A Bloom box, officially known as an Energy Server, is a modular construction of fuel cells that can be used in combination to produce the amount of energy required for a given application. Each fuel cell, which consists of a metal alloy plate sandwiched between two ceramic layers, generates 25 watts of power. A single fuel cell can power a light bulb; a stack about the size of a loaf of bread could power the average home.
Bloom Energy announced the Energy Server in February 2010. The name is a reference to the product's modularity, which is similar to that of servers in a data center. Individual cells can be hot-swapped or replaced. At the time of the announcement, five Bloom Boxes the size of a parking spot were providing 15% of the electricity for eBay's campus. Other beta customers for the product included Coca-Cola, FedEx, Google and Wal-Mart.
Although fuel cells aren't new, cost of production and other issues have made them impractical for widespread use. Energy Servers overcome some of the problems of what Bloom refers to as "legacy fuel cells." Hydrogen (previously the most common fuel used) is non-renewable and tricky to store. Energy Servers can use a variety of source fuels, including biofuels. The Energy Server installation at eBay, for example, currently runs on biogas from landfill waste.
A 100 kilowatt Bloom Energy Server, suitable for a business, costs $700,000–800,000. Google, Bloom's first customer, installed four 100 kW Energy Servers at its headquarters. The costs of production are expected to drop over time. Bloom hopes to make Energy Servers for homes available by 2020, at a projected cost of under $3,000 per unit.