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Geothermal energy. Diagram showing the principles behind electricity generation from geothermal energy. Water is pumped deep underground into rocks such as granite, heated by volcanic activity below. The water is superheated, beyond normal boiling point, but remains liquid due to the pressure in the system. The superhot water passes through a heat exchanger, where it causes water to turn into steam. The steam powers generators that produce the electricity. The steam is recondensed into water in cooling towers. This kind of power station is seen extensively in countries such as Iceland and New Zealand that have considerable geothermal activity. Excess steam can also be used for space heating and district water heating.
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