Dispatchable generation
Generation whose output can be scheduled, raised or lowered on request by the operator, independently of weather.
Dispatchable generation is any source whose output the plant operator or system operator can control within technical limits: start, stop, ramp up or ramp down to follow instructions. Examples include gas turbines, reservoir hydropower, coal, biomass, geothermal (to a limited degree), nuclear (with constraints) and battery or pumped storage while charge is available.
Plants differ widely in flexibility:
- Open-cycle gas turbines: start in 5 to 15 minutes, ramp 10 to 20% of capacity per minute.
- Combined-cycle gas: hot start 30 to 60 minutes, ramp 2 to 5% per minute.
- Hard coal: ramp 1 to 4% per minute, minimum stable load 25 to 40%.
- Reservoir hydro and batteries: seconds to minutes, near full range.
(Ranges from IEA and Agora Energiewende flexibility studies.)
By contrast, variable renewables such as wind and solar can be curtailed downwards but not raised above what the weather allows, so they are considered non-dispatchable or only partly controllable. As their share grows, the value of dispatchable capacity increasingly lies in providing firm power during low-wind, low-sun periods (the German "Dunkelflaute") and in supplying ancillary services. Their contribution to adequacy is measured by capacity credit, which is typically 80 to 95% for thermal plants.
Related terms
All terms →- Variable renewable energy (VRE)
Renewable generation whose output varies with weather and time of day, mainly wind and solar PV, and cannot be fully dispatched.
- Baseload
The minimum level of electricity demand on a grid over a day, season or year, historically served by plants that run continuously at high output.
- Load following
Adjusting a power plant’s output over minutes to hours to track changes in electricity demand or in variable renewable generation.
- Capacity credit
The fraction of a resource’s nameplate capacity that can be counted on to meet peak demand, used in adequacy planning and capacity markets.
- Ancillary services
Services beyond bulk energy that system operators procure to keep the grid stable and secure, such as frequency reserves, voltage control and black start.
- Combined-cycle gas turbine (CCGT)
A power plant that runs a gas turbine and uses its hot exhaust to raise steam for a second, steam turbine, reaching electrical efficiencies of 55–64%.