Energy Storage Basics
The demand for electricity is seldom constant over time. Excess generating capacity available during periods of low demand can be used to energize an energy storage device. The stored energy can then be used to provide electricity during periods of high demand, helping to reduce power system loads during these times.
Energy storage can improve the efficiency and reliability of the electric utility system by reducing the requirements for spinning reserves to meet peak power demands, making better use of efficient baseload generation, and allowing greater use of renewable energy technologies. A "spinning reserve" is a generator that is spinning and synchronized with the grid, ready for immediate power generation — like a car engine running with the gearbox in neutral.
The Independent System Operator (ISO) is required to maintain sufficient reserve generating capacity available for immediate power production. The term 'spinning' derives from the definition that spinning reserves must have generators spinning and synchronized with the grid, ready for immediate power generation.
Many renewable resources — wind and solar power, for example — are variable, i.e., they are not available all of the time. Storing energy from the renewable source allows supply to more closely match demand. For example, a storage system attached to a wind turbine could store energy captured around the clock — whenever the wind blows — and then dispatch that energy into the higher-priced midday market. And energy storage enables solar electricity to be used both day and night.
By reducing peak demands for power generation and offering greater flexibility among power supply options (including renewables), energy storage systems not only help utilities by improving their cost-effectiveness, reliability, power quality and efficiency, they also reduce the environmental impact of electricity generation, transmission, and distribution.