Blog Post

Flywheels: A Cleaner Way of Stabilizing Our Electricity Grid

Beacon Power pushing the envelope and creating a more resilient utility grid with large-scale flywheel power storage

Schematic of Beacon Power's Energy Smart 25 flywheel.Photo Credit: Beacon Power

After I wrote last week about a company developing power grid electrical storage systems using lithium-ion battery technology, a reader alerted me to another, very different approach for storing electricity to make the utility grid more stable and resilient: flywheels.

We've written before about flywheel electrical storage for use in data centers to provide instantaneous back-up power that can last for a few minutes until back-up generators can be started up. But I had not been aware of utility-scale projects that were in operation.

How flywheel electricity storage works

The idea with a flywheel for power storage is that a small amount of electricity is used to keep a heavy mass rotating at a very high speed—10,000 revolutions per minute (rpm) or faster. Then when power interruptions happen or some extra power is needed to stabilize the grid, that flywheel gradually slows down, generating power in the process. It essentially stores energy in a kinetic form until needed.

People like me who read Popular Science have been hearing about the potential of flywheel energy storage for decades; for me, it has been one of those technologies that has been perpetually “just a few years away" from commercialization.


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Beacon Power leading the way with flywheel storage

Flywheels arriving by truck at the construction site.Photo Credit: Beacon Power

The energy storage company Beacon Power, located in Tyngsboro, Massachusetts (north of Boston), has been a technology leader with utility-scale flywheel power storage since its founding in 1997. In September 2013 the company put online the first 4 megawatts (MW) of a planned 20 MW flywheel energy storage facility in Hazle Township, Pennsylvania. The full system should be completed in the second quarter of 2014.

Beacon Power almost became another Solyndra story. In 2010, Beacon Power received a $43 million loan from the government, and then filed for bankruptcy in October 2011.

Beacon Power’s bankruptcy was, in part, the result of a change in federal regulations that delayed the requirement for grid operators to pay more for electricity from sources that could feed additional power into the grid very quickly—this affected Beacon Power’s cash flow. Fortunately, the private equity firm Rockland Capital stepped in and acquired Beacon Power and has now paid back most of the Department of Energy loan.

The company is back on its feet and moving full steam ahead.

Stabilizing the utility grid with flywheel storage

Schematic showing the layout of a 20 MW Beacon Power flywheel system.Photo Credit: Beacon Power

The Pennsylvania flywheel energy storage facility can almost instantly (in less than one second) begin injecting significant amounts of electricity into the grid. This will help to stabilize the utility grid—the operation of which is a constant balancing act between supply and demand. Adding this capability—whether with a flywheel or a more conventional chemical battery—makes the grid less prone to blackouts and, thus, more resilient.

The flywheel system is modular, comprised of many of Beacon Power’s Smart Energy 25 flywheels, each of which can deliver up to 25 kilowatt-hours (kWh) of electricity. When delivering power at a capacity of 100 kW, full discharge takes about 15 minutes. When providing 150 kW (heavier power draw), full discharge occurs in 5 minutes with only 12.5 kWh delivered.

The flywheel itself, according to the Beacon Power website, has a rotating carbon-fiber composite rim, levitated on magnetic bearings so that it operates in a near-frictionless, vacuum-sealed environment. It rotates at 16,000 rpm and is designed for a 20-year life with 100,000 full-discharge cycles.

The Hazle Township 20 MW installation under construction.Photo Credit: Forbes Magazine

According to Beacon Power, the company’s flywheel power storage system “corrects imbalances more than twice as efficiently as traditional generators while consuming no new fuel, producing no emissions, and using no hazardous materials or water.”

The power grid of the future

Beacon Power’s flywheel system is one example of a variety of new energy storage technologies that promise to make tomorrow’s electric grid quite different from what we have today. As a higher percentage of renewable energy sources, such as wind and solar, feed power into the grid, it will become more and more important to have systems like this that can store power when there is excess available and deliver that power when needed.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. In 2012 he founded the Resilient Design Institute. To keep up with Alex’s latest articles and musings, you can sign up for his Twitter feed.

Published December 11, 2013

(2013, December 11). Flywheels: A Cleaner Way of Stabilizing Our Electricity Grid. Retrieved from

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December 23, 2013 - 9:37 am

I'm really interested in this technology and being able to get 85% of the energy back out is fairly good.  But I just don't see how it is very economical to use. 

It would be great to use this as a load shift, kinda like ice storage is used to shift cooling load to the nighttime when rates are lower.  But a single unit is only 25kWh.  It's not very much.  Looking at local rates, 25kWh at 6¢/kWh during the night will cost $1.50.  Selling 21kWh (85%) at 19¢/kWh during the day will pay $4.00.  A net profit of $2.50 a day.  But this is only weekdays for 4 months during the summer.  This is only about 26% of the year.  The other 269 days of the year will give a net profit of ~$1.00 per day.  For the year the net profit is only $570.

That is a large and hefty piece of equipment.  I'm guessing it costs in the tens of thousands of dollars.  The return on investment would take decades. They may need to find some cheaper material costs like using plastic for the structure and water for the weight.  Or make a larger diameter to increase the capacity, but then transportation and production costs go up more. I would like to see this technology work but I wouldn't buy it right now.