Solar energy is a clean energy, and its application is growing rapidly around the world. However, the cost of designing a solar LED lighting system is still relatively high. Judging from the current cost of solar LED lighting systems in China, the cost of solar cell components is about 60% to 70% of the total cost. Therefore, in order to fully and effectively utilize the solar energy, how to select the azimuth angle and inclination angle of the solar cell array is a very important issue. In order to make the solar cell module receive as much solar radiation energy as possible in one year, it is necessary to choose an optimal azimuth and tilt angle for the solar cell array.
In the design of the solar LED lighting system, the placement form and placement angle of the solar cell array have a great influence on the solar radiation received by the solar cell array, thereby affecting the power generation capacity of the solar cell. The solar cell array can be placed in two forms: fixed installation and automatic tracking. The automatic tracking device includes a single-axis tracking device and a dual-axis tracking device.
(1) Azimuth. The azimuth angle of the solar cell array is the angle between the vertical plane of the array and the positive south direction (the eastward deviation is set as a negative angle, and the westward deviation is set as a positive angle). Generally in the northern hemisphere, when the square array faces due south (that is, the angle between the vertical plane of the square array and due south is 0°), the solar cell generates the maximum power. When it deviates from due south (northern hemisphere) by 30°, the power generation of the phalanx will decrease by about 10%~15%; when it deviates from due south (northern hemisphere) by 60°, the power generation of the phalanx will decrease by about 20%~30%. However, on a clear summer day, the maximum solar radiation energy is late at noon. Therefore, when the orientation of the solar cell array is slightly westward, the maximum power generation can be obtained at noon.
In different seasons, the peaks of daily radiation in different directions are generated at different times. The orientation of the solar cell array is slightly east or west and it is possible to obtain the maximum power generation. The installation site of the solar cell array is restricted by many conditions. If the azimuth angle is adjusted to be consistent with the peak time of the load and the peak time of power generation in a day, the following formula can be referred to.
Azimuth = [peak time of load in a day (24-hour clock) – 12] × 25 + (longitude – 116)
(2) Inclination angle. The solar cell array is usually placed facing the equator and has a certain inclination relative to the ground plane, that is, the angle between the solar cell array plane and the horizontal ground. For a fixed solar cell array with uniform load throughout the year, if the radiation amount of the designed slope is small, it means that more solar cell components are needed to ensure power supply to the load; if the amount of solar radiation received by the solar cell phalanx varies greatly from month to month, it means that a battery with a larger capacity is required to ensure the electricity supply in the months with low solar radiation. These will increase the cost of the entire system. Therefore, determining the optimal inclination angle of the solar cell array is an indispensable and important link in the solar LED lighting system.
Due to the large span of north-south latitude in China, the installation inclination angle of solar cell modules should change with the latitude of the installation area. Under normal circumstances, the installation inclination angle in the area south of the Yangtze River is about 30°; the installation inclination angle in the area north of the Yangtze River is about 45°; and the northeast area should be about 50°.
The best inclination angle in a year is related to the local geographic latitude. When the latitude is higher, the corresponding inclination angle is also large. However, like the azimuth angle, the design also takes into account the constraints such as the inclination angle (slope greater than 50%~60%) of the snow falling. With regard to the inclination angle of snow falling, the total annual power generation may increase even in the snow-covered period when the power generation is small. For due south (azimuth is 0°), the tilt angle starts from horizontal (tilt angle is 0°) and gradually transitions to the optimum tilt angle, the insolation increases continuously until the maximum value, and then increases the inclination angle and the insolation decreases continuously. Especially after the inclination angle is greater than 50°~60°, the daily radiation amount drops sharply, until the last vertical placement, the power generation drops to the minimum. For the case where the azimuth angle is not 0°, the value of the insolation on the inclined plane is generally low, and the value of the maximum solar radiation is near the inclination angle close to the horizontal plane.
At present, there is a view that the inclination of the solar cell array equal to the local latitude is the best. The result of this is that in summer, the power generation of solar cell modules is often excessive and wasteful, and in winter, the power generation is often insufficient and the battery is undercharged, so this is not the best choice. There are also views that the inclination angle of the solar cell array should be such that the maximum solar radiation can be obtained in the month with the weakest radiation throughout the year. It is recommended that the inclination of the solar cell array should be increased by 15°~20° on the basis of the local latitude. Some design manuals in other countries also propose that the design month should be based on December (in the northern hemisphere) or June (in the southern hemisphere) with the least amount of radiation.
In fact, this view also has its limitations, which tends to make the amount of radiation obtained in summer too small, resulting in a small amount of solar radiation obtained by the solar cell array throughout the year. At the same time, the concept of the optimal inclination angle is different in different applications. In the solar LED lighting system, due to the limitation of the battery state of charge and other factors, it is necessary to comprehensively consider the continuity, uniformity and maximum of the solar radiation on the plane of the solar cell array, while the grid-connected solar power system usually always requires the maximum amount of solar radiation throughout the year. In the design, it is hoped to obtain the optimal inclination angle of the solar cell phalanx when the annual average power generation is the largest, and the optimal inclination angle in a year is related to the local geographic latitude. When the latitude is higher, the corresponding tilt angle is also larger.