In 2025 windfarms in the UK were paid £363 million to switch off when the power generated exceeded the capacity of the grid to transmit that energy to where it was needed [Montel].  

The curtailment of renewable energy happens due to the limitations of the grid infrastructure and the fact that so much energy is generated very far from the demand centres. The supply of energy needs to continually match the demand, and if too much is pushed into the system it can result in voltage and frequency spikes that may damage equipment and appliances [NESO, Margins]. 

In Great Britain and Northern Ireland, the grid is split between 14 regions with interconnectors at the boundaries limiting the power that can be moved between areas. In Scotland, there are two grid regions, North Scotland (owned and operated by SSEN) and South Scotland (owned and operated by SPT). The key boundary for curtailment is the B4 Boundary (Figure 1) between these two regions which is limited to 4 GW by the Tealing – Westfield 275 kV circuit. 

The boundary with England is B6 (Figure 2), and has a capacity of 6.7 GW at the Harker-Moffat 400 kV circuit

Figure 1: NESO map of the B4 Boundary – the boundary capability is limited to 4 GW due to thermal constraint on the Tealing – Westfield 275kV circuit 

Figure 2: NESO Map of the B6 Boundary The boundary capability is limited to 6.7 GW due to thermal constraint on the Harker-Moffat 400kV circuit. 

A huge amount of the wind generation capacity is located in North Scotland north of the B4 Boundary, where there is very little energy demand. This means that the B4 boundary is the primary pinch point for energy transmission. [UKERH]

In 2025 In the UK 10.14 TWh of energy was curtailed at a cost of £363 million with 10.06 TWh in Scotland and only 0.18 TWh in England and Wales. 87.5% of Scotland’s curtailed energy (8.8 TWh) was in North Scotland. [Montel] See download of the report here.

However all of the proposed hyperscale data centres in Scotland’s planning system (which have a combined capacity of 7.2GW) are in South Scotland, south of the B4 boundary [APRS Data Centre Map] (see Figure 3), so they will not be able to use the vast majority of the constrained wind produced.  

We are assuming that all the data centres wish to be positioned below the constrained B4 boundary so that they can access energy from the south, where there is more gas and nuclear generation and also the interconnectors with Europe, when the wind is not producing enough energy. The B6 Boundary currently has a capacity of 6.7GW so, on a high pressure winter day when there is very little wind is being produced, there is, in theory 2.5GW of headroom, as the maximum power demand of Scotland is 4 to 4.2GW.

In addition, the UK is building six interconnectors (see Table 1) to take energy from Scotland south, the total capacity of these will be 12GW and the first two are expected online in 2029 and will add 4GW transmission capacity between Scotland and England, thus eliminating much of the current curtailment issues.

Table 1: Undersea cables for energy transmission, under construction and planned

We conclude that the claims of the hyperscale data centre operators that they will use curtailed wind are largely bogus. Firstly because only 12.5% of Scotland’s curtailed energy is in the central belt, where all the data centres which are in the planning system are proposed, and secondly because, 12GW of transmission is being built to take energy from Scotland south. If they were more concerned about using curtailed energy than having access to the Grid Supply Points with the highest capacity, and a 6.7GW connection to the south when there is not enough generated from wind, then they would be proposing sites north of the B4 Boundary.

Figure 3: Map from APRS Data Centre map showing data centres in Scotland’s planning system

In order to access the Montel Report you need to request a copy so we have uploaded it here