Right, it just depends on the numbers. Taxes and credits have a lot to do with it. For example, a $10k (after credits) system might save at averaged $1200/year accounting for production lost, increasing a bit over time due to utility hikes. After 20 years, assuming the system is now worthless, that will compare similarly to an 8% stock market return plus initial capital after capital gains taxes. The solar system would return in a narrower range of performance than the stock market return.