To balance the supply and demand of electricity on short timescales, the UK National Grid has contracts in place with generators and large energy users to provide temporary extra power, or reduction in demand.
Frequency Service is designed to cope with the loss of two 660 MW sets in quick succession.
Similar arrangements operate in the United States and France and all other large power grids.
There are two forms of payment that National Grid will make as part of the service: STOR is subject to a number of restrictions and conditions which include a minimum capacity threshold of 3MW.
Above this capacity it is possible to tender directly to National Grid for the provision of STOR services or via the assistance of an agent.
National Grid therefore perceives the role of an Aggregator as essentially a "Reserve Provider", holding the STOR Contract itself whilst managing the necessary interfaces with the various individual asset owners.
If Frequency Response and spinning reserve fails to control grid frequency and it falls too far, then the fans feeding combustion air into power station boilers begin to deliver at an inadequate draft/pressure since they are synchronous, and the output of all power-stations in the grid, goes into irreversible decline.