What you need to know about flywheels


Updated: The bankruptcy of Beacon Power will likely draw attention to the flywheel industry, as Beacon was one of the better known companies in that field. So how exactly are flywheels used for energy storage, why do companies buy them, and why has the technology struggled? Here’s what you need to know:

What are flywheels: Flywheels are being used as energy storage devices and spin large discs very fast inside a vacuum. The rotation of the discs is stored as kinetic energy (movement).

What are flywheels used for: Flywheels are most commonly used as backup power for emergency power systems — what’s called uninterrupted power supply, or UPS — and these UPS systems are found in facilities like data centers, which will come online if the grid goes down. According to Lux Research, flywheels and ultracapacitors could take 10 percent of the datacenter UPS market by 2016. A few years ago Frost & Sullivan estimated that just 6 percent of the UPS market used flywheels. Sun has used flywheels in its green data centers, as has Cisco.

Beacon Power’s flywheels are largely used to help keep electricity flowing over the grid at the steady 60 hertz required. The company’s 20 MW plant in Stephentown, NY, was built to absorb and discharge energy to the electric grid, making it possible to use more variable renewable energy sources like solar and wind.

The Electric Power Research Institute (EPRI) has pegged 2012 as a turning point for grid energy storage in the U.S. because by then energy storage makers that have collectively received more than $250 million in federal stimulus funding are expected to complete research and development work and move into field trial stages in the U.S.

Why companies buy flywheels: Companies that buy flywheels like them because they don’t use toxic chemicals like batteries, they can come online very quickly when used as backup power, they need little maintenance over a 20-year period (so lower lifetime maintenance costs than batteries), and they are energy efficient. Flywheel maker Active Power once told us that a 10-megawatt flywheel-based UPS system could save a customer $20 million in energy and maintenance costs over 20 years.

Why flywheels have hit hurdles: Flywheels have had difficulty finding the right market and have faced competition from batteries, which have received a good amount of funding and support. Batteries have lower upfront costs than flywheels, and Beacon’s flywheels are more expensive than lithium-ion batteries on a capital cost basis, though Beacon says its flywheels are cheaper on a per-cycle basis.

Companies that make flywheels: There’s a handful of companies other than Beacon that are making flywheels, including Pentadyne (see update), and Active Power, which make flywheel UPSs for data centers. Pentadyne has developed magnetically levitated carbon-fiber flywheel systems that don’t use an external vacuum pump, have no mechanical bearings, and use 90 percent less power than other flywheels. Update: Pentadyne sold its flywheel assets to Phillips Service Industries (PSI) in 2010.

Smaller companies that I’ve learned about in recent years include Amber Kinetics and Velkess. The DOE gave Amber a $4 million grant to develop and demonstrate its flywheel energy storage technology for grid applications. Velkess is a three-year-old company that says it has developed a new kind of flywheel that is cheaper and more stable and safe than conventional flywheels.



“Velkess says it has developed a new kind of flywheel that is more stable and safe than conventional flywheels.”

Katie, are conventional flywheels unstable or unsafe? That would be news to me.


I think you meant: “The rotation of the discs is USED TO STORE kinetic energy…”

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