Balancing Mechanism Reporting Service
Just to add that BMRS is a service provided within the current European Union EU 27 and Great Britain and Irish electricity systems. Some links:
Quoting approximately and briefly from the final URL:
The balancing mechanism or BM is one of the tools used by system operators (SO) and transmission system operators (TSO), such as the National Grid (Great Britain) or 50Herz in northern Germany, to balance electricity supply and demand in close to real time.
The BM is needed because electricity cannot currently be stored at scale and must be manufactured at the time of demand. Where the SO or TSO predicts that there will be a discrepancy between electricity production and demand during a certain time period, they may accept a bid or offer from a market participant to either increase or decrease generation (or consumption). The balancing mechanism is used to balance supply and demand in each half hour trading period of every day.
See also ancillary services on wikipedia. Else web search on “electricity imbalance”.
PS: this will be a wikipost for circa ten weeks in case anyone wishes to correct or add material.