Flywheel Energy Storage

Flywheel energy storage systems store energy in the kinetic energy of fast-spinning flywheels. They have high power density, no pollutants, long lifespans, wide operational temperature ranges, and no limit on charge/discharge cycles. They are already widely used in power quality control and UPS (uninterruptible power supply) applications, grid frequency regulation, satellite power and altitude control, and rail regenerative braking.

Figure 1: Flywheel application by number of projects (left) and installed capacity (right) since 2010

According to CNESA's project database, since 2010, there are 14 flywheel projects in planning, construction, or operation - totaling 81 MW worldwide. These are most used in frequency regulation markets, distributed generation and microgrids, and rail energy recovery. Grid frequency regulation has been the hot spot for recent flywheel application. Following the installation of the 20 MW Beacon Power flywheel system at Hazleton, PA, a pair of flywheel projects (5 MW and 2 MW) were planned for Ontario, Canada to provide frequency regulation to the Ontario electricity market (IESO). It is worth noting that in the first half of 2015, Irish company EirGrid planned a 20 MW project that would be Europe's first such flywheel installation. Following the example of the North American markets and European electric markets addressing frequency regulation resource requirements, European grid operators are recognizing flywheels as fast response resource.

Figure 2: Global flywheel installation by company – contracted, under construction, and operational projects – since 2010

According to CNESA's project database, the major flywheel energy storage are Beacon Power, VYCON, Temporal Power, Active Power, Amber Kinetics, Boeing, and Quantum Energy. Beacon Power was founded in the 1990s, gradually transitioning from UPS to grid frequency regulation. Active Power and VYCON both primarily serve the UPS field, mainly as backup/reserve power in data centers, hospitals, and industry (esp. crane and rail car systems). Temporal Power is a Canadian company established in 2010, with most of its projects providing frequency regulation to Canadian electric markets.

Quantum Energy Storage is a newly emerging company founded in 2013, and is participating in the FractalGrid microgrid demonstration project at Camp Pendleton, near San Diego, CA.  Quantum Energy’s flywheel does not use the traditional cylindrical design, but rather is disk-shaped, less than 2 inches thick, and spins at only 6,000 RPM, compared to the 10,000 RPM speeds of Temporal and Beacon flywheels. The thinking is that lower speeds will reduce resonance damage and the possible damage caused by a wheel breakdown.

Source: Amber Kinetics, DOE Sept. 2012.

Source: Amber Kinetics, DOE Sept. 2012.

Compared to other technologies, costs remain high for flywheel energy storage, but as reflected by some firms, areas with high electricity prices like the Caribbean (about $0.40/kWh) can get payback periods of 3-5 years for flywheel systems replacing diesel generators. In several remote areas, ROI can be shortened to one year.

Compared to other countries, China's flywheel energy storage technology is lagging behind. There are, at present, no commercial or demonstration projects using flywheel energy storage. The most advanced research in this field in China is taking place at Tsinghua University, but we expect that commercial-sized installations will have to wait until Chinese regulators adopt policies that provide compensation for fast frequency response.