Calculation of received solar radiation

Calculation of received solar radiation

According to the horizontal plane solar radiation data, using the mathematical models of different operation modes of the solar cell array above, the solar radiation received by the solar cell array can be calculated. Because the calculation process is very complicated, only a computer program can be compiled according to the mathematical model for calculation. At present, there are many computer-aided design software for calculating the solar radiation on the inclined square array, such as the computer-aided design software PV-CAD developed by Beijing Jike New Energy Technology Development Company based on the solar radiation model, and the radiation calculation developed by Shanghai Electric Power University Software, and the photovoltaic system design software RetScreen jointly developed by the Canadian Environmental Resources Agency and NASA (NASA), which is widely popular in the world. Through these software, it is easy to calculate the solar radiation received by the solar cell array under various operation modes such as the fixed inclination of the fixed square array, the tracking of the horizontal coordinate in the east-west direction, the tracking of the polar axis of the equatorial coordinate, and the two-axis precise tracking. The following only takes a fixed square array with a fixed inclination angle as an example for calculation.

If computer-aided design software is used, the optimization calculation of the inclination angle of the solar cell array should be carried out. The difference between winter and summer radiation at the best inclination angle should be as small as possible, and the total radiation during the year should be as large as possible. Both should be considered. This is particularly important for high latitude areas. The difference in solar radiation between winter and summer at high latitudes is very large (the difference is 5 times in Heilongjiang in my country). If the design is based on the radiation on the horizontal surface, the storage capacity of the battery in winter is much larger than that of rainy days The storage capacity of the battery has increased the design capacity and investment of the battery. Choosing the best angle of inclination will reduce the difference between winter and summer radiation on the solar cell array. The capacity of the battery can be reduced, the cost of the system is reduced, and the design is more reasonable.

Without computer software, the inclination angle of the fixed solar cell array can be roughly determined by the following relationship according to the local latitude. In order to eliminate the difference between winter and summer radiation, generally speaking, the higher the latitude, the greater the inclination angle, as shown in Table 2-2 Shown.

Calculation of received solar radiation
Table 2-2 The rough relationship between the local dimension and the inclination angle of the fixed solar cell array

After the inclination angle is determined, special computer-aided design software can be used to calculate the solar radiation on the inclined surface.

After the inclination is determined, if there is no computer software, the radiation on the solar cell square can be estimated from the radiation on the horizontal plane. Generally speaking, the radiation on the square array of fixed-inclination solar cells is 5% to 15% higher than the radiation on the horizontal surface. The greater the direct component and the higher the latitude, the greater the amount of radiation that the inclined plane will increase compared to the horizontal plane.

China is located in the northern hemisphere, with a vast land and a vast territory, with a total land area of ​​9.6 million square kilometers. From the Zengmu Ansha in the Paracel Islands near 4°N latitude in the south, to the heart of Heilongjiang in Mohe, Heilongjiang Province at 5331’N latitude, to the west from the Pamir Plateau near 73°40’E, and east to Heilongjiang at 13°05’E. The confluence with the Niaosuli River, from south to north and west to east, is more than 5000km away. On the vast land of China, there are abundant solar energy resources. The total annual solar radiation across the country is 3340~8400MJ/m², with a median value of 5852MJ/m². Judging from the distribution of the total annual solar radiation in China, the total annual solar radiation in the Qinghai-Tibet Plateau, Northwest China, North China, most of the Northeast, and some low latitudes such as Yunnan, Guangdong, and Hainan are all above 5000 MJ/m². China’s solar energy resources are rich or richer regions. Especially the Qinghai-Tibet Plateau is the highest, reaching 6000~8000MJ/m². The Yangtze River Basin and eastern and central regions such as Sichuan, Chongqing and Guizhou have poor solar resources. The total annual solar radiation is below 5000MJ/m², especially in the Sichuan Basin, which is only 3300~4000MJ/m², which is the lowest solar resource in China. Area.

Solar radiation data can be obtained from county-level meteorological observatories or from the National Meteorological Administration. The horizontal plane radiation data obtained from the National Meteorological Administration includes total horizontal plane radiation, horizontal plane direct radiation and horizontal plane scattered radiation.

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