More than 12 terawatt hours (TWh) of renewable electricity were curtailed across Great Britain and Ireland in 2025 due to grid constraints, according to a new report from energy analytics firm Montel EnAppSys, highlighting mounting challenges as renewable capacity expands faster than networks.
The report said 12.3 TWh of clean power was turned off during the year, an amount equivalent to the annual electricity consumption of all domestic households in London.
Great Britain accounted for the bulk of the curtailed volumes, with 10.2 TWh, representing a 22% increase compared with 2024. Scotland made up more than 98% of Great Britain’s total, at just over 10 TWh, with northern Scotland alone responsible for 8.8 TWh.
Ireland curtailed 2.1 TWh of renewable electricity, which the report said would be sufficient to supply all homes in County Dublin for a year. In Northern Ireland, around 24% of available wind generation was curtailed.
“The analysis shows that only 61% of the wind power which could have been generated in Northern Scotland actually made it to the grid,” said Fintan Devenney, senior energy market analyst at Montel EnAppSys.
Devenney said rising curtailment volumes risk undermining renewable targets unless infrastructure keeps pace. “Whilst 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,” he said.
He added that the scale of lost generation was significant even beyond the power sector. “It’s also worth noting that the amount of electricity curtailed in GB could have powered every data centre in the country in 2025,” Devenney said.
The report called for a more coordinated policy approach to address bottlenecks. “A holistic view of policy which will enable the optimal siting of generation, sufficient investment in grid infrastructure and the correct investment signals to help alleviate grid constraints is now crucial and the strategic spatial energy plan will be key to achieving these aims,” Devenney said.
Britain and Ireland have both accelerated renewable deployment in recent years, but transmission build-out and system flexibility have lagged behind, leading to rising curtailment costs and growing pressure on policymakers to reform planning and grid investment frameworks.
