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.
The eco argument for fuel cells
The main byproducts of fuel cells are water and heat, with low levels of CO2 and other gases depending on the type of cell. Fuel cells, therefore, are considered very environmentally friendly technology. The major manufacturer of large fuel cells, United Technologies Corporation (UTC), acquired by ClearEdge Power in 2012, has reportedly installed nearly 300 large PAFC fuel cells to power data centers, hospitals and hotels.
The major impediments to wider-scale adoption continue to be cost and coping with the amount of heat released. PAFC units generate heat at about 600 degrees Celsius (1,100 degrees Fahrenheit). MCFC generators run at about the same temperature. Although too hot for many direct applications, the heat from these units can be used to generate steam. But the molten chemical salt in MCFCs is corrosive and requires special materials for containment. SOFCs have no liquid components, which means they can be mounted in any position, but they run at temperatures in the order of 800 degrees C to 1,000 degrees C (roughly 1,500 degrees F to 1,800 degrees F). That's far too hot for most equipment. While there is no perfect solution to the heat issue, strides are being made.
Fuel cells are usually thought of as highly efficient, but in reality they're not as impressive as one might expect. A fuel cell generator typically runs at only 40% to 60% efficiency if the waste heat is simply discharged. That compares with about 40% efficiency for a diesel generator. If you can use the heat, you might be able to realize as high as 85% efficiency from fuel cells. Data center designs could call on waste heat from fuel cells to warm the building in winter or produce domestic hot water, but there would still be a lot of leftover heat. Unless you're in a very cold climate year-round, this hot air will go to waste. One option is to use a high-temperature heat exchanger and run absorption chillers for cooling, but even high-temperature chillers don't operate much above 140 degrees C (285 degrees F), so there's a big, inefficient conversion to make. Cooling with heat would considerably reduce your electrical requirements -- chillers are usually the biggest power users in the cooling chain -- so the fuel cell size might be reduced for a double gain. But absorption chillers require regular maintenance, and if the fuel cell ever stops, so will the chillers. Backup grid power will pick up, but how would you quickly get steam to the chiller to maintain cooling?
An individual fuel cell generates only about 0.7 volts of electricity, so like batteries, fuel cells need to be "stacked" to produce the voltages necessary for major operations. Also like batteries, fuel cells produce direct current (DC) power, but most data centers distribute alternating current (AC), so there is another efficiency loss in making the DC-to-AC conversion. But fuel cells avoid the 7% to 15% power loss usually associated with the utility transmission grid, so there is actually a net efficiency gain. The UTC stationary fuel cells that power numerous data centers tend to be around 200-kW capacity, and are in 17-foot (5.2-meter)-long boxes about the size of small shipping containers. The Bloom Energy units run from 15 to 28 feet (4.5 to 8.5 meters) long, depending on power capacity. A one-megawatt installation would require five 200-kW boxes, or six for redundancy. It would also be wise to have dual fuel paths, even though natural gas supply is much more reliable than most electric services.
So with all these apparent complications, costs and concerns, what's the attraction of fuel cells, and why are Fujitsu, Apple, Verizon, First National Bank of Omaha and others using them? Part of the answer is image. The big energy users have faced some pretty harsh press for "dirty" power sources. But these companies can also afford to try more esoteric routes and, in so doing, demonstrate their progressiveness and eco-consciousness.
At the same time these early adopters blaze the trail for the rest of us, they certainly haven't ignored the economics. Fujitsu, for example, reported that the up-front cost of fuel cells significantly exceeded the cost of generators. But when they factored in the price of natural gas vs. electricity over twenty years, plus the virtually zero-maintenance on fuel cells and the utility rebates they received, the fuel cells came out ahead. And if, like Apple, they can also use methane biogas from a landfill or waste treatment plant, they have zero energy cost to generate their power. Fujitsu also sells excess power back to the utility.
About the author:
Robert McFarlane is a principal in charge of data center design at Shen Milsom and Wilke LLC, with more than 35 years of experience. An expert in data center power and cooling, he helped pioneer building cable design and is a corresponding member of ASHRAE TC9.9. McFarlane also teaches at Marist College's Institute for Data Center Professionals.