[akerl_]

It's possible the math works out differently for people whose roof already needs to be replaced, or for people whose roof can be nearly totally covered with generating tiles.

In my case, it's been a while since I crunched the numbers but the pay back period is effectively infinite, assuming that had I not bought the roof I'd invested the money instead. This is especially true as temperatures continue to swing more and more widely (winters that push below the efficient window for my heat pumps are murderous on my banked solar energy) and more states and electric companies switch from net metering to newer rate plans.