The dual-axis tracking system not only tracks the azimuth angle of the sun, but also tracks the altitude angle of the sun’s rays at the same time. Generally, the daily track tracking algorithm is used, and electric devices and gear meshing are used to adjust the angle and position of the photovoltaic modules completely according to the season, sunrise and sunset. The height axis and azimuth axis are simultaneously rotated to track the sun rays in real time to ensure that the sun rays are perpendicular to the panel surface of the module at every moment, so as to obtain the maximum power generation, which is suitable for use in various latitudes. Figure 1 is an example diagram of a dual-axis tracking system.
The dual-axis tracking system is further divided into two forms: altitude-azimuth dual-axis tracking and polar-axis tracking.
Altitude-azimuth dual-axis tracking is also known as dual-axis tracking in the horizon coordinate system. The photovoltaic module rotates east-west around the azimuth axis according to the daily change of the sun’s position to change the azimuth angle, and at the same time, according to the seasonal change of the sun’s altitude angle, it performs a pitching motion around the height axis. Change its height angle to realize real-time tracking of sunlight, so that the incoming rays of sunlight are always perpendicular to the photovoltaic modules.
The azimuth axis of the height angle-azimuth angle dual-axis tracking system is perpendicular to the ground plane and coincides with the axis of the support column. The height axis seat is installed above the column and can rotate around the azimuth axis. Install the pitch axis on the azimuth axis seat, and the pitch axis is perpendicular to the azimuth axis and parallel to the ground. The battery board is installed on the height axis and can be rotated around the height axis. The structure of the dual-axis tracking system is divided into a supporting part, a connecting part and a transmission part. The supporting part of the dual-axis tracking system is composed of main pillars, rotating supports and steel structure brackets, the connecting part is composed of aluminum profiles and bolts, and the transmission part is composed of worm gears, connecting rods, and reducers. The tracking direction of the dual-axis tracking system includes two directions of horizontal rotation and vertical pitch, realizing dual-degree-of-freedom tracking. The power input of the motor is decelerated by the reducer and input to the worm gear and worm to convert the rotary motion of the vertical plane into the rotary motion of the horizontal plane. At the same time, the position sensor collects the rotation angle of the system in real time, and inputs real-time data for the electronic control, so as to realize the horizontal rotation direction. Automatic tracking.
The polar axis dual-axis tracking tracking device is composed of a polar axis and an altitude axis. The polar axis points to the earth’s north pole and is parallel to the earth axis; the height axis is perpendicular to the polar axis. When working, the photovoltaic modules revolve around the polar axis from east to west at the angular velocity of the earth’s rotation. Rotate to track the sun’s hour-angle change (at a constant speed of 15° per hour). At the same time, regularly adjust the solar panel to make a pitching motion around the height axis to ensure that the normal of the photovoltaic module is always parallel to the sun’s rays. The polar axis of the polar axis biaxial system is parallel to the rotation axis of the earth, and the included angle with the ground is equal to the local latitude, and the polar axis is fixed on the base. The pitch axis seat is installed on the polar axis and can be rotated around the polar axis. A pitch rotation axis is installed on the tilt axis seat, the pitch axis is perpendicular to the polar axis, and the pitch axis can be rotated around the polar axis. The photovoltaic module is mounted on the pitch axis through a bracket and can be rotated around the pitch axis.
From the comparison of the two dual-axis tracking methods, it can be seen that when the photovoltaic modules tracked by the polar axis track and rotate, the angle between the upper and lower sides of the photovoltaic modules and the ground keeps changing; , the upper and lower sides of the photovoltaic module are always parallel to the ground. When the PV modules tracked by the polar axis track and rotate, the PV modules only need to rotate around the polar axis; when the PV modules tracked by the elevation and azimuth angles are tracked and rotated, the PV modules rotate around the pitch axis at the same time as the azimuth axis. Obviously, the polar axis tracking is relatively simple. It can be achieved by mechanically rotating around the polar axis and manually adjusting the polar axis tilt angle. The dual axis tracking of the altitude and azimuth angles needs to be controlled by calculating the sun’s altitude and azimuth in real time through the computer, or by Photoelectric sensors are used to track the position of the sun, and the controls are more complex. Each dual-axis tracking photovoltaic module has only one pillar, and the connection with the entire photovoltaic module has only one fulcrum, so the rotating parts of the solar panel and the fulcrum are required to have high strength.
The core of various dual-axis tracking systems is the trajectory setting and tracking control. The essence of tracking the trajectory is to make the position of the sun and the position of the panel surface of the photovoltaic module in the best corresponding state. The trajectory setting and control effect determine the performance of the dual-axis tracking system and the conversion efficiency of the photovoltaic system. According to the calculation method of the sun’s position, the two-axis automatic tracking system mainly has the following three schemes:
(1) Uniform tracking method
Generally speaking, it can be roughly considered that the rotation of the earth is uniform. Then it can be roughly analyzed that if the earth is used as a reference, the sun rises from the due east and moves westward every morning, reaches due south at noon, and sets in the west after reaching the west in the evening.
That is, the sun moves 360° a week in 24 hours in the east-west direction, then the speed of the sun’s movement is 15/h. The altitude angle of this method is equal to the local latitude (the azimuth angle is 0°, and the inclination angle is equal to the local latitude as a polar axis, which needs to be corrected by checking the local magnetic declination angle). This method is simple to control, but difficult to install and adjust, the initial angle is difficult to determine and adjust, and it is greatly affected by factors such as seasons. Therefore, the control accuracy is poor, and it is generally used in occasions with low requirements.
(2) Light intensity comparison method
A photoresistor is a sensor that can sense the current light intensity, and its resistance value changes with the change of the light intensity of the incident light. The input is an optical signal, and the output is an electrical signal. The photoresistor outputs the electrical signal to the microprocessor, and the microprocessor judges and controls how the servo system in the bracket operates by comparing the obtained electrical signal, so that the sunlight vertically irradiates the plane. The method is characterized by high sensitivity and simple circuit. However, it is greatly affected by the weather, and may operate frequently within a certain period of time, and may even cause malfunction of the servo system, resulting in system failure.
(3) Time-space synchronization method
This method takes into account the influence of time, season, and geographic location on the position of the sun, and obtains the position of the sun in different places and at different times by analyzing the movements of the sun and the earth. Therefore, the relevant data can be calculated by the program to calculate the position of the sun in the corresponding situation to achieve synchronization in time and space (of course, this method also needs to introduce a series of corrections). The method has high precision, good adaptability, and is easy to achieve all-day tracking. The main disadvantage is that the program is more complicated.