I've done these calculations, particularly after putting an 11.6Kw solar array on our last house, which was in St. Petersburg, FL, one of the sunniest places in the US.<p>We sold the house after having the system for ~6.5 years, but we were tracking for a 9 year ROI. My cost was ~$23K out of pocket at the time, with power bills of $500-$800/mo., depending on time of year. I think our average daily consumption was 69Kwh, and the system produced the majority of that most days.<p>Assuming an average power bill of $600/mo., $23K would cover roughly 3 years of power bills. However, if the money was invested in a decent-ish portfolio, it would be earning some interest along the way, which could stretch what it covers to 5+ years. Anyway, when I did all the math, the solar panels never really <i>made</i> money, but what they did was smooth out our monthly expenses and gave some hedge against rate increases.<p>The new house is the same general area, and our use is about the same, but going to wait to see if solar takes a bigger decrease in cost before doing another array. It's mostly maintenance-free, but I did not output decline when the panels got dirty, and one panel died about 1 year after installation (and by then the installer company had gone out of business).