It's a power-leasing deal. Some company pays you (either in dollars, or by selling you electricity at a lower cost than your regular utility) to put solar panels on your roof. The company banks revenue by creating power and banking state renewable energy credits. You get a slightly lower electrical bill.

You'd come out ahead if you purchased a solar panel array and paid a loan on it (this is what I did a few years ago, AMA). But if you're not in a position to do that, this would probably be at least a small savings on your energy bill.

So even though you could come out ahead with an arrangement like this, it's not really considered a "good" investment, since you're basically taking a thank-you cut from somebody else who's actually making profit. The underlying truth is that the area of your roof is very valuable in terms of using it to generate power. Either YOU can realize that value, or you can get a minimal payment to let someone ELSE realize that value.