One megawatt of grid storage, 10 big flywheels

Beacon Power says its latest flywheel will provide one megawatt of storage to the electricity grid by the end of the year.

The company's carbon fiber flywheels, which are one meter in diameter, spin constantly at up to 16,000 revolutions per minute--a surface speed of about Mach 2, Beacon CEO William Capp explained Friday. Each 8,000-pound unit can provide 100 kilowatts of electricity for 15 minutes.

Combining 10 of those flywheels will give a utility one megawatt of storage, or 25 kilowatt hours--the equivalent of what a home consumes in a day.

Fifteen minutes of storage may not sound like much, but it's enough to smooth out short-term fluctuations in demand and signal frequency, Capp said.

"These are used for fine tuning to keep everything in balance. The way it's done today is that a dispatcher sends a signal to generators...to increase or decrease output," he explained.

The kinetic energy that's generated from the spinning is converted into electricity when it's needed. Similarly, storage is added to the flywheels by using electricity to make them spin faster.

Utilities are starting to experiment with grid storage as a few technologies start to mature, including flywheels, batteries, and compressed air storage. Storage can prevent outages and store power generated from intermittent sources like solar and wind for times of peak demand.

The next generation of solar thermal power plants will use molten salt to store energy for several hours so that they can continue to meet demand for power after the sun goes down.

Flywheels can react quickly to changes in demand, which is more efficient than bringing power generators up and down, Capp said. He predicted that utilities will invest in them because they help lower their carbon emissions.

"Rather than generating the power using fossil fuels, we'll be recycling the energy," Capp said.

The company intends to combine its 100-kilowatt units into 20-megawatt storage facilities, he added.