LEARN / GLOSSARY
Curtailment
Reducing output or consumption below what was available or requested. For a generator it means output the system declined to take. For a large load it has become a negotiating position that changes how much capacity the system must hold.
Definition
Curtailment is a deliberate reduction below available capability, instructed by a system operator or agreed in advance by contract. Generation curtailment occurs when transmission cannot carry output or when supply exceeds demand. Load curtailment occurs when a customer agrees to reduce consumption under defined conditions.
Why the dictionary version is insufficient
Curtailment reads as waste, which is accurate for generation and misleading for load. A large customer that accepts curtailment during system emergencies is supplying a service: it reduces the amount of firm capacity the system has to build and hold for the rare hours that set the requirement.
Why it matters for capacity
NERC notes that because new large loads can be curtailed during energy emergencies, their effect on planning reserve margins is smaller than their raw size implies. For a manufacturer, whether a process can tolerate interruption is therefore a commercial variable rather than a technicality, and a continuous process that cannot be curtailed is buying a different and more expensive product.
Related terms
Large load · Firm power · Planning reserve margin
Appears in
Why Electricity Demand Is Growing Again
Data Centers and the Grid
Read next
Sources
- North American Electric Reliability Corporation, 2025 Long-Term Reliability Assessment. nerc.com
- Lawrence Berkeley National Laboratory, Queued Up: 2026 Edition. emp.lbl.gov
- U.S. Energy Information Administration, Hourly Electric Grid Monitor. eia.gov