Data centre power usage is soaring - the US Environmental Protection Agency estimates that data centre energy requirements will double in the next five years. To address that surge in energy use, some companies are turning to alternative sources of energy, including solar arrays, natural gas turbines, wind power, fuel cells and hydro power. But one big question is whether these power sources will deliver a return on investment (ROI) in the near future.

Ted Ritter, an analyst at Nemertes Research Group, says many companies are having a hard time justifying an investment in alternative power sources right now - especially if it means completely replacing the reliable AC power already coming into their buildings, as opposed to merely supplementing it.

But some users are forging ahead with alternative energy projects anyway, figuring on a payoff within 15 years.

For the North County Transit District (NCTD) in San Diego, solar was the most obvious choice for alternative power. The organisation's data centre is relatively small, but it's big enough to enable the agency to handle ticketing for 12 million public transportation users annually and process video from security cameras in transit stations.

Angela Miller, the transit agency's CIO, says her group felt a need to be a better environmental citizen. As part of a data centre redesign, the agency spent about $600,000 (£367,300) on a 30-panel solar array, invested in virtualisation technology for server and storage systems, and bought new pods that pull hot air out and help cool equipment inside the racks.

The NCTD sells solar-generated power back to the local utility to earn credits on AC power usage (which is allowed under California law), meaning the solar initiative has become a profit centre. The solar panels don't generate power for the building directly.

It works like this: The local utility sells AC power to the NCTD, then the agency sells the utility the solar energy for a 100 percent credit. The agency has a five-year plan in place to offset all AC power in its data centre. The NCTD generates up to 450 kilowatt-hours of electricity, and it plans to reach one megawatt-hour in five years.

"Solar is what has made the [data centre redesign] project even have an ROI," says Miller.

Bob Mobach, a consultant at systems integrator Logicalis Group, helped the NCTD redesign its data centre. He says a key to realising an ROI with alternative power is embracing virtualisation. The agency's data centre is about 80 percent virtualised, and that's a primary reason why the solar arrays are such a successful power source.

"Virtualisation was critical for so many reasons," says Miller, noting that the new setup is "way more efficient", makes better use of hardware, gives the data centre a smaller footprint and is easier to manage with fewer people. "My actual physical footprint went from not having any more slots in the racks available to having only half of the racks occupied and yet we've increased our applications this year," she says.

Analysts laud efforts like the NCTD's but warn that solar power isn't right for every data centre. "The level of efficiency you can get out of solar energy is dictated by the location of the data centre," says Forrester Research analyst Doug Washburn. "If you are in an area where the sun shines more frequently, you can take advantage of a solar investment."

One reason why solar may not be the best data centre power source is the fact that data centres use 10 to 100 times more energy per square foot than a typical office complex, Washburn says. Moreover, resiliency and uptime are so crucial to a data centre's operation that "it's a critical risk, and maybe even foolhardy to think you could power the majority of your data center from solar", he adds.

Washburn agrees that virtualisation is key to the success of a solar project. Increasing the number of hosts per machine, consolidating storage and decommissioning equipment that has been virtualised can make a data centre more efficient even before an energy switch-over, he says.

Power from jet engines

Christopher Sedore, CIO at Syracuse University, says the upstate New York school spent about $12 million to build a data centre that uses natural-gas-fired microturbines from Capstone Turbine to generate power on-site.

Microturbines are essentially jet engines that run on natural gas and provide power to generators. The turbines produce about a half a megawatt of power for the university's data centre and another 200 kilowatts for other uses, such as powering an adjacent building.

The turbines enable the university to have a co-generation setup, meaning they can help generate both heat and power for the data centre or nearby buildings. The university can also sell any extra power the turbines generate back to the local power company.

The turbines drive two 150-ton absorption chillers that turn the heat exhaust from the turbines into chilled water that cools the data centre. In the winter, the university uses cold outside air for data centre cooling, and hot water generated by the turbines is used to heat an adjacent building.

Banking on fuel cells

One of the most promising new technologies for powering data centres is the hydrogen fuel cell. Hydrogen fuel cells don't produce any harmful emissions, so companies such as Verizon, Whole Foods and Google have adopted them as an alternative power source for office or retail space.

Few organisations use fuel cells to power data centres, because they are expensive. But First National Bank of Omaha built a 200,000-square-foot fuel-cell-powered data centre in 1999 because such systems tend to be especially reliable. The data centre is about the size of a football field; it's surrounded by a dry moat and is powered entirely by four 200-kilowatt fuel-cell generators. If the data centre does lose fuel cell power, which is extremely unlikely, an uninterruptible power supply can carry a short-term load.

"With the fuel cells, we have seven-9s of reliability, or about two or three seconds of downtime per year," says Brenda Dooley, president of First National Buildings, a bank subsidiary that handles corporate real estate and facilities management. "We came from a system with backup batteries. When we'd lose power, the batteries just wouldn't be there. We did this for reliability."

Dooley explains that the credit card processing that's done at the data centre requires high reliability: Just one hour of downtime could result in a loss of as much as $6 million.

The bank knew that using fuel cells would be expensive. In Nebraska, AC energy costs only about five cents per kilowatt-hour, whereas electricity from fuel cells costs about 12 cents per kilowatt-hour. It would have cost $2.2 million to build a data centre that used AC power; using fuel cells raised the price tag to $3.4 million. Dooley says fuel cells are worth the higher price, and the ROI is excellent because the bank doesn't suffer lost transactions.

Of course, other enterprises might not be willing to pay such a high price for great reliability. "Fuel cell technology is not there in terms of volume and scale to support larger data centres," says Nemertes' Ritter. "But down the road, it is very interesting potentially as a backup power source."

Alternative power has a bright future for data centres. Ritter says there may be no other option in the coming years, if traditional-energy prices continue to soar. Whether it's solar power, gas turbines, fuel cells or some emerging option - such as harnessing the power of ocean waves - it's clear that new energy sources will play a role in the data centres of the future.