How Much Windpower can the UK Grid Handle?

This is a guest post by Roger Andrews. Roger is a British born, naturalised American mining consultant who is now semi-retired and lives on the West coast of Mexico where he spends some of his time sitting under a wavy palm tree blogging and drinking tequila.

In a December 2013 article in the Guardian Nigel Williams, head of electricity systems operations at the National Grid, was quoted as saying “I don’t see an upper limit to how much wind we can accommodate (on the grid)”. This was a curious statement for a grid operator to make because there clearly are limits as to how much intermittent wind power can be accommodated on a grid that continuously has to match supply to demand. But what are the limits for the UK National Grid? Here I will attempt to quantify them.

Methods and assumptions:

The basic procedures used were:

  • Download the 5-minute grid data for 2013 from Gridwatch
  • Apply generation mixes that contain progressively less coal, oil and gas generation and progressively more wind generation to these data.
  • Check whether 2013 peak demand would have been met had these generation mixes been in place in 2013 and evaluate other impacts of the generation mix change.

Using the actual 2013 numbers means that I did not have to make assumptions regarding future demand, power imports or how strongly the wind will be blowing X years from now. Running the generation mix cases, however, required the following assumptions regarding power generation, wind penetration and the “blackout threshold”:

  • Maximum Generation: According to the National Grid’s 2013/14 Winter Outlook the UK grid is presently capable of generating up to 60GW. (Although it may be optimistic. The demand peak of 56.7GW on January 16, 2013  came close to causing a blackout and with the capacity retirements since then probably would cause one if the same conditions repeated themselves now).
  • Generation Breakdown: About 50GW of the 60GW is generated by facilities that can be cycled to a greater or lesser extent to balance supply and demand during peak and off-peak periods (dominantly gas and coal with a small amount of oil, biomass, hydro and pumped hydro). The remaining ~10GW includes nuclear and wind and also power exports/imports, which often do not follow load.
  • Replacing Existing Generation: The 50GW of “peaking generation” is progressively replaced by wind power in the generation mix scenarios. The ~10GW of generation from other sources remains the same as in 2013. Increases in installed wind capacity are simulated by factoring 2013 wind generation upwards in proportion.
  • Merit Order: Wind generation displaces peaking generation until no more wind power is available, or until demand is met, or until the curtailment threshold is reached.
  • Curtailment threshold: Wind generation is commonly curtailed when it exceeds X percent of demand. I can find no data on X for the UK so I have assumed the 50% value used by the Irish grid for the generation mix options unless otherwise specified.
  • Spot price curtailments:  Wind curtailments caused by short-term changes in electricity spot prices in 2013 will be projected into the generation mix options.
  • Blackout threshold: Ofgem states that a 2.75 GW undersupply is the threshold above which “a large shortfall requiring the controlled disconnection of customers” could be expected. There were, however, several periods in December 2013 when the shortfall exceeded 3GW – briefly reaching 3.7GW on December 4th – without apparent ill effects (the shortfalls were caused by unusually large power exports to France and the Netherlands). I have therefore picked 5GW as the threshold above which blackouts will occur.
  • Supply/demand balance: The generation mix options balance supply and demand when sufficient power is available.

2013 Gridwatch data:

Figure 1 plots the Gridwatch data for Febuary 2013, a fairly typical winter month, for illustrative purposes:

Figure 1

The first graph shows demand ranging from around 30GW during off-peak hours to over 50GW during peaks (summer demand is approximately 10GW lower). The grid operates with a fairly consistent 0.5 to 1GW undersupply.

The middle graph shows the power generated by peaking facilities. Peak load cycling was performed mostly by gas but with a significant contribution from coal. Contributions from hydro and pumped hydro were minor.

The bottom graph shows the power generated by non-peaking sources, which consist of  nuclear, “other”, power imported or exported via interconnections, and wind. The most important contributor was nuclear. Overall more power was imported than exported but exports exceeded imports on a number of occasions.

During February 2013 coal supplied 44.2% of total UK generation, gas 26.8%, nuclear 18.7%, “Other” (hydro, pumped hydro, interconnections and “other”) 5.3% and wind 5.0%.

Now we will look at various options for expanding UK wind power utilization:

Replace peaking generation with enough wind capacity to replace the power lost:

Table 1 summarizes the impacts of progressively replacing peaking generation with as much additional wind capacity as is needed to replace the lost power. Wind generation is estimated by factoring up actual 2013 wind generation in proportion to the increase in installed wind capacity, which averaged ~10GW in 2013. “Blackout days” are defined by a demand shortfall of more than 5GW, as discussed above:

With this option less than 20% of the UK’s electricity can be supplied by wind before the lights begin to go out.

Figure 2 shows the impact of applying the generation mix in which peaking generation is cut from 50 to 35GW and installed wind capacity increased from 10 to 24GW, the point at which blackouts begin to occur, to the February 13 data. The “Other” plot in the generation mix graph shows actual 2013 generation from all sources other than peaking facilities and wind:

Figure 2

February 12th is the only February day with a shortfall exceeding the 5GW threshold – the other five occur in January and March – but there are another five days in February and 19 days in 2013 when the shortfall exceeds Ofgem’s 2.75GW threshold. Obviously the approach of simply replacing peaking generation with an equal amount of wind generation will not allow the large-scale adoption of wind power in the UK.

Replace peaking generation with wind, no limit on added wind capacity:

Table 2 summarizes the impacts of this option:

This option allows the UK to generate 50% of its electricity from wind and still meet 2013 peak winter demand, but 470GW of additional wind capacity is needed to do it, and at this level over 80% of the electricity the wind turbines are capable of generating gets curtailed.

Figure 3 further shows that admitting large amounts of wind power to the grid requires peaking facilities to be cycled at rates that would probably exceed rate-of-load-change limits. And even with 240GW of installed wind capacity there are still three days in 2013 (one in February) with an undersupply exceeding the Ofgem 2.75GW threshold. This option is clearly not viable either.

Figure 3

Import power during peak demand periods:

The UK wind regime is positively correlated with wind regimes elsewhere in Europe, meaning that when the wind is not blowing in the UK it likely will not be turning turbines across the Channel either. In this case everyone will be short of electricity and there will be no surplus power to import.

Store the wind power for re-use:

Battery storage seems to be a long way from large-scale commercialization, and a recent Stanford study concludes that the EORI of battery storage is too low to make it a viable proposition for wind power anyway. CAES, thermal, superconducting magnets and underground hydrogen storage seem equally distant. This leaves pumped hydro as the only alternative.

Estimating pumped hydro storage requirements is a complex exercise and I hesitate to present any firm numbers, but calculations indicate that storage on the order of hundreds of GWh – many times the present UK installed pumped hydro capacity of ~30GWh – would be needed to smooth out the wind power fluctuations in January 2013, the most “unbalanced” month. It is highly unlikely that this much additional pumped hydro storage could be built in the UK within a time-frame short enough to do any good if indeed it could be built at all.

Add wind but keep backup generation:

Under present circumstances this is the only option that allows the large-scale utilization of wind power while at the same time keeping the lights on. Wind capacity can in fact be added indefinitely if there is sufficient backup generation to meet peak demand when the wind is not blowing. As to how much backup is needed, the Table 1 and 2 results indicate that 45GW of peaking generation plus the ~10GW of nuclear and other generation that was on line in 2013 would be required. And with this backup generation in place the lights indeed never go out, but as shown in Table 3 wind generation becomes subject to progressively more curtailment as levels of penetration increase:

Compounding the problem is that at high levels of wind penetration there is a need for very rapid cycling of peaking facilities to balance abrupt changes in wind strength, while in periods when the wind is blowing most of the backup capacity sits idle. These effects are illustrated on Figure 4, which shows the generation mix that results from applying the 283GW of wind capacity contemplated in the DEFRA Level 4 scenario to the February 2013 data at a curtailment threshold of 75%:

Figure 4

The economics of this approach are also problematic. Wind power is effectively “free” (it has no fuel cost) so it makes economic sense to use as much of it as the turbines can generate and the grid can admit. On the other hand, another 200GW of wind capacity would cost over a trillion US dollars at the $5,600 installed capital cost/kw recently estimated by NERL for offshore wind turbines. As shown in Table 4 overall load factors also decline as more wind is added – to 22% with 100GW of additional wind capacity and to only 9% with 300GW of additional wind capacity. At such load factors the generation system would be inefficient to say the least, and while I have made no attempt to estimate generation costs it is reasonable to assume that they would be correspondingly high:

Finally comes the question of the impact of wind power on CO2 emissions. How large a reduction in CO2 emissions would be achieved if, say, half of the UK’s electricity was presently generated from wind? Approximately 75 million tonnes/year, representing about 17% of UK CO2 emissions and 0.2% of global CO2 emissions. It would be offset within about a month by increased CO2 emissions from developing countries at current rates of growth.

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31 Responses to How Much Windpower can the UK Grid Handle?

  1. Clive Best says:

    I also studied this and concluded that any expansion of wind capacity much more than 20% of total capacity makes no sense at all. Excess Wind energy is wasted outside peak demand and more fossil fuels are needed to balance demand when there is no wind than with a fossil fuel only grid.

    • Roger Andrews says:

      Clive: I read your post, which concentrated mostly on economic issues. I took a different approach by concentrating on security of supply issues to see if I could quantify at what levels of wind penetration the lights will begin to go out. It’s interesting that we came to pretty much the same conclusion.

      However, neither of us touched on the big problem, namely the continued retirement of fossil fuel plants under the EU Large Combustion Plant Directive, which no operator seems to be able to afford to comply with. I can’t get any firm numbers on the scale of the retirements but I’ve seen estimates ranging as high as 30GW by 2020. And if that much capacity gets retired the UK really will be freezing in the dark.

      I find it difficult to see how any government in full control of its faculties could have let things slide this far and still have no workable plan for solving the problem. Expressions like “fiddling while Rome burns”, “rearranging the deck chairs on the Titanic” and “shooting yourself in the foot” come to mind, but none of them does full justice to the situation.

      • Clive Best says:

        One of the biggest misunderstandings concerns The EU Large Combustion Plant Directive. This directive has nothing to do with carbon emissions or even coal for that matter. It is intended intended to reduce emissions of SO2, NO2 and soot from old power stations. Germany is building 19 new efficient clean coal power stations and the Dutch are opening another three modern stations – all are compliant with the directive. The UK could easily have done the same. Eon actually proposed to build a new clean coal plant at Kingsnorth in 2008 but FoE protests blocked it.

        No – the UK energy crisis is entirely self inflicted – you cant blame the EU. Government policy seems now to be driven by FoE because after the Kingsnorth fiasco they introduced a carbon floor tax to further penalise coal. Their policy now is that no new coal stations can be built without CCS. Neither Eon nor any other energy supplier will invest in CCS because it is uneconomic and have essentially halted any other new investment due to government interference. Kingsnorth has recently shut down with Eon have no plans for any replacement.

        • Roger Andrews says:

          It looks as if you’ll shortly be able to add Aberthaw, Didcot B, Cheshire, Conoco Phillips, Grimsby, Hythe, Stoke-on-Trent, Castleford, Sandbach and Thornhill. Another +/- 4GW of gas and coal down the tubes and no plans to replace any of it that I’m aware of.

          • Euan Mearns says:

            “Conoco Phillips” ?

          • Clive Best says:

            Oh and DRAX plans to burn 16 million tons of wood a year instead of coal ! WE can be proud that Britain is leading the world in returning to a pre-industrial society! Meanwhile the rest of the world choses instead to go for the cheapest and most abundant source of energy – coal. This from a recent IEA presentation.

            Coal is abundant and geopolitically secure. Coal-fired plants are easily integrated into existing power systems. No fuel draws the same ire, particularly for its polluting qualities both locally and in terms of greenhouse gas emissions. And yet no fuel is as responsible for powering the economic growth that has pulled billions out of poverty in the past decades.
            Over the next six years, additional coal production capacity of a half million tonnes per annum will be added worldwide each and every day. Coal prices are also falling. Coal price in ASIA is $4/mBTU whereas LNG prices are $16/mBTU – 400% higher.

            More than 60% of the rise in CO2 emissions since 2000 is due to burning of coal to produce electricity and heat. This rise in emissions is mainly occurring in ASEAN countries. In China, the scale of coal in the economy is simply incomparable to fuels elsewhere. Replacing coal with gas in Chinese power generation would require twice the volume of all global LNG trade. Coal therefore will continue to play an important role in economic growth and energy security worldwide for decades to come.

            If just the new coal plants under development in Asia were instead to be completed using latest technology it would save as much CO2 as all the wind turbines in Europe combined. Technical subsidies by Europe to achieve this would be a far cheaper and more effective means to tackle climate change than existing policies.

            Can you imagine an iron or aluminium smelter being powered by a wind turbine? We really would need extreme weather events then! The only non-carbon energy source that makes any sense at all is nuclear. The rest is dross.

            UK decarbonization policy and green posturing will do nothing to stop the rest of the world from doubling CO2 levels by the end of this century. Luckily though climate sensitivity is at most 2C so any impact will be fairly moderate. So instead of wasting 100s of billions on daft renewable energy we should instead be investing just 10% of that in a new cheaper generation of nuclear reactors. However, there is no chance of this happening until it is too late.

            Current energy policy seems to be driven more by spiritualisim than engineering.

      • Euan Mearns says:

        This is a reply to Clive’s comment about biomass. Globally, biomass is actually quite an important fuel in places like India and Africa and in the jungles of S America. But the minute you begin to try and power industrial society using it your forests disappear. This was the point we were at early 19th century in Europe and we started to burn coal instead. Davie and his Green cronies are on a headlong dash to take Britain back to the pre-industrial state if not the Dark Ages.

        It is utterly bonkers to import timber from N America to burn in Drax. I’d be interested to know how much FF is used to harvest and transport the timber.

  2. Hi Roger,

    Thank you for an interesting post. As I read your post, 50GW of wind with full backup would provide a quarter of UK electricity at a cost of 300 billion dollars. My guess is that other people’s money would run out long before 300 billion dollars.


    • Roger Andrews says:

      Dave: That sounds about right. For the trifling sum of $300 billion the UK can get 25% of it electricity from wind. And with a mere trillion dollars more and a little bit of luck it could get 50%. 🙂

  3. Joe Public says:

    An interesting set of analyses, Roger.

    There are two interpretations of Nigel Williams’ “I don’t see an upper limit to how much wind we can accommodate (on the grid)”. The practical aspect; and, the political aspect.

    I fear the greenie-brownie points trump the former.

  4. Interesting analysis – good to see some numbers put down. If we looked at wind just as a gas reduction tool and traded-off the capital cost of wind versus the cost of gas (+ operation and maintenance + carbon cost if applicable), we would likely get closer to the “true value” that wind provides, and get something closer to the most “efficient” level of wind (whatever that is) rather than relying on mandatory targets. Of interest is that the Australian Government has commissioned a review of the Renewable Energy Target (primarily wind), and the commentary suggests that the scheme may be wound back from the current 20% target.

    Re storage, EROI and penetration limits, I did some work on this for solar PV – storage puts the EROI below the useful threshold, although a small amount of storage can be useful for network support in a grid reliant on conventional generation. The same penetration issues arise, although embedded generation has different network issues.

    • Roger Andrews says:

      Graham: Whoa! Dozens of links in your comment – it will take me some time to go through them all. In the meantime I’m posting a reply to Euan’s comment on EROIs below which you might care to check out.

  5. Euan Mearns says:

    The Net Energy Cliff – one of the more famous charts I ever produced based on work of Nate Hagens and Charlie Hall. Should be self explanatory. As we move to the right there is less and less energy for society as the energy industries consume more. In monetary terms that translates to expensive energy – too many people involved in getting the energy for us. Multiple peer reviewed studies have shown wind has a decent ERoEI – but that is not the whole story.

    The electricity grid defines our society and the pattern of electricity demand is a mirror of how our society functions. Peak winter demand is more than double minimum summer demand in Scotland / the UK and the delivery system needs the flexibility and control to deliver that. Our society is founded on predictable energy stores, not random energy flows. We have a policy based on prioritising third class electricity that is also expensive. Third class can be converted to first class with the addition of storage. Storage is the elusive key. The energy, financial and environmental cost of storage needs to be added to wind, dragging its ERoEI to the right. The only storage show in town is pumped storage, and as I show in The Coire Glas pumped storage scheme – a massive but puny beast, even it is not scalable.

    PS I’ve never trusted the ERoEI for nuclear shown above, but it is based on a published meta analysis

  6. Roger Andrews says:


    ERoEI (or EROEI, or EROI, we really need to decide what to call it) was something I didn’t consider, the post being quite long enough already, and I doubt that the politicians who are presently formulating UK energy policy, if such it can be called, would be capable of comprehending it anyway. But while the ERoEI of wind power is high when it leaves the turbine it seems that it rapidly goes south when pumped storage is figured into the equation. There are some graphs showing how this might affect the decision to store or curtail wind power in the link below (sorry about the bit torrent) that you might want to look at:

    • Euan Mearns says:

      Roger, I don’t know where they get the ERoEI of 90 from. With a 20 year life cycle for a turbine (that may be optimistic) that implies that all the energy used to create the turbine and maintain it would be produced in the first 2.7 months of the turbine operation [(20*12)/90 = 2.7]. Does anyone believe that? If that were the case wind would be fabulously profitable and we would be rolling in energy and the surpluses so large that losing a bit on storage wouldn’t matter. That batch of weed that went round the Met Office must have made its way to Boston.

      • Graham Palmer says:

        Kubiszewski et al meta-analysis gives a favourable figure for wind of around 20. This assumes mostly a 20 year life, good capacity factor, no energy spillage, no storage.

        The issue of boundaries is a critical issue and a major problem for solar PV (which has guidelines established by the IEA-PVPS). The key I think is that intermittent sources do not replace conventional generation in the usual sense, hence it represents an additional cost to society (as this post shows). Hence a like-for-like comparison with dispatchable power makes no sense. I think it’s more meaningful to simply comparing the fuel savings (and abatement) to the capital cost.

        • Euan Mearns says:

          ERoEI of 20 for wind is about right, see my chart. But where do the Harvard boys get their number of 90 from?

          The UK needs to expand its primary energy production because energy imports are bankrupting the country but that is never talked about. Instead we have a juvenile energy policy called the “Climate Change Act” that is delivering absolutely nothing of value to society but is adding penalties by way of unreliable grid and rising energy costs (on top of already rising energy costs).

          My favoured solution is nuclear power. That maybe comes with higher costs, but it is reliable, and barring accidents, doesn’t wreck the countryside.

          • There’s a supplemental paper for the wind EROI here. I’d treat the Kubiszewski paper as more representative.


            Re nuclear, the UK has the option of expanding nuclear – Australia doesn’t have the same energy security issues – there’s another 500 years worth of open cut brown coal in my state of Victoria and without bi-partisan agreement to consider nuclear we’ll continue with brown and black coal, increasing wind, some solar, and gas. Our domestic gas prices are going to be more exposed to world parity pricing as export terminals open up for the coal-seam gas on the east coast so an expansion of baseload gas is looking less likely.

  7. Roberto Zavattiero says:

    the conclusion is obvious: wind power only benefit is to save some fossil fuel and not much of it, therefore the comparison on the cost of the kWh with the kWh generated by fossil or nuclear or hydro must be made ONLY with the fuel component cost that was wind power managed to save

  8. Nigel Wakefield says:

    I read an interesting article about converting excess electricity to ammonia (NH3) recently, though I cannot remember where. If I recall rightly the hydrogen came from electrolysis and the nitrogen was extracted from air.

    Ammonia can be stored very easily and used both as liquid transportation fuel and electricity generation fuel, . Sadly, the article did not comment on either of conversion efficiency or capital cost per unit of energy storage – from which I deduced that the former is low and the latter high.

    I suspect that if the the electricity storage conundrum is ever solved, it will likely be through conversion to relatively easily stored chemicals. I think very low capital costs (if achievable) would overcome relatively low conversion efficiencies (by which I mean 40-50% efficiency, which in itself may be a stretch).

  9. Luís says:

    In the EU states where wind is now over 20% of the electricity mix there has been a visible reduction in peak electricity supplied by fossil fuels. The introduction of wind automatically increases production from the hydro park at peak times, leading to a phase out of gas and diesel; coal and nuclear take the impact on a later phase. Ignoring this effect is crucial in the conclusions of this post.

    There is also a reduction in the costs of the electricity generated by hydro, since they run more, which is no where acknowledged.

    Finally, the capacity factors used are too low, probably referring to wind parks that are forced to halt production to protect the fossil fuel peakers. The last reference to a two thirds reduction in load factor with capacity expansion is also very dicey, especially when concerning off shore UK.

    • Roger Andrews says:

      Luis: Thank you for your comments. Here are mine:

      “In the EU states where wind is now over 20% of the electricity mix there has been a visible reduction in peak electricity supplied by fossil fuels.”

      Can you present some data to back this claim up? I can’t find any.

      “The introduction of wind automatically increases production from the hydro park at peak times, leading to a phase out of gas and diesel; coal and nuclear take the impact on a later phase.”

      The Gridwatch data show no correlation between wind and hydro generation during peak periods in the UK. Hydro contributes only about 1% of total UK generation anyway.

      “Ignoring this effect is crucial in the conclusions of this post.”

      According to the UK data the effect doesn’t exist, which makes it appropriate not to allow for it in the conclusions.

      “There is also a reduction in the costs of the electricity generated by hydro, since they run more, which is no where acknowledged.”

      I didn’t look into economics at all. But even if the claim is valid the overall impact would be negligible because of the minimal hydro contribution to total UK generation.

      “Finally, the capacity factors used are too low”.

      The capacity factors are what the data show. If there’s a problem it’s with my assumptions.

      “… wind parks that are forced to halt production to protect the fossil fuel peakers …”

      They are forced to halt production to protect the grid from overload, not to protect the “fossil fuel peakers”. Wind power takes precedence over fossil power at all other times.

      “The last reference to a two thirds reduction in load factor with capacity expansion is also very dicey, especially when concerning off shore UK.”

      I’m not sure what you are referring to here. Could you clarify?

  10. Graeme No.3 says:

    Nigel Wakefield:
    The short answer is no.

    The CSIRO in Australia is involved as well. (They seem to have been diverted to using the ammonia for carbon capture so expect nothing useful for some time).

    Another one trying;
    “aim is to produce “green” ammonia. By “green” he means produced using only renewable energy to separate hydrogen from oxygen in water molecules using electrolysis. (Ammonia is currently most often made using hydrogen stripped from methane or coal.) The “green” hydrogen would then be combined with nitrogen drawn from the air (which is 78 percent nitrogen) to form ammonia through the well-known and widely used Haber-Bosch process”.

    If electrolysis can’t compete with natural gas in generating hydrogen, then using this method is a guarantee of higher costs. NOTE that applies to continuous high pressure electrolysis at 75 -80% efficiency as against intermittent electrolysis at 45% efficiency (maybe). A 75% efficiency for storage and a 70% efficiency for energy recovery comes very close to doubling the cost of renewable energy.

  11. Leo Smith says:

    As the author of the Gridwatch site, I applaud the use you have made of the data: this was in fact one of the things I meant to use it for.

    I did in fact come up with a ‘adequate wind power to satisfy the whole grid even when the wind isn’t blowing’ scenario: it resulted in an average utilisation of less than 10% of the 600GW fleet, and would cost the consumer about £9.99 (around $16 per unit electricity).

    Current fossil fuel generates that at around £0.04p ($0.064)

    • Roger Andrews says:


      Well, thank you for providing your excellent site.

      Have you published your results anywhere? I’d be interested in seeing them, and I think others would too.

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