At present, in order to solve the energy crisis and environmental pollution problems, countries have formulated policies aimed at promoting the development of renewable and clean energy. Promoted by the new energy policies of all countries in the world, solar energy products have become the main role in the green energy series. Photovoltaic glass is one of the most important components in solar energy products. It affects the absorption of visible light by solar energy products and determines the conversion energy of photovoltaic modules. Therefore, the production of high quality and high transmittance photovoltaic glass is of great significance to the utilization of solar energy.
　　1. Introduction of Photovoltaic Glass
　　Photovoltaic glass is also ultrawhite glass, also known as low iron glass, colorless glass, high transparent glass, with high transmittance and high transparency. The transmittance of glass determines the quality of glass. The transmittance of ordinary float glass is 86%, while that of photovoltaic glass is more than 92%.
　　The quartz raw materials for glass production are natural quartz sand, quartz sandstone, quartzite and vein quartz, etc. The production of photovoltaic glass is more difficult, and the requirements for quartz raw materials are higher than ordinary glass.
　　2. Quality Requirements and Control of Quartz Sand for Photovoltaic Glass
　　In nature, few untreated quartz sand raw materials can be found to meet the requirements of glass production, especially ultra-white glass. Quartz sand raw materials are more stringent. The quality requirements of photovoltaic glass for quartz sand are mainly embodied in three aspects: chemical composition, particle size and refractory heavy minerals.
　　chemical composition
　　The biggest difference in chemical composition between photovoltaic glass and ordinary glass is the content of Fe2O3. Photovoltaic glass requires that the mass fraction of Fe2O3 should not exceed 1.50x 10-4.
　　The amount of iron oxide in quartz sand will directly affect the quality of solar glass. The amount of iron oxide affects the absorption of visible light by glass. It determines the conversion energy of photovoltaic modules. It is one of the key factors to measure whether it can be used as the principle of photovoltaic glass.
　　Iron oxide colors glass and reduces its transmittance. Fe2O3 can make glass yellow; Fe O can make glass blue; the coexistence of the two can make glass blue-green.
　　Iron oxides can absorb the heat radiation of glass melting strongly, which can easily lead to the difficulty of convection of glass liquid in the furnace and increase the difficulty of melting and clarifying.
　　granularity
　　The size of quartz sand particles affects the melting time of sand particles and the quality of glass products. Experiments have proved that it is difficult for coarse particles to melt, or even become scum, which may cause ribs or sand particles on the products. Although the melting speed of sand particles with particle size less than 0.1mm is fast, the formation of glass liquid too early affects the heat transfer, but slows down the overall speed. In addition, too fine particles are easily agglomerated because of the increase of viscosity due to electrostatic action. It makes melting difficult. Therefore, the grain size requirements of quartz sand for photovoltaic glass are as follows:
　　Refractory heavy minerals
　　Some refractory heavy minerals in quartz sand, such as chromite and zircon, have high melting point and stable chemical properties. They are difficult to be melted even at high temperature, so they are easy to form stones on the glass plate. It has a great influence on the quality of glass sheet and its further processing. The total amount of chromite and nickel-bearing minerals is not more than 5 ppm (in Cr2O3), and the diameter of single particle is not more than 0.25 mm. For other refractory heavy minerals, the diameter of single particle is not more than 0.25 mm.
　　3. Quality Control of Quartz Sand for Photovoltaic Glass
　　In the formation and growth of quartz, accompanied by a large number of impurity minerals, there is no quartz raw material that can meet the production of photovoltaic glass without treatment. Therefore, the quality control of quartz sand for photovoltaic glass is mainly realized through the purification of quartz sand. The common methods of mineral processing and purification of quartz sand are divided into physical and chemical methods.
　　Physical methods: water washing, magnetic separation, flotation, electrical separation, mechanical scrubbing, graded desliming, microwave-assisted, ultrasonic-assisted.
　　Chemical methods: acid leaching, alkali leaching and microbial leaching.
　　Control Method of Iron Content in Quartz Sand
　　There are various forms of iron-bearing substances in quartz sand. All the methods of mineral processing and purification of quartz sand can remove iron to a certain extent. Among them, graded desliming mainly removes argillaceous iron, magnetic separation removes iron-bearing substances from ores, gravity separation removes iron in the form of heavy minerals, flotation removes light silicates containing iron, etc. It is necessary to remove iron from quartz sand for photovoltaic glass. In actual production, the purification process with the lowest cost and the simplest process should be selected according to the chemical composition of quartz sand.
　　Particle Size Control of Quartz Sand
　　The particle size control of quartz sand for photovoltaic glass can be achieved by water separation and sorting. Among them, water separation is mainly fine mineral particles less than 0.1 mm; rolling screen and hindered settling machine are used to separate coarse quartz sand particles. According to the requirement of particle size separation, controlling the upper limit of feed size and choosing reasonable water washing separation process can improve the yield of quartz sand concentrate and product quality control.
　　Control Method of Refractory Heavy Minerals in Quartz Sand
　　The control method of refractory heavy minerals in quartz sand for photovoltaic glass is mainly realized by gravity separation. In gravity separation, the minerals with larger specific gravity tend to move faster in the trough and enter the tailings area, while those with smaller specific gravity tend to move faster outside the trough and enter the next process. It is noteworthy that in order to ensure the accuracy of gravity separation, it is necessary to feed ore evenly during gravity separation.