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British Energy ComplianceUTILITIES · ADVISORY · ASSURANCE
Glossary

Capacity Market

The UK's mechanism for procuring guaranteed electricity capacity in advance, paid for through a levy on suppliers and ultimately on bills.

The Capacity Market is the UK's mechanism for ensuring sufficient firm electricity generation and demand-side capacity is available at times of system stress, particularly winter peak. It was introduced in 2014 under the Energy Act 2013 and is operated by the National Energy System Operator (NESO).

How it works:

  • NESO holds an annual auction for capacity to be delivered four years ahead (T-4), with a top-up auction one year ahead (T-1).
  • Generators, demand-side response providers and storage operators bid to provide capacity; the cheapest bids that meet the volume requirement clear at the marginal price.
  • Successful bidders receive a regular capacity payment in return for a contractual obligation to be available when the system requires it during stress events.

The cost of capacity payments is recovered from electricity suppliers through a levy and passed through to customers as part of the unit rate or as a separate line item on B2B bills. For procurement, the implications are: capacity-market costs are now a small but persistent component of every UK electricity bill, and suppliers should pass them through transparently rather than bundling them into a forecast adder. For larger demand-side flexible customers — in particular sites with on-site generation, batteries or genuinely interruptible processes — bidding directly into the Capacity Market is itself a revenue opportunity.

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