Our Needs for Energy and Ways to Satisfy Them

Abstract

Our subject is not only a very important one, it is also very large and complex. As a physicist, I should first point out that the problem is not really one of energy. We have plenty of energy: the atmosphere has a temperature of around 300° absolute and so have our seas (this corresponds to about 50°F). If we could bring only a tiny fraction of their heat content into our houses in the winter, we would need no heating. Unfortunately, heat does not move from a colder region to a warmer one, that is it does not move from the outside of our houses in the winter to the warmer region inside—it flows in the other direction. When we speak about energy requirements, we really mean requirement of available energy and this is limited, even in principle, by the second law of thermodynamics. It is limited also by our lack of skill to make full use of even that part of the energy which seems to be available even if the second law of thermodynamics is taken into account. An expression for this latter amount was already given by Gibbs: if a container is available which can act both as a source and a sink of heat at a definite temperature T₀—and our atmosphere or our seas can furnish or accept heat at a temperature around 300°K—the amount of available energy is given by the expression G = U - T₀S where U is the actual energy difference between initial and final state of the material furnishing us with what we call energy in this discussion, and S is the difference between the entropies of the two states of this material, the difference of the entropies of its initial and its used-up state.