difference between Loch Sloy and Loch Lomond is about 270 m. Sloy’s
area is about 1.5 km2, and it can already store an energy of 20 GWh. If
Loch Sloy’s dam were raised by another 40 m then the extra energy that
could be stored would be about 40 GWh. The water level in Loch Lomond
would change by at most 0.8 m during a cycle. This is less than the normal
range of annual water level variations of Loch Lomond (2 m).

Figure 26.10 shows 13 locations in Scotland with potential for pumped
storage. (Most of them already have a hydroelectric facility.) If ten of these
had the same potential as I just estimated for Loch Sloy, then we could
store 400 GWh – one third of the total of 1200 GWh that we were aiming
for.

We could scour the map of Britain for other locations. The best loca-
tions would be near to big wind farms. One idea would be to make a new
artificial lake in a hanging valley (across the mouth of which a dam would

Figure 26.9. Dinorwig, in the Snowdonia National Park, compared with Loch Sloy and Loch Lomond. The upper maps show 10 km by 10 km areas. In the lower maps the blue grid is made of 1 km squares. Images produced from Ordnance Survey’s Get-a-map service www.ordnancesurvey.co.uk/getamap. Images reproduced with permission of Ordnance Survey. © Crown Copyright 2006.