In the world of energy, the Holy Grail is a power source that’s inexpensive and clean, with no emissions. Over 100 start-ups in Silicon Valley are working on it. One of them, Bloom Energy, is about to make public its invention: a little power-plant-in-a-box they want to put literally in your backyard. You’ll generate your own electricity with the box and it’ll be wireless. The idea is to one day replace the big power plants and transmission line grid. K.R. Sridhar … says he knows it works because he originally invented a similar device for NASA. He really is a rocket scientist. He invented a new kind of fuel cell, which is like a very skinny battery that always runs. Sridhar feeds oxygen to it on one side, and fuel on the other. The two combine within the cell to create a chemical reaction that produces electricity. There’s no need for burning or combustion, and no need for power lines from an outside source. “It’s cheaper than the grid, it’s cleaner than the grid.” Twenty large, well-known companies have quietly bought and are testing Bloom boxes in California. The first customer was Google. Four units have been powering a Google datacenter for 18 months. They use natural gas, but half as much as would be required for a traditional power plant. John Donahoe, eBay’s CEO, says its five boxes were installed nine months ago and have already saved the company more than $100,000 in electricity costs. eBay’s boxes run on bio-gas made from landfill waste, so they’re carbon neutral. “In five to ten years, we would like to be in every home.” [Sridhar] said a unit should cost an average person less than $3,000.