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How did the UK grid respond to losing a few nuclear reactors?

Posted on 30 September 2014 by Guest Author

This is a re-post from PassiiviIdentiteetti, written by Jani-Petri Martikainen.

Answer: mainly by increasing the use of coal in power production.

In the second week of August power company EDF decided to shutdown their reactors in Heysham and Hartlepool. This was a precautionary measure after finding a defect in the boiler of Heysham unit 1. In total 4 reactors that can produce up to 2.6 GigaWatts (GW) of electricity were turned off. On the week they were turned off, the UK used an average of 30 GW.

Some were quick to declare that wind power came to the rescue when nuclear power was proven unreliable (for example Ari Phillips in Thinkprogress, Greenpeace, Giles Parkinson in More recently Justin McKeating from Greenpeace repeated the claim: "...we see a reversal of the view that renewables need to be supported by nuclear power. Although nuclear and wind power do not have the same generation characteristics, nuclear reactors now needing to lean on renewables means the nuclear industry has a big problem." Given that the claim appears unlikely on meteorological grounds and no evidence for it was provided, I felt a more careful scrutiny was called for.

So, did wind power replace missing nuclear capacity? Short answer is, no it did not. Missing nuclear generation was mostly replaced by increasing use of coal.

In Figure 1 I show the output of relevant power sources in the UK between Saturday 8th August and Thursday 14th August. EDF reactors were ramped down during this period and this can be clearly seen in the figure. Equally clear is that when nuclear output was declining, wind power output was declining even more steeply. So rather than coming to the rescue, wind power was unfortunately galloping away when the action started. The reduction in the amount of wind and nuclear power was mirrored by a clear increase in gas and coal power. Contrary to earlier claims, low carbon sources were replaced by fossil fuels.

Fig 1: UK power production during the reactor shutdowns.

Fig 1: UK power production during the reactor shutdowns.

This quick check does provide the answer to our specific question, but with the data available we can learn more. In the following table I show the average power levels for the most relevant quantities shortly before and after the shutdowns. The most pronounced changes were in the amounts of power derived from fossil fuels, nuclear power, and wind power. There was also some increase in hydropower generation. Weeks following the shutdowns were in fact more windy (not unusually so) than weeks prior to shutdowns and power generation from fossil fuels has increased slightly. However, as the earlier figure makes clear, to understand which power source is replacing which one must look deeper than averages.

  Period 27th Jul-9th Aug [GW] 14th Aug-28th Aug [GW] Change [GW]
Demand 30.4 30.3 -0.1
Nuclear 7.9 6.0 -1.9
Wind 1.3 2.3 +1.0
Gas 12.4 11.5 -0.9
Coal 4.6 6.1 +1.5
Interconnects 2.6 2.6 0

To get a clearer insight as to how different power sources are connected in the UK, we can inspect the data for the year 2013. As an example, Figure 2 shows the scatter plot of wind vs. gas for one month period in 2013 together with a least square fitted line. When wind generation is high, gas generation drops by almost the same amount as wind power increased by. This fits with the idea that electricity companies use wind power to replace gas. The color indicates power demand at that moment. As demand goes up, the colour of the dots on the graph goes redder. This correlates with high gas use. In other words, when demand goes up, power stations burn more gas. There is no such correlation with wind power on short timescales: it's windier when it wants to be and that doesn't necessarily correlate with when we want to use the most power.

Fig 2: Scatter plot of the wind power generation vs. generation with natural gas for a month around April 2013. Color indicates power demand at that moment.

Fig 2: Scatter plot of the wind power generation vs. generation with natural gas for a month around April 2013. Color indicates power demand at that moment. Note: axes are unevenly spaced along y-axis relative to x-axis. Each dot represents a 5 minute period.

In the UK, wind power is attractive because the windiest months are in the dark and cool winter, when electricity demand is highest. However, the hour-to-hour or day-to-day windiness doesn't line up quite so well with UK power demand. The weather does what it wants. Although the weeks after the nuclear reactors went off saw a slight increase in total wind power from the weeks before, it didn't replace the lost nuclear power. Sadly, more coal was burnt to keep the lights on. If this happens again on calm, windless days, the UK would have to burn even more fossil fuels.

UK production and demand data suggest common sense relationships. Wind power acts mainly together with gas while missing nuclear reactors were (sadly) mostly replaced by burning more coal. In the long run it might be technically possible to do without coal. This could be done by using electricity storage like batteries or trading between countries, so that times or places where it's windy can export electricity to times or places when it's not. Changing power demand to match supply, so that power-hungry appliances and industries turn on when it's windy could also help. However, it will be some considerable time before wind power has the capacity to take the place of fossil fuels to meet our power needs.

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Comments 51 to 75 out of 75:

  1. keithpickering@1 "The problem with wind (and solar, for that matter) has always been how to back it up when the wind dies. Currently that's almost entirely gas, making wind a crypto-fossil energy source."

    Your analysis is incorrect or incomplete. You have included your solution in the analysis which is a poor start. If you do a correct assessment then the problem is variation in output of renewables, where the output may sometimes be greater than demand or at other times less than demand.

    OK now that we understand the problem then the solution must fill in those gaps when output doesn't meet demand and when we have to much output.

    The solution is energy storage and probably nuclear energy. Nuclear energy can't handle variation very well, France has to export it's electricity to cope with that like of flexibility. Energy storage is the real solution for filling the gaps.

    But also intelligent demand management can make a significant contribution. To often it is assumed that generation capacity should meet demand, but with modern technology it is possible to alter demand without sacrificing any degradation in the use of technology. It's called smart grid.

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  2. Paul, I don't think that's what Keithpickering has done at all. He made clear that gas is the current solution to intermittency. And it is: gas is what we currently use. It's all very well to say "The solution is energy storage and probably nuclear energy." And that is true. But only the latter actually exists and has been demonstrated in practice at the required scales. Unless and until energy storage, of what ever combination of technologies, can scale to national grid storage levels, intermittent renewables will continue to be balanced by gas. That's the reality we currently face.

    Nothing wrong, and quite a bit right, with demand shifting — as long as one accurately assesses its limitations and doesn't oversell its potential. 

    Energy storage is a huge problem. Solutions on the required scale do not exist and as far as I know, are yet to be identified. I mentioned the proposed large-scale Utah CAES system which, if used wisely actually could be grid scale on a state level, but again the question is geological availability — can it scale?

    What will be the availability of grid-scale electrochemical, fuel cell, and syn gas storage, their capacity and economics? There is a lot of research, but the inherent thermodynamics is not favorable compared with the size of the problem. (Won't stop me from driving an EV or plug-in hybrid, though.)    

    We also use hydro, but large hydro is pretty much tapped out, and I'm not sure many realize just how small large hydro really is. Hoover Dam was the world's largest concrete structure when completed in 1936. Lake Mead remains this country's largest man-made reservoir. Hoover Dam's 500 MW average output is slightly less than Vermont Yankee's 540 MW lifetime average; Hoover's 1.6 GW peak output is not quite San Onofre's 1.7 GW lifetime average. Small hydro, run-of-river hydro, really is small. Doesn't mean it can't make a contribution, but we musn't expect miracles.  

    Such is the scale of energy storage compared with the energy density of thermal generation. Wind oversupply is already a problem in some markets, notably Texas and Europe. It needn't be, but it is. Wind oversupply is in fact a big problem for nuclear for the reasons you identify. It is not technical, and there's no inherent reason (other than cost but that varies) not to overbuild wind. No. The wind oversupply problem exists purely as an artifact of the peculiar ways we have choosen to subsidize wind. Its all in our mind.

    In principle that can change, but as Ken has alluded, the problem is political: we gotta wanna. We gotta wanna sit down and agree upon our priorities. And if minimization of total carbon emissions at reasonable cost, starting with all the technologies we have today and extending to whatever future combinations we can come up with, isn't right at the top of the list, we're toast.    

    Somehow, I doubt we're in really large disagreement. Thanks for sharing.  

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  3. ed leaver

    Energy storage isn't so far away and it is probably the biggest expanding market now in energy.

    My personal favourite is PHES (pumped heat energy storage) which is cheap, scaleable, practical and uses todays technology. It will be a few years before it is commerical, but it is designed to work at grid level and as such is fit for purpose.

    The latest analysis shows it is likely to be as much as 90% efficient and cheaper than pumped hydro electric (30% of the cost). The first grid system is due to be tested on a substation in the UK in the Midlands, 2018.

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  4. We discussed some good energy storage solutions lately, including that of Isentropic PHES technology:

    There are solutions and there will be more if pressures exist to create them.

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    Moderator Response:

    [PS] fixed link

  5. Thanks Paul, Phillippe. I hadn't heard of isoenthalpic storage before; something new each day. Looks considerably more complex than adiabatic CAES, but the relatively low 12-bar pressure does hold certain attraction when siting the units. See how it scales, see how it goes. Good luck, and thanks for the links!.  

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  6. For the first time on an industrial scale, hydrogen produced using wind power is being injected into the natural gas grid in Germany. It’s a development that could enhance the value of wind power by making it useful no matter when it is produced.

    Problem solved... gas you can make via wind power and it is being done on a national scale in Germany.

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  7. ed leaver - Part of the intermittency solution, as I mentioned before, is more renewable sources. When the generators are spread over multiple weather patterns, intermittency due to weather decreases, and the average production of the grid as a whole moves closer to capacity values (Archer et al 2007). That isn't a 100% solution, of course, there will be some need for supplemental power at times, but the problem isn't as large as generally assumed. 

    An interesting and fairly recent study, NREL Western Wind and Solar
    Integration Study Phase 2
    , looks at 35% wind/solar penetration in the Western US. They found that cycling of the fossil fuel plants increased costs (maintenance) by $35-$157M, representing an added cost to wind/solar of ~$0.14–0.67 per MWh, but with fuel cost reductions of $28–$29/MWh. This mix also reduced ~30-35% of CO2 emissions, of course. 

    Storage will certainly have an important role to play, but even without storage and use of gas or other generators as fill-ins, large-scale renewable power appears to be a financially feasible option. 

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  8. Budischak et al provide data to suggest storage is not economic.  They say it is cheapest to overbuild renewables.  In their models building three times nameplate provides essentially 100% power.  Current hydrostorage plants were built to load balance nuclear power.

    Budischak et al do not use grid ties to other power systems or programs to reduce load on days when renewables are forecast to be low.  Both those strategies are currently used.  Budischak spill the excess power.  I expect that a use for excess power can be found.

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  9. At 400ppm CO2 we will experience increasing temperatures for the next 40 years until we reach equilibrium gloal warming of 1.8C above pre-industrial levels.  At this new equilibrium in 2055 the Arctic sea ice will have completely melted and the northern hemisphere will be largely snow and ice free by June 1 each year.  This albedo shift will produce a regional warming in the summer of over 8C above current averages.

    The IPCC AR5 report does not include this schedule in their analysis with most models projecting sea ice to remain perennial through 2065 and then reaching minimum in mid September.  Therefore their models severely underestimate the albedo forcing.

    The combined regional warming and albedo-driven warming will produce a massive decomposition of tundra.  This carbon cycle feedback is not included in the IPCC models.

    Over the next 100 years the CO2 equivalent emissions of arctic permafrost will far exceed the current U.S. cumulative annual CO2 emissions from coal-fired powerplants (about 1 Gt per year).  It is likely that total cumulative emissions from permafrost will be 200-500 Gigatonnes of CO2 equivalent emissions.

    What then to do if CURRENT atmospheric CO2 levels will bring about 4C of warming by 2100? 

    we can only survive this coming cataclysm if we start RIGHT now with an "all hands on deck" mentality of total resource mobilization.  This means the utilization of ALL potential non-fossil fuel energy sources (as well as transportation) AND the restructure of food production.

    Even then, we will be very hard pressed to remove 300 billion tonnes of CO2 from the atmosphere over the next 100 years.

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  10. Michael

    Budischak are using lithium batteries as the form of energy storage in their study and data from 2008. In contrast the links above to Isentropic are giving storage costs for that technology 1/4 the costs used by Budischak.

    This is a fast moving area and it would be interesting if they repeated their study for differing storage costs. I wonder how sensitive the over-build ratio is to storage costs?

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  11. Glenn,

    Budischak also found solar was cost effective for only about 5% of supply.  It strikes me that studies like this become rapidly dated and need to be redone.  Budischak was only offering a perspective, one that did not include storage.  Arguing that storage makes renewables too expensive is not necessarily true. 

    For our discussion I think we need to keep our minds open to a variety of options.  Price on a lot of strategies is rapidly changing and it is difficult to predict the winners now.  

    If nuclear can lower their costs with pre-approved designs it might become cost effective.  

    Until renewables are about 40% of supply on a regular basis it makes little difference, storage is not needed and backup is already built.  The change from 40% to 100 percent is where these issues become important.  Currently Holland uses the EU grid for renewable backup just as France uses the grid to off load excess nuclear at night.

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  12. Talking about "pumped heat energy storage" @53 and 54. 

    Take a close look at the video in the link @54. It seems to me there is something seriously wrong with the thermodynamics in these two (charge and discharge) cycles. In charging, the upper cylinders engage in adiabatic compression heating of the fluid, while the lower cylinders undergo an expansion/cooling power stroke. When the device is discharged, the upper cylinders undergo an expansion/cooling power stroke, while the lower cilinders must consume power to compress and heat the cold fluid. I don't think this adds up. 

    In addition, while a working fluid temperature change between 773 K and 113K (claimed in the video) would give a Carnot efficiency of 85%, the real temperature differences are between "ambient" (say 300 K) and 773 k for the hot fluid and 300 k and 113 K for the cold fluid, one being a compression and the other an expansion simultaneously.  I don't think this can possibly work, let alone give an efficiency of 90%.

    Does any of this pass the smell test?

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  13. tcflood

    The Isentropic system is based on the Brayton Cycle.

    Note particularly the sections on Closed and Reverse Brayton cycle. So the basic process is fairly standard. Also read the FAQ at Isentropic — this covers the question of the applicability f the Carnot Efficiency.

    During the discharge cycle the Carnot Efficiency applies to the conversion of heat to work. However during the charging cycle it is acting as a heat pump, a Carnot Refrigerator

    Carnot Efficiency for the discharge phase is (Thot - Tcold)/Thot

    So some of the heat flowing is extracted as work, the rest flows through to the cold store. Efficiency is less than 1.

    Whereas during the charging phase the Carnot Coefficient of Performance applies Thot/(Thot - Tcold)

    Work in plus some heat from the cold store is transferred to the hot store. CoP is greater than 1.

    It is because this is a cycle. If the system were perfectly reversible then they would get 100% of the energy they put in back out again. But because of irreversibilities they get less than this. Their performance claims are about the quality of the equipment and thus how close to true reversibility they can get. Carnot does not apply to that calculation

    This diagram might illustrate this:

    If all the processes are perfect, reversible processes then Win = Wout.

    It is only the irreversibility of the processes that leads to any losses.

    So yes, it does pass the smell test.

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  14. I find it surprising that apart from KR @25 nobody seems to stress the fact that the data is from such a short timescale and doesn't really answer the question of wether wind can cover for reduced nuclear. (Although the people stating that wind stepped in when nuclear failed is apparently wrong it's a very small question in the scope of it all, isn't it?)

    The market reaction to a short term energy shortage is not the same as the long term reaction to a long term energy shortage. If we shut down nuclear plants the short term market response might be the same, given insufficient time to adapt in advance but the long term response is given by which new form of energy is considered the most economically viable at the time. 

    For a better (more relevant) analysis i recommend looking at using a tool like MARKAL (, developed by the IEA, or simmilar and looking at the long term changes. An analysis like that would be truly worthy of SKS ;)

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  15. Gustafsson - I suspect that's because the topic, nuclear power, provided an opening for the general topic of nuclear power in a reduced carbon economy. As far as I know there aren't any specific threads for that. 

    Personal opinion: nuclear will certainly have its place. But given the failure of nuclear power to seize a large worldwide share over the last half century, and the general lack of solutions (economic and political) to nuclear ash and plant end-of-life, I have some doubts as to whether nuclear can present a really large scale alternative. We'll see...

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  16. Glenn @63

    Thanks. That helps a lot.

    Still, it looks like both the hot and cold storage reservoirs need a narrow region of thermal gradient bwtween the two isothermal zones. This seems to imply that 1) the system must be discharged as some point short of complete temperature conversion of a reservoir (limiting its storage time) and 3) prevention of widening of the gradient region might be a problem through numerous partial cycles.

    I realize this is getting off topic for this thread, but I don't know a proper thread and it seems important to me to have some idea of the reality of solutions to storage that are presented on the web.  

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  17. Some reflections: 1) Finland is highly technical developed and stable democratic society with a long history of running nuclear plants. If they can not build one nuclear plant on time and within budget, who will do it? Both investors and governments are likely to divert their money to other areas. 2) Are there any life cycle assesment of real (carbon) costs of nuclear energy, which includes mining, building (a lot of concrete) and long term waste disposal? A new study seems to be very favorable for renewables 3) The discussion here focus very much on production side of energy. As much as there is a need to vary energy production, what are technologies for smart changes in demand? If the wind is low during a day, how much can a combination of smart utilities and smart grid adsorb the need to lower demand? I think more out of the box thinking is needed.


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  18. tcflood@66 AFAIK the only limitation regarding storage time is 'leakage' of heat from the hot store and gain of heat from the surroundings in the cold store and that is down to how good the insulation is insulation. The storage medium is gravel and the gas used is Argon.

    This video might help:

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  19. A few minutes ago I heard that the French government has decided to reduce France's consumption of electricity from nuclear power from 75% to 50%. At the same time, France will be reducing its consumption of fossil fuels.

    Last week the new Swedish government announced policies that will lead to the shutdown of the aged reactors 1 and 2 at Oskarshamn, 1 and 2 at Ringhals, and stop Vattenfall's plans to build additional reactors there.

    Sweden has been building up its renewable infrastructure, and this year the nameplate capacity of Swedish wind power will exceed Denmark's.

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  20. Cosmicomics:

    Can you provide links to these claims?

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  21. Re. Sweden:
    Knockout til svensk atomkraft: Nye reaktorer droppes, og gamle må lukke
    (Swedish nuclear energy knockout: New reactors dropped, old ones to shut down)


    Sverige overhaler Danmark på vindkraft i 2014
    Sverige har færre, men større vindmøller og regner med at have mere kapacitet end Danmark, når året er omme.
    (Swedish wind power to pass Denmark's in 2014
    Sweden has fewer, but larger turbines, and expects to have more capacity than Denmark when the year is over)

    I haven't tried to find articles in English. The bit about Sweden passing Denmark would interest Danish readers, but probably not most others. Articles about the reductions in English could probably be found with appropriate search terms.

    Re. France:

    I heard the news on Danish radio yesterday, but here are some corroborating links: 1, 2, 3.

    I hope the links work (first time I've tried to do it this way) and that you find the information useful.

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  22. Cosmicomics,

    Thanks for the references.  It appears France announced that they are pulling back on nuclear last June.  I am surprised no one mentioned it before on this thread.  They have undoubtedly considered their neighbors successes and failures with renewables and the nuclear build they are currently doing in Finland.

    It looks like Sweden might be more of a political move  The Greens wanted nuclear out as part of an agreement to join the government.  Perhaps that could be reversed in the future if nuclear pans out.

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  23. michael sweet

    The new Swedish government was formed on 2 October. It's a minority government consisting of Socialdemokraterna (S) and Miljöpartiet (MP), the environmentalist party. The decision concerning nuclear power isn't directly to close the plants, but to make demands that will affect the profitability of some of the oldest plants, thereby causing them to close down.
    (I stedet for konkret at gå efter lukning af bestemte reaktorer kommer energiaftalens øgede sikkerhedskrav og forhøjede kerneaffaldsafgift fra 2,2 til 3,8 øre pr. kilowatttime ifølge Miljøpartiet til at betyde, at de fire ældste reaktorer lukker.)

    A spokesman for MP said that a parliamentary majority wouldn't be hard to find.
    (Det bliver ikke svært at finde flertal for det i Riksdagen, fortæller Miljøpartiets talerør, Åsa Romson.)

    The aim is to increase last year's renewable production of 18 TWh to 30 in 2020.
    (S og MP er blevet enige om, at mindst 30 terawatttimer (TWh) el i 2020 skal komme fra vedvarende kilder. Sidste år var det 18 TWh, og det nuværende mål er 25 Twh.)
    (Danish quotes from Knockout..., cited above.)

    In the French case the difference is that what before was intention has now become law.

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  24. In comment 28 I wrote:
    “The Danish Energy Agency recently found that onshore wind was the cheapest way for Denmark to generate additional electricity.”

    A new EU report has reached a similar conclusion:

    Onshore wind is cheaper than coal, gas or nuclear energy when the costs of ‘external’ factors like air quality, human toxicity and climate change are taken into account, according to an EU analysis.
    The report says that for every megawatt hour (MW/h) of electricity generated, onshore wind costs roughly €105 (£83) per MW/h, compared to gas and coal which can cost up to around €164 and €233 per MW/h, respectively.
    Nuclear power, offshore wind and solar energy are all comparably inexpensive generators, at roughly €125 per MW/h.”

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  25. For a brief time early this morning, Wind was the second largest contributor to the UK grid, and came within a whisker of being the largest



    (figures in GW)

    Obviously this is cherrypicking; demand at this time is at its lowest, and wind conditions appear to ideal for power generation at the moment. Nevertheless it does indicate that the UK grid can accomodate a substantial proportion of wind power. The interconnector to Holland was also fully importing, suggesting that mainland Europe also had an abundance of wind energy.

    Data from


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