It’s blowing a gale outside, why is that windfarm not spinning?

There are two seasons in Scotland: June and Winter (Billy Connolly). We get wind, rain, and cold temperatures almost all year round. Our climate does have its benefits, namely for renewable generation. We have close to 10GW of onshore/offshore wind farms currently installed in Scotland[1]. If operating at full capacity, this is enough energy to supply power to 10 million homes[2]. In reality, although it may seem to be windy all of the time here, the load factor (the % of a windfarms maximum capacity that it actually produces) tends to be around 27% for onshore windfarms and 40% for offshore. Across the year our onshore windfarms (total capacity 8.3GW) generally produce around 2.2GW of electricity (energy for over 2 million homes), and our offshore windfarms (1GW) produce around 400MW of electricity (energy for 400,000 homes).

One question often asked when it is blowing a gale outside is, why is that windfarm not spinning? In some cases this may be because the wind is actually blowing too fast and the wind turbines don’t spin for safety reasons. Another more common reason is that we are actually producing TOO much energy and we can’t transport the excess energy south of the border where it is needed. The consequence of which is that National Grid ESO (who operate the electricity market in the UK) are forced to PAY wind generators to STOP producing energy (i.e. shutdown your windfarm please), while at the same time they may have to PAY other generators down south to TURN ON their generators (this could be a gas plant, for example). HOW IS THIS POSSIBLE?! This is what is known as a constraint on the electricity network. This particular constraint is called SCOTEX (Scottish Export constraint). National Grid paid Scottish windfarms £130m in 2019 to stop producing energy[3]. This cost is passed through to the CONSUMER via Balancing Services Use of System (BSUoS) charges (generators pay 50% of the socialised cost, consumers pay the other 50%). This will form part of your electricity bill.

Why does this happen? Essentially there is too much generation in Scotland relative to demand – when this excess generation tries to move south of the border there is effectively a bottleneck where the network infrastructure cannot transport all of the electricity. As you cannot readily store this volume of electricity (battery storage and other forms of storage will be discussed in a later blog) National Grid are forced to pay generators to stop generating. Moves have been made to try to help mitigate this issue. The ‘Western Link’ is a £1billion piece of equipment – consisting mainly of undersea cables that have the capacity to transfer 2.2GW of this excess electricity from Hunterston in Scotland to Flintshire Bridge in North Wales – was built in 2017. The cost and complexity of building this piece of equipment highlights that there is no easy cost-effective solution to this problem. Generators themselves are also looking at installing batteries (Scottish Power’s Whitelee battery) which should at least be able to store the energy and release this onto the grid at a later time. Let’s hope that the industry can work together to prevent more waste of renewable energy!


[1] https://www.gov.uk/government/statistics/energy-trends-section-6-renewables

[2] https://www.ofgem.gov.uk/ofgem-publications/76160/13537-elecgenfactsfspdf

[3] https://www.ref.org.uk/ref-blog/354-a-decade-of-constraint-payments

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