Flywheels Gain as Alternative to Batteries

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With the growing emphasis on environmentally-friendly data centers, flywheels are gaining attention as an alternative to using batteries in a data center UPS (uninterruptible power supply) system.

A flywheel is a spinning cylinder which generates power from kinetic energy, and continues to spin when grid power is interrupted. In most data centers, the UPS system draws power from a bank of large batteries to provide “ride-through” electricity to keep servers online until the diesel generator can start up and begin powering the facility.

Advocates of flywheel technology say they are preferable to batteries, and can address most data center power interruption scenarios. “I don’t care much for batteries,” said John Sears, the marketing manager for Hitec Power. “I favor flywheels for a number of reasons. The products are mature, they’ve been on the market for a while, and can handle load for enough time to start the generator.” Sears also likes the smaller footprint of flywheel-based UPS systems, which take up considerably less space than battery banks.

Flywheels represent about 6 percent of the three-phase UPS market, according to analysts at Frost & Sullivan, which tracks the UPS market. Many data center managers have reservations about flywheels in a scenario where the generator doesn’t start immediately. But Frost notes that “flywheel UPS, with its longer life cycle and lower cost of maintenance, is likely to witness increased demand in the future.” Adoption of flywheels appears to be on the rise in Europe, where two large data center projects announced this spring that they would rely on flywheel UPS systems.


On May 16 DigiPlex Norway announced that it would install a 4 megawatt power system featuring a flywheel from Active Power. DigiPlex is owned by the Carlyle Group, which also owns CRG West, which operates data centers and carrier hotels in the U.S. “It’s important we have technology in place that seamlessly handles power fluctuations, sags and outages as our customers demand it,” said Dag Gjetring, DigiPlex Site Manager. “We were impressed with the integrated approach Active Power proposed and the exceptional levels of operating efficiency in their UPS.” Austin-based Active Power is a publicly held company (ACPW), and has shipped more than 1,500 flywheels since it was founded in 1992.

In March, Hitec Power Protection said that its flywheel UPS (which it calls a dynamic rotary UPS) will be installed in a new facility being built in Eemshaven, Netherlands by TCN SIG Telehousing that will soon be among that country’s largest data centers.

Another leading player in the data center flywheel UPS market is Pentadyne Power, which introduced carbon-fiber flywheel technology in 1993. The company has raised more than $32 million in funding from venture capital companies including Nth Power, Rustin Canyon Partners, DTE Energyand MVV Innovations. Pentadyne sells flywheel UPS systems through a distribution agreement with the Liebert unit of Emerson Network Power (EMR).

In May Pentadyne announced an order worth $4.5 million from Beaver Aerospace & Defense for an additional 100 Pentadyne VSS + DC systems. The purchase was part of a procurement contract with Pentadyne to be the exclusive supplier of more than 500 clean energy storage systems that will be deployed in homeland security military defense applications.

About the Author

Rich Miller is the founder and editor at large of Data Center Knowledge, and has been reporting on the data center sector since 2000. He has tracked the growing impact of high-density computing on the power and cooling of data centers, and the resulting push for improved energy efficiency in these facilities.