Electricity Supply

DOI: https://www.doi.org/10.53289/OYPQ4069

The role of wind in decarbonising the grid

Cathy McClay

Dr Cathy McClay FREng OBE is Director of Trading and Optimisation at Sembcorp Energy UK. Over her 20 year career, she has worked for energy companies in the UK, France and the Netherlands, specialising in modelling and analysis for energy trading, risk management, strategy and investment. Immediately prior to joining Sembcorp she was Head of Future Markets at National Grid ESO. She is a Visiting Professor at Imperial College and a Fellow of the Royal Academy of Engineering. In 2022 she was awarded an OBE for services to the Energy Sector and Promotion of Decarbonisation.


  • There is an aspiration to have 40GW of installed wind energy capacity by 2030
  • The system is incurring substantial costs due to an inability to export energy from, for example, Scotland to England
  • New wires will be required, but combined with smart technologies to optimise the system
  • Building new lines takes a long time, but some anticipatory planning could help
  • We need to be bolder in our targets and projects.

The UK is now looking at an electricity system where demand will be much higher due to decarbonisation. Yet that brings many challenges with it. Take for example the impact of wind on the system. Decarbonisation is going to be reliant on a great deal of offshore energy. On our system right now, there is about 100GW of generation servicing a peak demand of about 40-50GW on the transmission system. Within that, there is currently 25GW of wind, split pretty equally between onshore and offshore.

There is an aspiration to achieve 40GW of offshore wind by 2030. That is an increase of 28GW more than is currently connected on the system in total. Now, 2030 is only eight years away, it is not far. System operators expect there will be 30-40GW of generation in Scotland by then, if conventional technologies are used. Demand in Scotland is likely to be just 6GW. The rest of that power has to be transferred out of Scotland. Yet the current transfer limit of power to England is 6GW, after which the wires start overheating.

Of course, even with 30-40GW of generation in Scotland, it will not be producing the whole time. There is 25GW of wind on the system now but the peak I normally see is about 15GW and the lowest over the past year was 200MW. That is a very big swing to manage on the system!

A lot of the time, it is just not possible to get the power out of Scotland. Wind farms are being built but the output is wasted. Whenever power cannot be transferred, that incurs costs. Firms want to generate because every megawatt hour is paid for under their Contract for Difference or their Renewable Obligation Certificate. Instead, they are being paid £80 pounds per megawatt hour to switch off. The cost of those constraints on the system at the minute is about half a billion pounds a year.

System operators expect the cost of managing the system to rise to between £1 billion and £2.5 billion over the next five years because of these constraint costs. Windfarms are being built right now that cannot be used. What can we do about that? The first option is to attract more demand into Scotland, to take advantage of the surplus production. That could be achieved by setting a price reflecting the fact that wind energy in Scotland is not as valuable right now, because we cannot get it out. Perhaps technologies like hydrogen electrolysers could be brought in.

It may be possible to use the wires between Scotland and England more effectively and get more out of them by being smart in the way they are used. The transmission operator has managed to upgrade the transfer without actually building more wires. The final solution is to build more wires as well, but hopefully fewer wires because smart technologies are being introduced at the same time. The challenge with building lines is the time it takes: getting planning permission alone can take years. The first proposal is to build a line down the East Coast from Peterhead to Drax of two gigawatts. A second would take energy from Torness on the east coast of Scotland down to Hawthorne Pit near Durham.

Now, the system operator has been asking transmission companies to go ahead and build these two lines since 2018. Yet they only got regulatory approval in 2021. The proposals are now going through planning and are expected to be online in 2029 and 2030. That is more than 10 years since they were given the initial go-ahead. Indeed, the projects were first suggested in 2011, although at that point the network was very different: no-one envisaged all this offshore wind.

The new capacity will have to be built more cleverly. Today’s offshore windfarms are each connected to the coast independently. That means a large number of connections and they all need planning permission. There is no redundancy because there is only one connection onto land. What could be done differently?

The Offshore Transmission Network Review looks at how to build a grid in the North Sea. The

system operators have been asked by Government to meet the objective of connecting 40GW of offshore wind by 2030. The plan would be, instead of connecting each one separately, to look at this holistically and connect a network. The estimate for capital reduction of such an approach is £6 billion over the lifetime out to 2050, with only half of the onshore assets needed compared to conventional practice.

In terms of the system, there is a need to build more wires. It must be done cleverly, though, and more quickly if we are not going to waste the resource. What do we need to be able to do that? First, we need joined-up thinking. The UK has said it will build a lot more windfarms. But there has been no discussion of the wires that go with it, for example. So to realise the offshore potential, joined up-thinking is important and the Offshore Transmission Network Review will play a key role. 

So often, though, we come up with good ideas and then do not really commit: in this case we really must. To be successful needs joined-up thinking between the system operator, the regulator and Government. We probably also need a bit more central planning. At present, the system operator advises on what lines should be built through their networks options assessment process every year. But it is only advice, there is no compulsion behind it. The network operators do not have to agree or act on the advice. The system operators are in the process of splitting away from National Grid and forming an overall independent system operator. Perhaps the new body could take on the planning role.

Finally, we need to be a bit bolder in what we do. Building wires takes a long time with planning processes, etc. If we wait until we are absolutely certain we need a new line or something else before we build it, then it will arrive too late. Anticipatory planning would go some way to smoothing and speeding up this process. Being just a bit bolder will help us get to net zero.

The UK has said it will build a lot more windfarms. But there has been no discussion of the wires that go with it.