Dispatchable generation refers to sources of electricity that can be dispatched on demand at the request of power grid operators, according to market needs. Dispatchable generators can adjust their power output according to an order. Non-dispatchable renewable energy sources such as wind power and solar photovoltaic (PV) power cannot be controlled by operators. Other types of renewable energy that are dispatchable without separate energy storage are hydroelectric, biomass, geothermal and ocean thermal energy conversion.
Dispatchable plants have varying startup times. 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, coal and nuclear thermal plants are designed to run as base load power plants and may take hours or sometimes days to cycle off and then back on again.
Utility-scale energy storage can compensate for intermittent 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 primary benefits of dispatchable power plants include:
- providing spinning reserve (frequency control)
- balancing the electric power system (load following)
- optimizing economic generation dispatch (merit order)
- contributing to clearing grid congestion (redispatch)
These capabilities of dispatchable generators allow:
- 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 dispatchable 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.
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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
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- Archived 30 November 2019 at the Wayback Machine "three to four days"
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- How can renewables deliver dispatchable power on demand?