Upgrading Metallurgical Grade Silicon to Solar Grade Silicon

Abstract

The photovoltaics (PV) is a method of direct conversion of solar energy to electricity using semiconductor solar cells. In terms of globally installed capacity, PV remains third the most important renewable energy source after hydro and wind powers. 31.1 GW of PV systems were installed around the world in 2012 and up from 30.4 GW in 2011.There is a rapid growth of PV cell production and it is expected to increase further. However PV technology have to cost effective in comparison to hydro or wind powers and other sources of renewable energy. It has to reach the "grid parity" i.e. less or equal price for generated electricity power. More than 85% of solar cells (SC) are made from solar grade silicon (SoGSi). SoGSi is produced by purification of metallurgy grade silicon (MGSi) which is produced by carbon recovering silicon from quartz. Also Quartz is an initial and essential material for obtaining SoGSi and SC. Rich resource of quartz Sarykol located at southern part of Kazakhstan where the main factory for MG Si production «Каzsilicon» is situated. Upgrading of MGSi up to SoGSi consists is a number of technological steps and SoGSi is basis for PV industry. Therefore the cost of SoGSi determines the competitiveness of PV technology compared to other energy sources. There are several chemical and metallurgical technologies for SoGSi production. This paper briefly describes these technologies and shows main advantages of metallurgical technologies based on slag refining (oxygenation). Considered technologies are the basis for industrial production of SoGSi, solar cells with an efficiency of 15.8-17.1% and solar panels. The 1st power plant made from solar panels in Kazakhstan was launched in December 25, 2012 by «AstanaSolar» with a total capacity of 250 kW.

The Possibility of Silicon Purification by Metallurgical Methods: Part I

“…Further, it is quite easy to remove impurities from the surface of the particles using the acid leaching process, in case of optimal process parameters. As known from previous studies [16][17][18] the best Si impurity removal levels by the acid leaching process were achieved for the samples crushed to 0.5-3 mm size. Therefore, the acid purification step was completed with Si crushed to the specified size, according to a proven method.…”

“…The impurity composition of both MG-Si and Si obtained after slag refining is shown in Table 1. Based on previous studies [16][17][18], we calculated the new slag composition for 9 slag refining processes. MG-Si slag-refining method was worked out using the "Parallel" induction furnace during the experiments (Figure 1).…”

“…Samples obtained after each slag refining process were analyzed to determine the impurity quantities in the obtained purified MG-Si (Table 1). Based on previous studies [16][17][18], we calculated the new slag composition for 9 slag refining processes. MG-Si slag-refining method was worked out using the "Parallel" induction furnace during the experiments (Figure 1).…”

“…Namely, the slag refining method was used for purification. The Institute of Physics and Technology (Almaty, Kazakhstan) has conducted several studies on methods of metallurgical-grade silicon (MG-Si) production and purification of silicon to UMG-Si, as well as research on silane production methods [16][17][18][19][20][21][22]. As a result of previously conducted studies and works, purified silicon samples and Si crystals grown by the Czochralski method were obtained on a laboratory scale, approximately 2-3 kg.…”

“…Based on the results of the literature sources [23][24][25], as well as a number of our preliminary research concerning this topic [16][17][18][19][20][21][22], further development and improvement of technologies for obtaining and refining Si to solar quality is promising and of strategic importance for the Si industry of Kazakhstan.…”