My wife and I are frugal users of electricity, running $60 per month average SoCal Edison bills. Solar panel sellers say $150 or more billing per month is necessary to pay off the investment in a reasonable time. Even so, I calculate that solar would be a good investment on a strictly financial basis even at a 12-year break-even. I looked at my Solar City quote for a modest sized array that would cover our meager household usage plus expected annual Model S demand, and realized that even a 3kW system that would project out to cover only our present usage would be a good investment. Scaling the larger system down to cover just our house, I arrived at a price of $10740 (after Federal tax credit) which, against a $720 annual savings at today's rates (and they will certainly be going up) amounts to a 6.7% tax-free ROI with negligible risk. If I were to source components online and install the system myself (which any DIY with good roofing and electrical skills can do), I could pare the cost down to about $5,400 (after Federal tax credit) and a tax-free yield of about 13.3%. Our rental properties yield much better than that of course, but in a land littered with earthquake faults in a state with high unemployment/underemployment, they are not risk free. We have a very good investment manager handling our equities, but a low-risk portfolio can't match 6.7% tax-free, much less 13%, and the Market does have some risk. One might argue that lack of liquidity is a downside, but as long as we live here we have to use electricity and if we move we can get back the value of the system in a higher sale price and quicker sale vs similar properties without solar.