Scotland-England Electricity Transfers

Leo Smith from Gridwatch has been monitoring the electricity transfers between Scotland and England since 30 December 2015. This post presents a first look at these data.

  • The transfers are almost exclusively Scotland to England
  • The transfer peaks define a plateau of 3.5 GW that defines the inter connection capacity
  • The pattern of transfers follows wind supply quite closely. An argument can be made that all of Scotland’s wind power is currently exported.
  • Scotland currently meets 100% of indigenous demand from conventional sources, mainly nuclear, coal and hydro.
  • A diurnal demand cycle is embedded in the export pattern, but curiously, export peaks are centred on midnight.
  • There is evidence that wind-curtailment may be used as part of load following strategy.

Just before Christmas, George Lindsay sent me this link from National Grid that monitors electricity flows between Scotland and England. I sent the link to Leo Smith at Gridwatch and enquired if it could be monitored. Leo obliged and we now have the first couple of months of data. Many thanks Leo!

The interest here is to monitor Scotland – England electricity transfers leading up to and following the closure of the 2.4 GW Longannet coal fired power station at the end of March. Longannet is part of the backbone of Scottish electricity supply.

Figure 1 Scotland-England electricity transfers as published by National Grid. The raw data contains a large number of errors and omissions which have been repaired (See appendix). Click all charts for a large readable version.

Figure 1 shows the pattern of Scottish electricity exports to England. There are five occasions when exports fell to zero and went slightly negative but on no occasion was Scotland a significant importer. As we will see below the pattern of exports is correlated with wind, but wind is not the only controlling variable. There are some other key points to be made first.

First, electricity exports peak on a plateau value of 3.5 GW. Presumably this is the capacity of the inter-connection, substantially higher than the 2.66 GW I estimated in a recent post. Finding concrete details on the size of inter-connection has remained elusive, but I believe we now have the answer – 3.5 GW.

Second, there is a clear signal through most of the data that the Scotland-England interconnection is following diurnal load and is therefore engaged in load balancing. My immediate assumption that Scottish hydro was being deployed to help balance national load proved false. Looking closely at the data 22 to 28 February it can be seen clearly that Scottish exports to England are peaking around midnight and are reduced during late afternoon peak demand periods. This happened during a wind lull and Scotland exported less at time of UK peak demand. This is a form of negative balancing. Rather than produce more power when it is needed, Scotland simply exports less. This presumably places greater strain on the system south of the border,

Correlation with Wind

Figure 2 We do not have data on Scottish wind production and the Scottish output is based on pro-rating UK output based on installed capacity. Scotland = 0.41 of the UK.

Electricity exports follow the pattern of wind production but are normally significantly higher than wind supply (Figure 2). It should be clear that most of Scotland’s wind production is exported. If you are upset by a wind farm on the hillside opposite your house you should know that its only function is to send electrical noise to England. But this will change with the closure of Longannet. Cross plotting wind v exports shows R^2=0.49 (Figure 3). Wind clearly influences the export pattern but is not the sole variable. The other main variable is diurnal load following exchanges.

Further observations to make from Figure 2 are that wind peaks are following a plateau of 2.5 GW (41% of total UK wind) suggesting that curtailment may occur at values above this. And inspection of the graphs in UK Grid Graphed does indeed suggest that peak supply is following a plateau. There is also evidence for a diurnal cycle in the wind that is difficult to understand. In summer this could be explained by sea and land breezes but in cyclone dominated winter I don’t see that the wind should decide to blow harder at midnight. I will speculate that the diurnal cycle seen in the wind data may be down to curtailment used to follow load. Once again this is evidence for load following achieved by withholding supply rather than using balancing reserve.

Figure 3 Wind production versus Scotland-England exchanges shows a fairly high degree of correlation. The maximum exchange of 3.5 GW is clearly defined.

Scottish Generation

Figure 4 National Grid have not yet published Scottish demand data for January and February, hence the model above is based on pro-rating Scottish demand = 10% of UK demand. Adding exports (red) provides a picture of Scottish supply.

Adding exports to Scottish demand shows the pattern of Scottish supply for these two months. Peak supply defines a plateau of about 8 GW. The generating assets at disposal were as follows:

  • Hunterstone B nuclear 1 GW
  • Torness nuclear 1.2 GW
  • Longannet coal 2.4 GW
  • Hydro peak 1 GW
  • Peterhead gas 0.4 GW (+0.75 GW supplemental reserve)
  • Wind peak 2.5 GW (constrained?)

This provides a total capacity of 8.5 GW compared with the 8 GW peak output. Note that I have forgotten to include the 0.25 GW Moyle inter-connector (N Ireland) in this analysis and so peak demand and capacity are almost matched. Including exports to N Ireland, it is evident that all the generating assets have been deployed in January and February and were running flat out when demand was there.

Figure 5 Deducting wind from exports leaves this residual that represents the exported conventional supply.

We can scratch the data a little deeper. With exports normally following but running ahead of wind generated it is clear that a component of exports comes from conventional dispatchable power. Deducting wind from exports leaves a residual that represents this component (Figure 5). Two main observations here. The first is that this dispatchable component peaks at around 2.4 MW coincident with the output from Longannet. Second, the diurnal cycle is more strongly pronounced in the residual. But once again the export peaks are normally centred on midnight. Why on Earth are Scottish power stations sending electricity to England at times of low demand?

Figure 6 shows these various components. Generation from Longannet currently contributes to Scottish demand and provides  a surplus for export. Its closure will make Scotland dependant in part on wind to keep the lights on.

Figure 6 Scottish supply broken down into the three components of indigenous demand that is met from conventional sources, exported conventional surplus and exported wind.

Black Start

The main risk to the Scottish system lies in one of our nuclear power stations tripping in cold calm winter conditions and the risk that this trips the other nuclear power station leading to a nationwide blackout. Power stations require power in order to operate and re-energising the grid from a black start is a recognised risk.

This Scottish Government report describes the black start protocol as follows:

Scotland is a single Black Start contracting zone and currently the SO has Black Start contracts with Crauchan, Foyers, Errochty and Sloy with each TO having 1 LJRP to manage. If Longannet or Peterhead remain open the SO is able to use them with the hydro and pump storage stations to Black Start and provide skeleton restoration in the SP Transmission and SHE Transmission areas within 12 – 18hrs. If Longannet and Peterhead close then the SO will adopt the alternative strategy, which is based on energising from England and Wales transmission system, in conjunction with hydro and pump storage generation in Scotland providing a skeleton restoration in 24+hrs.

SO = system operator
LJRP = local joint restoration plan
TO = transmission owner
SP = Scottish Power (grid operator in the south)
SHE = Scottish Hydro Electric (grid operator in the north)
Cruachan and Foyers are pumped storage hydro schemes
Errochty and Sloy are conventional hydro schemes

Via email, engineers have raised concerns that Scotland will not manage a black start without Longannet that is a massive, robust and flexible beast at the heart of the generating system. And so it appears that Scotland may be dependent on the English grid but the same engineers expressed concern about the viability of black starting Scotland via the England – Scotland inter connections.

If you live in Scotland, there has never been a better time to invest in a wood burner and candles.

Appendix: Data

The Scotland-England exchange data are being archived alongside the other Gridwatch data but are not yet available from the web site. Leo sent me a link that accesses ALL the Gridwatch data that is very cumbersome and almost crashed my computer. So I’ve not published the link lest too many folks try to access it and crash the Gridwatch server. Anyone who wants the link only needs to ask.

The data are also full of timing errors, essentially missing lines and I had to spend several hours repairing it. This includes 14 hours of missing data on 20th / 21st January.

The data are recorded with 5 minute resolution. This has been converted to hourly averages to make the files more manageable.

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22 Responses to Scotland-England Electricity Transfers

  1. Euan: Here are the UK Grid Graphed plots of UK wind output for the last four Decembers:

    December 2012 looks like good old-fashioned non-dispatchable power, but there are some days when wind output broadly follows daily demand, e.g.1, 4, 7, 10, 15. Coincidence?

    December 2013 is a little less ragged than 2012, but again we see days when wind output broadly follows demand. Coincidence? Or curtailment?

    December 2014 is another semi-ragged profile, but there are yet more days when wind output peaks at or around the peak demand hour. Unless sea breezes blow in December it’s beginning to look like something other than natural variation.

    But there’s no doubt about December 2015 (I expect the plots for January and February 2016 would be similar). Wind-to-the-grid is somehow being adjusted to follow demand as closely as possible during high-wind periods. How are they doing it?

    • Euan Mearns says:

      Roger, thanks for noticing that. The other key is that 2015 plateaus on 8 GW, the same as 2014. I’m pretty sure capacity has risen and so I think the control is simply achieved via constraint. REF have put their constraint payments page behind a pay wall 🙁

      This is potentially pretty smart and I’m sure we may hear a lot about this in the near future. But it means a wind farm gets paid top $ for not producing power instead of a CCGT getting paid to follow load. The CCGT of course still has to run, just not cycle to the same extent. Not using “C free” wind means that CO2 gets produced.

      • To answer my own question, they’re doing it by curtailing output from 30 very large wind farms that represent about half of UK installed wind capacity. These farms are part of the “Balancing Mechanism” and are able to respond on a “second by second” basis to changes in demand.

        From the same article:

        Sometimes payments are made to a generator in return for reducing output because more electricity is being generated than can be used in a particular region because a grid ‘constraint’ exists – an analogy would be a road block – preventing that electricity being exported to a region where the electricity could be used. Such a constraint exists between Scotland and England. Increasingly more electricity is being generated in Scotland than can be used in Scotland, and the grid interconnections between Scotland and England are insufficient to take the excess electricity which is generated, usually at times of, often unexpectedly, high winds and low Scottish demand.

        • It doesn't add up... says:

          It is worth looking at the CFD conditions for constraint payments at the DECC website.

  2. Alistair Buckoke says:

    So is the word ‘export’ really the correct term to use, if so much Scottish output is being used to balance English demand? Might the late night use of wind surplus be on a contractual basis with big industrial users?

    One might then ask if wind farm construction and new power lines across southern Scotland (for example) are really being initiated by Scotland? Or actually being paid for by Scotland? What of Salmond’s ‘dash for wind’? Is the Scottish Government’s high renewable dependence stance being used or even supported by Westminster? Is southern Scotland an expedient place to dump unpopular but needed capacity, and electorally expendable to boot, leaving the more politically sensitive English shires largely sacrosanct?

    Your post provokes many questions!

    • willem post says:


      I think it is parochial to think about energy generation on a national basis.

      Europe needs more central planning regarding energy. Had that been the case, Germany, with poor sun conditions, would not have installed so many solar panels at enormous cost and get so little solar energy; CF = 0.10.

      Germany, guided by central planning, likely would have built them in Spain, Italy, Greece, Southern France, etc., where there IS sunshine.

      In the future, Europe will have an overlay grid to connect most of its parts, and the areas best suited for wind energy (windy, unpopulated areas) will have the most wind turbines, and those areas best suited for solar energy will have the most solar panels.

      Without such rational planning, Europe would have expensive energy costs, making it less competitive on world markets.

      • Alistair Buckoke says:

        But is it parochial to ask about a question where the public rhetoric says one thing but the reality of who is making the decisions and writing the cheques may be completely other than this?

        And what about a parochial context being representative of the whole, wider context?

        I wonder also whether it is all really planned as you suggest, across Europe. If it were planned the exact nature of intermittent generating capacity will have been understood and provided for. As it is, the indicators suggest the decision makers are following public rhetoric (and manipulating it as well) and not what engineers and scientists tell them.

        That rhetorically driven decision making does not seem to have included a clear priority over keeping the lights on suggests that there have been shortfalls in understanding, or over-focus on the short term, or both. Confidence in decision making becomes eroded, and this goes right back to a local level.

        And as for costs …………… .

        • willem post says:


          Energy planning bumbling will get the UK nowhere.

          BTW, bumbling in several areas has been a post-WW II UK trait.

          The focus should be how best to integrate the UK system with the EU system, so all have energy all the time.

          See my below comment to gaznotprom

          • Alistair Buckoke says:

            I accept your point, though would use the phrase ‘over-politicised’ rather than bumbling.

            At the same time, the rather later development of interconnection across Europe says that many governments have also been slow to see the flaws in high dependence on renewables. These governments have not been immune to thinking becoming insulated in a cocoon of rhetoric.

            Has a fortnight long winter anticyclone spreading across much of north west Europe been planned for I wonder? It has struck me that the 2011 EU Energy Roadmap is about as far as anyone would want to go along the intermittent renewables route, and represents a sensible and realistic balance of generating sources, allowing for eventualities. Presumably this policy is about to be redrafted, and probably not in sensible directions, unfortunately. One would also note that, from a system point of view, it is preferable for the parts to be fully representative of the whole. This means that each government would ideally seek a breadth of generation sources internally, rather than reaching for their neighbour for help when shortfalls in planning have been come across.

            My whole case is about the forging of policy through the public presentation of robust, detailed, forward-looking rational argument, rather than through the emotive soundbite. The Scottish Independence campaign was a dreadful example of the latter. I very much doubt that the former is anywhere fully-fledged in Europe.

    • Euan Mearns says:

      Drive down the M74 – M6, from Scottish borders to England. First a forest of windmills and pylons. And then RE free rural England. We can’t blame this on the English anymore than we can blame the closure of Longannet on UK legislation.

      The Scottish Government has gone all out for 100% renewables (albeit nuanced). End of story. The UK government has simply sat back and said “Hell Yeh” this helps us on multiple fronts – meeting targets and keeping English communities intact.

      Where are the dumb sitting?

      • Alistair Buckoke says:

        The Scottish people have been played, haven’t they?

        Who is doing the playing over the Longannet closure and its probable aftermath, I wonder? Or should this be rephrased as who is being played against themselves?

  3. Gaznotprom says:

    Hmmmm, central planning, heard of that somewhere before…. Hmmmm and from memory didn’t work out too well…

    • willem post says:


      Electrical energy travels at near the speed of light (1800 miles in 0.01 second). If it did not, modern electrical systems would not be possible.

      Whereas national planning of generation and grid systems, based on fossil, nuclear and hydro, have been prevalent for over 100 years, that will not be the case going forward.

      For example: In the future, much of Europe’s solar energy will come from Morocco, etc.

      Regional planning is a given. Such regions, as Euan has shown, likely would need to be large enough to include at least two, mostly independent, weather systems to ensure adequate decorrelation.

      BTW, gas from Russia likely would be the lowest cost energy source for Europe for many decades, regardless of what NATO/US and some elements of the EU are trying to push for, which is driving a low-cost producer out of the EU market. That would be to the advantage of the US.

    • robertok06 says:

      In RoC seems to have worked just fine… 🙂

  4. willem post says:

    Here is an article regarding bogus GW, which may be of interest to you.

  5. A C Osborn says:

    Rupert Darwall in the Telegraph has gone the full distance and is not just saying how useless Renewables are but now blaming them for basically destroying the UK Electricity Market.
    As reported at Not a lot of people know that.

    He also has a post on Mark Shorrock trying to revive the Swansea Lagoon White Elephant.

    Add to that the article in the The Times by Matt Ridley on the Hinkley C white elephant and the MSM are really starting to understand & report on the mess that subsequent governments have made of our power generation.

  6. Owen says:

    Are the Scottish Govt not claiming we are nearly at 100% renewables ?

  7. Pingback: One Step Closer to Blackouts | Energy Matters

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