Ancillary services

Ancillary services are functions that keep an electricity grid operating reliably alongside the production and delivery of energy. They include frequency control, operating reserves, and voltage support.

Frequency regulation: The continuous adjustment of electricity supply or demand to keep grid frequency near its target. It corrects short-term imbalances that would otherwise shift grid frequency.
Ancillary services market: A market in which providers are paid to supply specified services that support electricity-system reliability. It is one way operators obtain services from generators and other resources.
Electricity market: A system of institutions and rules for buying, selling, and scheduling electricity. Energy markets trade delivered electricity; ancillary-service procurement targets reliability functions.
Power grid reliability: The ability of an electric grid to provide electricity continuously and within required operating limits. Ancillary services support reliability alongside adequate generation and network capacity.
Operating reserve: Capacity held available to respond when generation or transmission becomes unavailable or demand exceeds forecasts. It supplies backup when contingencies create sudden shortfalls.
Automatic generation control: A control system that adjusts generator output to correct area imbalances and maintain scheduled interchanges. It dispatches resources to provide automatic frequency regulation.
Energy-only market: An electricity market that compensates generators for energy and scarcity pricing rather than separate capacity payments. It contrasts with arrangements that separately procure ancillary services.
Renewable energy integration: The incorporation of variable renewable sources, such as wind and solar, into electricity systems. Variable output changes the balancing and flexibility needs that services must meet.
Voltage support: The provision or absorption of reactive power to keep electric-grid voltage within acceptable limits. It manages voltage, a reliability need distinct from balancing active power.
Demand response: Changes in electricity use made in response to prices, incentives, or requests from grid operators. Flexible consumption can provide balancing and reserve capability without added generation.

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