Dispatchable generation refers to sources of electricity that can be dispatched at the request of power grid operators or of the plant owner; that is, generating plants that can be turned on or off, or can adjust their power output accordingly to an order. Often base load power plants such as nuclear or coal cannot be turned on and off in less than several hours. The time periods in which dispatchable generation plant may be turned on or off may vary, and be considered in time frames of minutes or hours. The 1,728 MW Dinorwig pumped power station can reach full output in 16 seconds.
The most common dispatchable power plant is natural gas. The only types of renewable energy which are dispatchable are biofuel, biomass, hydropower with a reservoir, ocean thermal energy conversion and concentrated solar power with thermal storage.
The main reasons for which dispatchable power plants are needed are: - to balance electrical system (load following, frequency control) - to optimize generation dispatch (merit order) - to provide requested power spinning reserves - to contribute to clear grid congestions/constraints - 
- Load matching - slow changes in power demand between, for example, night and day, require changes in supply too, as the system needs to be balanced at all times (see also Electricity).
- Peak matching - short periods of time during which demand exceeds the output of load matching plants; generation capable of satisfying these peaks in demand is implemented through quick deployment of output by flexible sources.
- Lead-in times - periods during which an alternative source is employed to supplement the lead time required by large coal or natural gas fueled plants to reach full output; these alternative power sources can be deployed in a matter of seconds or minutes to adapt to rapid shocks in demand or supply that cannot be satisfied by peak matching generators.
- Frequency regulation or intermittent power sources - changes in the electricity output sent into the system may change quality and stability of the transmission system itself because of a change in the frequency of electricity transmitted; renewable sources such as wind and solar are intermittent and need flexible power sources to smooth out their changes in energy production.
- Backup for base-load generators - Nuclear power plants, for example, are equipped with nuclear reactor safety systems that can stop the generation of electricity in less than a second in case of emergency.
The attractiveness of utility-scale energy storage is that it can compensate for the intermittency of wind power and solar power. However in practice, large-scale storage technologies other than pumped hydro remain in an early stage of development and are expensive.
- Cooper, Duncan (22 March 2012). "Johnson's Energy Club Competes in Renewable Energy Case Competition". Samuel Curtis Johnson Graduate School of Management. Retrieved 29 August 2012.
Most conventional energy sources are dispatchable, meaning that they can be turned on or off according to the demand for electricity. The amount of electricity they produce can also be turned up or down so that supply of electricity matches the amount demanded by users
- Welcome to First Hydro
- Electricity Grid: Key Terms and Definitions
- Global Energy Assessment: Toward a Sustainable Future
- Why solar energy?
- How can renewables deliver dispatchable power on demand?