Curtailment is an involuntary reduction of the electric generator output to maintain grid stability during periods of imbalance. Engineers call this action dispatch down when they need to lower production quickly.
Wind and solar facilities have quite low marginal electricity production costs because they lack fuel expenses but lose revenue whenever operators order them to stop generating power. Renewable owners cannot store their free wind or sun for later sale without expensive batteries.
Ireland lost 1.2 TWh of wind power in 2022 because existing lines could not move it efficiently. This loss occurred as insufficient transmission lines forced energy waste when local demand could not absorb all available supply.
Curtailments mainly happen for solar power at noon as part of the duck curve pattern which creates midday surpluses requiring scheduled reductions in modern grids. Solar output peaks when sunlight is strongest but often exceeds immediate consumer demand.
Before 2013, curtailment reached levels between 8% and 16% of total generation in West Texas. That infrastructure project reduced waste to near zero by connecting remote resources to central cities after ERCOT built a new transmission line from the Competitive Renewable Energy Zone.