How to ride through these very-long-timescale fluctuations? Electric
vehicles and pumped storage are not going to help store the sort of quantities
required. A useful technology will surely be long-term thermal storage.
A big rock or a big vat of water can store a winter’s worth of heat for
a building – Chapter E discusses this idea in more detail. In the Netherlands,
summer heat from roads is stored in aquifers until the winter; and
delivered to buildings via heat pumps [2wmuw7].


page no.

187The total output of the wind fleet of the Republic of Ireland. Data from [2hxf6c].

“Loss of wind causes Texas power grid emergency”. [2l99ht] Actually, my
reading of this news article is that this event, albeit unusual, was an example
of normal power grid operation. The grid has industrial customers
whose supply is interruptible, in the event of a mismatch between supply
and demand. Wind output dropped by 1.4 GW at the same time that Texans’
demand increased by 4.4 GW, causing exactly such a mismatch between supply
and demand. The interruptible supplies were interrupted. Everything
worked as intended.
Here is another example, where better power-system planning would have
helped: “Spain wind power hits record, cut ordered.” [3x2kvv] Spain’s av-
erage electricity consumption is 31 GW. On Tuesday 4th March 2008, its
wind generators were delivering 10 GW. “Spain’s power market has become
particularly sensitive to fluctuations in wind.”

Supporters of wind energy play down this problem: “Don’t worry – individual
wind farms may be intermittent, but taken together, the sum of all
wind farms is much less intermittent.”
For an example, see the website, which, on its page “debunking the myth that wind power
isn’t reliable” asserts that “the variation in output from wind farms dis-
tributed around the country is scarcely noticeable.”
intermittency debunk.html

...wind is intermittent, even if we add up lots of turbines covering a whole
country. The UK is a bit larger than Ireland, but the same problem holds there
Source: Oswald et al. (2008).

191Dinorwig’s pumped-storage efficiency is 75%. Figure 26.17 shows data.
Further information about Dinorwig and the alternate sites for pumped stor-
age: Baines et al. (1983, 1986).

192Table 26.7. The working volume required, V, is computed from the height
drop h as follows. If ε is the efficiency of potential energy to electricity

V = 100 GWh/(ρghε),

where ρ is the density of water and g is the acceleration of gravity. I assumed
the generators have an efficiency of ε = 0.9.

Figure 26.17. Efficiency of the four pumped storage systems of Britain.