Five to ten years from now, you could have a $3000 fuel cell power generator the size of a clock radio in your basement, turning natural gas into electrical power at twice the efficiency possible today. That's the promise of the Bloom Box, a tiny power plant that combines oxygen and natural gas, a biogas or solar energy, and creates electricity. So far, Bloom Boxes are the size of about four refrigerators, costing $700,000 to $800,000. Early adopters are companies such as eBay and Google, already saving money using these boxes.