Joe Desposito's Blog

Flywheels Land in Stephentown, New York

I read some interesting news recently that has to do with the power grid. A $69 million dollar battery farm was officially inaugurated on July 12th in Stephentown, New York. This is not your usual battery farm. No lithium-based batteries here. Instead, the farm is using 200 flywheels from Beacon Power Corporation to store excess power on New York’s electrical grid, which can be restored to the grid within seconds when needed.

You may recall that in December 2010, Popular Mechanics named flywheel energy storage as one of the 10 Tech Concepts You Need to Know for 2011. As for myself, I have not come face-to-face with a flywheel since around 2003, when I used to attend the Power Electronics Technology show.

How does flywheel energy storage work?  A cylindrical assembly called a rotor (flywheel) is accelerated to a very high speed, maintaining the energy in the system as rotational energy. How do you get the energy back? By slowing down the flywheel, of course. The flywheel system itself is a kinetic, or mechanical, battery spinning at very high speeds to store energy that is instantly available when needed.

At the core of Beacon's flywheel is a carbon-fiber composite rim, supported by a metal hub and shaft and with a motor/generator mounted on the shaft. Together the rim, hub, shaft and motor/generator assembly form the rotor. When charging—that is, when absorbing energy—the flywheel's motor acts like a load and draws power from the grid to accelerate the rotor to a higher speed. When discharging, the motor is switched into generator mode, and the inertial energy of the rotor drives the generator which, in turn, creates electricity that is then injected back into the grid. Multiple flywheels may be connected together to provide various megawatt-level power capacities. Performance is measured in energy units: kilowatt-hours (kWh) or megawatt-hours (MwH), indicating the amount of power available over a given period of time.

Beacon's Smart Energy 25 flywheel has a high-performance rotor assembly that is sealed in a vacuum chamber and spins between 8,000 and 16,000 rpm. At 16,000 rpm the flywheel can store and deliver 25 kWh of extractable energy. At that speed the rim must be enclosed in a high vacuum to reduce friction and energy losses. To reduce losses even further, the rotor is levitated with a combination of permanent magnets and an electromagnetic bearing.

Beacon Power's grid-scale Smart Energy Matrix is made up of multiple integrated systems of ten Smart Energy 25 flywheels, interconnected in an array, or matrix, to provide energy storage for certain utility applications. The Smart Energy Matrix can absorb and deliver megawatts of power for a period of minutes, providing highly responsive frequency regulation capabilities for increased grid reliability.

The Stephentown facility has 20 megawatts of storage capacity. The problem this plant is solving for the grid is essentially load balancing or frequency regulation. The flywheels can balance the load about 100 times faster than typical power plants.

Haresh Kamath, program manager for energy storage at EPRI, the Electric Power Research Institute said there have been smaller flywheel demonstration projects, but this appears to be the first large-scale regulation system hooked up to a power grid.

Flywheels have other interesting applications as well—for example, amusement rides. The Incredible Hulk roller coaster at Universal's Islands of Adventure features a rapidly accelerating uphill launch as opposed to the typical gravity drop. This is achieved through powerful traction motors that throw the car up the track. To achieve the brief very high current required to accelerate a full coaster train to full speed uphill, the park utilizes several motor generator sets with large flywheels. Without these stored energy units, the park would have to invest in a new substation and risk browning-out the local energy grid every time the ride launches. For more information, visit Beacon Power at


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