The rain in Spain may fall mainly on the plain, but the summer sun drenches the entire country nearly every day. General Motors intends to make the most of it, covering the roof of its largest manufacturing plant in Europe with 85,000 solar panels, a whopping 2,000,000 square feet of them. That's 10 megawatts of clean electricity, enough to power 4,600 households -- or to build a bunch of Opel sub-compacts. What's not consumed by the robots on the assembly line will be sold back to the grid, funding future rooftop installations at 19 other locations across Europe. We're thinking GM should maybe invest a little of that into powering the cars themselves via solar, or risk getting beaten to the punch by Toyota again.