Short answer: 17,464 GWh, or about 654 times more than we currently have.
How much would that cost?
World experience is that hydro projects cost about US$2,000/kW to US$4,000/kW-- Pumped-hydro energy storage – cost estimates for a feasible system.
At 2 to 4 $bn/GWh. Total storage costs for UK = £2 × 55 bn to £4 × 55 bn = $110 bn to $220 bn. UK hydro could not store the necessary energy, but could provide the power for a short time. We would need storage for 11643 million m³ of water. 11.643 km³. Let's take a proposed example. This massive scheme drowning a large area at Strathdearn in the Scottish Highlands would manage 4.4 km³ of water with a head of only 300 m. This is similar to the head at Ffestiniog. Scaling 4.4 billion m³ we expect 3365 GWh. This will be 20% of the capacity the UK would need to support wind intermittency.
Britain currently has 4 pumped hydro storage plants providing a total of 26.7 GWh of electrical storage. This pumped hydro isn't used for storage in the sense that renewable advocates want - to buffer intermittent generation. It's used to quickly bring peaking capacity online for quite short periods during late afternoon, early evening 4:30 pm to 7:00 pm.
station | power (MW) | head (m) | volume (million m³) | energy stored (GWh) |
---|---|---|---|---|
Ffestiniog | 360 | 320–295 | 1.7 | 1.3 |
Cruachan | 400 | 365–334 | 11.3 | 10 |
Foyers | 300 | 178–172 | 13.6 | 6.3 |
Dinorwig | 1800 | 542–494 | 6.7 | 9.1 |
Proposed: | ||||
Balmacaan | 300-600 | 500 | - | 30.0 |
Coire Glas | 300-600 | 500 | - | 30.0 |
Sloy | 60 | 280 | - | 20.0 |
Total: | 3520 - 4120 | 26.7 - 106.7 |
How much extra would a wind-powered Britain need?
I reckon we'd need enough to cover for days of greatest demand, assuming a very low wind period.
A high demand day fell on 12-December 2012 requiring an average of 47.9 GW. Demand varied from a minimum of 37.1 GW (4am) to a maximum of 56.9 GW (5pm). Britain used 1,149.6 GWh of electricity that day. 23 such days would demand 26,440.8 GWh.

A low wind period happened during the first 23 days of Sept 2014. Back then we had 11,187 MWe of wind generation capacity, but it only produced 587.3 GWh for those 23 days, averaging 9.5% capacity.
That gives us a good idea of what kind of day we need to cover for, and for how long.
In Britain average offshore wind power capacity is 33%, onshore 23%, and the average (of both) is 28%. A wind powered Britain would need 171 GWe of wind (assuming 50:50 offshore:onshore). That's because 171 GWe of wind running at 28% generates 47.9 GWe, which is exactly our average demand on a cold winter day (such as 12-Dec 2012).
How much would have 171 GWe of wind made during that 23-day Sept-2014 low wind period? It would've generated 587.3 × 171 ÷ 11.187 = 8,977 GWh. Yet 23 cold, low-wind, days similar to 12-Dec 2012 would require 23 × 1,149.6 = 26,441. The short fall is 26,441 - 8,977 = 17,464 GWh.
The thin green line on the chart shows the expected (or average) o/p, assuming 28% capacity utilization.
Day | GWh |
---|---|
1 | 30.0 |
2 | 17.3 |
3 | 19.8 |
4 | 16.1 |
5 | 12.6 |
6 | 25.2 |
7 | 43.5 |
8 | 17.3 |
9 | 6.7 |
10 | 13.2 |
11 | 21.2 |
12 | 18.0 |
13 | 30.7 |
14 | 56.5 |
15 | 27.3 |
16 | 14.2 |
17 | 22.2 |
18 | 24.7 |
19 | 14.1 |
20 | 27.9 |
21 | 62.4 |
22 | 29.6 |
23 | 36.9 |
24 | 93.9 |
25 | 128.1 |
26 | 123.2 |
27 | 59.5 |
28 | 28.9 |
29 | 15.1 |
30 | 72.1 |
Total days 1 - 23 : | 587.3 |
Expected daily average of 11,187 MWe wind plant @ 28% | 75.2 |
Source: Gridwatch downloads.
Note: The Gridwatch wind numbers show only metered wind, which is about 2/3 the total, so Gridwatch wind values are multiplied by 1.5 to get those shown above.
Time | Demand, GWe |
---|---|
00:00 | 38.2 |
00:30 | 38.6 |
01:00 | 39.0 |
01:30 | 38.2 |
02:00 | 38.0 |
02:30 | 38.4 |
03:00 | 38.2 |
03:30 | 37.8 |
04:00 | 37.3 |
04:30 | 37.1 |
05:00 | 37.3 |
05:30 | 38.6 |
06:00 | 40.8 |
06:30 | 44.1 |
07:00 | 48.6 |
07:30 | 51.4 |
08:00 | 51.8 |
08:30 | 51.8 |
09:00 | 52.4 |
09:30 | 52.9 |
10:00 | 52.9 |
10:30 | 53.1 |
11:00 | 53.1 |
11:30 | 53.1 |
12:00 | 52.9 |
12:30 | 52.4 |
13:00 | 52.2 |
13:30 | 52.0 |
14:00 | 52.4 |
14:30 | 52.4 |
15:00 | 52.7 |
15:30 | 54.3 |
16:00 | 55.5 |
16:30 | 56.9 |
17:00 | 56.7 |
17:30 | 56.5 |
18:00 | 56.3 |
18:30 | 55.9 |
19:00 | 55.1 |
19:30 | 53.9 |
20:00 | 52.7 |
20:30 | 51.4 |
21:00 | 49.6 |
21:30 | 47.8 |
22:00 | 44.9 |
22:30 | 42.4 |
23:00 | 40.6 |
23:30 | 39.0 |
Source: DECC
References
- How much bulk energy storage is needed to decarbonize electricity?, 2015, by Hossein Safaei and David W. Keith