The energy-efficient ‘Bloom Box’ power servers at eBay offices in San Jose, Calif., Wednesday is a Silicon Valley startup that is working on a new way to produce cleaner energy.

The company says it has developed a new method of making fuel cells, thus generating electricity through an electrochemical reaction. A single cell can produce about 25W, enough for a low-energy lightbulb, and a stack of cells the size of a brick will power an average home. One Bloom box which is the size of a chest freezer and which contains several stacks of fuel cells, will produce 100KW, enough for 100 homes.

“Compared to the US national grid, this is about twice as efficient,” said K.R. Sridhar, cofounder of Bloom. “So your carbon footprint is about half. If you use a renewable fuel, you’re carbon neutral.”

“Bloom fuel cells are powering a portion of Google’s energy needs at our headquarters here in Mountain View — this is another on-site renewable energy source that we’re exploring to help power our facilities,” said Jamie Yood, a Google spokesman.

“We have a 400kW installation on Google’s main campus. Over the first 18 months the project has had 98% availability and delivered 3.8 million kWh of electricity.”

Customers already include Walmart, Google, eBay, Federal Express and Coca Cola. Arnold Schwarzenegger, Colin Powell and the heads of Google and Walmart were at the launch today.