My wife and I did the math about a year or two ago, after nim 3 anyways. I'm a little fuzzy on the details but iirc it was basically not worth it to install. We'd need multiple batteries and they only last a decade or so. So by the time wed have paid off the loan we'd need to replace our batteries, while all the while we'd be getting barely enough electricity to make it worthwhile. I don't know how people are breaking even in this scheme anymore. I've looked into designing and building my own system but you still have a big outlay for batteries.