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  3. The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving

The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving

admin2020-04-14  30
问题     The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving parts. The basic problem with the use of solar photovoltaic devices is economics, but until recently very little progress had been made toward the development of low-cost photovoltaic devices. The larger part of research funds has been devoted to the study of single crystal silicon solar cells, despite the evidence that this technique holds little promise.
    The reason for this pattern is understandable and historical. Crystalline silicon, however, is particularly unsuitable to terrestrial solar cells.
    Crystalline silicon solar cells work well and are successfully used in the space program, where cost is not an issue. While single crystal silicon has been proven in extraterrestrial use with efficiencies as high as 18 percent, and other more expensive and rare materials can have even higher efficiencies, costs must be reduced by a factor of more than 100 to make them practical for commercial uses. Besides the fact that the starting crystalline silicon is expensive, 95 percent of it is wasted and does not appear in the final device. Recently, there have been some imaginative attempts to make polycrystalline and ribbon silicon which are lower in cost than high-quality single crystals; but to date the efficiencies of these apparently lower-cost materials have unacceptably small.
    This difficulty can be avoided by preparing completely disordered or amorphous materials. Amorphous materials have disordered atomic structure as compared to crystalline materials: that is, they have only short-range order rather than the long-range periodicity of crystal. The advantages of amorphous solar cells are impressive. Crystalline silicon must be made 200 microns thick to absorb a sufficient amount of sunlight for efficient energy conversion, whereas only 1 micron of the proper amorphous materials is necessary. Crystalline silicon solar cells cost in excess of 100 per square foot, but amorphous films can be created at a cost of about 50 cents per square foot.
    Although many scientists were aware of the very low cost of amorphous solar cells, they felt that they could never be manufactured with the efficiencies necessary to contribute significantly to the demand for electric power. This was based on a misconception about the feature which determines efficiency. For example, it is not the conductivity of the material in the dark which is relevant, but only the photoconductivity, that is, the conductivity in the presence of sunlight. Already, solar cells with efficiencies well about 6 percent have been developed using amorphous materials, and further research will doubtlessly find even less costly amorphous materials with higher efficiencies.
In this passage, the author mainly describes ______.
选项 A、the advantages of solar cells
B、the efficiencies of solar cells
C、how solar cells are manufactured
D、in what ways solar cells are used
答案B
解析 全文有四段，前两段关于晶体硅太阳能电池的性能，后两段关于非晶体太阳能电池的性能，可见本文主要关于太阳能电池的性能，这也可从文中多次出现efficiency，efficiencies这一字眼看出来，故选B。
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