- Introduction to silicon pv material
- Technology development of silicon pv material
- Modified Siemens method - rod silicon technology
- Fluidized bed method - granular silicon technology
- Technology comparison of different silicon pv material
- Demand side of silicon pv material
- Silicon pv material supply side
- Development trend of silicon pv material
With the acceleration of the global carbon neutralization process and the increasing demand for home energy storage, the cost of superimposed photovoltaic power generation continues to decline, the economy continues to improve, and the high growth of photovoltaic installed capacity demand is more certain. This article will focus on silicon pv materials.
1. Introduction to silicon pv material
Silicon pv material is the core raw material of photovoltaic power generation system. Silicon pv material, that is, solar-grade polysilicon (SoG-Si), is the most upstream raw material in the photovoltaic industry chain, and is a gray-black solid with metallic luster. Silicon pv material has the characteristics of high melting point (1410 ℃), high hardness, brittleness, chemical inactivity at room temperature, etc., and has semiconductor properties. It is an extremely important and excellent semiconductor material, and is called "black gold" in the photovoltaic industry chain.
Silicon pv material is the core raw material that determines the power generation capacity of photovoltaic systems. Polysilicon is purified from industrial silicon and can be divided into metallurgical grade, solar grade and electronic grade according to the purity. Industrial silicon, also known as metal silicon, is a product smelted from quartz and coke in an electric heating furnace. The silicon content is generally above 99% (2N), and the remaining impurities are iron, aluminum, calcium, etc., which is the upstream raw material of polysilicon. At present, the preparation technology of polysilicon mainly includes chemical method and physical method.
In terms of product form, silicon pv materials can be divided into two types: rod-shaped silicon pv material and granular silicon pv material. The current mainstream polysilicon production technologies mainly include the modified Siemens method and the silane fluidized bed method, and the product forms are rod-shaped silicon and granular silicon pv materials respectively. Among them, the production process of the improved Siemens method is relatively mature, and rod-shaped silicon products are currently the mainstream of the industry, with a market share of 95.9% in 2021.
In 2021, the production capacity and output of silane-based granular silicon pv material will increase slightly, and the market share will increase by 1.3 pct year-on-year to 4.1%. In the future, if the production capacity of granular silicon pv material is further expanded, and with the improvement of the production process and the expansion of downstream applications, its market share is expected to further increase.
Compared with other links in the industrial chain, the silicon pv material industry has the characteristics of heavy assets + low turnover + high ROE.
2. Technology development of silicon pv material
① Modified Siemens method - rod silicon technology
The improved Siemens method is improved from the Siemens method to realize a closed loop of polysilicon production. Due to the low production conversion rate of the Siemens method and the production of a large amount of highly toxic by-product STC (silicon tetrachloride), the improved Siemens method with the addition of tail gas recovery and STC hydrogenation process was proposed based on the Siemens method. The modified Siemens method realizes a closed loop of the polysilicon production process.
The improved Siemens method has multiple advantages over the Siemens method, and has now become the mainstream production technology in the industry. Compared with the Siemens method, the improved Siemens method mainly has the following advantages: energy saving, material consumption reduction and pollution reduction. With the improvement of CVD technology, the progress of intermediate gas production technology and the prominence of large-scale benefits, the improved Siemens method has become the most mature, widely used and fastest-expanding production technology for photovoltaic polysilicon production.
② Fluidized bed method - granular silicon technology
At present, the fluidized bed reduction technology has two technical paths based on silane and TCS: silane fluidized bed technology is the second polycrystalline silicon pv material preparation process, and silane is used for reduction. The silane fluidized bed method is the same as the first half of the improved Siemens method, both of which are obtained through industrial hydrosilation to obtain trichlorosilane and separate the tail gas. However, in the silane fluidized bed method, trichlorosilane is hydrogenated to form silane in the second half, and it is passed into the fluidized bed reactor for continuous thermal decomposition.
A vapor deposition reaction then occurs on the prefabricated silicon seed crystals in the fluidized bed reactor to produce granular polycrystalline silicon pv material products. TCS fluidized bed technology directly uses TCS for reduction, but the reduction process is more difficult. Compared with the silane fluidized bed method, the TCS fluidized bed method directly uses TCS as the raw material, eliminating the process of disproportionating TCS to silane, and the front-end gas production process is simplified. However, the difficulty of the back-end reduction process has increased, and the difficulty of energy consumption and exhaust gas treatment has also increased accordingly.
③ Technology comparison of different silicon pv material
Compared with rod-shaped silicon pv material, the production cost of granular silicon is effectively reduced, and it is more suitable for automated production. The core advantages of granular silicon products compared to rod silicon include:
- Low production cost.
- No need for crushing, the production process is automated.
- Lower production cost of single crystal for downstream customers.
There are still problems in the use of granular silicon pv material, and currently it is mostly used as an auxiliary material with a proportion of no more than 30%. At present, there are still some problems in the use of granular silicon pv material. Therefore, at present, granular silicon pv material is mostly used as an auxiliary material to reduce costs, and it is used with rod-shaped silicon pv materials doping. The follow-up improvement of the existing problems of granular silicon still needs further process improvement.
At present, the problem of large surface area and easy adsorption can be solved by vacuuming and dust removal and double-layer wrapping packaging to avoid impurity pollution. In view of the problem of more silicon powder, there is a solution of vacuuming to reduce the friction between silicon particles, and later transitioning to a large tank, which is established on the user side and connected to the single crystal furnace through a pipeline. The problem of material skipping can be effectively solved by adding a heating step to further reduce the hydrogen content.
3. Demand side of silicon pv material
The global carbon neutralization process is accelerating, and clean energy is the general trend of the future. Under the global theme of carbon neutrality, the development of new energy is the general trend. The cost of photovoltaic power generation continues to decline, and the economy drives the demand for new installed capacity. From a global perspective, according to relevant data, the global levelized cost of electricity (LCOE) of photovoltaics will drop from US$0.417/kWh in 2010 to US$0.048/kWh in 2021. The decline is 88.49%, the cost is falling, and the economy is greatly improved.
From a horizontal comparison, other new energy power generation methods, such as offshore wind power/onshore wind power, will reduce electricity costs by 60.11%/67.65% respectively from 2010 to 2021, which is far behind that of photovoltaics. The global photovoltaic installed capacity continues to increase, and it is expected that the newly installed capacity will reach 270-330GW in 2025. According to IRENA data, in the context of the acceleration of global carbon neutrality, the cost of superimposed photovoltaic power station continues to decline, and the economy continues to improve. The global installed photovoltaic capacity has increased from 17.46GW in 2010 to 132.81GW in 2021.
According to the forecast of CPIA, the newly installed photovoltaic capacity in the world will reach 270-330GW in 2025. The expansion cycle of silicon pv material is longer than other links, and there is a mismatch with the demand for photovoltaic installations. The polysilicon industry is characterized by a long construction period for expansion, which is about 18 months. The production capacity of silicon wafers/cells/modules in its downstream links expanded rapidly, for 12/9/6 months respectively, and the annual production capacity of downstream links was significantly higher than that of silicon pv materials.
Therefore, there may be a periodical shortage of silicon pv material at certain stages. On the other hand, the production of silicon pv materials needs to maintain a high operating rate, so the quarterly output is at a relatively stable level, while the demand for photovoltaic installations has low and peak seasons with large seasonal fluctuations, so there is a certain mismatch between the supply of silicon pv materials and the demand for photovoltaic installations. The direct downstream link of polysilicon is silicon wafers, and the large-scale expansion of silicon wafers drives the growth of demand for silicon pv materials.
In the photovoltaic industry chain, the most closely bound with the silicon pv material link is its direct downstream link, the silicon wafer end. In recent years, with the acceleration of the replacement of polycrystalline silicon wafers by monocrystalline silicon wafers, the gross profit margin of silicon wafers has increased rapidly, which has attracted new and old silicon wafer manufacturers to significantly expand their production capacity. The large-scale production of silicon wafer production capacity has further increased the demand for silicon pv material procurement, and silicon wafer companies have begun to sign long-term silicon pv material procurement orders to ensure the supply of raw materials.
4. Silicon pv material supply side
The production of silicon pv material has high technology and capital barriers, and has high requirements for companies. The chemical properties of the silicon pv material industry are relatively obvious, and it mainly has the characteristics of two highs and one long: high purity requirements, high equipment investment and long production expansion period. China's polysilicon production capacity continues to increase, leading the global production capacity growth. With the large-scale production of low-cost polysilicon production capacity in China, the global higher-cost polysilicon production capacity has gradually withdrawn from the market.
According to forecasts, China's silicon pv material production capacity will reach 1.177 million tons in 2022, a year-on-year increase of 88.92%, accounting for about 91.52% of the global silicon pv material production capacity. The global silicon pv material production capacity will reach 1.286 million tons, a year-on-year increase of 66.15%. In 2023, China's silicon pv material production capacity is expected to reach 3.102 million tons, a year-on-year increase of 163.55%, accounting for 96.61% of the global silicon pv material production capacity.
The global silicon pv material production capacity is expected to reach 3.211 million tons, a year-on-year increase of 149.69%. The global polysilicon production capacity has increased year by year, gradually concentrating on Chinese companies. As of 2021, the number of Chinese companies in the top ten global polysilicon production companies will be as high as 8, and the market share of Chinese silicon pv material companies will be large.
5. Development trend of silicon pv material
The N-type era leads the demand for high-quality polysilicon, and the improved Siemens method has a bright future. In 2021, the market share of PERC cells will be 91.2%. The relative cost of N-type cells is relatively high, and the scale of mass production is still small. The current market share is about 3%. In 2021, the average conversion efficiency of N-type TOPCon cells will reach 24.0%, and the average conversion efficiency of HJT cells will reach 24.2%, both of which have been greatly improved compared with 2019. In the future, with the reduction of production costs and the improvement of yield, N-type battery will become the main development direction of photovoltaic battery companies.
N-type silicon wafers have higher requirements on the purity of silicon pv materials. As downstream cells and silicon wafer products move towards the N-type era, the quality requirements for polysilicon are gradually approaching from solar-grade polysilicon to electronic-grade polysilicon. At present, some polysilicon products produced by Tongwei, Tianhong Ruike and other companies using the improved Siemens method can already meet the requirements of electronic-grade polysilicon and can be used for N-type monocrystalline silicon wafers.
The purity of granular silicon produced by the fluidized bed method is 6-9N, which can only meet the requirements of solar-grade products. Whether it can meet the use of N-type silicon wafers in the future remains to be verified. In the future, the cost of improving Siemens technology still has a lot of room for decline, and it will still occupy the mainstream position in the industry. According to the forecast of CPIA, in the future, with the improvement of production equipment technology of polysilicon companies, the improvement of system optimization ability, and the increase of production scale.
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