Variable renewable energy

Variable renewable energy is electricity generated from renewable sources whose output changes with weather and time, especially wind and solar power.

Wind power: Electricity generated by converting the kinetic energy of moving air into electrical power. Wind turbines produce output that varies with wind speed and turbine operating limits.
Grid integration: The planning and operation of an electric grid that connects generators, networks, storage, and consumers. It covers the technical and operational changes needed to incorporate variable resources.
Dispatchable generation: Electricity generation whose output can be adjusted on demand within operational limits. It contrasts with weather-driven output that operators cannot directly schedule.
Residual load: Electricity demand remaining after variable renewable generation is subtracted. Its changing shape determines what other resources must supply and when.
Solar power: Electricity generated by converting sunlight into electrical power, usually with photovoltaic cells or solar-thermal systems. Solar output follows daylight, cloud cover, and seasonal changes.
Electricity market: A system of rules and transactions for buying and selling electrical energy and related services. Market rules shape when variable generators produce and how their output is valued.
Intermittent energy source: An energy source whose availability is discontinuous or not continuously controllable. The term is often used for wind and solar, but can obscure their forecastable variation.
Duck curve: A graph of daily net electricity demand whose shape reflects substantial solar generation. It illustrates how daytime solar output can create steep evening ramping needs.
Capacity factor: The ratio of a generator’s actual energy production over a period to its maximum possible production. It distinguishes variable output from the average energy a wind or solar plant supplies.
Ancillary services: Grid services beyond energy supply that maintain reliable electricity-system operation. Frequency control and reserves help manage rapid changes and forecast errors.

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