On The Bonnie, Bonnie Banks o’ Loch Lomon’
I couldn’t resist using the first line of one of the most famous Scottish traditional songs, as the title of this post.
But a very significant power station project, is to be undertaken in the area.
These are the opening few sentences of the Wikipedia entry for the Loch Sloy Hydro-Electric Scheme.
The Loch Sloy Hydro-Electric Scheme is a hydro-electric facility situated between Loch Sloy and Inveruglas on the west bank of Loch Lomond in Scotland. It is also within the Arrochar Alps. The site was originally suggested as the location of a huge pumped-storage scheme in 1936 by Edward MacColl, but this was rejected as being uneconomic. After the North of Scotland Hydro-Electric Board was created in 1943, it became the first of their proposed schemes.
This Google Map shows Loch Lomond and Loch Sloy.
Note.
- Loch Sloy is in the North-West corner of the map.
- Loch Lomond is on the Eastern side of the map.
- The red arrow indicates the main buildings of the LochSloy Hydro-Electric Power Station.
- Loch Sloy is eight-hundred feet above Loch Lomond.
- The total generating capacity of the power station is 152.5 MW.
The facility is operated by Scottish and Southern Energy, and is normally in standby mode, ready to generate electricity to meet sudden peaks in demand. It can reach full capacity within 5 minutes from a standing start.
This second Google Map shows the power station to a larger scale.
Note.
- Loch Sloy is to the North-West of the North-West corner of the map.
- Loch Lomond is on the Eastern side of the map.
- The red arrow indicates the main buildings of the Loch Sloy Hydro-Electric Power Station.
- The four pipes carry water from Loch Sloy to the actual power station.
- The single-track West Highland Line crosses over the four pipes at their South-Eastern end.
The design of Loch Sloy Hydro-Electric Power Station is typical of many hydro-electric stations all over the world.
This third map is an OpenRailwayMap of the area.
Note.
- Loch Sloy is on the Western side of the map.
- Loch Lomond is on the Eastern side of the map.
- The yellow track is the single-track West Highland Line between Glasgow and Mallaig via Fort William
- The blue arrow indicates Ardlui station.
The railway goes close to the power station.
A Platinum Celebration for Sloy Power Station!
The title of this section is the same as this must-read web page on the SSE web site, which dates from 2020.
Sloy Power Station Development Plans
This second must read web page on the SSE web site is entitled Sloy Power Station.
This is the sub-heading.
We’re Proposing To Convert Our Iconic 1950s Hydro Station To Pumped Storage Hydro
This is the introduction to the development.
In April 2025, we submitted a planning application to the Scottish Government to convert the iconic Sloy Power Station into a pumped storage hydro scheme.
Our proposals would bolster energy security and help provide the large-scale and flexible renewable energy back-up needed in a future UK net zero power system, helping meet the UK Government’s ambition of Clean Power by 2030.
If approved for delivery, the converted Sloy scheme would be capable of delivering up to 16GWh of long-duration electricity storage capacity.
It could provide firm, flexible renewable energy for up to 100 hours non-stop.
It appears that the upgraded power station will effectively become a 160 MW/16 GWh long duration energy store.
Currently, the UK’s largest pumped storage power station is the 1727 MW/9.1 GWh Electric Mountain in North Wales.
The updated Sloy power station will have less output, but more storage capacity, than Electric Mountain.
Should There Be A Railway Station At Loch Sloy Power Station?
Google AI gives this answer in reply to “Loch Sloy Railway Station”.
There was never a permanent public railway station called Loch Sloy, but temporary private platforms like Inveruglas railway station and Faslane Platform railway station served the area. These stops were built in 1945 by the London and North Eastern Railway (LNER) to haul materials and workers—including prisoners of war—for the construction of the Loch Sloy Hydro-Electric Scheme.
Note.
- Surely, similar reasons to those in 1945 could apply to the development of the power station. Materials and workers could be brought in by rail.
- Given, the power station’s historic significance, I believe that it could become a tourist attraction and/or education centre.It could be a stop for the Caledonian Sleeper.
I believe that as time passes, the power station’s historic significance will increase.
Are There Any Other Hydro Power Stations, That Can Be Upgraded To Pumped Storage Hydro?
Google AI can’t find anything at present.
Earba 1.8GW Pumped Storage Hydro Project Secures Approval
The title of this post, is the same as that of this article on the Solar Power Portal.
These three paragraphs introduce the article.
Gilkes Energy has been awarded planning consent for its Earba Pumped Storage Hydro (PSH) scheme.
The Earba PSH scheme is set to be the largest project of its kind in the UK, with an installed capacity of 1.8GW and a storage capacity of 40GWh, meaning that it can provide 22 hours of storage at full power. The planning application for the project was submitted to the Scottish government in early March 2024.
The project will be located at Loch Earba in the Scottish central Highlands. Gilkes Energy states that this location was chosen because the area has an ideal combination of geology and topography, which the firm states will make it one of the most economically viable PSH projects under development in the UK.
In Gilkes Reveals 900MW Scottish Pumped Storage Plan, I said that Loch Earba was a 900 MW/33 MWh PSH scheme, but now it appears a it is 1.8 GW/40 GWh scheme, which will probably put it in the largest twenty PSH schemes in the world.
It will be one of four PSH schemes under development in Scotland.
- Coire Glas – 1.3 GW/30 GWh
- Loch Earba – 1.8 GW/40 GWh
- Loch na Cathrach (formerly known as Red John) – 450 MW/2.8 GWh
- Loch Sloy – 160 MW/16 GWh
In addition.
- Cruachan is being extended to 1 GW/7 GWh.
- Highview Power are planning to build two 200 MW/2.5 GWh of their liquid air batteries in Scotland.
Everything totals up to 5.1 GW/100.8 GWh, which compares with a UK electricity production as I write this article of just under 29.5 GW.
I wouldn’t be surprised to see some high-energy industries moving to Scotland because of all this renewable and hopefully reliable power.
SSE Files Plans For 100 MW Pumped Hydro Scheme
The title of this post is the same as that of this article on reNews.biz.
This is the sub-heading.
Proposal aims to convert iconic Sloy Power Station into storage facility by end of 2030
These three paragraphs outline the proposals.
SSE has submitted plans to the Scottish Government for the 100MW Sloy pumped storage hydro scheme.
The plans would see the existing Sloy Power Station – a conventional hydro power station – on the banks of Loch Lomond converted into a pumped storage hydro scheme with a pumping capacity of up to 100MW.
If given the green light, the converted Sloy scheme would be capable of delivering up to 16GWh of long-duration electricity storage capacity.
SSE intend to make an investment decision by late 2027 and this is said about increasing capacity.
As part of the planning application, SSE Renewables is also proposing to upgrade the existing 32.5MW G4 turbine to match its sister units, which would increase the station’s generating output by 7.5MW to 160MW.
This appears to be a world-class example of canny Scottish engineering.
The project would turn the current 152.5 MW hydroelectric power station into a 160 MW/16 GWh pumped storage hydroelectric power station.
Not a bad transformation, that was opened three years after I was born.
The UK’s Pumped Storage Hydroelectricity
This post is a simple list of the UK’s pumped storage hydroelectricity.
- Balliemeanoch – 1500 MW/45 GWh – In Development
- Coire Glas – 1500 MW/30 GWh – Under Construction
- Corrievarkie – 600 MW/14.5 GWh – In Development
- Cruachan – 1000 MW/7.1 GWh – In Operation
- Fearn – 1800 MW/37 GWh – In Development
- Dinorwig – 1800 MW/9.1 GWh – In Operation
- Earba – 900 MW/33 GWh – In Development
- Foyers – 305 MW/10 GWh – In Operation
- Ffestiniog – 360 MW/1.44 GWh – In Operation
- Loch Kemp – 600 MW/9 GWh – In Development
- Loch Sloy – 152.5 MW/25 GWh – In Operation
- Red John – 450 MW/2.8 GWh – Under Construction
Note.
- Cruachan is only 440 MW and is being upgraded.
- The storage capacity at Foyers may be wrong, as I can’t find my original source.
When fully developed the total will be 10969.3 MW/223.94 GWh.
Price Framework Paves Way For Vast Electricity Storage Scheme
The title of this post, is the same as that of this article on The Times.
This is the sub-heading.
SSE welcomes step forward in plans to build the £1.5bn Coire Glas hydroelectric project
These two paragraphs outline the article.
Ministers have provisionally agreed to a power pricing framework that could pave the way for more pumped storage hydroelectricity projects in Britain, including a gigantic £1.5 billion scheme from SSE that is starting to take shape in the Scottish Highlands.
The Department for Energy Security and Net Zero said it intended to develop a “cap and floor” pricing mechanism that would advance the Coire Glas storage project being developed by SSE, the energy company, and could unlock further pumped storage power stations.
Coire Glas will be one of the largest renewable power projects ever built in the UK.
- It will have a power output of 1.5 GW, which is comparable with some of the large wind farms in the North Sea or four gas-fired power station or Rolls-Royce SMRs.
- It will be able to store 30 GWh of electricity and provide 1.5 GW for twenty hours.
- Coire Glas has a web site.
- Coire Glas will more than double pumped storage hydroelectric capacity in the UK.
Bath County Pumped Storage Station in Virginia, US claims to be the world’s largest battery, but Coire Glas will be able to store more electricity.
You wait decades for one of these monsters to come along in the UK and SSE also have another on the way.
- Loch Sloy hydroelectric power station is the largest conventional hydroelectric power station in the UK.
- It has an output of 152 MW.
- It opened in 1950 and was largely built by German and Italian prisoners-of-war.
SSE plan to convert Loch Sloy power station into a pumped storage hydroelectric power station.
- It will be able to store 25 GWh of electricity.
- Loch Sloy will be the upper lake.
- Loch Lomond will be the lower lake.
- The existing dam, upper lake, pipes and powerhouse will be retained.
- The developments have a web page.
The project is aimed at a commissioning date of 2028.
This paragraph explains how the ‘cap and floor’ mechanism works.
In the scheme, operators would be guaranteed a minimum level of revenue, while consumers would be protected by a price ceiling, above which surplus revenue would be returned to them.
And these two paragraphs give SSE’s reaction.
Finlay McCutcheon, 46, director of onshore Europe at SSE, said the pricing framework was welcome news. He said that a deal for Coire Glas was needed by the end of this year to secure a firm investment decision by early 2026. Planning for the project started in 2007.
“Given the time taken to reach this point, much work is now needed to ensure an effective mechanism is finalised and put in place as early as possible to enable Coire Glas to take final investment decisions and move into construction,” he said.
I believe that the negotiations between the Government and SSE will lead to a monster on Loch Lochy and another one on Loch Lomond.
Conclusion
There are also these pumped storage hydroelectric schemes under development.
- Balliemeanoch Pumped Hydro – 1.5 GW/45 GWh
- Balmacaan Pumped Hydro – 600 MW/15-20 GWh
- Corrievarkie Pumped Hydro – 1.5 GW/14.5 GWh
- Fearna Pumped Hydro – 1.8 GW/37 GWh
- Glenmuckloch Pumped Hydro – 400 MW/1.6 GWh
- Loch Earba Pumped Storage Hydro – 900MW/33 GWh
- Loch Kemp Pumped Storage Hydro – 300MW/9 GWh
- Loch Na Cargeach/Red John Pumped Storage Hydro – 450 MW/2.8 GWh
These total up to 7.4 GW/100+ GWh.
This page on the Strathclyde University web site, gives these GWh figures for the possible amounts of pumped-storage that can be added to existing schemes.
- Errochty – 16
- Glasgarnock – 23
- Luichart – 38
- Clunie – 40
- Fannich – 70
- Rannoch – 41
- Fasnakyle – 78
- Tummel – 38
- Ben Lawers – 12
- Nant – 48
- Invermoriston – 22
- Invergarry – 41
- Quoich – 27
- Sloy – 20
That is a total of 514 GWh.
Scotland will be the Saudi Arabia of energy storage.
National Grid To Accelerate Up To 20GW Of Grid Connections Across Its Transmission And Distribution Networks
The title of this post, is the same as that of this press release from National Grid.
These four bullet points, act as sub-headings.
- Connection dates of 10GW of battery projects accelerated at transmission level, and 10GW of capacity unlocked at distribution level, both part of the Electricity System Operator (ESO)’s connections five-point plan.
- Battery energy storage projects connecting to the transmission network to be offered new connection dates averaging four years earlier than their current agreement.
- The accelerated 20GW equates to the capacity of six Hinkley Point C nuclear power stations.
- Work is part of ongoing collaborative industry efforts, together with Ofgem and government, to speed up and reform connections.
This is the opening paragraph.
National Grid is accelerating the connection of up to 20GW of clean energy projects to its electricity transmission and distribution networks in England and Wales as part of ongoing collaborative work across industry.
As I write this, the UK is generating 38.5 GW of electricity, so another 20 GW will be a large increase in capacity.
I shall look at what National Grid are proposing in sections.
10 GW Of Battery Power
These two paragraphs, outline the plan for 10 GW of battery power.
On its transmission network, 19 battery energy storage projects worth around 10GW will be offered dates to plug in averaging four years earlier than their current agreement, based on a new approach which removes the need for non-essential engineering works prior to connecting storage.
The new policy is part of National Grid’s connections reform initiative targeting transmission capacity, spearheaded by the ESO – which owns the contractual relationship with connecting projects – and actioned jointly with National Grid Electricity Transmission (ET), the part of the business which designs and builds the transmission infrastructure needed in England and Wales to plug projects in.
It looks to me that someone has been doing some serious mathematical modelling of the UK’s electricity network.
Fifty years ago, I provided the differential equation solving software, that enabled the Water Resources Board to plan, where reservoirs and pipelines were to be built. I have no idea how successful it was, but we don’t seem to have any serious water supply problems, except when there is equipment failures or serious drought.
But modelling water and electrical networks is mathematically similar, with rainfall, pipelines and reservoirs in the water network and power generation, transmission lines and batteries and pumped storage hydroelectricity in the electricity network.
I’d be interesting to know what software was used to solve the mathematical model.
I certainly agree with the solution.
Two of our modern sources of renewable energy; solar and wind are not very predictable, but cost a lot of capital investment to build.
So it is very wrong not to do something positive with any excess electricity generated. And what better place to put it than in a battery, so it can be retrieved later.
The earlier, the batteries come on stream, the earlier, the batteries can save all the excess electricity.
So moving the plug in dates for battery storage four years earlier is a very positive thing to do.
A simple calculation shows that for 10 GW, we would need nineteen batteries of about 526 MW.
Ideally, like power stations, they would be spread around the country.
Could Pumped-Storage Hydroelectricity Be Used?
The largest battery in the UK is the Dinorwig pumped-storage hydroelectric power station, which is commonly known as Electric Mountain or Mynydd Gwefru if you’re Welsh.
- It opened in 1984, after a ten years of construction.
- It has a power output of 1.8 GW.
- The energy storage capacity of the station is around 9.1 GWh.
Roughly, every gigawatt of output is backed up by 5 GWh of storage.
If the proposed nineteen new batteries have the same power to storage ratio as Electric Mountain, then each battery will have a storage capacity of 2.63 GWh
SSE Renewables are planning two large pumped-storage hydroelectric power stations in Scotland.
- Coire Glas – 1.5 GW/30 GWh – Possible completion in 2031.
- Loch Sloy – 152.5 MW/25 GWh – See SSE Unveils Redevelopment Plans For Sloy Hydro-Electric Power Station.
A quick calculation, says we’d need seven pumped-storage hydroelectric power stations, which need a lot of space and a handy mountain.
I don’t think pumped-storage hydroelectric would be feasible.
Could Lithium-Ion Batteries Be Used?
My mathematical jottings have shown we need nineteen batteries with this specification.
- An output of about 526 MW.
- A storage capacity of around 2.63 GWh
This Wikipedia entry gives a list of the world’s largest battery power stations.
The current largest is Vistra Moss Landing battery in California, which has this specification.
- An output of 750 MW.
- A storage capacity of 3 GWh
Reading the Wikipedia entry for Vistra Moss Landing, it appears to have taken five years to construct.
I believe that nineteen lithium-ion batteries could handle National Grid’s need and they could be built in a reasonable time.
Could Any Other Batteries Be Used?
Rounding the battery size, I feel it would be better have twenty batteries with this specification.
- An output of 500 MW.
- A storage capacity of 2.5 GWh
Are there any companies that could produce a battery of that size?
Form Energy
Form Energy are well-backed with an MIT heritage, but their largest proposed battery is only 10 MW/1 GWh.
They could be a possibility, but I feel it’s only a small chance.
Highview Power
Highview Power say this about their next projects on this page of their web site.
Highview Power’s next projects will be located in Scotland and the North East and each will be 200MW/2.5GWh capacity. These will be located on the national transmission network where the wind is being generated and therefore will enable these regions to unleash their untapped renewable energy potential and store excess wind power at scale.
Note.
- This is more like the size.
- Work is now underway at Carrington – a 50MW / 300MWh plant at Trafford Energy Park near Manchester.
- Highview’s technology uses liquid air to store energy and well-proven turbo-machinery.
- Highview have a co-operation agreement with Ørsted
They are a definite possibility.
10 GW Of Extra Unlocked Capacity
These two paragraphs, outline the plan for 10 GW of extra unlocked capacity.
On its distribution network in the Midlands, South West of England and South Wales, the additional 10GW of unlocked capacity announced recently is set to accelerate the connection of scores of low carbon technology projects, bringing forward some ‘shovel ready’ schemes by up to five years.
National Grid has already been in contact with more than 200 projects interested in fast tracking their distribution connection dates in the first wave of the capacity release, with 16 expressing an interest in connecting in the next 12 months and another 180 looking to connect within two to five years.
This page from National Grid ESO, lists the actions that were taken to release the extra grid capacity.
Conclusion
This looks to be a very good plan from National Grid.
Scotland’s 25 GWh Energy Storage Arriving By Stealth
In SSE Unveils Redevelopment Plans For Sloy Hydro-Electric Power Station, I introduced SSE Renewable’s plan to convert the UK’s largest hydro-electric power station into a pumped storage hydroelectric station, that can store 25 GWh of electricity and generate 152.5 MW of electricity.
After a public consultation in July, which unfortunately, I was unable to get to, SSE have now published a comprehensive document, which details their plans.
These are some points from the document.
- There will be no increase in the generating capacity of 152.5 MW, which is about half the size of a gas-fired power station.
- SSE designed a similar scheme for Sloy in 2009.
- Pumped storage systems need a lot of water. The Loch Sloy scheme has Loch Lomond.
- The development of pumped storage at Sloy would only require construction work to be carried out in the grounds of the existing power station.
- No permanent new works would be required at Sloy Dam or outside of the existing station boundary.
- A new above ground structure would be required which would contain a main hall with vehicular access, laydown areas, an overhead travelling crane, electrical switchgear and control systems.
- A new underground pump hall would be required to house two pumps. This would link to the intake structure and would be approximately 20m below the existing ground level.
- The existing tailrace to Loch Lomond, will be used to bring water to the pumps.
- Construction could start in 2025, with completion in 2027.
This redevelopment is a much less complex construction project, than building the original power station in the 1950s.
It also looks like the construction will not cause much disruption in the local area.
Hence my view, that this storage is arriving by stealth and won’t be noticed by those passing the power station.
After reading this SSE document, I wonder how many similar 1950s hydroelectric power stations have been upgraded to pumped storage stations in the last few years.
Also, if their Sloy scheme is successful, will SSE be looking for other hydroelectric power stations to convert to pumped storage?
This article on renews.biz is entitled Vattenfall Plans To Build 730MW Of Swedish Hydro Power, where this is a paragraph.
Vattenfall is also conducting a pilot study to investigate reinstating the Juktan power station on the Storjuktan lake adjacent to the Umeälven river in Västerbotten, to a pumped storage plant with a capacity of up to 380MW.
Note.
- Juktan power station was built as a pumped storage station and converted to a standard one.
- It has a web page.
- As the paragraph says it could be converted back!
So other companies and countries are thinking the same way!
Strathclyde University’s Prediction
This page on the Strathclyde University web site, gives these figures in GWh for the possible amounts of pumped storage that can be added to existing schemes.
- Errochty – 16
- Glasgarnock – 23
- Luichart – 38
- Clunie – 40
- Fannich – 70
- Rannoch – 41
- Fasnakyle – 78
- Tummel – 38
- Ben Lawers – 12
- Nant – 48
- Invermoriston – 22
- Invergarry – 41
- Quoich – 27
- Sloy – 20
That is a total of 514 GWh.
These figures must give SSE food for thought.
These new schemes are also being planned.
- Balliemeanoch – 1.5GW/45 GWh
- Coire Glas – 1.5 GW/30 GWh
- Corrievarkie – 600 MW/14.5 GWh
- Fearna – 1.8 GW/37 GWh
- Loch Earba – 900 MW/33 GWh
- Loch Kemp – 300 MW/9 GWh
- Loch Na Cathrach/Red John – 450 MW/2.8 GWh
These could bring the potential pumped storage in Scotland to 685.3 GWh.
ILI Group To Develop 1.5GW Pumped Storage Hydro Project
The title of this post, is the same as that of this article on the Solar Power Portal.
This is the sub-heading.
The pumped hydro facility will be located at Loch Awe, which is also home to Kilchurn Castle.
These paragraphs outline the story.
Clean energy developer ILI Group has begun the initial planning phase for a new pumped storage hydro project in Scotland.
The Balliemeanoch project at Loch Awe, Dalmally in Argyll and Bute will be able to supply 1.5GW of power for up to 30 hours. It is the third and largest of ILI’s pumped storage hydro projects, with the other two being Red John at Loch Ness and Corrievarkie at Loch Ericht.
The Balliemeanoch project will create a new ‘head pond’ in the hills above Loch Awe capable of holding 58 million cubic meters of water when full.
Note.
- At 1.5 GW/45 GWh, it is a large scheme and probably the largest in the UK.
- This is the third massive pumped storage hydro scheme for the Highlands of Scotland after SSE’s 1.5 GW/30 GWh Coire Glas and 152 MW/25 GWh Loch Sloy schemes.
- I describe the scheme in more detail in ILI Group To Develop 1.5GW Pumped Storage Hydro Project.
The article also has this paragraph.
It follows a KPMG report finding that a cap and floor mechanism would be the most beneficial solution for supporting long duration energy storage, reducing risks for investors while at the same time encouraging operators of new storage facilities to respond to system needs, helping National Grid ESO to maintain security of supply.
A decision on funding would be helpful to all the energy storage industry.
How Britain’s Biggest Natural Battery Can Help Deliver Net Zero
The title of this post, is the same as that of this article in the New Statesman.
This is the sub-heading.
SSE wants to double the nation’s flexible electricity storage capacity.
These two paragraphs introduce the article.
After previous delays and false starts, governments and businesses across the world are pushing towards the common goal of net zero. The energy sector is arguably the area with the biggest responsibility to work towards this target, and there is no time for complacency.
Ensuring clean, renewable energy sources such as hydrogen, wind and solar power become a larger part of the grid will be critical for the sector in its push towards net zero. A key facet of the clean energy drive will be having sufficient storage for each renewable power source kept in reserve, to be used as and when required as a crucial back-up mechanism. In last spring’s energy security review the government outlined its commitment to support long duration storage projects.
It is certainly very comprehensive and a must read.
This sentence illustrates the financial problem with pumped storage.
SSE is calling on the UK government to help it commit to building the Coire Glas storage facility by providing one simple policy decision that will send a clear signal as to how government intends to support the deployment of long duration electricity storage. The project doesn’t need subsidising, SSE states, but it would benefit from revenue stabilisation, and clarity on such support sooner rather than later.
Hopefully, this article will help get the required support.
Coire Glas
Coire Glas will have an output of 1500 MW and a storage capability of 30 GWh.
There is more information at the Coire Glas web site.
The project could be up and running by the early 2030s.
Loch Sloy Pumped Storage
The article also mentions the Loch Sloy Pumped Storage scheme, that has been recently announced by SSE.
I wrote about this 25 GWh scheme in SSE Unveils Redevelopment Plans For Sloy Hydro-Electric Power Station.
SSE haven’t announced much more about this scheme and it is not mentioned on the Sloy/Awe web site.
The Anonymous Widower 