Feasibility of the Production of Silicon in Trinidad for Use in Solar Cells

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The demand for renewable sources of energy in Trinidad is increasing because the historical reliance on fossil fuels is being challenged by increasing environmental awareness and its depletion because it is a non – renewable resource. As a reliable and versatile form of renewable energy, solar photovoltaic systems are expected to become a dominant energy source to the world in the future so Trinidad needs to take measures to ensure it has a reasonable share in the renewable energy source markets in the future or else its continued reliance on fossil fuels will destroy its economy. The majority of photovoltaic systems today use silicon as a means of converting solar energy to electrical energy. Silicon is produced from silica, which is abundant in the Earth’s crust. There are different types or grades of silicon produced and producing solar grade is an expensive process. First silica is converted into 98% pure silicon or metallurgical grade silicon, which is then used to produce semiconductor grade silicon or polysilicon. This polysilicon is very valuable but is needed to produce solar grade silicon which is less valuable but is needed for photovoltaic systems. For a proposed solar grade silicon plant in Trinidad it was found to be most feasible to buy metallurgical grade silicon since it is cheap and use it to produce polysilicon which is the converted to solar grade silicon, however most of the polysilicon produced has to be sold to the semiconductor industry rather than converting it all to solar grade silicon or else the plant will not produce enough revenue to be feasible.

1Literature Survey7
1.1Silicon and its Properties7
1.2Photovoltaics and Solar Cells9
1.3Silicon Processing for Photovoltaics13
1.3.1Purification methods13
1.3.2Silicon Production14
1.4Solar Grade Silicon Crystalline Technologies18
1.4.1Monocrystalline Silicon20
1.4.2Multicrystalline Silicon25
1.5Thin - Film Technologies28
1.5.1Amorphous Silicon28
1.6Energy Invested In The Production Of Photovoltaic Modules:31
1.7Pay Back Period And Lifetime For Silicon Wafers32
1.8Environmental Impact Of Solar Grade Silicon Production32
1.9Markets and Economics for the Photovoltaic Industry33
1.10The Silicon Supply Problem35
1.11Silicon Production For Photovoltaic Cells In Trinidad37
2Calculations and Results41
2.1Process description41
2.2Material balance44
2.3Energy Balance56
2.4Feasibility Study82
2.4.1Equipment Sizing and Costing82
2.4.2Economic Evaluation93
3.2Environmental impact of proposed silicon plant114
3.3Arguments For And Against Photovoltaics As A Source Of Energy114

Figure 1: Silicon crystal lattice structure7
Figure 2: A Solar Panel9
Figure 3: Metallurgical Grade silicon production skematic15
Figure 4: Cross section of the polysilicon chemical vapour deposition reactor17
Figure 5: A rod of polysilicon17
Figure 6: A polysilicon chunk18
Figure 7: outlining materials, respective price on the world market (1994) and the process undergone to form the next material19
Figure 8: Equipment used in the Czochralski growth process for monocrystalline silicon production20
Figure 9: The purified silicon chunks are melted in a quartz crucible before melting20
Figure 10: The purified silicon chunks in a quartz crucible after melting21
Figure 11: Ingot of crystalline silicon21
Figure 12: Multi – wire sawing process to cut silicon ingots into wafers23
Figure 13: Diagram of the floatzone process24
Figure 14: Pie chart showing market shares of the different solar grade silicon technologies used for making solar cell wafers25
Figure 15: Diagram of block casting apparatus26
Figure 16: Diagram of block casting process for multicrystalline silicon26
Figure 17: Diagram showing the distinction...
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