The Anonymous Widower

Repurposing The Tummel Hydro-Electric Scheme

The Tummel hydro-electric scheme was built in the 1930s and 1950s, by the North of Scotland Hydroelectric Board.

  • The scheme is now owned by SSE Renewables and has a page on their web site.
  • There are nine individual power stations; Gaur, Cuaich, Loch Ericht, Rannoch, Tummel, Errochty, Trinafour, Clunie and Pitlochry.
  • There are four dams; Gaur, Errochty, Clunie and Pitlochry.

This map from the SSE Renewables web site shows the layout of the dams and power stations.

This description of the scheme is from Wikipedia.

The Tummel hydro-electric power scheme is an interconnected network of dams, power stations, aqueducts and electric power transmission in the Grampian Mountains of Scotland. Roughly bounded by Dalwhinnie in the north, Rannoch Moor in the west and Pitlochry in the east it comprises a water catchment area of around 1,800 square kilometres (690 sq mi)[1] and primary water storage at Loch Ericht, Loch Errochty, Loch Rannoch and Loch Tummel, in Perth and Kinross. Water, depending on where it originates and the path it takes, may pass through as many as five of the schemes nine power stations as it progresses from north-west to south-east. The scheme was constructed in the 1940s and 50s incorporating some earlier sites.


  1. There are no underground power stations.
  2. The scheme is what is known as a run-of-the-river hydroelectric scheme.

The sizes of the power stations in the scheme are as follows.

  • Gaur – 75 MW
  • Cuaich – 2.5 MW
  • Loch Ericht- 2.2 MW
  • Rannoch – 44 MW
  • Tummel – 34 MW
  • Errochty – 75 MW
  • Trinafour – 0.5 MW
  • Clunie – 61 MW
  • Pitlochry – 15 MW

This gives a total power of 309.2 MW.

This Google Map shows the same area as the SSE Renewables Map.


  1. Dalwhinnie is at the North of the map.
  2. Gaur is in the South-West corner of the map.
  3. Pitlochry is in the South-East corner of the map.

There are no underground power stations.

Strathclyde University And Pumped Storage Power For Scotland

This page on the Strathclyde University gives a list of the pumped storage potential for Scottish hydrogen-electric dams and power stations.

These figures are given for the dams and lochs in the Tummel scheme.

  • Errochty – 16 GWh
  • Clunie – 40 GWh
  • Rannoch – 41 GWh
  • Tummel – 38 GWh

It would appear that based on research from Strathclyde University, that the Tummel scheme could support over 120 GWh of pumped storage.

Water Flows In The Tummel Scheme

Looking at the SSE Renewables map of the Tummel scheme and reading this section in the Wikipedia entry for the Tummel scheme, which is entitled Water Route, water flows appear to be as follows.

  • Loch an t-Seilich to Loch Cuaich
  • Loch Cuaich to Loch Ericht via Cuaich power station and the Cuaich aqueduct
  • Loch Garry to Loch Ericht via Ericht power station.
  • Loch Ericht to Loch Rannoch
  • Loch Eigheach  to Loch Rannoch via Gaur power station
  • Loch Rannoch to Dunalastair Water via Kinloch Rannoch weir
  • Dunalistair Water to Loch Tummel via Tummel power station
  • River Bruar and River Garry to Loch Errochty
  • Loch Errochty to Loch Tummel via Errochty power station
  • Loch Errochty to Trinafour power station
  • Loch Tummel to Loch Faskally via Clunie power station
  • Loch Faskally to Pitlochy power station


Water from Loch an t-Seilich can take various routes to Clunie and Pitlochry power stations.

Water from Loch Eigheach goes through Loch Rannoch, Dunalistair Water and Loch Tummel to Clunie and Pitlochry power stations.

It seems a complicated scheme but it does have a capacity of 307 MW, which compares with 389 MW of Bankside power station.

Refurbishing And Repurposing The Tummel Scheme

Perhaps as the power stations are now over fifty years old, one simple way to increase the generating capacity of the Affric/Beauly scheme  might be to selectively replace the turbines, with modern turbines, that can generate electricity more efficiently.

I suspect that SSE Renewables have an ongoing program of improvements and replacements for all of their hydro-electric stations in Scotland. Some turbines at Sloy power station have already been replaced with larger ones.

In The Affric/Beauly Hydro-Electric Scheme, I wrote about the control system needs of that scheme, which I felt could be fairly challenging.

I suspect the control of the Tummel scheme is equally challenging.

Adding Pumped Storage To The Tummel Scheme

I’ll look at each possibility in turn.

Loch Errochty

Strathclyde University estimated that 16 GWh of pumped storage could be added to Loch Errochty.

This Google Map shows the Eastern end of Loch Errochty.

Note the dam at the Eastern end of the loch.

  1. The dam is 354 metres long by 49 metres high.
  2. The dam was built in 1957 and the lake is man-made.
  3. The loch stands at 330 metres above sea level.
  4. Water flows from the loch to the Errochty power station at the Western end of Loch Tummel, through a ten kilometre long tunnel.

This Google Map shows Errochty power station and Loch Tummel.


  1. Errochty power station is at the top of the map in the middle on the channel connecting it to the River Tummel.
  2. Errochty power station has two turbines and a maximum output of 75 MW.
  3. There is what appears to be a large switching station at the Western side of the map.

I obviously don’t know for sure, but I suspect this could be an easier scheme to convert, if the current turbines could be replaced with pump/turbines.

There is a section with the title; Water Supply To The Loch in the Wikipedia entry for Loch Errochty, where this is said.

Loch Errochty’s main feeder streams are the Allt Sléibh and the Allt Ruighe nan Saorach which both rise in the high ground to the west of the head of the loch. Other small streams flow directly off the 892-metre-high (2,927 ft) mountain of Beinn a’ Chuallaich which stands just to the south. Supplementary water is diverted into the loch from the east by the Errochty catchwater, a system of tunnels and surface pipelines at a height of approximately 380 metres which redirects water from five small tributary streams of the River Garry, and the Garry itself. The catchwater then goes through a tunnel in the hill which separates the Garry and Errochty valleys to join the loch. This method of re-directing water allows it to be used more often to generate electricity. Some of the water within the Tummel scheme passes through five of the power stations and thus generates electricity five times.

That strikes me as being very sophisticated for the 1950s and if the engineering and tunnels are up to a high standard, it might be that conversion of this power station to a 75 MW power station with 16 GWh pumped storage is a distinct possibility.

It might even be possible to increase the generating capacity of the power station.


Strathclyde University estimated that 40 GWh of pumped storage could be added above Clunie power station.

This Google Map shows the River Tummel between Clunie and Pitlochry power stations.


  1. Clunie dam and power station is marked by a red arrow labelled Scottish and Southern Energy in the North-West corner of the map.
  2. Pitlochry Dam and power station are in the South-East corner of the map.
  3. River Tummel and Loch Faskally  link the two dams.

There is a large volume of water between the two dams.

In a pump-back hydro-electric water is pumped back from the lake below the dam into the reservoir above the dam. Such a system was added to the Grand Coulee Dam in the United States to increase its generating and storage capacity.

This Google Map shows how the water to the West of Clunie dam and power station stretches to the other end of Loch Tummel.

As there would be large volumes on both sides of the dam, I am fairly sure, that a pump-back system could be employed at Clunie power station.

Whether 40 GWh of storage could be added, would be one for the designers of the rebuilt dam and power station?


Strathclyde University estimated that 38 GWh of pumped storage could be added above Tummel power station.

This Google Map shows the Eastern end of Loch Rannoch, Dunalastair Water, the River Tummel and Tummel power station.


  1. Loch Rannoch is at the Western end of the map.
  2. Dunalastair Water is the smaller lake in the middle.
  3. Tummel power station is indicated by the red arrow at the East of the map.

This Google Map shows Tummel power station.


There appears to be two branches of the River Tummel.

  1. At the bottom of the map, it appears to be in an aqueduct and above the power station.
  2. Running across the top-right corner of the map, the second branch appears to be a low-level branch of the river.
  3. The height difference will mean that power station works well and generates its full 34 MW.

As with Clunie power station, I am sure there is scope for Tummel power station to pump water from Loch Tummel to Dunalastair water, when there is a surplus of wind-generated electricity.

But could space be found above Tummel power station to store enough water to create a massive 38 GWh pumped-storage power station?


This description of Lord Rannoch is from Wikipedia.

It is over 15 kilometres (9.3 mi) long in a west–east direction with an average width of about 1.2 kilometres (0.75 mi), and is deepest at its eastern end, reaching a depth of 130 metres (440 ft).

The loch could hold almost a half a billion tonnes of water.

This Google Map shows Loch Rannoch and Loch Ericht



  1. Loch Rannoch is along the bottom of the map with Loch Dunalastair to the right.
  2. Loch Rannoch has an altitude of 205 metres.
  3. Rannoch power station is indicated by the red arrow.
  4. Rannoch power station was built in 1930 and the history of the power station is told in this page on the SSE web site, which is entitled A Real Gem In Hydro History.
  5. Loch Ericht runs to the North from above the power station.
  6. Loch Ericht has an altitude of 350 metres.

This Google Map shows Rannoch power station to a larger scale.

Rannoch power station is on the shore of Loch Rannoch and is described in this section in Wikipedia. This is said.

Rannoch Power Station, on the northern shore of the loch, is part of the Tummel hydro-electric power scheme, which is operated by SSE. The power station has a vertical head of 156 m (512 ft) and a total generating capacity of 44 MW, and uses water fed by pipeline and tunnel from Loch Ericht which is discharged into Loch Rannoch.

There are four pipes running down the hill from Loch Ericht, which deliver water to the power station.

The layout of Rannoch power station seems very similar to Sloy power station, which I described in A Lower-Cost Pumped Hydro Storage System.

  • Both power stations sit on a large deep loch.
  • Both have pipes to supply water going up the hill and then in a tunnel to a large loch over a hundred metres above the lower reservoir.
  • Rannoch power station is a 44 MW power station built in 1930.
  • Sloy power station is a 152.5 MW power station built in 1950.

SSE have been examining if a pumped-storage station could be added to Sloy power station.

Given the similarity of the layouts of the two stations, it could be that if it is possible to add pump storage to Sloy, that this could also be done at Rannoch.

Could 41 GWh be stored above Rannoch power station? I won’t say it is not possible.


Research at Strathclyde University gives these figures for possible storage capacity for these dams and lochs in the Tummel scheme.

  • Errochty – 16 GWh
  • Clunie – 40 GWh
  • Rannoch – 41 GWh
  • Tummel – 38 GWh

Adding these up gives a total of 135 GWh of stored energy for the Tummel scheme.

But that assumes every power station and dam is expanded to fit Strathclyde’s research.

SSE Renewables are currently calling for tenders for Coire Glas, as I wrote about in SSE Renewables Launches 1.5GW Coire Glas Construction Tender.

This was my conclusion in that post.

It looks to me, that it’s almost certain that Scotland will get a 1.5GW/30 GWh pumped-storage system at Coire Glas.

Coire Glas could supply slightly more power than Sizewell B nuclear power station for twenty hours.

Now that’s what I call backup!

But in the Tummel scheme, there could be three places, where a 30 GWh pumped-storage scheme could be developed and one where a 16 GWh scheme could be developed.

I would expect that a conservative figure of between 40-60 GWh of pumped-storage capacity could be added to the Tummel scheme.




February 25, 2022 - Posted by | Energy, Energy Storage | , , , , , ,

1 Comment »

  1. […] analysis in Repurposing The Tummel Hydro-Electric Scheme, showed the […]

    Pingback by Scotland’s Energy Storage « The Anonymous Widower | March 2, 2022 | Reply

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