I pulled the trigger on a 4.8 kW system early this year. I purchased the system outright. The numbers are working out as planned which is to see an ROI right about 4 years.

I wouldn’t count on the salespeople to do the numbers for you as I found a lot of them to play the smokes and mirrors game about systems/efficiency/quality/etc., that the real goal of ROI is lost. In the end, it’s not about an expensive hobby and that it should be rooted in sound economics. Not to discount those topics as there are indeed a lot of variables and technicalities, but I found the sales people in general to be only concerned about marketing and selling. Also, you want to make sure the company is not a sales only operation, and that you actually want to work directly with an installer.

That said, all the variables are really captured in two numbers – price per watt and estimated annual production for the proposed system. And of course, you want to go with a reputable warrantied installer and hardware with a production warranty. My installed price/watt was better than $3/watt on an ideal south facing install, without space or obstructions related compromises.

Actually, my ROI is actually better than 4 years, as I’ve jumped both feet in an bought an electric car to go along with the system.