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Geothermal Energy

Earth's internal heat, fueledby radioactivity, provides the energy for plate tectonics and continentaldrift, mountain building, and earthquakes. It can also be harnessed to driveelectric generators and heat homes. Geothermal energy becomes available in apractical form when underground heat is transferred by water that is heated asit passes through a subsurface region of hot rocks (a heat reservoir) that maybe hundreds or thousands of feet deep. The water is usually naturally occurringgroundwater that seeps down along fractures in the rock; less typically, thewater is artificially introduced by being pumped down from the surface. Thewater is brought to the surface, as a liquid or steam, through holes drilledfor the purpose.



By far the most abundant form of geothermalenergy occurs at the relatively low temperatures of 80° to 180° centigrade.Water circulated through heat reservoirs in this temperature range is able toextract enough heat to warm residential, commercial, and industrial spaces.More than 20,000 apartments in France are now heated by warm underground waterdrawn from a heat reservoir in a geologic structure near Paris called the ParisBasin. Iceland sits on a volcanic structure known as the Mid-Atlantic Ridge.Reykjavik, the capital of Iceland, is entirely heated by geothermal energyderived from volcanic heat.


Geothermal reservoirs with temperaturesabove 180° centigrade are useful for generating electricity. They occurprimarily in regions of recent volcanic activity as hot, dry rock; natural hotwater; or natural steam. The latter two sources are limited to those few areaswhere surface water seeps down through underground faults or fractures to reachdeep rocks heated by the recent activity of molten rock material. The world'slargest supply of natural steam occurs at The Geysers, 120 kilometers north ofSan Francisco, California. In the 1990s enough electricity to meet about halfthe needs of San Francisco was being generated there. This facility was then inits third decade of production and was beginning to show signs of decline,perhaps because of over development. By the late 1990s some 70 geothermalelectric-generating plants were in operation in California, Utah, Nevada, andHawaii, generating enough power to supply about a million people. Eighteencountries now generate electricity using geothermal heat.


Extracting heat from very hot, dry rockspresents a more difficult problem: the rocks must be fractured to permit thecirculation of water, and the water must be provided artificially. The rocksare fractured by water pumped down at very high pressures. Experiments areunder way to develop technologies for exploiting this resource.


Like most other energy sources,geothermal energy presents some environmental problems. The surface of theground can sink if hot groundwater is withdrawn without being replaced. Inaddition, water heated geothermally can contain salts and toxic materialsdissolved from the hot rock. These waters present a disposal problem if theyare not returned to the ground from which they were removed.


The contribution of geothermal energy to the world'senergy future is difficult to estimate. Geothermal energy is in a sense notrenewable, because in most cases the heat would be drawn out of a reservoirmuch more rapidly than it would be replaced by the very slow geologicalprocesses by which heat flows through solid rock into a heat reservoir.However, in many places (for example, California, Hawaii, the Philippines,Japan, Mexico, the rift valleys of Africa)the resource is potentially so largethat its future will depend on the economics of production. At present, we canmake efficient use of only naturally occurring hot water or steam deposits.Although the potential is enormous, it is likely that in the near futuregeothermal energy can make important local contributions only where theresource is close to the user and the economics are favorable, as they are inCalifornia, New Zealand, and Iceland. Geothermal energy probably will not makelarge-scale contributions to the world energy budget until well into thetwenty-first century, if ever.

14题
1 Heat reservoirs with a temperature from 80° to 180° centigrade can be used, as in France and Iceland, to heat buildings.
2 A number of countries now use geothermal reservoirs that contain water or steam above 180° centigrade to generate electricity.
3 Most heat reservoirs with a temperature above 180° centigrade cannot be used for energy because they are usually too close to recent volcanic activity.
4 The sinking of land above heat reservoirs and other environmental problems arise when water is pumped into a heat reservoir under high pressure.
5 Experiments are under way to determine if geothermally heated waters could be used as a source of certain minerals that have been dissolved out of hot rocks deep within Earth.
6 A number of issues, including how to extract heat from reservoirs that do not have a natural supply of water, will significantly limit the use of geothermal energy for the foreseeable future.

答案是146，我选的是124
关于6的选项中that do not have a natural supply of water的信息在文中找不到
而第三段信息与选项2吻合

哪位帮我分析分析好吗？~

STOOIBT1UID: 2921281

我版本的答案好像是 126  没4

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