Proven in outer space, fuel cells have come back down to earth and are now a very viable consideration as a data center power source.

We live in an energy-hungry world, and IT is an energy-voracious industry. Large generating plants and transmission lines aren't built at a rate that matches energy demand. A growing number of data center operations are adopting fuel cells to generate on-site power without reliance on the grid. This distributed generation adds new power supply and, unlike conventional generators, puts quiet, clean fuel cell generators on-site that consume relatively inexpensive fuel.

Most people know of fuel cell generator technology because it provided power, as well as water, for space flights, from Project Gemini through shuttle missions. Fuel cells provide power like giant batteries. But unlike batteries, which run out of power once their chemicals are depleted, fuel cells will keep generating reliable power as long as fuel is delivered to them. The hydrogen fuel can be derived from a number of different combustibles like natural gas, methane (a biogas byproduct of waste treatment) or even methanol. Hydrogen can be supplied from tanks or derived internally in the cell from other fuels.

The cost of fuel cell technology, along with some technical problems in its manufacture and use, kept fuel cells out of mainstream commercial installations until recent years. Now we have fuel cells in cars, buses, hospitals, hotels and data centers. So what's changed, and where might this technology go?

Fuel cell options There are many different types of fuel cells, but their fundamental principles are the same: Hydrogen is separated from its electrons, which then flow through the external electrical circuit. Oxygen added from the other direction completes the flow path, combines with the hydrogen and creates the byproduct water. The key is the complex electrolyte that separates the hydrogen and oxygen. Fuel cell types are defined by the electrolyte they use. Most of them need precious metals like platinum, or use liquefied materials that are hard to contain and/or are corrosive. Additionally, fuel cells produce a lot of heat, most at temperatures so high they require special materials for the generator body. This all drives up the cost, but progress is being made on all fronts. The Department of Energy is promoting polymer exchange membrane fuel cells for vehicles, so this product type is pretty hardy and well-developed. But it operates at low temperature -- necessary for quick startup in cars but not a good choice for large continuous loads like data centers. APC (now part of Schneider Electric) until recently marketed a rack-mountable, 10-kW fuel cell that used the early proton exchange membrane technology with hydrogen tanks outside the building. Three units could be stacked for capacities up to 30 kW, and it was marketed as a standby power source for smaller data center environments that, like its larger counterparts today, didn't want the noise or pollution control problems of diesel generators. It was progressive thinking, but clearly ahead of its time. Primary among the large fuel cell generators in use today are phosphoric acid fuel cells (PAFCs). These are well-proven, first-generation designs that use liquid phosphoric acid as the electrolyte. Seven 200-kW PAFC units have been used at Verizon's call-switching center and office building in Garden City, N.Y. for ten years. But the greatest interest seems to be in solid oxide fuel cells (SOFCs) and molten-carbonate fuel cells (MCFCs). These are also high-power, ultra-reliable designs that are good for large, stationary power generation such as is required for data centers, but earlier designs suffered from stability problems. Bloom Energy claims to have overcome the high-temperature materials challenges of SOFC technology. The company is reportedly putting a 4.8-MW, 24 fuel cell system at Apple in North Carolina.

Fuel cells are not UPS systems Large fuel cells take time to come up to temperature and full power, so they run best on loads that remain reasonably steady 24 hours a day, 7 days a week, year-round. This makes data center power an ideal application. So long as it is supplied with fuel, a fuel cell generator can be expected to run continuously and reliably for at least 20 years. Don't replace uninterruptable power systems (UPSs) with fuel cells; a fuel cell generator should take the place of diesel or gas generators. Since they run all the time, they also become the primary power to the facility. The public utility grid power becomes the backup alternative. Because fuel cells are so reliable, battery UPS is no longer really needed, so flywheel UPS is often used as both a power converter and a way to guard against any short-term fluctuations or anomalies that might occur. Several installations have noted that getting rid of batteries, and their attendant reliability problems and replacement costs, was a major consideration in their choice of fuel cells.