The Coire Glas pumped storage scheme – a massive but puny beast

The Scottish Government has just given consent to utility Scottish and Southern Energy (SSE) to convert the Coire Glas into Britain’s biggest battery. Picture courtesy of Scottish hills.

I am instinctively in favour of pumped storage as a means of load balancing. The UK’s 4 existing pumped storage schemes were built to store surplus nuclear and coal base load power produced at night and to release this energy into the late afternoon peak in electricity demand. Coire Glas is different, designed to store surplus wind power produced when it is windy and to release that energy when it is not. It is a massive beast, but does it make any sense?

Vital statistics

Information is from this non-technical summary from SSE.

  • Generating capacity = 600 MW
  • Storage capacity = 30 GWh
  • Generating duration at capacity = 50 hours
  • Cost £800 million
  • 5 years to build
  • 150 workforce during construction
  • 12 permanent jobs

This is the equivalent of a large combined cycle gas turbine with capacity to run for a little over 2 days before needing to be recharged.

A massive but puny beast

The idea is to pump water into the reservoir when it is windy. The UK wind carpet recently produced 6GW peak output and so let’s assume that 3 of those 6GW were used to pump water into Coire Glas and other such schemes, and 3GW got fed directly onto the grid. If we are to have a renewables based system that can run independently of fossil fuel back up then it needs the stamina to survive a 7 day lull in the wind. So what we need to know is the amount of storage for 3GW of supply to run continuously for 7 days. This also assumes that we had 7 days producing 6GW of wind beforehand to fill the reservoirs – and we are still light years away from achieving that!

3GW * 24 hours * 7 days = 504 GWh of storage

That is 17 times greater than Coire Glas and 3 GW is only about 5% of UK peak demand. Coire Glas, therefore, is simply window dressing in efforts to “Green” UK power supply with pylons, turbines and dams.

There are different ways to skin this cat. How much power could Coire Glas provide operating continuously for 7 days?

2 / 7 * 600 MW = 171 MW

Which is also puny compared with the scale and cost of this structure and when compared with UK peak demand that is of the order 50,000 MW.

A partial solution

It may no doubt be argued that Coire Glas is only meant to be part of the load balancing solution which is fair enough. But what this means is that we are getting wind turbines, lots and lots of them, pylons and dams and still need to keep virtually all of the legacy fossil fuel plant going to provide back up power when the wind isn’t blowing. We are heading for an effective doubling of our energy infrastructure – Green irony!

Environmental considerations

SSE have conducted an environmental impact assessment. One question I had was about the impact of pumping water from and release of water into Loch Lochy and subsequent impact upon the flow of the River Lochy. The Coire Glas will be run in conjunction with other hydro schemes in the area to ensure stable water levels in Loch Lochy.

No free lunch in the energy world

My 2050 pathway, that I hope to present to this forum soon, currently includes 90 GW of nuclear power plus 4 GW of pumped storage that I envisage being deployed along the Great Glen in sites similar to Coire Glas. This scheme goes some way towards providing that – a good hedge for SSE. Pumped hydro for Nuclear requires more muscle and less stamina and so I wonder if the Coire Glas scheme could be adapted to provide 2400 MW for 12 hours? Turbulent times perhaps for Loch Lochy. Delivering 2400 MW for 12 hours every day seems much more valuable than 171 MW for a week – though I wonder if the battery could be charged in time?


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27 Responses to The Coire Glas pumped storage scheme – a massive but puny beast

  1. james philip says:

    I think that your viewing these green projects from the wrong perspective they are not capable of providing the energy that society as it is currently set up requires and that is not the goal.

    I think they are an insurance policy given a currency collapse, which makes imports of any kind prohibitively expensive, you know how dire domestic fossil energy production is.

    Put bluntly this project is designed to stop the nations sewers backing up, not to keep the lights on.
    As for nuclear difficult to see how it could function safely in the absence of fossil fuels, and sooner or later that is where we are going. (remember Hinkley C, if built, should still be operating in the 2080s and not finally decommissioned until 2200; if its safe today is not the point.)

    • Euan Mearns says:

      James, thanks for that perspective. I don’t buy into the self fulfilling prophecy that society as we know it is going to collapse and so we might as well make it collapse now so that our grandchildren (who would likely never get born or survive under the power down now scenario) don’t have to deal with a nuclear legacy they don’t understand. Humans and society are inventive and adaptable. I agree that we cannot or should not go on importing fossil fuel on credit and so something needs to be done. Renewables sound great until you see exactly what is required to make them scale to even a fraction of current energy use. I am a somewhat reluctant nuclear advocate but for the time being see that as the only option to maintain our society along with the schools, universities and hospitals.

  2. Kit P says:

    Not a very polite posting. It is filled with inaccurate words to evoke a emotional response. Puny, massive, beast! So let’s look at the facts.
    600 MWe is not puny. I keep my boat on a lake created by dam. The lake is more than 30 miles long. If you visit the power house you might call it massive. It has mass. Every thing has mass. City people surrounded ‘massive’ buildings hate the dams because they scar the environment. Actually it was glaciers and volcanoes that caused the scar. I happen to think where my boat is a very beautiful place. The water is 30 foot deeper thanks to the dam. Often large cooling lakes are created for thermal power crating beautiful places to live. Apparently people go out of their way to eat at a restaurant with a view of a coal plant. If you get a telephoto lens, you can take a picture of a coal pile making sure to leave out the obvious popularity of the lake. There are even million dollar homes built near the existing nuke plants. If fact, I think I would love to have a cute little cottage over looking the picturesque lake.

    • Euan Mearns says:

      Kit, I’ve pointed out to you before that there are horses for courses. I’ve been to Lake Havassu, Lake Mead and Lake Powel – you ever been to Scotland? Great works of engineering providing electricity, irrigation, flood control and recreation – either on the water or in Vagas. Scotland is a much smaller country. Now I accept that we can’t make our energy omelette without breaking eggs. So I think our landscape could put up with 4 to 6 large pumped storage schemes to provide load balancing service to an expanded nuclear fleet that would provide all our electricity. But I’m far from happy with the prospect of having 30 Coire Glas scale projects set alongside thousands of turbines to provide about 5% of our electricity. Now I know they are never going to build 30 of these things – we probably don’t have enough sites – so what’s the point in this one that will never be more than a partial “solution”.

      A lot of folks over here enjoy hiking in our beautiful mountains – including me. We do have a large number of very small hydro schemes by US standards. Sure the lochs they create provide recreation. But the salmon don’t like the dams much.

      • Kit P says:

        My point was that you are making an emotional argument rather than a logical one. Just for the record, I have yet to meet anyone who says things like ‘salmon don’t like the dams much’ who have actually made a serious study of a complex issue.
        So so you know there is a huge number of small hydroelectric plants and mountains to hike in the US.
        And pump storage:
        Smith Mountain Lake is the closest power plant to where we live now.

  3. bob Peckham says:

    hello Euan
    In your reference to your pathway to 2050 did you really mean 90
    GW nuclear, or 9 GW nuclear ?

    Apart from that I am really enjoying reading your posts, and the replies.

    Bob Peckham

    • Euan Mearns says:

      Hi Bob, Yes it was 90GW. The calculator is a bit clunky, offers 4 options for nuclear reactors that are rated at 3GW each – 0, 13, 30 and 50. So my approach was if we are going to have 13, might as well have 30. Electrify everything and its job done. Did my Christmas shopping today, so going to try and get this written up for next Friday. I always reserve the right to change my mind, but this should provide an interesting talking point. Glad you enjoying this, I am. And always open to reasoned debate. We have choices to make and one of the main ones is whether or not we are to have reliable and affordable electricity. Best Euan

      • Bob Peckham says:

        Hello Euan. Thanks for the reply re 90GW nuclear by 2050. At first glance it seemed to me somewhat unrealistic. I see now that you are using the DECC calculator. The trouble is the more I think about it the more unrealistic it seems! If you consider the problems of finding the sites for them, getting the planning consents, persuading investors to invest in them, not to mention time and cost overruns which have been the experience up to present.
        It is my impression that it is going to be extremely difficult to build any new nuclear stations on sites other than the existing nuclear sites – where people have accepted them. And Scotland (and probably Wales) have more or less ruled out any new nuclear sites. So it means you have to find in the order of 20+ new sites in England. Then I think – what is our present rate of construction of nuclear capacity? Maybe it is averaging out at barely half a GW per year if we are lucky. If we extrapolate that to 2050 it seems to me that we will be very lucky to get a total of 25GW Nuclear installed by then. Maybe you should choose the DECC option of 13 x 3GW as the biggest one which is remotely feasible.
        Sorry to be so negative. Looking forward to seeing your pathways anyway.
        Bob P.

  4. Roger Andrews says:

    A few miscellaneous musings:

    Hydro is presently the only viable option for storing large amounts of wind power.

    The vaunted Danish wind power industry in fact wouldn’t exist in its present form were it not for the hydro plants in Norway and Sweden, where the wind power generated in Denmark that the Danish grid can’t handle gets stored. (How much of total Denmark wind generation is this? It’s difficult to come up with hard numbers because of the complex workings of the Nordic grid, but I’ve seen estimates as high as 75%).

    But the storage doesn’t have to be PUMPED hydro. In theory surplus wind power can be “stored” simply by admitting it to the grid while throttling back on the water flow at conventional hydro plants, which means that all of the ~200MW of installed hydro capacity in Europe is potentially available for surplus wind power storage.

    But that’s in theory. As the noted philosopher Yogi Berra once said: “In theory there is no difference between theory and practice. In practice there is.”

    If the Coire Glas pumped hydro is dedicated to storing wind power then the cost of the pumped hydro should be added to the cost of the wind power. How much difference would this make? (Note that the capital cost estimate is almost certainly optimistic. Preliminary capital cost estimates almost always are.)

    There would be a lot of public opposition to a dam in Coire Glas, no? Is there anywhere in UK where you could build a dam without lots of public opposition?

    Here’s another pumped hydro proposal, but a lot more expensive:

    • Euan Mearns says:

      Roger, if you dig around in the annals of The Oil Drum you’ll find the second guest post i wrote there was linked to Danish wind being balanced by Norwegian and Swedish Hydro. The post was based on a report by an engineer called Hugh Sharman who has since become a good friend. The electricity trading system between the three countries was designed by a guy called Paul Frederik Bach – Google a bit and you’ll find him too.

      An important distinction needs to be appreciated comparing Norwegian and Scottish hydro. Norway is huge, gets lots more rain, has higher relief and has a small population. Norwegian hydro runs 24/365.25. Scottish hydro from memory has a load factor in the vicinity of 15% (could be wildly wrong there). So when the wind blows in Denmark, the Norwegians and Swedes shut off their hydro and use Danish wind. When the wind stops blowing, they open the sluices and export electricity to Denmark. I’m sure Scottish hydro is used in part to balance wind, but it doesn’t have the muscle or stamina to balance a growing UK wind carpet.

      • Roger Andrews says:

        Euan: I bookmarked Hugh Sharman’s report a couple of years ago, along with the Rebuttal” from 14 Danish wind power “experts” that promptly followed it. I’ve always had questions as to how two reviewers analyzing the same data can come up with opposite conclusions but this probably isn’t the place to ask them. 😉

  5. Hi Euan,

    Thanks for the post. 3p/Wh sounds a lot cheaper than batteries. I think of lead-acid batteries as being about 20 cents US/Wh. Better lifetime for the hydro storage also?


    • Euan Mearns says:

      Dave, interesting cost comparison. I’d like to see the size of the pile of batteries to deliver 30GWh @ 600MW. No one should get me wrong, I think the UK needs more storage and pumped storage is the the only show in town at present. Interestingly, SSE will make their investment decision in 2015 – after the Scottish referendum on continued membership of the UK. The SNP have a no new nuclear policy and so it wouldn’t surprise me if this scheme goes ahead but as a conventional nuclear battery.

    • Roger Andrews says:

      Here’s some stuff on battery storage vs. pumped hydro costs that may be of interest. No guarantees given as to accuracy.

  6. james philip says:

    I don’t think there is going be a collapse either, but I think growth is over and there will be a slow atrophy of our capabilities, that said when viewed over the scale of decades those capability loses will be significant. (I believe that finance may do extreme swings but they will stabilise over a couple of years)

    My position on nuclear prior to fukushima was identical to yours, but I thought I understood nuclear better than I in fact did. You are alas right regards the ability of renewables to replace so much as a fraction of our current energy. Hard choices, I think what I would like to see a real attempt to make efficiency gains before making a decision on nuclear and then I would want as little nuclear as humanly possible (even then there are forms of nuclear which are just a no no).

    Regards schools, universities and hospitals I know its a euphemism for the higher parts of society; but if you exclude heating what electricity does a school actually need a few Rasberry Pis and a few lights I think PV could handle that even in Aberdeen, Universities more power needs but not massively so unless its in hard sciences at postgrad level which is a part of system that is already atrophying. Hospitals so many variables. But all these things existed prior to electricity and would continue to exist in its absence, not that I believe it will be absent.

    Regards heating passivschule, woollen garments, both?

    Also thank you for pointing out gridwatch it demonstrates the problems of wind.

    • Euan Mearns says:

      James, economic growth is closely linked to population (the growth in the number of workers) and the cheap energy available to those workers to do work. Sprinkle some innovation, demand, energy efficiency, debt load etc. I view pensions and State handouts – education, healthcare etc, as the surplus net energy from our energy system. Without a big hose of reliable and “cheap” energy then economic growth will founder. It is the tax flow from economic growth that funds all government services – health, education, welfare etc.

      Strongly pro-nuclear pre-Fukushima I am less pro-nuclear now, especially in light of what we learned about pumps, spent fuel ponds and H gas explosions. Greed and compromise on safety. I assume that properly designed new generation reactors will be safe (fail safe?) and that a properly regulated authority will ensure the industry is run safely.

      The alternative for the UK is fairly rapid economic atrophy. And so there is a choice to be made.

  7. Steve Argent says:


    Extra pumped storage in Scotland will serve several purposes. One is to help manage the limited transmission capacity between Scotland and England. This is particularly a problem at weekends when electricity demand falls, but there is a risk of wind output (in Scotland) being high, resulting in bigger exports into England. If onshore wind output has to be constrained due to grid limitations, National Grid compensate the generators (so-called constraint costs). Such constraint costs have reached £1M per day in the past.

    Another benefit of extra pumpe storage generation is to provide voltage and stability to the Scottish grid when wind output (in Scotland) is low and demand is high, particularly when existing Scottish coal and nuclear generation closes over the next decade. (In this case, the limited transmission capacity between Scotland and England might otherwise require demand to be constrained in Scotland (on rare occassions)


    • Euan Mearns says:

      Steve, I agree that the UK / Scotland will benefit from more pumped storage and that Coire Glas is likely as a good a locality as any. The main question is where this is heading?

      when existing Scottish coal and nuclear generation closes over the next decade

      This is the strange / surreal bit. Scotland currently exports about 40% of the electricity we produce to England (from memory). Its great, we have bags of energy security, a diverse generating mix and a large electricity export industry. Who in their right mind wants to end that?

      • Steve says:


        The existing Scottish AGRs will probably close over the coming decade (subject to plant life extensions) and no new nuclears are envisaged in Scotland (for political reasons mainly). Cockenzie has already closed and Longannet is likely to close by 2023 due to IED requirements. Currently no new coal can be built without partial CCS. All other things being equal, developers generally prefer to build new generation nearer to main electricity importing regions in order to reduce transmission charges.

        • Euan Mearns says:

          Hunterstone B circa 800 MW
          Torness circa 1200 MW
          Longannet 2400 MW (currently co-firing biomass)

          All set to close with no real plan for replacement. We’re certainly going to have a carbon free electricity system – no electricity system at all 🙁 This is simply bonkers. We have to assume that Salmond loses the referendum and that we return to normal party politics where the interests and welfare of the population are somewhere on the political agenda.

        • Kit P says:

          Steve, how many offshore wind turbines will break and not be fixed in the next decade? Having excess wind power to store is a temporary problem if 100% of the wind turbines last only a decade. The nuclear industry is doing a very good job of making reactors last a long time. I am waiting for the wind or solar industry to start bragging about equipment lasting longer than the design life. Hell I am waiting for them to brag about performance at five years. The only reason to talk about what you expect or estimate is that the real data is very dismal.
          I am not against wind or solar. In the context of replacing coal or nuke plants that have provided customers years of service, you may want to check how long the equipment keeps working.

  8. Kit P says:

    “My position on nuclear prior to fukushima ….”
    All nuke plants in Japan exceeded design expectations for safety for a 1000 year event that was beyond the design basis of the plants. No one was hurt, that is what safety is about.
    Everything else is just economics. How much money do you spend protecting equipment (things) from unlikely events compared to replacing things if the event occurs. My house is insured for fire and wind damage. If a tornado comes we will hide in the basement. If a fire occurs we will wait across the street for the fire department.

  9. Roger Andrews says:

    It’s difficult to see how wind power will ever fill more than a small fraction of UK electricity demand if it can’t be used as a stand-alone source of baseload generation, which at present it can’t.

    This being the case the highest and best use of Coire Glas might be as a “demonstration” facility that converts ~1,500MW of unpredictable wind capacity with an average load factor of ~30% into 500MW of predictable baseload capacity with a load factor of 90% or better. This should be achievable if Coire Glas can deliver 500MW for 60 hours without replenishment (there won’t be many 60-hour periods when the wind isn’t blowing somewhere) and according to my crude back-of-the-envelope calculations it wouldn’t add all that much to the delivered cost of the electricity.

    But I could be way off base. Wouldn’t be the first time. Has anyone else done any work on this?

  10. Roy says:

    A few months ago a new pumped storage scheme got the go ahead in North Wales.

    Energy storage project approved on Snowdonia’s edge

    Like the existing Dinorwig pumped storage scheme it will be in a disused slate quarry but whereas Dinorwig can produce a 1,728 MW, the new one will be a lot smaller, producing 600 MW.

    • Euan Mearns says:

      Roy, thanks for info. Dinorwig is a massive beast, but can only run for hours. Given the wind capacity we already have, no doubt that more pumped storage will help smooth out the bumps on a diurnal basis. Store night wind for release into the afternoon peak, for example. But it still leaves us 100% dependent upon FF and nuclear back up.

  11. clivebest says:

    Wind power without energy storage makes no economic sense. A Phd thesis by Eleanor Denny clearly shows that once wind exceeds 20% of peak capacity than the costs outweigh any benefits. More gas is burned balancing wind with greater CO2 emissions than having no wind at all. Currently the UK has about 8GW total wind capacity which is about 16%. Doubling this capacity is economic madness unless the energy storage problem can be solved.

    It would be cheapest to store excess wind energy on site at the wind farm. One idea would be to charge up flywheels buried in the ground overnight but this would only work on timescales of hours. Other ideas would be to generate hydrogen from H2O or even generate methane with excess electrical energy on site.

    Euan is right that eventually only nuclear can generate enough energy to power a modern society including transport. However, we are being rail-roaded towards “decarbonization” for ideological reasons too soon and it will all end in tears. For the rest of this century we must rely on fossil fuels which can only diminish slowly. Perhaps unconventional gas and coal seem gas can see us through until fusion finally works. Otherwise it is back to neolithic living.

    • Euan Mearns says:

      Clive, flywheels sound expensive and can only be charged when the wind blows. Round trip efficiency of H2 is something like 30% I think – so we then need 3* the number of turbines.

      For the rest of this century we must rely on fossil fuels which can only diminish slowly.

      If the North Sea is anything to go by, parts of the FF supply may go down fast, like Gulf of Mexico, Brazil, Nigeria, Angola etc. I suspect coal is going to be off the menu because of health issues associated with it. Any reason we can’t live off fission this century? And still interested to learn more on the viability of fusion.

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