The phrase “everything old is new again” certainly applies to today’s flywheel technology. Forget the mechanical bearing, standard atmosphere 5,000 RPM steel behemoths of the past, many of today’s flywheel designs feature compact carbon fiber composite rotors on magnetic bearings, turning in a vacuum at up to 60,000 RPM.
As flywheel technology continues to improve, flywheel energy storage (FES) systems are gaining in use across a wide variety of applications, from frequency regulation in power utilities to energy recovery in trains and industrial equipment to rack-mounted uninterruptible power supplies. With demand rising for reliable, cost-effective, and environmentally friendly energy storage, especially to support the growth of green power solutions like wind and solar, FES is quickly coming into its own.
Compared to other energy storage solutions, FES systems have long lifetimes with minimal maintenance requirements, high energy densities (~ 200 kJ/kg), and large maximum power outputs. The round-trip efficiency (ratio of energy out per energy in) of flywheels can be as high as 90%, with power output capacities ranging from 2 kWh to 133 kWh, and an FES system can typically reach full charge in as little as 15 minutes. Compared to batteries with low capacity, long charge times, heavy weight, and short usable lifetimes, FES presents a bright spot in tomorrow’s clean energy solution.