Flywheel Power Looks For A New Spin

Batteries only last a few years and contain noxious chemicals, says Active Power

Green considerations will prompt more data centres to adopt mechanical flywheel-based uninterruptible power supplies (UPSs) to replace environmentally damaging batteries, a London conference heard.

Mechanical flywheels can store enough energy to keep data centres running in the event of a power cut, and they compare well with batteries on most measures, Active Power said, and showed a containerised flywheel power supply at the Data Center Dynamics (DCD) event in London.

Kinetic energy is cleaner than chemicals

“Batteries are temperature dependent and last about five or six years,” said Graham Evans (pictured), Active Power’s head in Europe. Batteries also face stringent rules for their storage and disposal, he added.

UPS systems provide contionuous power when there is an interruption, and usually contain a battery to keep systems running while a diesel generator is started.

They operate continuously, conditioning the power in normal use, he explained. Normally, battery UPSs are scaled to provide a minute’s power, but a flywheel can store enough kinetic energy to keep the systems running long enough for the generators to start – though they tend to store energy that will last a shorter time.

Flywheels have been treated with some scepticism by data centre designers in the past, but Evens believes environmental concerns will bring them to the fore, as they appear in high-profile sites such as the Marilyn data centre in Paris.

Unlike other flywheel makers, Active Power packages its flywheel with the diesel generator, in sizes from 500kVA to 1.5MVA (roughly equivalent to tookW to 1.5MW). Flywheel maker Beacon has gone bankrupt, despite making ambitious 20MW units, but Evans does not expect similar problems at Active Power, thanks to its focus on delivering whole UPS systems.

At the DCD event, Actiove Power had a 500kW UPS system, featuring two 250kW flywheels and a diesel genset, on display in a shipping container. The flywheel system is not as exciting to look at as one might have hoped.

The wheel is about 1m across, and spins horizontally in a sealed chamber with a partial vacuum. With no noise and no way to see the wheel spinning, there was little to see – but Evans believes this very dullness and predicatbility should endear flywheels to data centre managers.

In the image here, the wheel is in the anonymous compartment in the centre of the image, above the electric motor (dimly visible at the bottom) and below the power-conditioning electronics.