The amount of renewable electricity curtailed in Great Britain in 2025 would have been enough to meet the combined annual electricity demand of every household in London, according to a new report.

The report from energy market analysis provider Montel EnAppSys, Curtailed Renewables in GB and Ireland, investigates and quantifies the volume of curtailed renewable power in both Great Britain and Ireland. It uncovers a growing disconnect between renewable generation and grid infrastructure capacity.

The report reveals that over 12 Terawatt hours (TWh) of renewable power was curtailed in 2025. Of this, just over 10TWh was curtailed in Great Britain, representing a 22% increase from 2024. Over £1bn was spent on upward actions to replace lost wind generation, a 20% increase from the previous year. 

Almost all of the curtailment in Great Britain (98%) resulted from the turning down of wind turbines in Scotland.

The volume of power available from renewable sources is sometimes curtailed (reduced or switched off at source) due to limited grid capacity to transfer the power. As such, generators are instructed by the system operator to turn down their output.

This means that no matter how much power is produced in a given area, only a certain amount flows through the transmission network and makes it to consumers at any one time.

Fintan Devenney, senior energy market analyst at Montel EnAppSys, said: “The analysis shows that only 61% of the wind power that could have been generated in Northern Scotland actually made it to the grid. 

“While the government’s goal of meeting 95% of annual demand with electricity generated from renewable sources by 2030 is laudable, ensuring the efficient siting and production of power to meet demand will become increasingly important.” 

The report highlights that the growing number of new data centres expected to come online in the coming years, together with the electrification of heating and transport, will only place additional strain on the electricity grid.

Devenney said: “The amount of electricity curtailed in GB could have powered every data centre in the country in 2025. A recent policy paper suggested that data centres choosing to site themselves in Scotland could receive, in effect, an energy price discount of up to £24/MWh. 

“This is an interesting method of incentivising the optimal siting of demand to solve these issues, particularly as the paper also suggests there will be no knock-on effect to billpayers.”

The report calls for a holistic view of policy that will enable the optimal siting of generation, sufficient investment in grid infrastructure and the correct investment signals to help alleviate grid constraints.