The nitty-gritty details of the Bloom Energy box

Bloom Energy CEO K.R. Sridhar spelled out, to a green-technology Web site, some of the finer details of how his start-up's technology works.

The Sunnyvale, Calif.-based company on Wednesday rolled out, with great fanfare, the Bloom box fuel cell, which is designed to be stacked into small blocks and housed in a unit about the size of a refrigerator and sold as an alternative to electricity from the grid. Multiple 100kW units, costing between $700,000 and $800,000 each, are combined and sold to large companies. Bloom already has heavyweight customers such as eBay, Wal-Mart Stores, and FedEx.

Sridhar, in an interview with Greentech Media (see embedded video), explained some of the details of the technology not published widely in the media.

Sridhar explained, for example, how the device creates energy. "It mixes with water, which is a byproduct of our exhaust. Water and methane goes into the system and within the system the methane and the water react," he said.

Sridhar continued. "And you get what is called a syngas right on the surface of our fuel cell and oxygen comes from the air side of the fuel cell and mixes with CO [carbon monoxide] of the syngas to form carbon dioxide and oxygen comes across the membrane again from the air side, mixes with the H2 [hydrogen] in the syngas to form water, and both of those reactions are accompanied by electrons flowing on the outside and that's the basic reaction," he said.

Some of the other points Sridhar explained in the Greentech Media interview, include:

• The ability of the electrodes to handle multiple fuels without the need for a switch.
  
• The ability of the electrodes to take the fuel without the need for an external reformer (a reformer turns fuel into hydrogen.)
  
• The ability to make metal plates that have the same thermal expansion throughout the temperature range so the ceramic tiles are not stressed as they heat and cool down
  
• And Sridhar explained why Bloom uses high temperature technology. "Chemistry says the higher the temperature the higher the efficiency; it's just fundamental thermodynamics. Why do people [rival technologies] go to lower temperature? They don't know how to handle the high temperature and they don't know how to handle the material challenges associated with the high temperature. We have figured out the material science and thermal packaging. And once you do that, you have a wide variety of fuels that you can use."
  
• The cost is 9 to 10 cents a kilowatt hour, which includes maintenance, installation, natural gas.
  

In a related article, Greentech media editor Michael Kanellos compares Bloom's technology to solar and delves further into the economics of the Bloom box.