Dispatchable generation refers to sources of electricity that can be used on demand and dispatched at the request of power grid operators, according to market needs. Dispatchable generators can be turned on or off, or can adjust their power output according to an order. This is in contrast with non-dispatchable renewable energy sources such as wind power and solar PV power which cannot be controlled by operators. The only types of renewable energy that are dispatchable without separate energy storage are hydroelectric, biomass, geothermal and ocean thermal energy conversion.
Dispatchable plants have different speed at which they can be dispatched. The fastest plants to dispatch are hydroelectric power plants and natural gas power plants. For example, the 1,728 MW Dinorwig pumped storage power plant can reach full output in 16 seconds. Although theoretically dispatchable, certain thermal plants such as nuclear or coal are designed to run as base load power plants and may take hours or sometimes days to cycle off and then back on again.
The attractiveness of utility-scale energy storage is that it can compensate for the indeterminacy of wind power and solar PV power. During 2017, solar thermal storage power has become cheaper and a bulk dispatchable source. Earlier, affordable large-scale storage technologies other than hydro were not available.
The main reasons why dispatchable power plants are needed are:
- to provide spinning reserves (frequency control),
- to balance the electric power system (load following),
- to optimize the economic generation dispatch (merit order), and
- to contribute to clear grid congestion (redispatch).
Use cases for dispatchable generators comprise:
- 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.
- Cooper, Duncan (22 March 2012). "Johnson's Energy Club Competes in Renewable Energy Case Competition". Samuel Curtis Johnson Graduate School of Management. Archived from the original on 16 June 2012. 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.
- Electricity Grid: Key Terms and Definitions
- Global Energy Assessment: Toward a Sustainable Future
- "Welcome to First Hydro" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2013-01-08.
- Archived 30 November 2019 at the Wayback Machine "three to four days"
- "Dispatchable Concentrated Solar Power Broke Price Records in 2017". Retrieved 22 September 2017.
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- Lewis, Dyani (5 April 2017). "Salt, silicon or graphite: energy storage goes beyond lithium ion batteries". The Guardian. Retrieved 1 September 2017.
- How can renewables deliver dispatchable power on demand?