26 Fluctuations and storage

The wind, as a direct motive power, is wholly inapplicable to a system of machine labour, for during a calm season the whole business of the country would be thrown out of gear. Before the era of steamengines, windmills were tried for draining mines; but though they were powerful machines, they were very irregular, so that in a long tract of calm weather the mines were drowned, and all the workmen thrown idle. William Stanley Jevons, 1865

If we kick fossil fuels and go all-out for renewables, or all-out for nuclear, or

a mixture of the two, we may have a problem. Most of the big renewables

are not turn-off-and-onable. When the wind blows and the sun comes out,

power is there for the taking; but maybe two hours later, it’s not available

any more. Nuclear power stations are not usually designed to be turn-offand-

onable either. They are usually on all the time, and their delivered

power can be turned down and up only on a timescale of hours. This is a

problem because, on an electricity network, consumption and production

must be exactly equal all the time. The electricity grid can’t store energy. To

have an energy plan that adds up every minute of every day, we therefore

need something easily turn-off-and-onable. It’s commonly assumed that the

easily turn-off-and-onable something should be a source of power that gets

turned off and on to compensate for the fluctuations of supply relative to

demand (for example, a fossil fuel power station!). But another equally

effective way to match supply and demand would be to have an easily

turn-off-and-onable demand for power – a sink of power that can be turned

off and on at the drop of a hat.



Either way, the easily turn-off-and-onable something needs to be a big

something because electricity demand varies a lot (figure 26.1). The de-

