The Anonymous Widower

A Lower-Cost Pumped Hydro Storage System

Whilst writing some of the posts recently about pumped storage I came across the Loch Sloy Hydro-Electric Scheme.

This is the introductory sentence in Wikipedia.

The Sloy/Awe Hydro-Electric Scheme is a hydro-electric facility situated between Loch Sloy and Inveruglas on the west bank of Loch Lomond in Scotland.

This page on the Greenage web site gives comprehensive details of the power station and is well worth a read.

This Google Map shows the Lochs Sloy and Lomond.


  1. Loch Sloy is in the North-West corner of the map.
  2. The page on Greenage says that Loch Sloy can store 14 GWh of electricity
  3. Loch Lomond is the body of water towards the Eastern side of the map.
  4. Inverglas is on the West bank of Loch Lomond to the North of the Loch Lomond Holiday Park, which is indicated by the green arrow with a tent.

This second Google Map shows the power station and Inverglas.


  1. It is a classic layout for a hydro-electric power station.
  2. In the North West corner of the map is the valve house, which is connected to Loch Sloy by a three kilometre tunnel.
  3. The valve house controls the water flows to the power station by Loch Lomond.
  4. There are four two-metre pipes running down the hill, one for each of the four turbines.
  5. According to the page on Greenage, the power station has three 40 MW turbines and one 32 MW turbine, which gives a total output of 152 MW.
  6. The water discharges into Loch Lomond after doing its work in the power station.

Loch Sloy is the largest conventional hydroelectric power plant in the UK.

Extending The Loch Sloy Hydro-Electric Scheme

This page on Hydro Review, which is dated the 10th of November 2010, is entitled SSE Gets Government Consent For Sloy Pumped-Storage Hydropower Project.

These are the first paragraph.

SSE Generation Ltd., the wholly owned generation business of Scottish and Southern Energy, has received consent from the Scottish Government to develop a 60-MW pumped-storage hydro project at its existing Sloy hydropower station at Loch Lomond, SSE reported.


  1. Two 30 MW pumps will be added to the power station to pump water up the hill from Loch Lomond to Loch Sloy.
  2. According to the page on Greenage, if the two pumps worked together for six hours, they would transfer 432,000 m3 of water. Note that a cubic metre of water weighs a tonne.
  3. Water would be transferred, when there was a surplus of energy being generated over the demand.

It would appear to be a simple scheme, as it is just adding two pumps to pump the water up the hill.

  • As pumps rather than pump/turbines as at Foyers are used, there is no corresponding increase in generating capacity.
  • Water also appears to be pumped up to the valve house in the existing pipes.
  • Loch Sloy and Loch Lomond would not need major works to enable the scheme..

The page on Greenage gives the cost at just £40 million.

Originally, the project was supposed to have started in 2012, but as there are environmental problems with the fish, the work has not started.

These problems are detailed on the page on Greenage.


For £40 million, 14 GWh of pumped storage can be created at Sloy.

  • But it could be bigger than 14 GWh, as this page on the Strathclyde University web site, says 20.4 GWh is possible.
  • This would surely, be a project that could be first in the queue, once the environmental problems are solved.

20 GWh of pumped storage would be nice to have reasonably quickly.


February 16, 2022 - Posted by | Energy, Energy Storage | , , , , ,


  1. No metion of the penstocks!

    Comment by Matthew | February 16, 2022 | Reply

  2. There are currently valves in the valve house and probably penstocks in the existing power station. But as I see the plan, the new part of the plant will only be pumping water up hill and all generation will be done by the existing plant.

    Comment by AnonW | February 16, 2022 | Reply

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

    Pingback by Repurposing The Tummel Hydro-Electric Scheme « The Anonymous Widower | February 25, 2022 | Reply

  4. […] discussed Sloy power station in A Lower-Cost Pumped Hydro Storage System and came to these […]

    Pingback by Repurposing The Sloy/Awe Hydro Scheme « The Anonymous Widower | March 1, 2022 | Reply

  5. […] Loch Sloy – 14 GWh […]

    Pingback by Will Coire Glas Start A Pumped Storage Boom In Scotland? « The Anonymous Widower | June 3, 2022 | Reply

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