Flywheels look to be increasingly interesting as sources of short-term power. The kinetic energy stored by virtue of their spinning can make for a "green" way of providing energy for short durations.That's one reason the Dept. of Energy's ARPA-E program for promising energy technology is funding at least one flywheel project.
But flywheels aren't strictly science-fiction-type ideas. You can find a few of them in backup power supplies. One of the latest indications of the trend is a recently introduced system from Vycon billed as the first flywheel and battery energy storage system combo. Called the Hybrid VDC XEB, it uses its built-in flywheel to provide power during short outages of a couple minutes or less which, Vycon says, comprise 98% of the power outages most facilities see. According to the Electric Power Research Institute (EPRI), 80% of all utility power disturbances last less than two seconds and 98% last less than 10 seconds. For longer problems, the batteries kick in. Dividing power backup tasks this way lengthens battery life, Vycon says.
Flywheels have been used in commercial backup power supplies before, but they tended to be relatively heavy devices spun at low speed, usually 10,000 rpm or less. The low speed keeps down centrifugal forces which can eventually cause the flywheel to disintegrate. The Vycon device, though, spins at 14,000 to 36,750 RPM. The amount of up time it provides depends on the power factor of the load. With a 0.8 pf, the device provides 300 kVA for 1.4 minutes, 2.9 minutes with pf of 0.9.
The Vycon flywheel uses a high-performance steel rotor and a permanent magnet motor generator. Like other modern flywheels, it sits on a magnetic levitation system rather than on mechanical bearings. It also resides in a vacuum chamber to eliminate losses from air resistance.
Typical applications are in data centers, healthcare facilities, industrial control systems and other mission-critical operations that may require several minutes of backup power. Upon a prolonged power outage, the VDC XEB will gracefully transfer to onsite generators.
Vycon Energy, Yorba Linda, Calif., www.vyconenergy.com
Machine Design Magazine did an overview of modern flywheel technology a few years ago: http://machinedesign.com/article/new-spin-for-flywheel-technology-0916