- Why should polysilicon with purity higher than 6N be used in the production of photovoltaic cells
This is based on the photoelectric conversion efficiency of photovoltaic cells. At present, the photoelectric conversion efficiency of monocrystalline silicon photovoltaic cells required internationally is more than 17%. According to our current production technology, only polycrystalline silicon with purity higher than 6N can be competent, so polycrystalline silicon with purity lower than 6N is not used. However, it is not to say that polycrystalline silicon with purity less than 6N cannot produce photovoltaic cells. Polycrystalline silicon with purity below 6N can also produce photovoltaic cells. At present, tycorun manufacturers in China have produced photovoltaic cells with 5N polycrystalline silicon produced by physical method, and the initial photoelectric conversion efficiency of the produced cells has reached about 15%.
However, the retention period of the photoelectric conversion efficiency of this kind of photovoltaic cells is too short and decays too fast. After one or two days of illumination experiment, the photoelectric conversion efficiency of these photovoltaic cells decays to 10% ~ 12%. This kind of photovoltaic cell can also generate electricity, but the difference is that with the same power, the required photovoltaic cell area is large, there are many photovoltaic cells, and the service life is short. In a word, this kind of photovoltaic cell has low quality and low use value, which is not suitable for development.
The quality of photovoltaic cells produced with 5N polycrystalline silicon is low, so the quality of photovoltaic cells produced with less than 5N polycrystalline silicon is naturally even lower. Therefore, according to the current production technology, polycrystalline silicon less than 5N cannot be used to produce photovoltaic cells.
- What is the distribution of solar energy resources in China?
The amount of solar energy resources is expressed by the total amount of solar radiation and the total sunshine hours of the whole year. China is rich in solar energy resources, with 2 / 3 of the regions having annual total solar radiation of more than 5024mj / m2 and annual total sunshine hours of more than 2000h. Due to China’s vast territory, different latitudes, different landforms and different climatic conditions, the distribution of solar energy resources is also extremely uneven.
China’s Tibet, Qinghai, Xinjiang, Gansu, Ningxia and Inner Mongolia have the highest total solar radiation and total annual sunshine hours in China. In addition to the Sichuan Basin and adjacent areas, the solar energy resources in most parts of China exceed or equal to those in foreign countries at the same latitude, better than those in Europe and Japan. In particular, the Qinghai Tibet Plateau is the largest, with an average altitude of more than 4000m, a thin and clean atmosphere, good transparency and long sunshine time. For example, Lhasa, known as the “sunshine city”, has an average annual sunshine duration of 3005.7h from 1961 to 1970, which is higher than other provinces and regions in China and regions at the same latitude. The total annual solar radiation in Sichuan and Guizhou provinces is the smallest in China, especially in Sichuan Basin, where there are more rain, fog and less sunny days. For example, Chengdu, known as the “fog city”, has an average annual sunshine duration of only 1152.2h.
According to the annual solar radiation, China can be divided into four regions.
(1) Class I is greater than 6700mj / m2, including most of Tibet, the west of Qinghai, the northwest of Gansu and the west of Inner Mongolia.
(2) Class II 5400 ~ 6700mj / m2, including Xinjiang, the middle and east of Inner Mongolia, most of Beijing, Tianjin, Hebei, Shanxi and Shaanxi, most of Ningxia and Gansu, the north of Shandong, the east of Qinghai, the east of Tibet, most of Yunnan, the west of Sichuan and the west of Hainan.
(3) Class III 4200 ~ 5400mj / m2, including most of Shanghai and Sichuan, most of Henan, Jiangsu, Anhui, Guangdong, Guangxi, Zhejiang, Jiangxi, Fujian, Taiwan, Hubei, most of Hunan, most of Guizhou, the east of Hainan, the south of Shaanxi, the south of Gansu, the south of Shandong and the east of Yunnan.
(4) Class IV is less than 4200mj / m2, including the east of Sichuan, the north of Guizhou, the northwest of Hunan and the southwest of Hubei.
The first three areas account for 76% of the land area. The low value center is in the southwest of Sichuan and the north of Guizhou, with 3340mj / m2; The highest value is in southern Tibet. Because the Himalayas block the water vapor of the Indian Ocean, the total annual solar radiation of the Qinghai Tibet Plateau is as high as 9200mj / m2, and the total annual sunshine hours are 3200 ~ 3300h. It is not only the region with the best solar energy resources in China, but also the region with the most abundant solar energy resources in the world.