solar cells - The human population has now crossed the 6.5...

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The human population has now crossed the 6.5 billion mark, and the world is starting to show the strain we humans place on it. 6.5 billion people need a great deal of energy to run their 3.3 billion cell phones and over half a billion cars, but the planet has a limited supply of energy that was built slowly over four billion years. This is why solar power has captured the attention of all but those whose fortunes are tied to the success of non-renewable energy sources. Along with wind, wave, and thermal energy, solar power is an element of the renewable energy class. Barring a failure of our sun, solar power can never diminish in intensity or availability. In addition, generation of solar power does not detract from the environment, whereas most other sources of power emit toxins and pollution that do, causing solar power to be a commonplace technology. Despite its prevalence, most people do not understand the inner workings of a solar panel. A solar panel is a large array of solar, or photovoltaic, cells. The word photovoltaic is derived from the words “photo”, meaning light, and voltaic, meaning “producing electricity”. This is clearly the essence of a solar cell. In general terms, light shines on a semiconducting material, which produces free electrons, which in turn follow an electric field to create a current. The detailed explanation of a solar cell will follow this chronological order, beginning with the most essential factor: light. The sun produces an infinite supply of light at the earth, with an intensity of around 300 W/m 2 (3) , which, when collected by a decently-sized solar panel, is more than enough to power the average US home, which uses power at a rate about 1.2 kW (4) . Commercial solar panels have about 20% efficiency (5) , resulting in a necessary 20 m 2 to power the average US home. The seemingly low efficiency is actually near on par with the internal combustion engine, which provides near 30% efficiency. However, the low efficiencies exist for different reasons. The low
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efficiency in a solar cell is due to a large part (more minor effects exist, such as resistance, reflection of light, etc…) to the band gap in the solar cell semiconductor. A semiconductor (usually silicon in the case of the solar cell, but more choices exist) has
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This note was uploaded on 05/09/2008 for the course PHYS 124 taught by Professor Starkman during the Spring '08 term at Case Western.

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solar cells - The human population has now crossed the 6.5...

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