The total share of renewable energy (RE) in Scotland currently exceeds 170% of electricity consumption, contributing significantly to the UK’s overall RE share reaching 50%. The wind share is particularly high, already exceeding 130%, which is likely among the highest in the world.

Scotland’s power system is not a single control area in itself, but forms part of the Great Britain (GB) control system and single synchronous zone operated by the National Energy System Operator (NESO), owned by different transmission system owners, Scottish Power (SP) Energy Networks and Scottish and Southern Energy Networks (SSEN). However, if it can be regarded as a single transmission grid – similar to South Australia, which is known for its ability to accommodate high share of wind and solar – Scotland’s VRE share far exceeds that of South Australia, though this is not widely known.

Scottish grid is characterised by long-distance transmission lines extending away from major consumption centres, therefore known as a ‘weak terminal system’ within the wider Great Britain (GB) system. Three are limited routes to the neighbouring areas; only two alternative current (AC) routes to England, one direct current (DC) route to Wales, and one DC to Northern Ireland. Such grids have traditionally been understood to be unsuitable for VRE. This paper analyses why Scotland has been able to integrate such a large scale of wind power into its grid, and how this can be managed in the future, focusing on options for curtailment and flexibility.

This paper focuses on the Scottish grid, a unique power system, and analyses its characteristics. In the context of integrating wind power into the power system, two main characteristics are examined. The first is curtailment, which is one of the impacts resulting from the increasing share of wind (and solar in other areas); the second is the flexibility potential, which forms part of the measures to accommodate large amounts of wind (and solar). These two characteristics can be assessed using the C-E (Curtailment and Energy Share) Map and the Flexibility Chart, quantitative and objective tools proposed by the IEA’s Technology Cooperation Programme (TCP) Wind Task 25, ‘Operation and Planning of Power Systems with High Shares of Variable Generation’ (now Task 36). The authors use these tools to analyse the unique Scottish grid.

In the UK, no official statistics on curtailment have been published by public bodies. Although NESO provides data on curtailed energy for individual wind farms across the UK, it is difficult to aggregate this data on an annual basis or by sub-region. Fortunately, a volunteer-run website has developed code to calculate and publish annual statistical data, enabling the location of wind farms across the UK to be identified by sub-region.

According to this volunteer-based data, the annual curtailment of wind power in 2024 was 8.0 TWh, with an annual curtailment ratio calculated at 13.6%. This figure may sound high when compared to other areas of the world. However, given that the wind share exceeds 130%, this curtailment ratio can be considered rather modest.

Also, it has become clear that the Scottish grid balances a diverse mix of flexibility resources, including combined heat and power (CHP), gas turbines, battery storage, pumped hydro storage (PHS) and hydro reservoirs. Furthermore, interconnection capacity with neighbouring areas is very rich, exceeding 150% of annual peak demand in 2024, and is scheduled for further expansion from 2030 onwards.