The radiation streaming incessantly towards us from the sun provides more energy than humanity needs for even its most extravagant technological endeavours.
The sunnier regions of this planet receive an estimated 9 million kilowatt-hours per acre ever year, and the total energy received in this way is about 50,000 times greater than the world's current or foreseen requirements.
The problem is to capture even a part of this energy in a useful way.
Many schemes have been devised over the years. Lemuel Gulliver, for example, finding himself on the little island of Laputa, was allowed to visit the Grand Academy of Lagado, and found there a man "who had been eight years engaged upon a project for extracting sunbeams out of cucumbers, which were to be put into vials hermetically sealed, and let out to warm the air in raw inclement summers".
Obviously, this particular methodology has not survived - but there are others.
The most convenient way to harness solar energy is to transform it directly into electricity, using a solar battery, or photovoltaic cell. This consists of a flat "sandwich", or plate, of two carefully chosen materials which, in combination, react to sunlight.
The radiation knocks some of their electrons "out of place", so to speak - a phenomenon known as the photoelectric effect. If the plate is made part of an electrical circuit, the movement of these electrons constitutes an electric current.
The amount of current from a single photovoltaic cell is very small indeed, but if a large number are placed in series with each other, electricity can be produced on a scale which is useful for some purposes.
Photovoltaic cells, in fact, are commonly used as a source of power for earth-orbiting artificial satellites, and in recent times have come into use closer to home, for powering small electrical devices like calculators and digital watches.
Solar batteries have the big advantage that they contain no liquids or corrosive chemicals and have no moving parts; they just keep on generating electricity indefinitely, merely by being exposed to the sun.
It has been estimated that if large "unused" areas of the world, subject to a lot of sunshine - Death Valley, for instance, in the United States, or the Sahara in Africa - were to be completely covered with solar batteries, they could provide for the world's energy needs many times over.
But there are obvious practical difficulties to such a plan, and in any case, the cost would be prohibitive; unfortunately, the resulting energy would be many times more expensive than electricity generated by conventional means.