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Energy Storage Solution for the UK: Large Scale Pumped-Storage Site

Julian Hunt's picture
University of Oxford

Julian Hunt submitted his D.Phil (PhD) thesis to the Department of Engineering Science at the University of Oxford in January 2013. During his D.Phil he developed a decision support system called...

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Storing energy is an endeavour that has come to the attention of various research groups and companies. New technologies such as the hydrogen fuel cell and graphene ultracapacitors are being developed but are not technically mature. Other companies such as Siemens are developing prototypes for decentralising energy storage which might work for small scale systems. However, around 99% of all bulk generation capacity based on storage schemes, equivalent to 130 GW, comes from pumped-storage due to its low cost and high energy conversion efficiency (70% to 80%).

Energy is stored so that the excess electricity supply from intermittent technologies such as wind and solar can be consumed at different times. Nuclear reactors can operate at full capacity at night when the demand for electricity is low as the energy is stored. For example, around 9% of Japan’s electricity generation capacity is pumped-storage as Japan once relied heavily on nuclear power.

Most people have assumed that the UK does not have enough feasible pumped-storage potential for a renewable energy revolution to take place. Wind energy in Scotland is abundant and given its high speed and frequency it is arguably one of the cheapest sources of energy in the world. However, the problem of intermittency is the biggest challenge for the wind power sector as electricity has to be generated when there is demand for it and, unfortunately, the wind can blow at dawn when there is low demand for electricity and stop blowing when people wake up to start the day.

It turns out that the lower reservoir of a pumped-storage site can be a drained lake and the drained water can be used to increase the height of a new upper reservoir. This is the case of Loch Morar, the deepest loch in the UK with a depth of 310 metres. If a 280 metres high and 1.8 km long dam is built on the surrounding highlands, an upper reservoir with a water level of 300 metres above sea level can be created. As the water is drained from Loch Morar its altitude could reach as low as -300 metres. This results in a height difference of 600 metres between the two reservoirs.


This pumped-storage site would have the capacity to store 1,300 GWh of energy, which is equivalent to 1.2 days of electricity consumed during the winter in the UK and 1.7 days of the electricity consumed during the summer in the UK. The generation capacity installed, however, would vary with the amount of wind turbines and nuclear power plants available. Perhaps, 15 GW generating capacity could be installed until 2020 and 30 GW until 2050.
A first cost estimate for this pumped-storage site with 15 GW of pumped-storage capacity is around £12B, which is cheap given the amount of energy it can store. This estimate, however, could considerably increase if there is the need to create an impermeable layer for the upper and lower reservoirs to reduce leaks. In addition, the transmission costs required are relatively high and will increase the project’s final cost.
The availability of cheap energy storage will allow investment in the UK energy sector, especially the wind industry. This site can store energy from wind turbines in the UK and Ireland or from the excess energy generated at night from nuclear energy, coal with carbon capture and storage, and geothermal if a transmission line connecting Iceland and the UK is built.
This is a big and challenging project, but the technology is available and it would allow the UK to take up a strategic position in the area of energy generation.
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I K's picture
I K on Mar 24, 2013

Whoever told you that site can store 1,800 GWh is barmy. You are looking at 200GWh which is considerably lower

Its 2.3km3 volume of water = 2.3 x 10^12 kg
Mean Depth: 87 meters

If you are proposing to move that to an artificial reviver 300 meters above it, with say the same mean depth. (so the water moves an average 300+87+87 = 474 meters)

E = 2.3 x 10^12 x 9.8 x 474 = 10.7 x 10^15 joules
1GWh = 3.6 x 10^12 Therefore 297 GWh total

And that is a MAXIMIUM figure if you drain every drop and have no loss in turning that potential energy to electrical energy. A more realistic figure where you pump 75% of the water up/down and suffer 10% electrical loss would yield you a “battery” of about 200GWh. Only about 3 hours of peak winter demand.
So if you wanted 100 days of storage you would need 500 of these sites. If your cost of £12B each is correct thats £6 trillion of british pounds, only about £220,000 per household in the UK.

There is another way you can do it, not that site but plenty of sites available and you are looking at 500TWh storage.....not cheap but maybe possible for $500B.

Roger Faulkner's picture
Roger Faulkner on Mar 26, 2013

Do not forget that Loch Morar is a real live lake with an ecosystem that would be devastated by regular changes in level that are as great as you state. And I agree with IK that you apear to have made a big mistake as well. I myself have proposed pumped storage operating between two Great Lakes in North America (Lake Erie is 100 meters above Lake Ontario; Niagara Falls is between them). I calculate for that case that one could store 1300 GW-hours if the smaller of the two lakes (Ontario) is allowed to shift its level by at most 30 cm per cycle (less than the average annual depth variation, which is about 45 cm). Even that much of a change in level is bad for some shoreline habitat (though I think that could be mitigated for such a small swing in lake level). What is unique about the proposed Niagara Pumped Storage (NPS) scheme is that it could operate for 130 hours in output mode, so if connected to a North American supergrid NPS could balance out wind variability on a three week time cycle (aggregated wind over North America shows variability on several time scales, including a strong 3-week variation period, related to jet stream phenomena I do not really understand).

But of course this is politicaly impossible at the moment.

I K's picture
I K on Mar 26, 2013

Plus the need for storage is overplayed.

For instance in the uk you could go to about 50 percent of our electricity needs with offshore wind without building additional storage capacity. 

47GW of offshore wind woukd produce half our 330TWh need. That amount of wind would almost never exceed 40 GW which is a figure the national grid can handle. 

A worse case sinario wouod be a very strong wind producing  40GW during a sumner night when demand plus export capacity tops out at 30GW. The excess 10GW can be b dumped into storage heaters or you can just switch off 10GW of wind.  That diesnt soubd good but yiu are prbably looking at less than 1 percent of tge time yiu would need to do that.  Far easier and cheaper than building hundreds of pumped storage sites. 


Oh this assumes no nuclear in our grid. The wind figure would be a lot less with nuclear. Obviously trying to derive more than 50 percent gets exponentially difficult. Using onshore or solar would be a lot more difficult

Julian Hunt's picture
Julian Hunt on Mar 26, 2013
Hi I K,
Thanks a lot for your reply.
I really like your approach for estimating the amount of energy stored! It will save me a lot of time in the future.
However you missed a 0 in your calculation. 
(10.7 x 10^15) / (3.6 x 10^12 ) = 2,972
Your estimate, which was relatively good, gives 2,972 GWh, not 297 GWh.
The estimated 1,800 GWh assumes 75% overall efficiency, a dam 350 m high (not 300 m high), a variation of 100 m in the upper reservoir and was calculated with the actual height of the reservoir, taking into account the level variation on both reservoirs. This was done in excel and the calculations assumed 10 m intervals based on the variation of the upper reservoir.
The estimation for a 300 m high dam is 1,325 GWh. I am sorry for the confusion.
I would be very interested to hear more about your other sites!
I K's picture
I K on Mar 26, 2013

Hi Julian,
Sorry it does look like I missed a 10

At that site you would find it hard to draw more than perhaps 10% of the total mass to use because if you tried to take 100% of the water, as that other poster noted you would blend every living critter in the lake. 10% may even be too much to take but that would put the figure down to something closer to 130GWh

Anyway there is no need for that site. You can just use the north sea, or Irish sea.
Find a  section say 200 meters deep and build a circular barrier say 10km in radius and ~200 meters thick. Pump out the water in the middle to store your excess energy, let the sea flow back in to generate electricity

Lets say you engineer it so you can fill the centre upto 150 meters from the bottom so you give a minimum head of 50 meters which will be sufficient pressure

Mass = pi R squared x height x 1 tonne per cubic meter = 4.71 x 10^13kg

E = M x g x H = 4.71 x 10^13 x 9.8 x 125 = 5.77 x 10^16

1,6000 GWH storage

Or better yet build a 100km radius version, would yield 160,000 GWh of storage.
Plus it is on the doorstep to all those future planned offshore wind farms so you would not need many extra connections. When the wind does not blow the site generates power and feeds it through the idle wind cables.

Of course any sane person will consider a 100km radius hole in the ocean farcical and in a way it is. It just goes to show you how huge a volume of water you need to store bulk long term energy. 160TWh is a lot but still only about 6 months average demand in the UK.

The good news is, it wouldn’t be that difficult to build. You just dredge the ocean floor for sand/stone and pile it up to form a barrier. But again....a spectacle viewable from space..... cant see it it every happening.

Also as noted you don’t really need that much storage for offshore wind. You can generate upto around 50% of UK needs from offshore without building more storage.

Julian Hunt's picture
Julian Hunt on Mar 27, 2013

Hi I K,

Your idea sounds good. The main problem would be to build the circular barrier. It would be extremely expensive.

The reason why pumped-storage is viable is because the reservoirs are already in place.

An alternative to your idea is to use sea water pumped storage as shown in:

A major problem is that you wouldn’t find many manufacturers building turbines that runs on salt water.

Maybe we can start our own company and manufacture them. We would make a lot of $$$ :)

Julian Hunt's picture
Julian Hunt on Jun 2, 2015


Hi Scottish Scientist!

I m glad to learn that there are sensible people out there that understand the benefits of large scale pumped storage.

Thanks a lot for you kind compliments and interest in the Loch Morar Project!

Please send me your email to and I will send you an presentation on the Morar Project and will send you an even better, cheaper and with considerably less environmental impact project. This project is in Loch Maree and could store cheaply around 980 GWh.

Please feel free to add it to your blog after I send you!

Apart from the Loch Maree project, I have patented a technology named “Enhanced-pumped-storage” and published in the energy journal. It is almost becoming a reality in Brazil!

Thanks again for your kind worlds and let’s push these projects forward  and contribute to a real change!

Best wishes,


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