Peak load
The highest electricity demand recorded on a grid during a given period, which sets the capacity the system must be able to supply.
Peak load is the maximum instantaneous (or hourly average) demand on a power system in a day, season or year. It determines how much firm generation, import capacity, storage and demand response must be available, and therefore drives a large share of system cost even though peak hours are few.
Timing depends on climate. Northern and central European systems peak on cold winter evenings (electric heating plus lighting); Texas (ERCOT) and much of the US Sun Belt peak on hot summer afternoons with air conditioning. ERCOT set records above 85 GW in 2023; France, with heavy electric heating, reached about 102 GW in February 2012 (RTE). India's peak passed 250 GW in 2024.
Typically the top 1% of hours (about 88 hours per year) accounts for 10 to 15% of required capacity, so plants built only for peaks, often open-cycle gas turbines, run at very low capacity factors. Planners hold a reserve margin above the forecast peak, commonly 10 to 20% (NERC reference levels around 15%).
Electrification of heating and transport is expected to raise peaks faster than energy demand unless managed through smart charging, storage and time-of-use tariffs.
Related terms
All terms →- 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.
- Reserve margin
The amount by which available or accredited capacity exceeds forecast peak demand, expressed as a percentage of peak.
- Load factor
The ratio of average demand to peak demand over a period, indicating how evenly a consumer or system uses electricity.
- Demand response
Changes in electricity consumption by end users, in response to price signals or operator requests, to balance the grid.
- Capacity market
A mechanism that pays resources for being available to supply power or reduce demand at times of system stress, alongside payments for energy.
- 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.