Is fossil solar energy the only one that may be used in modern life and civilization? That is the question. Though the internal energy of the earth may produce terrible disasters through volcanic eruptions and earthquakes, it can hardly be used by man. The energy derived from the rotation of the earth (the tides) can hardly be counted upon, on account of the enormous quantities of water that would have to be handled. If man ever succeeds in availing himself of the internal energy of the atoms, his power will surpass by far the limits assigned to it today.

At present he is limited to the use of solar energy. Let us see, however, whether the actual energy may not supplant that stored up in fossil fuel. Assuming for the tropics a day of only six hours of sunshine, we should have, for the day, an amount of heat equivalent to that furnished by 1.35 kilograms of coal. For a square kilometer we should have a quantity of heat equivalent to that produced by the complete combustion of 1,000 tons of coal.

A surface of only ten thousand square kilometers receives in a year, calculating a day of only six hours, a quantity of heat that corresponds to that produced by the burning of 3,650 million tons of coal. The quantity of coal produced annually in the mines of Europe and America is calculated at about 925 million tons and, adding to this 175 million tons of lignite, we reach 1,100 million tons, or a little over 1 billion.

Even making allowances for the absorption of heat on the part of the atmosphere and for other circumstances, we see that the solar energy that reaches a small tropical country—say, of the size of Latium—is equal annually to the energy produced by the entire amount of coal mined in the world. The Sahara desert, with its six million square kilometers, receives daily solar energy equivalent to 6 billion tons of coal.

The enormous quantity of energy that the earth receives from the sun—in comparison, the part that has been stored up by the plants in the geological periods is almost negligible—­is largely wasted. It is used in waterfalls (white coal) and by plants. Several times its use in a direct form through mirrors has been tried, and now some very promising experiments are being made in Egypt and in Peru; but this side of the problem is beyond my power to discuss.

The energy produced by water power during the period of one year is equal to that produced by 70 billion tons of coal. It is, however, very small, as might be expected, in comparison with the total energy that the sun sends to the earth every year.

Let us now see what quantity of solar energy is stored by the plants: on the total surface of the various continents, which is 128 million square kilometers, there is a yearly production of 32 billion tons of vegetable matter, which, if burned, would give the quantity of heat that corresponds to the total combustion of 18 billion tons of coal. It is not much, but even this is seventeen times as much as the total present production of coal and of lignite.

Solar energy is not evenly distributed over the surface of the earth; there are privileged regions, and others that are less favored by the climate. The former ones would be the prosperous ones if we should become able to use the energy of the sun. The tropical countries would thus be conquered by civilization, which would in this manner return to its birthplace. Even now the strongest nations rival one another in the conquest of the lands of the sun, as though unconsciously foreseeing the future.

Where vegetation is rich, photochemistry may be left to the plants, and by rational cultivation solar radiation may be used for industrial purposes. In the desert regions, unadapted to any kind of cultivation, photochemistry will artificially put their solar energy to practical uses.

On the arid lands there will spring up industrial colonies without smoke and without smokestacks; forests of glass tubes will extend over the plains and glass buildings will rise everywhere; inside these will take place the photo­chemical processes that hitherto have been the guarded secret of the plants but that will have been mastered by human industry, which will know how to make them bear even more abundant fruit than nature, for nature is not in a hurry and mankind is.

If in a distant future the supply of coal becomes completely exhausted, civilization will not be checked by that—life and civilization will continue as long as the sun shines! If our black and nervous civilization based on coal shall be followed by a quieter civilization based on the use of solar energy, that will not be harmful to progress and to human happiness.

The photochemistry of the future should not, however, be postponed to such distant times; I believe that industry will do well in using from this very day all the energies that nature puts at its disposal. So far, human civilization has made use almost exclusively of fossil solar energy. Would it not be advantageous to make better use of radiant energy?

Contributor

Giacomo Ciamician

From “The Photochemistry of the Future.” Ciamician taught chemistry in Rome and Padua before joining the faculty of the University of Bologna, where he conducted experiments on the roof to study the behavior of organic compounds when exposed to light; in 1987 the university named its chemistry department in his honor. In this lecture, Ciamician expressed reservations about society’s dependence on coal, which it used “with increasing eagerness and thoughtless prodigality for the conquest of the world…but coal is not inexhaustible.” The lecture was quickly published in Science and translated into multiple languages.

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