Curtailment
Deliberate reduction of a generator’s output below what it could produce, usually wind or solar, because of grid, market or system constraints.
Curtailment occurs when a plant that could generate is instructed or chooses to produce less. For wind and solar it represents lost zero-marginal-cost energy. Causes fall into three groups:
- Network congestion: transmission lines cannot carry the power to load centres (common in northern Germany, west Texas, Inner Mongolia).
- System security: operators must keep enough synchronous plant online for inertia, voltage control or reserves.
- Economic: prices fall below zero, so generators without subsidies on output reduce production (see negative prices).
Typical rates: Germany curtailed around 3 to 4% of renewable output in recent years, with redispatch and compensation costs exceeding EUR 3 billion annually (Bundesnetzagentur). California (CAISO) curtailed about 3.4 TWh of wind and solar in 2023, concentrated in spring middays. China cut wind curtailment from about 17% in 2016 to around 3 to 4% after building UHV transmission lines.
Some curtailment is economically efficient: building enough grid or storage to absorb every last kWh costs more than the energy is worth. Studies (NREL, IEA) often find optimal curtailment of a few percent at high VRE shares. Remedies include HVDC lines, storage, flexible demand, electrolysers and better market design.
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.
- Negative electricity prices
Wholesale prices below zero, when generators pay to deliver power because inflexible supply exceeds demand.
- Interconnector
A transmission link, AC or HVDC, that connects the grids of two countries, regions or market zones and allows electricity to be traded between them.
- HVDC (High-Voltage Direct Current)
Transmission technology that carries bulk power as direct current, with lower losses over long distances and the ability to link asynchronous grids.
- Duck curve
The shape of net load over a day in solar-rich grids: a deep midday dip as PV output peaks, followed by a steep evening ramp.
- Inverter clipping
Energy lost when the DC power available from a PV array exceeds the inverter AC rating, so the inverter caps output at its maximum.