You are going to read an article about using energy from the sun. Six sentences have been removed from the article. Choose from the sentences A–G the one which fits each gap (37–42). There is one extra sentence which you do not need to use.

Solar energy – the sun’s gift to humanity

by Andy Groves

The sun is a huge ball of atomic activity, which emits solar energy in the form of light and heat. This energy travels through space to the planets, providing us with daylight and warmth. It is an incredible free gift. Many thousands of years ago, humans were already using solar energy in a variety of ways. Early civilisations learned, for instance, how to use the sun’s heat for drying meat, fruit or fish to keep them for later eating; the sun baked clay into bricks for building; animal skins were dried for clothing.

Later, when people started living in purpose-built houses, the value of solar energy for heat was understood and eventually became incorporated into the design. In many medieval castles there was at least one room called the ‘solar’ which faced south and had as big a window as could practically be made in those days. (37)……………  

In more recent times, the term ‘solar energy’ has taken on a somewhat different significance. Modern man uses energy in many forms and ever- increasing quantities. Generally, this energy has been obtained from fossil fuels, such as coal, oil or gas, extracted from under the ground or beneath the sea. (38)……………  Burning them is also having a terrible effect on the environment of our planet.

Because we in industrialised societies have become used to such a high level of energy usage in our everyday lives, the thought of doing without is no longer considered a realistic option. (39)……………  Fortunately, the good old sun can provide one, and solar energy is becoming crucial to our future requirements.

Solar energy is renewable, non-polluting, available everywhere, is not (yet) owned by anyone or any country and is free. It can be used directly to heat air and so provide heat for buildings in a way that is similar to how greenhouses work. Alternatively, the heat can be collected by solar panels and passed on to heat water for washing or central heating. Light-sensitive devices can convert the light from the sun into electricity. (40)……………  Initially, it was mainly used for pocket calculators, but now it powers radios, pumps, lights, and even cars.

Electricity generated from solar energy can bring power to remote areas and, together with some form of storage, such as a battery, can provide lighting for individual houses or run machinery on farms. (41)……………  To cover more extensive areas, some companies and local authorities are now using large numbers of cells to collect and convert solar energy. Some installations are large enough to provide power for a whole town.

The sun sends its solar energy to Earth at a huge rate, every day of the year. Much of this is absorbed by our dense atmosphere, the oceans and the land, or reflected back into space by the polar ice caps. (42)……………  So much, in fact, that it is estimated the sun provides as much energy in one hour as the world’s population uses in a year. This is one great gift and we should make sure we use it well.