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Take Home Test 2.docx

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CHEM 1105
Riley Mcminn

Chantz Delgado Chemistry and Society November 8 , 2011 Take Home Essay: Exam 2 Conversion of Solar Energy to Electricity As technology progresses, scientists are hoping to find alternate ways of converting energy to electricity other than combustion. The fastest growing alternative energy technology is currently the conversion of solar energy. There have been a number of breakthroughs to support the efficiency of this advancement in technology. Moreover, the combustion technique is proving to be unreliable due to the depletion of fossil fuels. Asolar panel, otherwise known as a photovoltaic module, is a confined and connected assembly of photovoltaic cells. It is used as a component of a bigger photovoltaic system, which is basically taking energy from the sun and converting it to electricity to provide energy for homes and businesses. This process is very complex and tedious because solar energy is thinly spread out and difficult to concentrate. Photovoltaic cells or solar cells are devices that can be made from a variety of substances, but most are made from elemental silicon. In a crystal of pure silicon, the atoms have four valence electrons and are covalently bonded to four other silicon atoms. In order to make a solar cell, one must mix small amounts of impurities with the silicon to transform it into single crystals. “One type of crystal has about 1 ppm of arsenic added.Arsenic atoms have five valence electrons, four of which are used to form bonds to silicon atoms. The fifth electron is relatively free to move around. Because this material has extra electrons, and electrons are negatively charged, it is called an n-type semiconductor.Adding about 1 ppm of boron to silicon forms a different type of material. Boron has three valence electrons, producing a shortage of one electron and leaving a positive hole in the crystal. This boron-doped silicon is called a p-type semiconductor.” In other words, when the n- type crystal and the p-type crystal forms together, the outcome is a photovoltaic cell in which the electrons flow from the n-type region to the p-type region. When the sunlight hits the photovoltaic cell, electricity is generated. The photons knock electrons out of the single bonded silicon atoms creating more energetic electrons thus producing more positive holes. Lastly, an external circuit connects the two crystals and since the barrier at the junction between the two semiconductors causes the electrons to stay put through the interface, the electrical current can be used directly. Unfortunately, solar cells are not very efficient, although using lenses or mirrors with the system led an efficiency of more than forty percent. Most of the sunlight is reflected back into space or converted into heat. If we decide to only use solar energy, in order for us to generate enough energy to meet a small portion of the nation’s energy demands, it would require covering large areas of desert land with solar cells and that is almost impossible. “It would require 2000 hectares (about 5000 acres) of cloud-free desert land to produce as much energy as one nuclear power plant. Fortunately, research has led to more efficient and cheaper solar panel systems. For instance, the breakthrough of silicon and thin film technology has caused the efficiency to increase. One must understand that using solar energy requir
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