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  3. Solar-generated electricity docs not carry the health or environmental risks of nuclear energy. We can never run out of solar en

Solar-generated electricity docs not carry the health or environmental risks of nuclear energy. We can never run out of solar en

admin2010-06-18  47
问题    Solar-generated electricity docs not carry the health or environmental risks of nuclear energy. We can never run out of solar energy, because the sun is a renewable energy source.
   Two kinds of systems generate solar energy: passive and active. A passive solar energy system generates energy from fixed glass plates built into the structure, without the use of mechanical devices. A greenhouse is a good example of a building heated by passive solar energy. The sun’s rays penetrate the glass panels to heat the interior of the greenhouse, and the heat is retained through tight construction. The same principle can be applied to heating homes and other buildings on sunny days.
   An active solar energy system makes use of mechanical devices and moving parts to maximize the amount of energy collected. For example, solar energy can be generated with photovoltaic cells, which are made from silicon, an abundant element. A bank of photovoltaic cells can be encased in glass and wired together to produce electricity. The bank of cells can be mounted on the roof at an angle that maximizes exposure to direct sunlight.   
   Another device to generate solar energy is a flatplate collector, which is an insulated glass box, typically placed on the sun-facing roof. Inside the box are pipes filled with air or water. The heat that builds up in the pipes can be used for home heating and hot-water supplies.
   Two questions persist about solar energy:
   How can solar energy be used in colder climates?
   How can solar energy be used on cloudy days?
   Scientists have the technological means to overcome both problems, but the solutions may make solar energy more expensive for many people than other alternatives.
   The energy released from the sun is about 10,000 degrees F, but by the time the rays reach the earth the temperature is considerably lower, because the sun’s energy has diffused over a large area during its long journey. To be useful energy in colder climates, the sun’s diffused rays must be concentrated.
   The process of concentrating the sun’s rays is not difficult. Scouts learn that sunlight focused with a lens at the proper angle can burn a piece of paper. In warmer climates, the sun’s rays can provide heat and hot water with little concentration. In colder climates, compensation is made simply by collecting more of the sun’s rays by building a larger collecting device and rotating the lenses as the sun’s position in the sky changes. In cloudy weather, another system can store the energy generated from the sun. For example, water heated by the sun can be retained in protected storage containers.
   Because of high installation coasts, solar energy is more expensive than other sources of energy for most consumers. At this time, electricity provided by a solar power plant costs two or three times the amount of a coal-fired plant. But solar equipment is generally installed on the consumer’s roof rather than at a central power plant, as is the case with other energy sources. A family must pay several thousand dollars to construct a solar energy system capable of providing virtually all household heat and electricity. The family is also responsible for maintenance and repair of the system.
   While initial construction costs are much higher, monthly heating and electricity bills are much lower once the system begins operation. Users of solar energy do not face rising monthly electricity bills from a power company, which passes to its consumers the increasing costs of purchasing fossil fuels and constructing new facilities. Solar energy is economical for consumers who remain in the same house for many years and can benefit from low monthly operating costs. For most families, solar energy will become more attractive when other energy sources become more expensive. One indication of solar energy’s bright future is that petroleum companies have bought the major U.S. manufacturers of photovoltaic cells.
Which of the following is NOT TRUE of solar energy?
选项 A、The technical problem of providing heat on cloudy days are not yet solved.
B、It costs much to have a solar energy system installed at home.
C、There are basically two types of solar energy.
D、Solar energy is clean, inexhaustible and free of risk.
答案A
解析
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