November 14, 2013, 2:41 PM — Data centers powered by fuel cells, not the public power grid, could cut both capital and operational costs, improve reliability, pollute less and take up less space, according to Microsoft researchers.
This technology could make data center expansion possible in regions where utility-supplied power is tapped out but natural gas is abundant, according to a paper posted by Microsoft Research. Also, since the reliability of gas supply is better than that of electrical power, these data centers would suffer less downtime.
The researchers say there are many variables that need to be taken into account in engineering these facilities, but overall they hold potential for greener data centers.
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The researchers looked at distributing relatively small fuel cells similar to those used on propane-powered buses - around data centers to power a rack or two of servers each and found several potential benefits. It eliminates the need for the wired electrical distribution system in a traditional data center. If a fuel cell were to fail it would affect a limited number of servers, which data center management software could handle. Since the power is DC, the AC to DC converters in the servers could be eliminated.
In that configuration the power supply would be nearby each rack so there would be no need for a data center-wide electricity distribution system with its attendant transformers, high-voltage switching gear and distribution cabling. Pipes to distribute natural gas and leak sensors cost less. The tradeoff in the amount of space the gear occupies means a 30% reduction in the required square footage for a data center as a whole, the researchers say.
The fuel cells emit 49% less carbon dioxide, 68% less carbon monoxide emissions and 91% less nitrogen oxide, than traditional power methods, the researchers say.
Fuel cells do require specialized equipment that is not needed in traditional data centers such as reformers that pull hydrogen from methane, batteries and startup systems and auxiliary circuits.
Design of a fuel cell powered data center would have to take into account the spikes in server usage that require instantaneous power supply increases. Fuel cells, which perform best under constant load, can lag seconds behind changes in demand. "Some of the spikes can be absorbed by the server power supply with its internal capacitors. But large changes like flash crowd and hardware failures must be handled by an external energy storage (batteries or super-caps) or load banks," the paper says.
The researchers figured use of rack-level power cells at $3-$5 per Watt, and planned for a five-year replacement cycle for them. The entire system life was set at 10 years. They eliminated the cost of diesel generators and uninterruptible power supplies because the natural gas supply is so reliable. Distribution at the rack level eliminates the need for transformers, high voltage switching gear and distribution cabling. Pipes to distribute natural gas and leak sensors cost less. The tradeoff in the amount of space the gear occupies means a 30% reduction in the required square footage for a data center as a whole.
This issue could be addressed by installing server-sized batteries that could jump in with extra power when server hardware is starting up or shutting down, the times of greatest change in power draw. Fuel cells give off heat, so these data centers would need greater fan capacity to cool them.
The capital cost of a traditional data center is $313.43 per rack per month. A rack-level fuel cell data center is between $50.72 and $63.36 less than that, researchers say. Operating expenses per rack per month for a traditional data center are $223.51 vs $214.06 for one powered by polymer electrolyte membrane fuel cells. The savings would be greater with a different type of technology called a solid oxide fuel cell. Savings would also fluctuate depending on the price of electricity where the data center is located.
Reliability of natural gas distribution systems is better than that of the electrical grid, and that would on average cut annual downtime from 8 hours, 45 minutes to 2 hours, 6 minutes, the researchers say.
The researchers considered using large fuel cells to plug into a traditional data center design as a direct replacement for a utility-provided electric service, but they decided that the larger the fuel cell the greater the chance of failure. Plus the cost was high.
They also considered tiny fuel cells to power individual servers. A failure would affect just one server, and because the cell is integrated there is no DC transmission loss. However, lots of tiny cells may add up to a less efficient and less cost effective use of energy than the slightly larger ones needed for racks.
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