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We have extensive experience of designing plants for the solar industry.
Our lives literally revolve around the sun. Its almost inexhaustible power inspires many ideas and developments. For our customers, it is a valuable source of energy that can be used technically in the form of electricity, heat or chemical energy. Sunbeams are electromagnetic waves. The amount of energy that reaches the surface of the earth each year is more than 5,000 times greater than humanity's total energy requirement. Solar energy reduced CO2 emissions by 3.6 million tons.
Environmental protection and reduced depletion of resources are just two of the benefits resulting from the use of solar energy. The solar industry has developed into an important sector of the economy, and it is also a major employer.
EPC can look back on many years of wide-ranging experience of designing plants for the solar industry, such as plants for manufacturing ultrapure silicon, and solar factories for producing ingots, wafers and modules. All our know-how is also at your service to help you plan the delivery, commissioning and maintenance of important subsidiary processes, such as slurry handling systems, waste gas cleaning, monosilane and hazardous substance stores, as well as supply and disposal systems. Evaluation of the economic efficiency along the entire value added chain, from the project idea through to the finished concept, is the essential factor that ensures that your plant will run profitably and remain competitive in the market over the long term.
Silicon ingot / wafer/ cell / module factories
Polysilicon is initially processed to form ingots (blocks or rods of mono- or multicrystalline silicon) in crystallisation furnaces developed for this purpose. The silicon rods are comminuted, and then melted in a quartz crucible. After which silicon blocks form as the melt is allowed to cool slowly. Diamond wire saws then cut the ingots into a number of equally sized cuboids, known as bricks. These bricks are then sliced into wafer-thin silicon plates. The wafers are cleaned and examined for saw damage. This is followed by chemical cleaning, and subsequent texturing to roughen the surface to increase the light coupling in the solar cell. The wafers are exposed to gas containing phosphor in a diffusion furnace. This doping of the wafers improves their absorption of sunlight. An anti-reflection coating is applied to the front surface of the wafers to improve their absorption and electrical properties even further. The front and the back of the cells are electrically insulated to prevent recombination losses and short circuits. The finished cells are now ready for module processing.
The EPC Group offers its customers all the know-how along the entire added value chain required to construct plants for the solar industry. We design plants for manufacturing ingots, wafers, cells and modules, together with all the ancillary plants for exhaust air and waste water treatment, redundant power supplies, hazardous substance stores and handling systems for monosilane and other essential substances. As an experienced general planner, we can assist at every stage of the construction of a new solar factory, or the extension and renovation of an existing factory.
The method of producing ultrapure silicon from metallurgic silicon is based on the thermal decomposition of highly pure, rectified chlorosilanes or silanes to form silicon with the separation and recycling of gaseous byproducts. The conventional commercial technology passes through the stage of producing trichlorosilane in a fluidized-bed reactor from metallurgic grade silicon and hydrogen chloride. The trichlorosilane is then subjected to multi-stage rectification until the purity required for the desired application is reached (solar grade or electronic grade). The thermal decomposition of trichlorosilane in a chemical vapor deposition (CVD) reactor to form silicon at 900 °C creates a mixture of gaseous by-products, which have to be prepared for recycling (vent gas recovery) back into the process. We have optimized the process for producing ultrapure silicon from monosilane. It now offers a significantly higher efficiency as temperatures are only around 600 °C, and the collection efficiency has been increased to almost 100% in comparison to the mere 25% achieved by conventional processes. Monosilane is obtained by the disproportionation of trichlorosilane and recirculation of the disproportionation products. Trichlorosilane is thus required in both methods.
The gas mixture produced by the thermal decomposition of trichlorosilane in a chemical vapor deposition (CVD) reactor has to be separated into its constituent parts before the individual products can be recirculated. The monosilane method does not need these cycles, however Vent Gas Recovery is still part of our range or products.
The monosilane synthesis gas is stored temporarily in vacuum-insulated containers prior to further processing or filling. The containers are equipped with a pressure build-up vaporizer and an internal cooling coil to facilitate cooling. The containers are a special product of our subsidiary company, CRYOTEC, which specializes in special cryogenic applications.
Silicon tetrachloride is the main by-product of both the production of trichlorosilane from metallurgic silicon with HCl in a fluidized-bed reactor and the disproportionation of trichlorosilane. The thermal decomposition of trichlorosilane in a CVD reactor also creates large quantities of silicon tetrachloride. The silicon tetrachloride is converted with hydrogen into trichlorosilane in a conversion reactor. This process can be run homogeneously with hydrogen at approximately 1,000 °C in graphite reactors. We use the more elegant heterogeneous method of controlling the process by feeding silicon into a fluidized-bed reactor.