单选题
In addition to the established energy sources such as gas, coal, oil and nuclear, there are a number of other sources that we ought to consider. Two of these are hydroelectric and tidal power.
These two sources are
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in that they are both renewable.
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, hydropower is more widely used than tidal. In
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, a substantial amount of electricity is already produced in HEP (hydroelectric power)stations worldwide,
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tidal stations are still in the very early
5
of development.
As far as geographical
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is concerned, HEP projects are to be found on lakes and rivers. while tidal
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are constructed only at river mouths where tidal
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is great. Unfortunately these are
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in number. At present HEP stations are found mainly in Norway, Canada, Sweden and Brazil, whereas tidal plants are in
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in France, Russia and China.
As regards capital
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, both require very high investment. On the other hand, generating
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are quite low in both cases. In fact, a large scale HEP plant is capable of producing power more
13
than conventional sources, such as coal, oil and nuclear plants. Tidal power also compares
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with nuclear and oil generated electricity,
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the amount of money on production.
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HEP stations, tidal constructions have a long life
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. It is estimated that they can operate for over 100 years. With respect to
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of supply, tidal stations
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from HEP ones in that they often can only supply power
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. HEP stations, however, provide a constant supply of electricity.