Question to the Department for Energy Security & Net Zero:

To ask the Secretary of State for Energy Security and Net Zero, with reference to his Department's publication Electricity Generation Costs 2023, updated in November 2023, what the evidential basis is for the assumption that windfarms commissioned in 2025 will (a) not experience any decline in output over their lifetimes and (b) have an average output of 61% of capacity.

The Department’s Generation Costs Report 2023 is regularly updated based on externally reviewed evidence; these external reports are also published containing detailed description of underlying assumptions.

The 61% net load factor assumed for offshore wind plants commissioning in 2025 is derived from DESNZ modelling of wind turbine load factors. This calculation combines a theoretical turbine power curve (power output as a function of wind speed, modelled using turbine technology parameters including rotor swept area and hub height) with historic site-specific Virtual Met Mast (VMM) hourly wind speed data sourced from the UK Met Office.