I am afraid you are a bit late to the party. Solar stocks are mostly on the decline overall, due to the number of competitors out there, which has driven down the prices of their products, which in turn reduces their profits.
And here is something to keep in mind ... solar stocks tend to follow the price of oil ... when oil goes up, solar goes up ... when oil goes down, solar goes down. The reason being, when oil becomes too expensive, people tend to look for cheaper alternatives, with solar being one of them, but when oil becomes cheaper, people relax and fall back to the same routines they have become accustomed to.