http://en.wikipedia.org/wiki/List_of_rooftop_photovoltaic_installations With a 5 million square foot plant in a relatively sunny climate, Tesla is in a position to get some very positive coverage by becoming both the largest rooftop solar installation in the world and the only "solar powered auto factory". Under the Solar City contract approach it shouldn't cost Tesla anything as long as they have an investor (who would get the added PR benefit of association). The later claim of being solar powered seems like a reasonable target for a one shift operation at the current scale. Obviously there are a lot of ways to measure it...but it's a reasonable goal to produce enough power to run the plant in real time under optimal conditions and come close to zero net power from the grid. The video of gleaming Tesla red robots moving against clean white powered by nothing but the sun on the roof is pretty striking. As PV prices have fallen it's gotten to be a better value. Since Tesla is profitable and doing great in the markets finding a willing investor is easier. Of course it's also a high profile/value project for Solar City. Announcing the supercharger network as fully Solar Powered was an effective approach even though it's possible for critics to quibble about the details, the same applies to the Tesla Plant. The project can hit reasonable markers for being full solar power...and that's a worthwhile story.