An energy giant has been fined almost £10million after an Ofgem investigation found it had overcharged Britain's electricity system operator.
SSE breached its licence by securing "excessive payments" from the National Grid ESO for reducing output at Foyers power station in Scotland, the regulator said.
Cathryn Scott, director of enforcement and emerging issues at Ofgem, said: "Protecting consumers is a priority for Ofgem, and we will continue to monitor the wholesale energy markets in Great Britain and ensure their integrity on behalf of energy users.
"This enforcement action sends another strong signal to all generators that they must put in place controls to ensure that their bid prices are set in a way that ensures that they do not obtain excessive benefits during transmission constraint periods.
"If they fail to do so, they will face significant consequences."
The months-long investigation found that in 2020, SSE made the bid prices it charged the National Grid ESO to reduce output at the power station "significantly more expensive," including during periods of so-called transmission constraint.
The watchdog said it had not seen any evidence that the violation was deliberate, but SSE acted in the knowledge that the revision would breach its licensing conditions.
SSE co-operated with the investigation and has committed to a new pricing methodology to properly reflect its costs, Ofgem said.
