UK offshore wind farm development

The UK government has announced an intention to allow offshore wind farm development around most of the UK. John Hutton suggested that about 33 GW capacity could be added by 2020. This would provide about 25% of current UK electricity demand (which is itself rising by 1 to 2% per year).

Simple calculations suggest that this change may add about 15-25% to UK electricity bills. Offshore wind is more expensive to construct and operate than onshore wind farms. The announcement may suggest that the government believes that offshore wind can be pushed through but that onshore farms are likely to be successfully opposed. The big push for offshore wind seems to mean that the government is losing faith in nuclear.


The UK continental shelf is a good place to build wind farms. Wind speeds are high and the UK’s oil and gas industry has given us the capacity to work in harsh regimes. After a period of experimentation with smaller offshore wind projects, the 300-turbine London Array, shortly to be constructed, will become the largest marine wind farm in the world.

The government has given increasingly clear signs that it viewed offshore wind as a renewable technology of choice. It increased the proposed support from one ROC (currently worth about £45) to one and a half in the 2007 Energy White Paper. It now seems also to be willing to over-ride the Ministry of Defence’s concerns about the impact of wind farms on military radar. The worries over the turbines dicing small wading birds have been pushed aside.

The basic numbers The government wants another 25 GW on top of the current 8 GW in various stages of planning. These figures refer to the maximum output of the turbines on a windy day. The actual output is likely to be between 30 and 35% of this figure. (Data from Scroby Sands, an early offshore farm, suggests a lower figure, but the turbines have suffered from reliability problems which have depressed the output.)

33 GW of offshore wind capacity will provide about 100-110 TWh, or perhaps 25% of total UK demand. This approximately equates to the electricity demand from households today.

When the wind is blowing hard, the total offshore capacity envisaged by Mr Hutton will almost match the minimum total demand during a winter’s day.

Total UK electricity demand (MW) in the 24-hour period to noon on Tuesday 11 December 2007

Total UK electriticy demand

This chart is copied from National Grid real-time data. The y axis is MW. A GW is 1,000 MW. So the minimum demand on 11 December 2007 was reached at about 5am with a total demand of about 35 GW, about 10% more than would be generated on a very windy night all around the coasts.

If – and this is a very big if – the existing value of ROCs is maintained, then the possible subsidy from all electricity users to offshore wind if all 33 GW capacity is built is about £7bn. Over a year, this would raise the price of each kilowatt hour of electricity by about 1.8p, compared to the current retail price of about 10p. In addition, there will have to be substantial payments to other generators to incentivise them to build and hold ready gas-fired capacity for use when the wind isn’t blowing.

Offshore wind is expensive because its construction cost is high. The British Wind Energy Association mentions a figure of £2m per MW of capacity, compared to less than £1m for onshore wind. The total investment required to build 33 GW might therefore be as much as £64bn, about 6% of UK GNP. The BWEA figure looks a little high to me and the actual cost might be somewhat lower at perhaps £50bn.

The problems The government’s announcement was broadly supported by the other main political parties. It is the easiest source of renewable energy to back, even though it is expensive. The ROC subsidy system disguises the true cost of switching to wind and other sources, so politicians must assume that the extremely heavy expense of wind will not be obvious enough to be politically dangerous.

The problems for offshore energy lie elsewhere:

  • Turbine supply: only a small number of suppliers make marine-ready turbines. Vestas and Siemens, both based in Denmark, have made most of the ones already supplied. The worldwide shortage of top quality turbines is likely to persist for some years. New manufacturers will be enticed into the market if government support looks robust, but this could take the best part of a decade. Some of the existing turbines have severe problems with gearboxes (as at Scroby Sands) but we can expect these issues to be overcome eventually.
  • Grid connections: powerful arrays of turbines must be located close to points on the high voltage transmission network. It is no good putting a hundred turbines 50km from the nearest point of interconnection unless you can be sure to get planning permission for the National Grid to run pylons. (I think I am right in saying that the substation to handle the electricity coming onshore from the London Array was the last part of the infrastructure to get planning permission.)
  • Skills: the UK has offshore skills as good as most other countries, but getting 7,000 turbines built by 2020 is an extremely challenging task.
  • Intermittency: offshore wind is reasonably predictable and strong. Below is the wind map from the BBC on the afternoon of Tuesday 11 December 2007: UK wind map In the southern portion of the UK coastline, wind speeds will be low because of the prevailing cyclonic weather. But further north, the west coast is seeing reasonable wind speeds. Days of real quiet are surprisingly infrequent. Nevertheless, if we are to generate 25% of our electricity from offshore, we will need substantial back-up capacity. Very approximately, the UK has about 8 GW spare capacity. By ‘spare’ I mean unused generating capacity above what is likely to be the peak on a very cold December day at about 5.30pm. We will need to have much more when we have 33 GW of offshore power. I haven’t yet seen an estimate, but I suspect that it will be at least 12 GW more than we have at the moment. The capital cost of the gas plant to deliver this is likely to be over £4bn.
  • The interaction with nuclear: it hasn’t been picked up by the press, but a 25% target for offshore wind is not easily compatible with a large nuclear industry. Nuclear needs to run all the time as baseload. If the wind is blowing strongly when demand is lowest (about 5am on a summer’s day) then the UK will run the risk of having too much electricity supply. Either nuclear or wind would have to be disconnected or the UK would have to invest in more of what is called ‘pumped storage’. Surplus electricity is used to push water uphill into reservoirs. The reservoir can be discharged later, turning hydro-electric turbines when demand is higher. It is difficult to encourage large amounts of both nuclear and wind, and the government’s new wind policy must mean that it is losing interest in nuclear.

The conclusion Offshore wind is expensive and still somewhat untried. The government’s apparent decision to allow rapid development around a large portion of the UK coast is path-breaking. Most observers think that getting to 33 GW is an extremely optimistic target for 2020. However, industry people think that it may be possible to get as high as 20 GW, probably generating over 15% of UK power.