Energy Storage and Technology

Chemical storage relies on energy stored in chemical bonds. These bonds are a tremendous source of energy and are the basis of all energy production. This includes such diverse processes as burning petroleum and biomass, storing and releasing energy in high-tech batteries, and even the most basic processes of biology.

Lead-acid Batteries

A lead-acid battery has the advantage of being robust, stable and recyclable. It was the first battery technology to be rechargeable, and is still widely used for vehicles, heavy equipment like forklifts and other stationary industrial applications.

*If you need to dispose of a lead-acid battery from a car, boat or other vehicle, review What to Do With Items Banned From Landfills - PUB0186.

Lithium-ion Batteries

Lithium-ion batteries can be recharged thousands of times and are commonly used for portable electronics and electric vehicles. Increasingly, large lithium-ion batteries are seeing use in electric vehicles and large, stationary industrial applications. Compared to lead-acid batteries, lithium-ion batteries are longer lasting and more tolerant of fast charging but are also more expensive to produce and more difficult to recycle.

*If you need to dispose of household batteries, visit Household Hazardous Waste.

Hydrogen

Hydrogen (chemical formula H₂) is perhaps the simplest method of storing electricity in chemical bonds. Hydrogen can be produced through electrolysis of water when there is excess energy, and then later converted back into electricity by burning in typical boiler or in a hydrogen fuel cell. Hydrogen is a very small molecule and difficult to store but can also be easily converted into (and back from) Ammonia (NH₃) to make transportation and storage easier.

Mechanical storage uses the physical properties of materials to store energy. Kinetic, potential and thermal energy storage all fall into this category and are some of the oldest forms of energy storage.

Flywheels

A flywheel stores energy in the form of rotational momentum for a spinning rotor or wheel. Flywheels have been used to store kinetic energy since the 1950’s in motor vehicles, aircraft carriers and even roller coasters. The kinetic energy of the wheel converts directly to electricity when needed, or an attached motor can increase the speed of the wheel when the grid has excess energy. Flywheels can operate at much smaller MW sizes than other forms of storage but may require specific conditions to be viable.

Pumped Hydropower

Hydropower generation relies on water and gravity to rotate a turbine to generate electricity. Pumped hydropower stores electricity by pumping water to an elevated reservoir (typically during times of low demand) that can subsequently be released to generate electricity during times of higher demand. The oldest pumped storage systems date to the 1890’s and are found all over the world, including the 450 MW Taum Sauk Hydroelectric Power Station in southeast Missouri.

Compressed Air Storage

Similar to pumped storage hydropower, compressed air storage uses excess energy to compress air in a tank, which can then later be released to generate electricity. These systems have comparable energy density to lead-acid batteries but, unlike batteries, the supplied discharge voltage varies greatly with the stored pressure.

Thermal Storage

Thermal energy storage uses electricity to heat a material for later use, either to convert the heat back to electricity or for direct use of the thermal energy. One household example of thermal storage is a hot water heater. For the electric grid, thermal storage generally uses steam, advanced ceramics or molten salts as a storage medium. Solar thermal power plants are designed around this integrated thermal storage, and the largest of these can store up to six days of power at peak production.

Combined Heat and Power (CHP)

Combined Heat and Power (CHP), also known as cogeneration, is on-site generation of electricity and usable thermal energy (heating or cooling) from the same fuel source.