Submitted by Bill Fernie
2nd October 2026
There was a time when building a huge hydroelectric scheme in the Scottish Highlands was regarded as a remarkable feat of engineering.
Dams were built, tunnels driven through mountains and lochs harnessed to produce electricity.
Some of those projects were enormous undertakings for their time.
Yet decades later, many are still working.
That raises an interesting question for Scotland today.
Could we be on the verge of building another generation of Highland hydro schemes, this time turning Scotland's mountains into Britain's giant electricity battery?
It is an idea that deserves rather more attention.
Scotland has done this before
Scotland already has a long history of using its landscape to produce electricity.
The hydro schemes built across the Highlands transformed remote areas of the country.
They brought roads, construction activity, employment and infrastructure, while creating electricity-generating assets that have lasted for generations.
This is perhaps one reason why the idea of another round of major hydro investment feels rather different from building yet another piece of short-lived infrastructure.
A dam, reservoir and tunnel can have a very long life.
The machinery can be replaced and the turbines can be upgraded but the basic geography remains.
The Scottish Government describes pumped hydro as a well-established technology with a long lifespan, and its assessment of the existing Cruachan hydro infrastructure assumes an operating life of 50 to 100 years for enhanced capacity.
That is infrastructure on a completely different timescale from most political decisions.
But this time the water works backwards
Traditional hydroelectricity is relatively simple.
Water stored behind a dam or in a reservoir is released downhill.
Gravity does the work.
The water turns turbines and electricity is produced.
Pumped storage reverses part of that process.
When there is surplus electricity on the grid, pumps use it to move water uphill into a higher reservoir.
When electricity is needed, the water is released downhill through turbines.
So the same water can effectively be used again and again.
It means that electricity generated by a wind farm at 3am on a Sunday morning does not necessarily have to be used immediately.
It can be stored until Monday morning when people are getting up, businesses are opening and electricity demand is much higher.
The mountain has effectively become a giant rechargeable battery.
And Scotland already has the technology
This isn't a futuristic idea.
Scotland currently has two operational pumped-storage hydro facilities with a combined capacity of about 740 MW.
Overall, Scotland had 27 operational electricity-storage projects by the end of June 2026, with total storage capacity of 1,663 MW. The pumped-storage schemes account for 740 MW of that total.
What is changing is the scale of what is now being proposed.
The Scottish Government says that, including projects awaiting construction, there is a pipeline of more than 10 GW of pumped-storage hydro projects at various stages of development.
That is potentially a very substantial addition to the electricity system.
And it is happening because Britain's electricity system is changing.
Wind creates the storage problem
Britain is increasingly dependent on renewable electricity.
That brings an enormous advantage: wind and sunshine don't have to be imported and don't require fuel to be burned.
But there is a problem.
We cannot tell the wind to blow when electricity demand rises.
Sometimes there can be enormous amounts of renewable electricity available.
At other times, particularly during periods of low wind, the system needs electricity from elsewhere.
Storage provides one way of bridging that gap.
Ofgem describes long-duration electricity storage as taking electricity when renewable generation exceeds demand, or when prices are low, and making it available later when demand is higher or prices rise.
That is exactly what pumped hydro can do.
Coire Glas gives us an idea of the scale
The most striking example is Coire Glas, on Loch Lochy in the Highlands.
The proposed project would have a generating capacity of 1,440 MW and at least 45 GWh of storage.
SSE says that at full output it could generate continuously for more than 30 hours.
The upper reservoir would hold up to 40 billion litres of water.
This is not simply an idea for the distant future.
Significant preparatory engineering work has already taken place, and Coire Glas is one of the projects being considered under Ofgem's new long-duration electricity storage support mechanism.
In June 2026, Ofgem provisionally selected a portfolio of 16 long-duration storage projects for support under the new scheme, designed to encourage investment in storage that can operate for much longer periods than conventional batteries.
The final decisions are expected later in 2026.
This could be another great Highland infrastructure project
This is where I think the discussion becomes particularly interesting.
We tend to assess major infrastructure projects by asking whether they are affordable today.
That is understandable.
But Scotland's old hydro schemes provide another way of looking at the question.
What if the appropriate timescale isn't ten years?
What if it is 50 years?
Or 100 years?
A pumped-storage scheme could involve enormous construction expenditure.
There would be dams, tunnels, reservoirs, roads, underground power stations, transmission connections and thousands of tonnes of material being moved.
But once built, much of the physical infrastructure could remain useful for generations.
That is precisely why the Scottish Government describes pumped hydro as having a long lifespan and regards it as nationally important infrastructure.
It could also create a second economic legacy
The original hydro schemes did more than produce electricity.
They created construction employment and infrastructure in parts of the Highlands.
Modern pumped-storage projects could do something similar.
Coire Glas alone has been described by the Scottish Government as representing more than £1 billion of investment, with more than 500 construction jobs anticipated and additional community investment.
And that is just one project.
The wider pipeline could therefore represent a considerable amount of engineering, construction and infrastructure work.
There could be opportunities for Scottish companies in civil engineering, construction, electrical engineering, transport, maintenance and specialist services.
And then there is the longer-term economic activity created around the infrastructure.
That is potentially much more interesting for Highland communities than simply looking at the number of jobs permanently employed inside a power station.
Could it benefit the landscape as well?
This is where Scotland's experience with hydro becomes particularly relevant.
There is a tendency to assume that major energy infrastructure automatically means an environmental loss.
Sometimes it undoubtedly can.
Large reservoirs, dams, tunnels and construction sites have impacts.
But Scotland's existing hydro infrastructure demonstrates that the relationship between major engineering and landscape isn't necessarily permanent environmental damage.
Some hydro landscapes have become part of the Highland environment and visitor economy.
The challenge with new projects will be to ensure that the environmental costs of construction are properly assessed and that local communities receive a lasting share of the benefits.
The Scottish Government already recognises that hydro projects can provide community benefits, and SSE has established a £10 million hydro community benefit fund covering communities around its existing hydro infrastructure.
So perhaps the lesson from the first generation of Scottish hydro isn't that every new scheme should automatically be approved.
It is that major infrastructure should be judged over the length of its useful life and by what it leaves behind.
There is, however, a bill to be paid
There is an important catch.
Pumped hydro is expensive to build.
And investors have traditionally struggled with the fact that the financial returns may take many years to justify the enormous initial investment.
That is why the UK has introduced the new cap-and-floor mechanism for long-duration electricity storage.
Under the system, projects receive protection against revenues falling below an agreed floor, while excess revenues above a cap can flow back to consumers through reductions in network charges.
In other words, there is a recognition that the electricity market may not on its own provide sufficient certainty to persuade investors to spend billions on infrastructure designed to last for generations.
That does not mean consumers get the infrastructure for free.
It means the cost and risk of building it have to be shared in some way.
And that makes the economic case particularly important.
The Caithness connection
For Caithness, there is an additional reason to watch what happens.
The county is already heavily involved in Britain's renewable-energy expansion.
Wind generation is one of the area's major energy stories.
But generating electricity is only one part of the challenge.
The electricity also has to get to where it is needed.
And increasingly, Britain needs ways of storing renewable electricity when it is abundant so that it can be used when it isn't.
That means the Highlands could potentially have two complementary roles in Britain's electricity system.
Generate the electricity from the wind.
Store some of it using the mountains.
That is a much more sophisticated energy system than simply covering the landscape with more generating capacity.
Perhaps we should think in generations, not Parliaments
There is something rather appealing about the idea of another generation of major Scottish hydro investment.
The engineers who built some of Scotland's great hydro schemes decades ago could hardly have known exactly how the electricity system would look in 2026.
Yet much of the infrastructure they built is still working.
Today's engineers face a similar challenge.
They have to make decisions about infrastructure that could still be operating long after today's political arguments have disappeared.
A pumped-storage scheme built today could potentially be producing and storing electricity in 2075.
Perhaps even in 2125.
That is a very different proposition from buying something that will need replacing in ten years.
And it changes the question we should be asking.
Rather than simply asking:
"How much will this cost us?"
perhaps we should also ask:
"What are we leaving behind?"
Scotland's first great hydro projects left behind electricity infrastructure that has lasted for generations.
The next generation could leave behind something different.
A network of Highland reservoirs, tunnels and turbines capable of storing the surplus electricity produced by Britain's renewable-energy system.
In effect, Scotland's mountains could become Britain's giant battery.
And, if history is any guide, that battery could still be working long after most of us who are debating the idea today are gone.
Coire Glas - SSE Renewables