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Dramatic oil prices increase that we watched in 2008 called for alternative competing energy sources. One of them is sustainable solar energy, which in most applications is being converted to electricity using silicon photovoltaic modules. Polycrystalline silicon is a key component of solar panel construction. The photovoltaic solar industry is growing rapidly but is likely going to be very limited due to severe shortages and allocations of the polysilicon material.
June 17th, 2009
Solar Cells: New technology for cheap crystalline silicon fabrication using microwave plasma discharge
In 2006 for the first time over the half of world's polysilicon supply was used for production of renewable electricity solar power panels. Currently, there are only twelve production plants for solar grade polysilicon in the world. It causes scarcity of materials for solar panels and due to that the prices for polysilicon and monosilicon scrap quickly increase.
The hydrogen pyrolysis of SiHCl3 is currently widely used to produce polysilicon. It is a very energy consuming chemical process and has low efficiency. The utilization of SiCl4 as a raw material to produce polysilicon could decrease the effectiveness of the process even lower. In addition the latter process runs in a very aggressive environment under very high temperature, which spoils purity of polysilicon. Obviously there is a need in a new highly efficient, energy saving and environmentally clean pure polysilicon production technology.
The scientists at General Physics Institute, Russian Academy of Sciences (http://www.gpi.ru/eng/index.php ) developed a new technique to produce pure polysilicon from the silicon containing gas phase chemical substances using microwave plasma discharge instead of traditional high temperature hydrogen pyrolysis.
Cost of manufacture
Cost of polysilicon manufacturing using traditional approach is high primarily due to very high electrical energy consumption. In proposed technology the electricity consumption is several orders of magnitude less (about 20-40 kW.h/kg), which leads to a substantially lower cost (at least 10 times). Thanks to the microwave discharge narrow area localization, the plasma does not touch the device's walls, which allows increasing the purity of final product. The product's purity only depends on the purity of initial reagents. Thus this product could be used not only for the solar elements manufacturing, but even to grow the monocrystalline silicon with electronics grades.
Preliminary calculations show that the cost of 1 Kg polysilicon manufacturing (with production capacity about 3,000 Kg per month) will not exceed $10. Current market allows to price polysilicon at least for $100/Kg, and there still will be high demand. Thus even mentioned small production will result into $270,000 revenue per month or more than $3 mln. per year.
The increase of production throughput to 10,000 Kg per month would drop the production cost to potential $6-7 per Kg.
The key role in the process developed by the General Physics Institute scientists plays the microwave plasma torch. The idea and design of plasma torch had been patented. The design is based on the traditional and very common parts, which makes the new plasma torch very inexpensive. The most important accomplishments obtained during numerous experiments:
-stable microwave plasma plume;
-practically any gas could be used for plasma discharge (tested: air, oxygen, argon, hydrogen, nitrogen, dichlorodifluoromethane, methane, and various combinations of listed gases;
-plasma plume size 1-1.5 cub. Dm;
-cheap torch design (100-1000 times cheaper than traditional plasma torch).
New technology major advantages
The following major new technology advantages could be listed:
-reduced power consumption (more than 10 times);
-increased silicon purity due to localization of plasma reaction;
-high reaction speed, and correspondingly, high throughput;
-expanded list of raw ingredients to produce polycrystalline silicon;
-better environmental friendliness;
-substantial (several times) decrease of hydrogen consumption;
-wide selection of construction materials to build the chamber for chemical reaction due to low reaction temperature and localized plasma plume;
-the equipment could be used in the future to produce other materials from gas phase: diamond -like thin films; diamond -like particles; SiC, Ti powders and various other materials.