Flywheels Show Promise for Storage of Renewable Energy
Diagram of a room stocked with flywheel energy storage devices. (image: cogeneration.net)
One of the big challenges for solar or wind power is that they are intermittent, not constant. The sun only shines half the hours at best (not even counting clouds or rain), and similarly, the wind does not blow continuously. To make these energy sources more practical, efficient power storage is necessary; you need to be able to top up the “battery” when the power is on and then use it to provide electricity at night, on overcast days, or when the air is still.
As reported by the New York Times Monday, a Massachusetts company thinks it has a solution to the problem of energy storage: flywheels.
A flywheel is a nothing more than a heavy wheel that rotates or spins freely. If you connect it the right kind of dual-purpose electric motor—some electric motors, like the ones in hybrid and electric cars, can function as both motors and generators—you can use the motor to spin the flywheel up to speed when there’s a surplus of power. Then, when you need energy, you slow down the wheel and convert its momentum back to electricity. If the wheel is heavy enough and spinning fast enough—the ones that Beacon Power is installing near Albany, New York, weigh a ton each and spin up to 16,000 times a minute (267 times a second)—you can store an enormous amount of energy in them.
The facility near Stephentown, New York is not intended primarily for alternative energy use. It’s designed to help utilities generally balance power distribution. With conventional energy sources, like coal, nuclear, or natural gas, efficient generation means constant generation, but demand for power fluctuates during the day. Having a way to store excess power when demand is low and then release it when demand is high makes for better operation of the electrical grid.
However, the same system will work admirably for alternative energy, where supply and demand both vary hourly. There are other ways to store power from solar or wind generation:
• excess solar heat can be used to heat molten salt, which then gives up its heat later, when the sun is down, similar to how a pizza stone holds heat from an oven
• surplus electricity can be used to compress air; when power is needed later, the compressed air can be released to spin turbines
But these methods have their limitations. Molten salt only works with solar thermal systems; and compressed air requires a convenient cavern system nearby, to hold the air. Flywheels are more flexible, in that they can be used with any source of electrical energy; they are highly efficient, returning up to 85 percent of the power placed in them; and they are fast to both charge and discharge.
Good power storage systems may go a long way towards making alternative energy truly feasible.
