Poor Icarus! Icarus, you may recall, was imprisoned with his father, Daedalus, on the island of Crete by Minos, the island's king. Flight, in the literal sense, was their only hope of freedom, and Daedalus arranged just that: he built them both a set of wings. The wings were made of countless feathers, carefully arranged and held in place by thread and wax. When they were completed, the pair soared high above their Aegean prison, and headed west for Italy.
But Icarus came to a ignominious end. So much did he exult in his new power, that despite paternal warnings, he soared into the heavens and close to the blazing Mediterranean sun. The sun attacked his flimsy aerofoils, and so:
With melting wax and loosened strings,
Sank hapless Icarus on his faithless wings;
Headlong he rushed through the affrighted air,
With limbs distorted and dishevelled hair.
But the sun need not be destructive: it can be captured and imprisoned like our two mythological aeronauts, and made to serve our earthly purposes in constructive ways.
The solar energy received by the sunnier regions of this planet has been estimated at over 9 million kilowatt-hours per acre per year; the total energy received in this way is about 50,000 times greater than the world's current requirements. The challenge is to capture even a fraction of this energy in a usable form.
The most convenient way to harness the sun's energy is to transform solar radiation 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 electrons "out of place", so to speak - a phenomenon known as the photo-electric effect. If the plate is made part of an electrical circuit, the movement of these electrons constitutes an electric current.
The current from a single photo-voltaic cell is very small indeed, but if a large number is placed in series with each other, electricity can be produced on a scale which is useful for some purposes. They are, in fact, 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 watches.
Solar batteries have the 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 sunlight.