Can Infrastructure Keep Pace with Renewables Supply?

Wind and solar generators across Great Britain and Ireland were forced to curtail enough clean energy to meet London's annual electricity needs in 2025, according to new analysis from Montel.

The energy analyst's report, Curtailed Renewables in GB and Ireland in 2025, exposes how outdated transmission networks are creating an expensive barrier to the energy transition, with curtailment rising 22% year-on-year to reach 10 TWh in Great Britain alone, while Ireland saw 2.1 TWh of renewable power go unused.

The figures reveal a fundamental infrastructure supply chain challenge; renewable generators are producing record volumes of clean electricity, but the grid can not transport it from upstream generation sites to downstream population centres.

Northern Scotland emerged as the most critical congestion point, with 8.8 TWh of wind power curtailed (sufficient to cover all Scottish domestic electricity demand for a year).

The problem stems from transmission boundaries between Scotland and England reaching maximum capacity, preventing power inventory from flowing south to major demand centres.

Montel's analysis states: "Only 61% of the energy which could have been generated in the [Northern Scotland] region made it to the grid."

This geographical mismatch between generation and consumption could mean billpayers face mounting costs, with the report warning that "outdated transmission networks could continue to drive up consumer bills as NESO, EirGrid and SONI are forced to operate networks unfit for the net-zero future."

Scottish constraints dominate curtailment costs

According to the report, 98% of Great Britain's curtailed renewable volumes occurred in Scotland, highlighting the concentration of the infrastructure problem.

When wind farms are asked to switch off due to grid constraints, they receive curtailment payments. Simultaneously, grid operators must pay gas plants and battery storage to provide replacement power, creating a double cost burden for consumers.

While direct curtailment payments in Great Britain fell 10% to £363m in 2025, the total cost of replacing lost wind power through upward actions exceeded £1bn (US$1.34bn), representing a 20% increase from the previous year.

This apparent efficiency in curtailment procurement costs reflects newer wind farms like Moray West entering the market with cheaper bid prices due to their subsidy structures, but the savings are more than offset by rising replacement power sourcing expenses.

Claire Coutinho, the shadow energy secretary, has criticised Energy Secretary Ed Miliband's renewable expansion plans in light of these figures.

According to reports, she said: "We are paying more than ever before to pay wind farms to switch off when the wind blows. Costs are set to triple by 2030 as he approves more wind farms than ever before. He cares far more about his own Clean Power 2030 target than looking after consumers."

In previous statements, Octopus Energy has warned that curtailment payments could add £8bn (US$10.7bn) to consumer bills by 2030 if infrastructure improvements do not keep pace with renewable capacity additions.

Infrastructure investment faces delivery timeline

To address the transmission bottleneck, regulator Ofgem has approved plans for the UK's three transmission operators (National Grid, Scottish Power and SSE) to spend up to £90bn (US$120.8bn) on new lines and substations.

However, these infrastructure upgrades will require at least five years lead time to build, meaning constraint payments could continue rising in the interim as Energy Secretary Ed Miliband approves additional wind and solar projects under his 2030 decarbonisation target.

Some progress emerged in 2025 with the commercial launch of the Greenlink interconnector linking Wales to the Republic of Ireland.

This new transmission route helped reduce Northern Irish wind curtailment from 30% in 2024 to 24% in 2025 by providing an alternative to the older Moyle interconnector.

Despite this improvement, Northern Ireland still switched off 24% of available wind energy during the year.

Solar curtailment remained relatively minor but showed significant growth trajectory.

According to Montel: "Solar curtailment costs rose over the year to total over £252,000. While this is substantially lower than the corresponding figures for wind, it represents a rise from the negligible costs associated with solar curtailment in 2024."

Irish solar curtailment increased fourfold between 2024 and 2025, suggesting grid constraints are beginning to affect multiple renewable technologies as deployment accelerates.

The total 12.1 TWh of curtailed renewable electricity across Great Britain and Ireland in 2025 exposes a growing disconnect between generation capacity and transmission capability, with infrastructure investment timelines lagging behind renewable deployment rates.