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.
Besides solar power is very green. It will not only increase the value of your house, it makes hippie chicks puddle. And who can put a dollar value on that.