GeothermalEnergy(TPO21-1)
Earth’s internal heat, fueled byradioactivity, provides the energy for plate tectonics, continental drift,mountain building, and earthquakes. It can also be harnessed to drive electricgenerators and heat homes. Geothermal energy becomes available in a practica form whenunderground heat is transferred by water that is heated as it passes through asubsurface region of hot rocks (a heat reservoir) that may be hundreds orthousands of feet deep. █The water is usually naturallyoccurring groundwater that seeps down along fractures in the rock; lesstypically, the water is artificially introduced by being pumped down from thesurface. █The water is brought to thesurface, as a liquid or steam, through holes drilled for the purpose. █
By far the most abundant form ofgeothermal energy occurs at the relatively low temperatures of 80℃ to 180℃ centigrade. █Water circulated through heatreservoirs in this temperature range is able to extract enough heat to warmresidential, commercial, and industrial spaces. More than 20,000 apartments inFrance are now heated by warm
underground water drawn from a heat reservoir ina geologic structure near Paris called the Paris Basin. Iceland sits on avolcanic structure known as the Mid-Atlantic Ridge. Reykjavik, the capital ofIceland, is entirely heated by geothermal energy derived from volcanic heat. Geothermal reservoirs with temperaturesabove 180℃ centigrade are useful for
generatingelectricity. They occur primarily in regions of recent volcanic activity ashot, dry rock; natural hot water; or natural steam. The latter two sources arelimited to those few areas where surface water seeps down through undergroundfaults or fractures to reach deep rocks heated née the recent activity ofmolten rock material. The world’s largest supply of natural steam occurs at TheGeysers, 120 kilometers north of San Francisco, California. In the 1990s enoughelectricity to meet about half the needs of San Francisco was being generatedthere. This facility was then in its third decade of production and wasbeginning to show signs of decline, perhaps because of over development. By thelate 1990s some 70 geothermal electric-generating plants were in operation in California,Utah, Nevada, and Hawaii, generating enough power to supply about a millionpeople. Eighteen countries now generate electricity using geothermal heat.
Extracting heat from very hot, dryrocks present a more difficult problem: the rocks must be fractured to permitthe circulation of water, and the water must be provided arterially. 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 geothermal 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 energyto the world’s energy future is difficult to estimate. Geothermal energy is in a sensenot renewable, 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.
1. According to the processes describedin paragraph 1, what is the relationship between radioactivity and the steamproduced by geothermal heat?
Geothermally heated steam is producedwhen water is exposed to radioactivity deep underground.
When water is introduced into holesdrilled thousands of feet in the ground, it becomes radioactive and turns tosteam.
Radioactivity heats Earth's interiorrock, which in turn can heat water to the point it becomes steam.
When a reservoir of steam in subsurfacerock is produced by radioactivity, it is said to be geothermally heated.
2. The word %usable plentiful economical familiar
3. The word \economical familiar plentiful useful
4. According to paragraph 2, which of the following is true about heat reservoirs with a temperature in the range of 80° to 180° centigrade? They are under international control.
They are more common than reservoirs that have a higher temperature. Few of them produce enough heat to warm large industrial spaces. They are used to generate electricity.
5. According to paragraph 3, what is the connection between underground faults and naturally occurring steam?
Underground faults enable the heat from molten-rock material to escape upward to regions where it can heat surface water enough to produce steam.
Underground faults are created by steam that is produced in geothermal reservoirs deep inside Earth.
Underground faults create spaces in which natural steam is sometimes trapped.
Underground faults allow surface water to reach deep rocks that are hot enough to turn it into steam.
6. In paragraph 3, why does the author mention that in the 1990s The Geysers was in its third decade of production?
To provide the historical context of the geothermal production of electricity in the United States
To imply that The Geysers was the first geothermal site to be put into production in California
To help explain the signs of decline shown by The Geysers
To explain why 70 new geothermal sites were put into electricity production in the late 1990s
7. Which of the following can be inferred from paragraphs 2 and 3 about geothermal reservoirs?
Volcanic heat is associated only with geothermal reservoirs that have a temperature over 180° centigrade.
More countries produce power from geothermal reservoirs than use them for heating buildings.
Most geothermal reservoirs are suitable for producing electricity.
A higher geothermal reservoir temperature is needed to generate electricity than is needed to heat homes.
8. According to paragraph 4, extracting heat from very hot, dry rocks is difficult in part because
the underground rock must be fractured before heat can be removed from it the water above the rock is under very high pressure the rock breaks apart when water is pumped into it
the water circulated through the rock must be much cooler than the rock itself
9. The word \locating increasing making use of
estimating the size of
10. How is the problem that the surface may sink related to the problem that water heated geothermally may contain toxic materials?
Both problems could be solved by returning groundwater that is removed from an underground heat reservoir back to the reservoir after heat is extracted from it.
The problem of sinking is more difficult to solve than is the problem of toxic materials. Land at the surface sinks because the rock beneath the surface is weakened when salts and toxic materials are removed from it in the process of extracting geothermal energy. Both problems are caused by the fact that the hot groundwater in a heat reservoir
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