Energy sources may initially be divided into two kinds: non-renewable and renewable. The former group includes coal, oil, gas and, in the long run, nuclear; the latter waterpower, solar power and wind power. The energy from all these sources ultimately derives from the sun. There is a further source一geothermal- which depends on the earth's own heart. In practice this may be classed as non-renewable as it is exploitable in only a few places and is limited. There is a second difference that is often made, between traditional and non-traditional energy sources. A traditional energy source is one which is at present widely exploited. It will be realized, broadly, that the traditional sources are the non-renewable ones. This is not entirely true, however, as a good deal of oil is locked up in solid form in rock and this source, though not renewable, is also non-traditional, since it has not so far been developed very much.
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waterpower, solar power, wind power
