Before 1800 (Table 1.1), all of the world’s power needs were satisfied by wood, wind, and water, all of which were energy sources that could be renewed.

Simultaneously with the growth of industry, indeed as an initiator for much of the growth, energy from coal deposits began to supply an ever — increasing proportion of the world’s requirements at the end of the 19th

century. This growth in coal use continued until it supplied 90% of the world’s requirements by the beginning of this century.

However, the growth of the population in recent times has a doubling time of about 40 years, and the energy demand rises even faster with a doubling time of about 25 years. Thus the supply of energy by coal could not keep pace with the demand.

A partial solution was found around 1930 when the problem of the transportation of naturally occurring oil and gas was solved, so that these two new sources of energy began to supply an ever increasing proportion of the amount required. In particular, the growth of modern transport absorbed a large proportion of the energy produced from oil. Thus by 1970 coal was supplying about a fifth of the demand with coal and oil each sup­plying in the neighborhood of one-third to two-fifths. The amount of energy supplied by wood, wind, and water had undoubtedly increased with the advent of new hydroelectric plants but nevertheless it supplied a very small fraction of the total (Fig. 1.1).

Unfortunately coal, gas, and oil are all exhaustible sources of energy. With the power demand rising on an increasing scale it behooves us to look to the future. The United States has the highest energy demand in

the world, but the growth of that demand is relatively small compared to that of other nations. Figure 1.2 shows that the growth rate is larger for countries with smaller gross national products, as one might expect. This means that as the world becomes more and more affluent, the power re­quirements will rise to extremely high values.

Nevertheless our use of coal, oil and gas has been so rapid already that coal is likely to be exhausted in the world by about the year 2200 (2) with gas and oil not far behind. Thus the energy demand will not be satiable.

Certain solutions open to us are: the curtailment of population growth; the curtailment of energy demand per head of population; and a new source of energy which is renewable.

As I have said the final answer will be given by society, but I would suggest that the first two courses of action will only partially answer the problem. A new energy source will have to be made available.

Solar energy, energy derived from the fusion of light elements, tidal energy, and nuclear energy derived from fission are all candidates. Indeed Table 1.1 shows that nuclear energy is already supplying a significant pro­portion of the demand.

Research in the conversion of solar and fusion energy has not yet shown that these will ever be adequate sources of power for an industrial com-

0.50

Fig. 1.2. Per capita growth of energy usage as a function of the gross national product per capita (7). Legend: — 1955-1960; 1960-1965.

munity, while tidal power is limited in locality and availability. Nuclear power alone seems to provide the answer and by the year 2000 it is expected to provide nearly a fifth of the total needs.

Moreover, fast reactors are essentially a renewable form of energy. So while thermal reactor systems are undoubtedly short term solutions, it is only the fast breeder which will supply the long term needs in an inex­haustible form. We are thus led to the conclusion that fast reactor power plants will necessarily be built.