The only channel of solar-energy flux which lends itself readily to large-scale industrial power production is water power. According to the Federal Power Commission, the maximum ultimate water-power capacity of the United States is approximately 161,000 megawatts. Of this, the present installed capacity of 45,000 megawatts amounts to 28 per cent. The corresponding water-power capacity for the whole world is estimated to be about 2.9 million megawatts. Of this, it is significant that the conti­nents of Africa and South America, both of which are deficient in coal, have the highest capacities —780,000 and 577,000 megawatts, respec­tively.

The total installed water-power capacity of the world by 1964 amounted to 210,000 megawatts, which is only about 7.5 per cent of its potential capacity. The total installed electrical power capacity of the world is about 734,000 megawatts, which is only a quarter of the poten­tial water-power capacity.

It appears, therefore, that if fully developed, the world’s water-power capacity would be comparable to the world’s present rate of energy con­sumption. Offsetting this, however, would be the necessity of a prior in­dustrialization of the areas where the power is potentially available. Also, there is the problem of silting reservoirs. Most water-power sites require dams on storage reservoirs, and only about one to three centuries are re­quired to fill the reservoirs with sediments. Unless a solution to this prob­lem can be found, water power also may be relatively short-lived.