A flywheel can be used to store kinetic energy in rotating mass. While flywheels have been used for many centuries, modern materials and other innovations are spurring research on making flywheel systems that are smaller, lighter and cheaper, with greater capacity and better efficiency. Flywheels are used in a variety of applications, including energy storage, uninterruptible power supplies, grid conditioners for high-cost manufacturing, and in some cases, are even used to power vehicles. (The gyrobuses used in Sweden in the 1950s were powered by flywheels.)
Like batteries, flywheels have a fixed energy capacity, but that capacity can be drawn down quickly or slowly depending on need. Flywheels are used in remote applications to level loads , they can also be used in renewable energy applications allow a dispatchable generator to be brought online when necessary. Like batteries, typical storage times are rated by the number of minutes of power that can be provided. Flywheels do, however, have several advantages over batteries. They are very durable, require minimum maintenance, and have fast response time. Although flywheels are limited by the strength of the materials used for the spinning rotor, thus limiting capacity. Most commercial flywheels are modular, so both capacity and rated power can be increased by using multiple units.
There are several research and development issues with the technology. Although recent developments such as magnetic bearings have reduced losses, flywheels have a parasitic energy loss to keep the unit spinning and a relatively quick self discharge if additional energy is not provided. Overloaded flywheels also have the potential for catastrophic failure.
PowerCorp (Australia) has successfully integrated its flywheel system with wind and wind-diesel projects. The use of flywheels has allowed wind-diesel systems to operate at reportedly high penetration (up to 90%) of wind power to offset diesel generation. They have also used flywheels to achieve grid stability, typically in mining applications.
A capacitor is a passive electrical component that can store energy. Capacitors are commonly used in personal electronic devices to maintain the power supply while batteries are being changed. While they have no moving parts allowing a very high cycle life, fast and consistent response, capacitors have low power density, meaning that large arrays are required to store meaningful amounts of energy. Conventional foil-wrapped capacitors are used extensively on electric grids today to provide voltage support. While maintaining a very high cycle life (>100,000 cycles). Ultracapacitors and supercapacitors, which are electrochemical can store significantly more energy than conventional foil capacitors. Capacitors have a higher voltage capability than batteries, but they store much less energy. Both capacitors and batteries are systems with multiple components and high capital costs, and can be distributed throughout the system. Capacitors are expensive, and currently there are no commercial manufacturers of large-scale capacitor storage systems.
Links, Resources, and Documents
- Hertrich, D. (2012). Williams – High Powered Flywheels. Hatch. 2012 Energy Storage Workshop: Power Point Presentation.
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