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| Solar Cells |
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| Solar cells are expensive and are used only when supplying electricity becomes difficult. |
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| Solar cells are the devices where solar energy is directly converted into electricity. Solar cells are used in spacecrafts, radios, television, refrigerators, buoys and other navigation aid. |
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| Solar Cell |
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| Sunlight can be used to run machinery and
generate electricity. In photovoltaic cells, electricity is produced when
light is incident on photosensitive materials. Even though they are costly today they will become cheaper to make when new methods are invented. The cost making the solar cells is expected to decrease, when new methods are invented in future. |
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| About hundred years ago it was found that
when sunlight falls on a thin layer of selenium electricity is produced. But
the efficiency of the conversion was low (as low as 0.6%). Solar cells were
not popular for a long time because of its low efficiency. |
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| The first practical solar cell was constructed in 1954 with an efficiency of 1%. Today we have selenium based solar cells with an efficiency of 25%. |
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| Semiconductors whose conductivity is more than insulators and less than metals are used in electronic devices. The conductivity of the semiconductors increase when light falls on it. Wafers of doped semiconductors are so arranged that when sunlight falls on the arrangement, potential differences are developed and the energy is stored. This forms the solar cell. The energy developed is proportional to the surface area of the wafer exposed to light. The efficiency of the solar cells made from semiconductors is around 10% to 15%. |
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| Here a number of solar cells are arranged so that, the potential difference developed is the sum of the potential difference developed across the individual ones. These solar panels are used mostly in remote and isolated areas. |
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