The great thing about writing a regular column is that reader feedback sometimes introduces me to new products and systems. So it was last week when I wrote about a company developing power grid electrical storage systems using lithium-ion battery technology.

From a reader of the column, I learned about another, very different approach for storing electricity to make the utility grid more stable and resilient: flywheels.

I have written in the past 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 generates power, gradually slowing down in the process.

Those of us 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 "just a few years away from commercialization" for decades.


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Beacon Power leading the way with flywheel storage

The energy storage company Beacon Power, located in Tyngsboro, Massachusetts (near Lowell), 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 (Solyndra was the solar panel manufacturer that went bankrupt after receiving a $535 million U.S. Department of Energy loan through the American Recovery and Reinvestment Act, giving the loan program a black eye and fanning the flames of right-wing opposition to renewable energy subsidies.) In 2010, Beacon Power received a $43 million loan from the same program, 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 DOE loan.

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

Stabilizing the utility grid
with flywheel storage

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.

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 Wilson is the founder of BuildingGreen, Inc. and the Resilient Design Institute (www.resilientdesign.org), both based in Brattleboro. Send comments or suggestions for future columns to alex@buildinggreen.com.