storage be ramped up? Can we imagine solving the entire lull problem
using pumped storage alone?

Can we store 1200 GWh?

We are interested in making much bigger storage systems, storing a total
of 1200 GWh (about 130 times what Dinorwig stores). And we’d like the
capacity to be about 20 GW – about ten times bigger than Dinorwig’s. So
here is the pumped storage solution: we have to imagine creating roughly
12 new sites, each storing 100 GWh – roughly ten times the energy stored
in Dinorwig. The pumping and generating hardware at each site would
be the same as Dinorwig’s.

Assuming the generators have an efficiency of 90%, table 26.7 shows a
few ways of storing 100 GWh, for a range of height drops. (For the physics
behind this table, see this chapter’s endnotes.)

Ways to store 100 GWh E
drop from
upper lake
working volume
(million m3)
example size
of lake
area  depth
500 m 40   2 km2×20 m E
500 m 40 4 km2×10 m E
200 m 100 5 km2×20 m E
200 m 100 10 km2×10 m E
100 m 200 10 km2×20 m E
100 m 200 20 km2×10 m E

Is it plausible that twelve such sites could be found? Certainly, we could
build several more sites like Dinorwig in Snowdonia alone. Table 26.8
shows two alternative sites near to Ffestiniog where two facilities equal to
Dinorwig could have been built. These sites were considered alongside
Dinorwig in the 1970s, and Dinorwig was chosen.

(million m3)
energy stored
Bowydd 2.40 250 17.7 12.0
Croesor 1.35 310 8.0 6.7

Pumped-storage facilities holding significantly more energy than Dinorwig
could be built in Scotland by upgrading existing hydroelectric facilities.
Scanning a map of Scotland, one candidate location would use
Loch Sloy as its upper lake and Loch Lomond as its lower lake. There is
already a small hydroelectric power station linking these lakes. Figure 26.9
shows these lakes and the Dinorwig lakes on the same scale. The height

Table 26.7. Pumped storage. Ways to store 100 GWh. For comparison with column 2, the working volume of Dinorwig is 7 million m3, and the volume of Lake Windermere is 300 million m3. For comparison with column 3, Rutland water has an area of 12.6 km2; Grafham water 7.4 km2. Carron valley reservoir is 3.9 km2. The largest lake in Great Britain is Loch Lomond, with an area of 71 km2.
Table 26.8. Alternative sites for pumped storage facilities in Snowdonia. At both these sites the lower lake would have been a new artificial reservoir.