Some grid operators use batteries to store energy that can then be expended to balance variations in load to regulate frequency. Batteries can quickly store and release energy as required. Battery systems can also be found at the distribution level of the electricity grid and at individual customer sites.

A flywheel energy storage system uses power to drive a motor that spins the flywheel at high speeds to store energy – the greater the rotational spin of the flywheel, the more energy that is stored. When energy is needed, the rotational speed is reduced, allowing energy to be retrieved. As with batteries, this can be done quickly.

Compressed air energy storage takes energy generated from one of the many sources (such as solar, wind or hydro) and forces pressurized air into a containment area such as an underground cavern. When there is a demand for the electricity, the air is released through a turbine which generates the electricity.

Electric vehicle batteries can be considered a form of electricity storage, as customers charge their vehicles and store the electricity for use as needed.

Thermal energy can be stored during off-peak periods then used to provide heating or cooling during on-peak periods. Solar thermal systems can store and supply heat and hot water needs, while ice storage systems help keep buildings cool.

Electricity can be used as an input in the production of other types of fuels such as hydrogen and biofuels. These fuels store the energy that can be used to generate electricity. Off-peak electricity can also be used for compressing natural gas, an emerging usage in the transportation sector.

With magnetic energy storage, the electrical energy is stored as an electric current. The magnetic field is generated by a DC current travelling through a superconducting coil that has been cooled below the superconducting critical temperature. This type of storage may be limited due to the high cost of the superconducting wire and is currently suitable for short-term storage only.

Pumped storage is a type of hydroelectric energy storage that uses two water reservoirs at different heights. Water passes through a turbine as it moves from one reservoir to the other, creating power.

This is a high-capacity capacitor that bridges the gap between electrolytic capacitors and rechargeable batteries. It typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerates many more charge and discharge cycles than rechargeable batteries.

In addition to these energy storage devices, some electricity customers are installing energy storage solutions behind-the-meter. This allows them to draw and store energy at non-peak times when power costs are the lowest, to be used during peak times when costs are highest. This practice can also benefit the electricity grid by reducing peak demand.

Source: Independent Electricity System Operator (IESO)