The solar power system should be valued at about the present value of future generation. You add that to the price of the house when you move. If the system was economical that value would exceed the initial investment. Of course that value is based on assumptions regarding the life of the system and future electric rates, so there is always lots of weasel room.
Sorry.
The solar power system should be valued at about the present value of future generation minus maintenance costs.
I'm not convinced that it is fully applicable to the sale of residential property. Consider that one generally does not recoup near the cost of a finished basement or add-on porch, even though those have value and generally hold that value for decades. I don't think that the cost of a solar power system would fare any better.
Now, if the system were small enough that it could be packed up and moved with me, that would be very positive. Of course, it would still have to pay for itself in just a few years IMHO.
Not if my wife says, "Ewwwwwww, what are those ugly things on the roof? And get those dirty, stinky, dangerous battery thingies out of here!" :-)