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Data center power backup isn't just about batteries anymore

Batteries have been the dominant backup power supply in the data center, but alternatives such as flywheels and thermal energy are giving companies more options.

Batteries continue to be the main choice for short-term power backup in the data center, but alternatives from...

the ancient past and near future are offering IT managers with more choices than ever.

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Will bad batteries be your undoing?

Pulling power from thin air

Companies are taking another look at flywheels and some new technologies to replace or work in conjunction with batteries, which are often seen as a cheap upfront cost but are somewhat unreliable and a pain to replace every few years. These alternatives may emerge as a viable option for data centers to be able to sustain short outages or bridge the gap until the generator kicks on for larger outages.

James Alt is the manager of voice communications at Meriter Hospital, a 448-bed nonprofit hospital in Madison, Wis. Alt convinced the hospital's data center to incorporate flywheel technology into the backup power supply along with batteries, a project the hospital started earlier this year.

"We had a number of issues with batteries," he said. "Limited life, replacement of them. It made sense to us to consider an alternative to batteries."

Alt said that battery manufacturers were claiming a 10-year lifespan, uninterruptible power supply (UPS) providers were saying five, and the reality was two to three years, sometimes shorter. The hospital was running parallel strings of batteries for its backup power supply, and decided to replace one string with flywheel technology.

"The one thing I'm hoping for is better reliability," Alt said.

Using a flywheel for energy is nothing new, in fact the technology has been around for decades. Modern flywheels are encased in vacuum cylinders that minimize friction, allowing the wheel to spin longer and generate more energy.

The primary power source gets the flywheel spinning. This builds up kinetic energy based on the mass of the flywheel and the speed at which it rotates, which can be as fast as 54,000 rotations per minute. When the power goes out, even if it's for a second or two, the flywheel releases the built-up kinetic energy back into the data center until power resumes or a backup generator turns on.

There are a few players in the flywheel energy storage market. Meriter Hospital has two of Chatworth, Calif.-based Pentadyne's flywheels and is ordering three more. Another major manufacturer is Active Power in Austin, Tex. Other producers include Beacon Power in Wilmington, Mass., and Vycon in Cerritos, Calif.

For smaller data centers, flywheels can be used as a replacement to the battery-powered UPS. For most operations, they work side-by-side with batteries.

"What kills batteries is how often you cycle them," said Frank DeLattre, Pentadyne's senior vice president of sales and service. "Most of the power outages you have are these short, one-second glitches. You don't see it because it's so quick, but the batteries see it."

Supporters of the technology call it battery hardening. The Electric Power Research Institute in Palo Alto, Calif., estimates that 98% of utility interruptions last less than 10 seconds. If a flywheel can sustain power for that time, it can prolong the life of a string of batteries by reducing how many times they are "cycled."

Flywheels don't provide power for a long time; usually 15 to 20 seconds to bridge the gap until the primary power returns or a generator takes over.

Active Power, meanwhile, has patented a different way to provide backup power and cooling to the data center at the same time. When power goes out, a valve releases compressed air stored in tanks powers a small turbine that can provide power. Meanwhile, the process produces leftover cold air that can be used to cool the data center.

The company claims that their process provides power and cooling for longer periods of time.

"It gives you longer runtime and simultaneous power and cooling," President and CEO Jim Clishem said. "I think it is specifically catered for data centers that don't have gensets."

All of these power backup alternatives have their uncertainties. Flywheels and the Active Power CoolAir system are mechanical processes, which some fear could break down more easily than the chemical process of running batteries.

But batteries have been a potential source of problem for as long as they've existed, according to data center design expert Robert McFarlane, president of the Interport Financial Division of New York-based Shen, Milsom & Wilke Inc. However, most data center managers aren't seeking options other than batteries, he said.

"I think given an alternative to batteries they would express an interest, so [there is] a potential market for alternatives," McFarlane said. "I'm starting to consider recommending a combination of UPS and something like flywheel."

The number one obstacle is unfamiliarity. Back at Meriter Hospital, Alt said he was pushing to have the power backup be completely run by flywheels. But, it wasn't happening.

"I was trying to talk our data center manager into just going to flywheel," he said. "But he's still kind of old school and wanted to go with a combination of flywheel and batteries. In the event that the generators won't work, batteries give us enough time for an orderly shut down."

Let us know what you think about the story; e-mail: Mark Fontecchio, News Writer.

This was last published in July 2006

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