Seagreen Wind Farm Wastes Three Quarters of Power Output Due to Grid Constraints

Scotland’s largest offshore wind farm has squandered approximately 77 per cent of its potential electricity generation because of insufficient capacity on Britain’s national grid. The Seagreen development, operated by SSE, the FTSE 100 energy company, has received tens of millions of pounds in compensation payments from the National Energy System Operator to deliberately curtail turbine output and prevent grid overload.

The facility comprises 114 turbines positioned 17 miles offshore from Angus in the North Sea. With a maximum generating capacity exceeding 1 gigawatt, Seagreen became fully operational in late 2023 as a joint venture between SSE, which holds a 49 per cent stake, France’s TotalEnergies, and Thailand’s PTTEP. Financial accounts covering the year to March 2025 reveal a stark performance gap; the wind farm could have generated 4,590 gigawatt-hours of electricity but delivered only 1,040 GWh to the grid.

Constraint payments represent the financial mechanism through which grid operators compensate renewable energy generators forced offline due to transmission bottlenecks. When insufficient cabling capacity exists to transport electricity from remote generation sites to population centres, the National Energy System Operator selects specific installations for curtailment and compensates them accordingly. The operator then purchases replacement power from conventional generators located on the opposite side of the bottleneck, creating substantial cost increases across the energy system.

Data from the GB Renewables Map website suggests this unfavourable trend has persisted throughout 2025; an estimated 2,725 gigawatt-hours of Seagreen’s potential output faced constraints during the year. Independent analysis estimates that compensation payments to SSE exceeded £30 million for curtailed generation in 2025 alone. This pattern reflects broader systemic challenges affecting multiple renewable installations in geographically remote locations.

SSE’s Viking onshore wind farm, comprising 103 turbines in the Shetland Islands with a maximum capacity of 443 megawatts, experienced similar difficulties following its completion in late 2024. The facility generated approximately 1,082 gigawatt-hours of constrained output in 2025, with compensation payments totalling almost £10 million. These two SSE projects exemplify the mounting costs associated with grid infrastructure inadequacy across Britain’s renewable energy sector.

National constraint costs reached an unprecedented £1.5 billion during 2025, representing a significant increase from previous years. These expenses flow through consumer energy bills via regulatory levies. Ofgem, the energy regulator, estimated that rising constraint costs would add £15 to typical household annual energy bills from October 2025. The regulator has subsequently approved a £70 billion investment programme by major energy companies to upgrade Britain’s high-voltage transmission network over the coming five years, adding approximately £60 to annual bills by 2030.

Despite substantial planned infrastructure investment, constraint costs are projected to increase by £10 per household annually; however, regulatory analysis indicates costs would rise by a further £55 per household annually without these upgrades. SSE announced a £27 billion capital investment programme between 2025 and 2030 specifically designed to eliminate transmission bottlenecks and unlock the full generating potential of renewable installations across its portfolio.

The situation underscores a fundamental challenge in Britain’s energy transition; renewable generation capacity has been deployed in geographically optimal locations for wind and solar resources, yet the transmission infrastructure required to transport this power to demand centres has not kept pace. Industry observers recognise that resolving these constraints represents a critical prerequisite for achieving decarbonisation targets whilst managing consumer energy costs effectively.