Electric power may need to be stored when there is excess power available so that it can be released when needed. StanislavPejovic, in a recent seminar, proposed that we need as much storage capacity as the amount of intermittent renewablesto provide for those days when there is no wind or sun. Although with widely distributed grids this is less likely to happen, it is certainly something to ponder.
There are a variety of ways that this can be done ...
- Pumped hydro - Conventional pumped hydro uses two vertically-separated water reservoirs. During off peak hours water is pumped from the lower reservoir to the upper reservoir. When required, the water flow is reversed to generate electricity.
- Thermal energy storage - Molten salt can be employed as a thermal energy storage method to retain thermal energy collected by a solar tower or solar trough so that it can be used to generate electricity in bad weather or at night.
- Compressed-air energy storage (CAES) uses off peak electricity to compress air into either an underground structure (e.g., a cavern, aquifer, or abandoned mine) or an above ground system of tanks or pipes.
- Hydrostor is a project planned for Lake Ontario. According to Hydrostor's site: "The Hydrostorsystem efficiently converts electrical energy to compressed air via an advanced adiabatic compression system. This air is then sent to a series of flexible accumulators located 50-500 meters below the surface of a body of water. Once in the accumulators, the energy can be stored until required by the grid. When the energy is required, the weight of the water pushes the air back to the surface where our system directs it through an expander driving a generator thus supplying energy to the grid and completing the storage cycle."
- Batteries - electrochemical devices that convert chemical energy into electrical energy during battery discharge and, during battery charge, convert the electrical energy back into chemical energy for long-term storage.
- Flywheels - Most modern high-speed flywheel energy storage systems consist of a massive rotating cylinder (a rim attached to a shaft) that is supported on a stator by magnetically levitated bearings.
- Vehicle to grid (V2G) - a system in which plug-in electric vehicles, such as electric cars (BEVs) and plug-in hybrids (PHEVs), communicate with the power grid to sell demand response services by either delivering electricity into the grid or by throttling their charging rate.
- Hydrogen - excess energy can be use to convert water into hydrogen. Tyler Hamilton posted a blog about hyrdogen storage at http://www.cleanbreak.ca/2013/04/09/catalyst-breakthrough-could-change-economics-of-hydrogen-energy-storage/
Tyler Hamilton blogs about clean technology in general at cleanbreak.ca. His research on energy storage is at cleanbreak.ca/category/energy-storage/