at me, and then showed me numbers that said that the panels would never pay for themselves.
His reasoning was something like this.
If you install panels on your house, you also have to install a new roof at the same time.
Solar panels only work during the warmer months, when the sun is high enough in the sky.
Optimistically, solar panels would save me about 33% on my electric bill during the 5 months of warm weather here in Texas (mid-May to mid-October).
If my electric bill were $300/month for those five months, then I would save about $500 per year in electric bills.
It would cost about $15,000 to install panels on my roof.
Working backwards on the numbers, it would then take me 30 years just to break even.