Distribution of solar energy resources in the world
According to the total solar radiation power, the average distance between the sun and the earth, and the average diameter of the earth, it can be seen that the solar radiation power of the solar energy resources reaching the upper boundary of the earth’s atmosphere is 1.73 × 1011MW, which is about 3 × 104 times the power consumed by the world in 1970. About 30% of it is reflected into space by the atmosphere, 23% is absorbed by the atmosphere, and only 47%, or 8.2×1010MW, reaches the earth’s surface, which is commonly called the solar resource on the ground. About 79% of the solar radiation reaching the Earth’s surface hits the oceans and 21% hits the land. Among them, about half of the solar radiation irradiated on land is irradiated in uninhabited or rarely populated areas, and only about half, ie, 8.1×109 MW, is irradiated in areas inhabited by humans. This is the real solar energy resource available now and in the near future.
Due to the limitations of natural conditions such as day and night, seasons, geographic latitude and altitude, the solar radiation energy reaching the earth’s surface is both intermittent and unstable. In order to facilitate the utilization of solar energy, countries all over the world give the average value of the daily total, monthly total and annual total solar radiation on the local horizontal surface through the multi-year measured results of meteorological stations all over the world. In order to unify solar radiation measurement standards around the world, the World Meteorological Organization has held six international direct heliostat comparisons since 1959. At present, various insolation instruments are divided into three categories: standard, first-class and second-class according to their performance (only standard direct insolation meters are subdivided into first-class standard and second-class standard).
The National Aeronautics and Space Administration (NASA) has built a database containing sunshine data in various places, and the sunshine situation in the middle of the world is shown in Figure 1.
Distribution of solar energy resources in China
China is located in the eastern part of the Eurasian continent, and its land accounts for 1/14 of the world’s land area, and most of it is in the north temperate zone. Therefore, China is very rich in solar energy resources. The total amount of solar radiation received by land is about 1.9×1016kW·h every year, which is equivalent to 2.4 trillion tons of standard coal. The measurement data of relevant national units show that the total annual solar radiation in all parts of the country is basically 3340~8400MJ/㎡, and the average value exceeds 5000MJ/㎡ (equivalent to the heat of 170kg/㎡ standard coal), and the annual sunshine time of 2/3 of the country’s land area exceeds 2200h.
According to the data from the Solar and Wind Energy Resource Evaluation Center of China Meteorological Administration, China’s Tibet, Qinghai, Xinjiang, Gansu, Ningxia, and Inner Mongolia Plateau have the highest total solar radiation and sunshine hours in the country, and are one of the world’s richest regions in solar energy resources. The Sichuan Basin, the Lianghu area and the Qinba Mountains are low-value areas of solar energy resources. Eastern, southern and northeastern China are medium-sized regions for solar energy resources.
The distribution of solar energy resources in China is higher in the west than in the east, and basically lower in the south than in the north (except Tibet and Xinjiang), which is not consistent with the law that usually varies with latitude, and areas with small knot degrees are lower than areas with large latitudes. This is mainly caused by the influence of atmospheric cloudiness and the distribution of mountains. For example, the cloud cover in southern China is significantly larger than that in the north. In the Qinghai-Tibet Plateau, the average altitude is above 4000m, the atmosphere is thin and clean, the transparency is good, and the sunshine time is long, so the solar energy resources are the most abundant, and the highest value is 920kJ/(cm2·year).
The annual total solar radiation distribution of each solar resource belt is shown in Figure 2.