MAGNETIC STORAGE AND PESSIMISM

But to illustrate the secondary difficulties, consider the mag-netic field in which utilities hope to store electric energy one day. One of the few drawbacks of electricity (as against fuels) is that it cannot be stored in large quantities when it is not needed. It has first to be converted to some other form of energy, most often to the potential energy of water pumped into storage behind a dam, to be reconverted to electricity by flowing out through turbines. But some 50% of the original energy is lost in the pumps¾the equivalent of half your coal rotting away when you store it for a few hours. Yet utilities need to store their electric energy to tide them over the peak hour the alternative is to build additional capacity which is used only for one or two hours per weekday.

A possible solution is to store the energy in the magnetic field of a coil carrying an electric current. This makes no sense with an ordinary coil, because one has to keep the current flowing to make up for the heating losses in the coil¾like pumped storage with a sieve instead of a dam. But superconducting coil should carry the current in the (shorted) coil forever, or at least until tapped as needed, because there are no heating losses. The only losses are those incurred in keeping the coil superconductive, that is, in the energy needed to cool the liquid helium or nitrogen surrounding the coil. With the proper design, these losses could be kept to 20% of the stored energy, a substantial improvement of the 50% lost in pumped storage (and other contemporary methods).