For photovoltaic power generation, the use of tracking devices can significantly improve the utilization rate of solar energy, while the single-axis tracking method can use relatively simple equipment to achieve an ideal tracking effect. Compared with the fixed operation type, the single-axis tracking method improves the utilization efficiency of solar energy; compared with the dual-axis tracking system, the tracking device is slightly simpler, and has the advantages of low risk and low maintenance cost. The single-axis tracking photovoltaic power generation system can be divided into three types according to the rotation mode of the tracking axis: flat single-axis tracking system, inclined single-axis tracking system, and vertical single-axis tracking system.
(1) Flat single axis tracking system
In the single-axis tracking system, the flat single-axis system is the most used method, which is divided into two forms: north-south axis tracking and east-west axis tracking. The east-west axis tracking has no obvious advantages over the fixed inclination installation form, and the north-south axis tracking effect is better than the east-west axis tracking system. According to whether there is an inclination in the north-south direction, it can be divided into a standard flat uniaxial tracking type and a flat uniaxial tracking type with an inclination angle.
Figure 1 is a schematic diagram of a flat uniaxial tracking array. The rotating shaft of the photovoltaic array is parallel to the north-south direction line of the ground, and the rotating shaft is installed on the support column, and the photovoltaic array can rotate around the rotating shaft east-west direction day by day. The rotation of the rotating shaft is controlled by the sun tracking device, so that the vertical plane of the rotating shaft of the array is parallel to the sunlight. According to the calculation of the power generation of the array, there can be single-row, double-row and multi-row photovoltaic modules on each rotating shaft. A bearing seat is installed on the upper part of the support column to fix the rotating shaft. The rotating shaft passes through the bearing seat and is connected with the photovoltaic modules. The single-row form directly The photovoltaic modules and the rotating shaft are connected by pressing blocks, and in the double-row form, a truss is installed on the rotating shaft, and then the photovoltaic modules are connected through the truss.
Another form of flat uniaxial tracking is based on the standard flat uniaxial, by increasing the north-south angle of the short vertical pole to lift the photovoltaic module on the rotating shaft, which can further improve the amount of solar radiation received.
It can be seen from Figure 2 that the vertical line of the solar panel of the flat single-axis tracking system always has an included angle with the incoming ray of sunlight. The value of the included angle is related to the local latitude and season, and also varies within a day.
(2) Inclined single axis tracking system
There is always an included angle between the normal line of the photovoltaic module of the flat single-axis tracking system and the incident ray of sunlight. In high latitudes, this angle is relatively large, and the improved power generation efficiency is limited compared to the fixed operation type of photovoltaic modules. Therefore, in order to improve the efficiency of photovoltaic modules, the rotating shaft can rotate in the east-west direction while setting a certain inclination angle to the south, and rotate around the inclined axis to track the azimuth of the sun to obtain greater power generation, which is suitable for applications in higher latitudes.
Figure 3 is a schematic diagram of the array of the inclined single-axis tracking system. Compared with the flat single-axis tracking, the rotation axis of the inclined single-axis tracking system is still north-south, but has an angle with the ground, and the rotation axis is basically parallel to the ground axis. The rotating shaft is installed on the bracket, and the photovoltaic array rotates east-west around the rotating shaft. Similar to flat single-axis tracking, the rotation of the rotating shaft is controlled by the solar tracking device, so that the normal plane of the rotating shaft of the photovoltaic module is parallel to the sunlight.
(3) Vertical single-axis tracking system
The inclination angle of the photovoltaic array of the vertical single-axis tracking system is fixed, which is generally the best local inclination angle. The tracking method is to move through orbits or rotating gear discs, so that the azimuth angle of the photovoltaic array changes with the incident direction of sunlight. Among the single-axis tracking systems, the vertical single-axis tracking system has the highest power generation. However, because its structure is more complex than the flat uniaxial and inclined uniaxial, the initial cost and post-maintenance cost are high, so it is less used in actual engineering.
(4) Linkage of single-axis tracking system
Usually a photovoltaic power station has multiple photovoltaic racks, and these photovoltaic racks operate synchronously, so several rows of photovoltaic racks can be pushed by a lever. Figure 5 is a schematic diagram of an inclined single-axis linkage tracking system. A drive arm is installed on the rotating shaft of each photovoltaic array, and the other end of the drive arm is connected with a control link, which is driven by a motor and a drive device to drive multiple rows of photovoltaic supports to rotate synchronously.
(5) Comparison of three single-axis tracking systems
In summer, the three single-axis tracking photovoltaic power generation systems are more effective in utilizing solar radiation energy than the fixed type. Because the sun moves to the northern hemisphere at this time, the intensity of solar radiation increases and the altitude angle becomes larger. But in winter, the solar radiation utilization of the horizontal axis tracking system is much lower than the other two forms. This is because the horizontal axis tracking system tracks the sun azimuth. In winter, when the sun moves in the southern hemisphere, the sun altitude angle decreases. At this time, tracking the sun altitude angle increases the incident angle and reduces the solar absorption absorbed by the horizontal axis tracking system. radiated energy, thereby affecting the amount of electricity generated.
In terms of cost, the vertical axis tracking system needs to adjust the azimuth angle of the entire photovoltaic array, so it occupies the largest area, the photovoltaic support structure is the most complex, and the system cost and post-maintenance cost are the highest. The system cost of the horizontal axis tracking method and the oblique single axis tracking method is equivalent.
Therefore, from the two aspects of investment and power generation, the inclined single-axis tracking system has certain engineering advantages.