I don't have a good calculator, but step 1 is to make sure you BUY the panels, and not rent them or fall into any kind of weird plans where you resell some ener

I don't have a good calculator, but step 1 is to make sure you BUY the panels, and not rent them or fall into any kind of weird plans where you resell some energy for free panels or whatever. So your ROI is pretty much calculated with: How much do the panels cost (installed) How long do they last, whats expected maintenance, etc How much energy are they expected to produce Whats your electricity bill. From there its pretty simple math. The hardest part is how much energy they are expected to produce, and no online calculator will help figuring out how much sun hits your roof.