The Changing Face of UK Power Supply

Joint post with Neil Mearns

UK Grid Graphed provides a graphic summary of daily, monthly and annual UK electricity generation from 2012 to 2015 based on BM Reports as archived by Gridwatch. This post provides an overview of the UK Grid Graphed resource and the key observations to be made from the data. In summary, coal generation is in steep decline to be substituted by rising wind, solar, biomass and imports. Demand for electricity is also falling and government should be concerned about the extent that this is caused by rising electricity prices and policy.

Many readers of this blog will be familiar with Gridwatch that monitors and records data for the UK National Grid from Balancing Mechanism (BM) Reports. It is simple to access all of the metered generation and inter-connector flows starting on 13 May 2009. We all owe Leo Smith a debt of gratitude for proving this resource that allows us to keep an eye on Big Brother. But it’s not so easy to get an overview of daily, weekly, monthly and annual trends in generation without a lot of work. Amongst other things, data are recorded with 5 minute resolution producing 105,120 lines of data for each year. We therefore set out to chart most of the data starting in 2012 to provide a simple look-up resource.

Starting in 2012, charts are archived under UK Grid Graphed. There are links in the menu bar above and in the right margin. This substantial body of work was done by my son Neil who is home at present looking for work. More on Neil at the end of this post. We will begin with a quick tour of UK Grid Graphed followed by a summary of monthly and annual trends.

UK Grid Graphed

For each month, a standard set of charts has been produced as shown below for January 2015. The data have been converted to half-hourly averages to make it more manageable. These charts enable some general observations to be made as detailed below.

Nuclear: The electricity used in pumped storage has been deducted from nuclear giving rise to the daily dips. Otherwise, in January 2015, nuclear hummed along producing between 8000 and 9000 MW uniform supply. The variance up likely reflects two reactors being brought back on line and the trend down reflects two reactors going off line. Note that the standard UK power station is 1000 to 1200 MW and each has two 500 to 600 MW reactors.

Coal provided about 9000 MW of base load and up to around 8000 MW of load following supply. We can also see that coal was wound down during low demand at New Year and on some weekends, e.g. 9th and 10th of January.

Biomass has plateau production just below 1200 MW which probably represents 3*400 MW generators at Drax Power Station. Biomass does not participate in load following and is being run in base load mode which is disappointing to see. Biomass has priority in the merit order, and the owners of the plant are clearly aiming to make as much money as possible. The blocky nature of the profile will reflect individual generators coming on and off line but it’s not clear why this is happening. One could speculate that it is determined by the availability of wood chips.

Gas in the shape of combined cycle gas turbines (CCGT) provides little base load but  a large amount of load following service, balancing wind and solar and following the diurnal demand pattern. An examination of the wind data in the panel below shows that the period 17th to 23rd was calm, and gas stepped into the breach at that time. The maximum output achieved by gas in 2015 was of the order 21,000 MW and this probably defines the effective capacity of the CCGT fleet.

Hydro: Conventional hydro, somewhat surprisingly, is run mainly as base load with only minor load following. While there is much talk and hype about using hydro to balance wind or solar, the way the finances, subsidies and grid are currently rigged clearly does not incentivise hydro to contribute to provide grid balancing service. I suspect this may have something to do with controlling flows in Scottish rivers.

Pumped hydro feeds into the daytime peak demand and the spikes up reflect the provision of acute load balancing at times of need during the tea time peak. UK pumped hydro is configured to consume surplus night time nuclear and may be considered a form of stored nuclear power.

Interconnectors: The interconnector trace is a bit of a mess showing the combined output of 4 cables that individually define more consistent trends. This is described in greater detail below.

Wind is split into two components. Large wind farms are connected to the high voltage grid and are metered by BM reports. Small wind farms are connected to the low voltage grid and are seen by National Grid as negative demand. This embedded wind is accessed via National Grid. While the main control on wind power is the wind blowing, we can also see that the metered wind peaks seem to define a plateau value of around 6000 MW. It seems likely that wind is being constrained to this output.

Solar: The solar chart is scaled to summer output and shows that solar is a total waste of time in the UK in winter time when demand is highest. What is more, the peaks are centred on midday and come 6pm in December and January, the sun has set across the UK and solar output falls to zero.

Interconnectors: The UK is currently connected to the outside world by 4 interconnectors:

  • 2000 MW to France
  • 1000 MW to The Netherlands
  • 500 MW to The Republic of Ireland (East West)
  • 250 MW to Northern Ireland (Moyle)

We can see that the France interconnector was set to import electricity at 1500 and then 2000 MW for most of January 2015. The excursions to zero and occasionally to export, occur during low wind periods. So, even though the UK was in need of extra power, so was the continent who outbid us. It is a similar story on BritNed that was pretty well set to import 1000 MW for the whole month.

The cables to Ireland are rather different. These are pretty well set to export power and also follow diurnal load, helping the Irish grid to stay in balance. But there are occasions when we import from Ireland, notably at times when imports from the continent have fallen.

Summary: Finally we can stack all of these components to show the wonderfully ordered pattern of UK electricity demand with a large diurnal cycle and late afternoon demand peaks. Note that the way Excel stacked area manages negative numbers (occasional net electricity exports) is to deduct these from neighbouring categories.

Annual and Monthly Trends

Annual Supplies in GWh: There are three main observations to make from this chart.

  1. Nuclear, gas and hydro production is more or less flat 2012 to 2015
  2. Coal is on steep decline
  3. Biomass, interconnectors, wind and solar are rising quite steeply

These trends are a direct reflection of government energy policy that now includes the phasing out of coal by 2025.

Variable compensation: Looking at the components that are varying with time we see that the growth in biomass, inter-connectors, wind and solar does not fully compensate for the decline in coal. UK electricity consumption is also in decline (see next graph).

Annual Consumption: UK electricity consumption is declining slowly. This has both virtuous and non-virtuous sides to it. Improved energy efficiency and saving energy are on the virtuous side of the balance sheet. On the non-virtuous side are high energy prices suppressing demand and spreading energy poverty, ongoing anaemic economic growth and offshoring UK manufacturing.

Annual distribution: This graph shows that solar, wind and imports now make up 20% of UK electricity supplies doubling share in 4 years. It also emphasises how puny UK hydro resources are.

Nuclear monthly distribution: This is one of the most boring charts. It shows that UK nuclear routinely churns out over 5000 GWh / month. It also shows vulnerability of nuclear supplies when unscheduled outages coincide with scheduled outages that may have occurred in October – November 2014.

Coal monthly distribution: This chart shows the planned decline of coal discussed above but also reveals an important annual cycle where coal plants come on line in winter and go offline in summer. This large annual cycle of 6000 GWh / month will have to be met from gas in the future. The UK does not have large gas storage facilities.

Biomass monthly distribution: Biomass, in the form of wood chips imported mainly from North America are burned in Drax, formerly coal-fired, power station. Half the station has been converted to burn bio-mass, the remainder is currently scheduled to be mothballed.

Gas monthly distribution, like nuclear, is a fairly boring chart with a largely flat trend. The ups and downs will reflect gas responding to market conditions.

Hydro and pumped hydro monthly distribution has a distinct annual cycle with peaks in the winter months. This will reflect the annual rainfall pattern.

Interconnectors monthly distribution shows that since March 2012 the UK has become a permanent importer of electricity most of which will have origins in the French nuclear fleet. The steady growth in imports will also directly reflect energy policy and the planned decline of UK coal. While politicians and renewables advocates repeat over and over that interconnectors are a positive development, the reality is that the UK has developed import dependency that harms trade balance, Sterling and the economy in general. With a further 7.3 GW of interconnection planned, this situation is scheduled to become much worse.

Wind monthly distribution also has a pronounced annual cycle with peaks in the winter months and is closely correlated with hydro. Wind output is also growing as the size of the fleet grows.

Solar monthly distribution displays a beautiful annual cycle with peaks in the summer months. In the winter troughs, November, December and January, solar falls close to zero. While solar is positively correlated with demand on the daily cycle it is negatively correlated on the annual cycle.

Summary: adding this all together provides this picture showing the annual cycle and steady decline in UK electricity demand. The main substitution is growth in solar, wind, biomass and imports to compensate for the decline in coal.

Assist Neil Mearns

Neil has been home now for several months looking for work. He has an MA (upper second class honours) in Geography from the University of Edinburgh and an MSc in Marine Science from Heriot-Watt University. He is one of many thousands of unemployed graduates, a victim of wholly misguided Education policy that fails to match the number of graduates to the number of graduate jobs.

Neil has spent about three months compiling these charts. If you wish to show your appreciation you can do this in two ways. First you could visit the donate button at the top right margin. All donations to Energy Matters up to and including 10th April will go to Neil.

But if you really wanted to help you could offer Neil a job or send his CV to business associates who may be able to help. Any relevant job anywhere will be considered.

Download CV for Neil Mearns.

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22 Responses to The Changing Face of UK Power Supply

  1. GeoffM says:

    I don’t like it when hydro and pumped are lumped together. What purpose does this serve, except to confuse young undergraduates or newly-qualified graduates who are trying to push the pro-newable agenda to build a career for themselves? Pumped hydro traditionally originates from excess coal+nuclear energy, and is not a primary energy source. You can have as much or as little as you want, within limits.
    A couple of years ago I noticed that the IEA were putting a strange figure in their data for UK hydro generation, a figure way higher that what DECC were saying. I was suspicious that IEA were adding hydro+pumped, and when I did the maths this was exactly what they were doing. I wrote to complain and a chap in Paris defended their position, claiming that their foot notes clarified things. I investigated the footnotes and what he said wasn’t true, so I wrote back. This time he agreed and said he’d suggest to someone else that the footnotes should be improved. I don’t know if this happened.

    • Willem post says:


      I would go one step further and take pumped hydro out of the graphs.

      Pumped hydro is merely pumping water back into a reservoir. It occurs because too much other energy was generated, usually wind energy, that should have been curtailed.

      The water was pumped into the reservoir not because the reservoir needed it, but because curtailment did not take place and the pumps were available to pump.

      I think this is an idiotic way to run a power system.

  2. GeoffM says:

    sorry I spelt “renewable” wrongly!

  3. Joe Public says:

    “But it’s not so easy to get an overview of daily, weekly, monthly and annual trends in generation without a lot of work.”

    A complementary alternative depiction of the data is Stephen Morley’s:

    • Hugh Sharman says:

      @neil! Good work! It is not easy to know how to advise you but I will give it thought. It could make be a good presentation for the SNP, as Scotland ceases to be a net exporter of electricity for the first time ever?
      @joe public, thanks for drawing my attention to Stephen Morley’s blog! Nice coding! What is his game, I wonder? He only allows us to know something of him through his (quite interesting) blogs!

    • gmlindsay says:

      Interesting to note that Morley includes nuclear generation in the “Brown energy” category rather than in the “green” category??

  4. stone100 says:

    We really need to try and get biomass and hydro to do load following as much as they can. If there was a large carbon-tax (eg as in the carbon fee and dividend scheme) instead of a renewables subsidy, then might hydro and biomass become configured to take advantage of high wholesale electricity prices when the wind wasn’t blowing? Perhaps for flood prevention (and nature conservation) we could do with having a very large expansion in UK woodland. Biomass energy might be seen as a dual benefit from that primary purpose.

    To get hydro to do load following, would it entail a massive cost in terms of making the dams higher etc? Would the environmental impacts be prohibitive?

    • GeoffM says:

      stone100, you are misunderstanding various aspects of mass electrical generation.

      You want load following to be done by hydro+biomass. Take a look at Gridwatch. In the last 24 hrs demand varied from 30 GW to 50 GW. So with your idea hydro+biomass would need to find 20 GW. Gridwatch suggests that conventional hydro can only give 1 GW. So biomass would have to give 19 GW. And how long would our trees last having to give 19 GW? These days Gridwatch shows biomass maxing at 2 GW, and in the press 2 years ago a spokesman for Forestry Commission Scotland stated that Scotland will run out of trees at the present rate by around 2030.

      You also want bigger dams. But the amount we can get from hydro is mainly to do with how much rainfall we have upstream of the dam; building bigger dams would give us a bit more but that bit maybe wouldn’t compensate for all the energy (and CO2 emissions from all the concrete manufacture) consumed to enlarge the dams.

  5. Willem Post says:


    “Amongst other things, data are recorded with 5 minute resolution producing 10,512 lines of data for each year.”

    You are lucky to have such a smart father, who obviously has guided you well on your way. It will be just a matter of time before you get a good job. In the meantime, please learn as much as possible from Energy Matters.

    If 5 minute intervals, 12 per hour, and 8760 h/y, yields 105,120

  6. gmlindsay says:

    Excellent job by the indomitable father and son team – I downloaded the massive spreadsheet provided by Leo with the 5 minute interval data and was overawed but you guys have done a stalwart job of analysing and sorting this raw data and have given us a better understanding of what is actually going on. It’s a shame that not all wind is metered by the grid and that the embedded wind is only reflected as a decreased demand but the picture ic clear in that a variety of generations systems is a must and that we cannot rely on wind and solar alone – whilst still maintaining a reliable electricity supply.
    I have every confidence that Neil will not remain unemployed for too much longer – the work demonstrated in this report.must be a major addition to your CV.

  7. guber says:

    Euan, say a big thank you to Neil for the work. With the education, as far as I can see, he would fit perfect for the business of Wind-Power-Offshorefoundations, or subsea-Interconnectors. But I do not have personal contacts there, and it would be against your persuasions.
    Nevertheless I did look around a bit in german language, and maybe he can get in contact to some places:

    Non fits really good, but maybe worth a phonecall or similar, if noone else reacts.

  8. Superb graphics. Well done, Neil.

    The “Annual Supplies in GWh” plot makes it clear that the obvious short-term fix for the UK’s energy shortage problem is simply to stop shutting down coal plants.

  9. philsharris says:

    Likewise (see above) congrats to Neil for a fine piece of sustained work.

    Interesting you should mention the effects on river flow as the possible reason for not using Scottish hydro for peak lopping. Would be nice Euan if you could confirm that.

    I understand that there is a bottleneck in interconnection between Scotland and England. Any thoughts?

    Have you seen the Poyre report on costs and benefits of GB interconnection, February 2016? I was provided a link to a nearly complete pdf file.

  10. gweberbv says:


    when you have a hammer (“I don’t trust interconnectors.”), soon everything will look like a needle (“Look, they are outbidding us!”). When you look at electricity prices in UK at the beginning of January 2015 it looks more like you island monkeys underbid the continent. 🙂

    See here:

    Data on power prices I obtained from here: (N2EX)

  11. confused mike says:

    I have always thought pictures tell great stories especially when the data are enormous so like others it is good to see all this information in one easier to digest place.

    I wonder, however, whether some other business information data along side this would be both useful and could create a tool which others might wish to use – and hence create a (potentially paying) role for Neil as well.

    There could be different audiences for the results – maybe including HMG but also potential power generation investors – if there are any!

    I confess I do not know how arduous this data trawling would be so understand if this messenger gets shot!

    I’m thinking of information (monthly or annual I open the discussion) such as:

    Coal price in dollars per tonne loaded or landed price

    Gas price in p/Therm or dollars per MMBTHU

    Utilisation factors for available generation capacity by source – this could show how much solar and wind is really used and how FF capacity is tightening

    Electricity wholesale price (UKP/MWh) – maybe even along side retail price (our electricity bill figure) in pence/KWh since this may show that even as FF commodity prices and electricity wholesale prices have moved how consumer prices have moved in tandem or not as a result of the changing green levy burden.

    Carbon intensity of power generation – using an assumed factor for coal fired and gas fired generation to start with.

    The list is a relatively quick brain dump. I’m sure there are others with more expertise who can trim or adjust?

    This may then enable the current results to show where the future is possibly going to go?

    It may also be possible to flag where HMG nudges from the Electricity market reform have caused changes – or unexpected consequences.

    After all the UK power generation is a business – not that joined up to my view – and this sort of KPI dashboard may help in terms of where it is heading or has come from?

  12. Gaznotprom says:

    Good work you 2 Mearns – again!

    Common sense (H/T Mr Andrews) would be not to close existing coal plants until alternatives are folded into and fully operational in the existing grid!
    Hasn’t happened and isn’t happening, that’s not in the plan…

    • Graeme No.3 says:

      As you say, good work by the 2 Mearns and it does show that the authorities are proceeding at different speeds on parts of their “plan” (unless of course the plan is to run the UK into blackouts, followed by the disappearance of any remaining industries.

      Perhaps then they will start asking for advice from people who actually know about these problems.

  13. Jonathan Madden says:

    Thank you Euan and Neil for a comprehensive and easy to digest summary of UK electricity. It shows how much benefit we would derive by contracting power from French nuclear plants scheduled for closure, combined with upgraded interconnections across the Channel, as per the recent tongue in cheek post by Euan. Hinckley Point seems just as uncertain as ever…

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