The first thing to know is that Buffett tries to never overpay for anything. He only buys when he’s sure that an asset is undervalued and is likely to have bottomed in market price. So this could be a sign that after all the softening prices and bankruptcies, that the solar industry is on its way to better days (or at least, it won’t get much worse). Or at least that at today’s prices, you get more value than what you pay for when you invest in solar.

http://www.treehugger.com/renewable-energy/warren-buffett-buys-worlds-largest-solar-project-sunpower-25-billion.html