[ToddF]

How much electricity you use does not affect the payback of solar energy, ironically (unless you have a peak use of 40 kW in Minnesota). Most new systems are interconnected to the utility so these customers buy and sell, (unfortunately) usually at the same rate. Whether they use any electricity is unimportant because they either avoid costs or get money back. These are the same slot in the payback calculation.

My generic answer to "does it pay?" came from summarizing practically every payback calculation I have done in the past year as a solar installer. It is most valid for Minnesota's climate but is close in most areas of the country. I might change it to 25 years payback if pressed.

If modules and other equipment goes down in price, if buyback rates or rebates change or if the prevailing climate changes, this will alter payback. My feeling is that all of these variables will improve solar electric payback.