There are many ways to track the sun, but there are only two ways to use photoelectric tracking and tracking according to the trajectory of the sun. The latter tracking method can be further divided into dual-axis tracking and single-axis tracking.
- Photoelectric tracking
The commonly used photoelectric tracking devices in China are: gravity photoelectric tracking device, electromagnetic photoelectric tracking device, and electric photoelectric tracking device. These photoelectric tracking devices all use photosensitive sensors, such as silicon photocells, which are close to the shading plate, adjust the position of the shading plate so that the shading plate is aimed at the sun, and the silicon photoelectric water heater is in the shadow area. As the sun moves west, the shadow of the visor moves with it. The photocell is exposed to direct sunlight, outputs a certain value of micro-current, sends out a deviation signal, which is amplified by the amplifying circuit, and controls the tracking device to aim at the sun to complete the tracking. The advantages of photoelectric tracking are high sensitivity and convenient structure design. The disadvantage is that it is greatly affected by the weather. If dark clouds cover the sun for a long period of time, the sun’s rays often cannot shine on the silicon photocells, resulting in the tracking device not being able to align with the sun, and even causing the actuator to malfunction.
- Single axis tracking
Single-axis tracking generally adopts the following three tracking methods: inclined arrangement, east-west tracking; focal line north-south horizontal arrangement, east-west tracking; focal line east-west horizontal arrangement, north-south tracking. These three methods are basically north-south or east-west tracking with single-axis rotation, and the working principles are basically similar. Taking the third tracking method as an example, the principle of single-axis tracking is described. Figure 3-1 shows the principle of this tracking method. The axis of rotation (or focal line) of the tracking system is arranged in an east-west direction. Then, according to the change of the sun’s declination angle, the cylindrical parabolic mirror is made to pitch and rotate around the rotation axis to track the sun. When this tracking method is adopted, only at noon in the day the sunlight is perpendicular to the generatrix of the cylindrical paraboloid, and the heat flow is the largest at this time. In the morning or afternoon, the sun’s rays are oblique, so the change of heat flow during the day is relatively large. The single-axis tracking method is characterized by a simple structure, but because the incident light cannot always be parallel to the main optical axis, it is not ideal for collecting solar energy. If the sun can be tracked in both the solar altitude and the declination angle, the most solar energy can be obtained, and the full tracking, that is, dual-axis tracking, is designed according to such requirements.
- Dual axis tracking
Dual-axis tracking can be divided into two ways: polar-axis full tracking and altitude-azimuth full-tracking.
One axis of the polar-axis full-tracking condenser points to the north pole of the celestial sphere, that is, it is parallel to the rotation axis of the earth, so it is called the polar axis. The other axis is perpendicular to the polar axis and is called the declination axis. When working, the mirror surface only needs to rotate around the polar axis with a fixed rotation speed in the same direction and opposite to the angular velocity of the earth’s rotation to track the apparent diurnal movement of the sun. In addition, the reflector is rotated intermittently around the declination axis to adapt to the change of the declination angle according to the seasonal changes. This tracking method is not complicated, but the quality of the mirror does not pass through the polar axis, which makes the design of the polar support device difficult.
The altitude-azimuth full tracking method is based on the horizon coordinate system, tracking the altitude and azimuth of the sun, so this kind of solar tracker has an azimuth angle perpendicular to the horizontal plane and an elevation axis parallel to the local horizontal plane. tracking. The horizon coordinate system tracking method is a relatively advanced tracking method at present, and the tracking accuracy is relatively high.
The tracking algorithm mainly solves two main problems: one is to track the azimuth angle of the sun, which can be controlled by a servo motor driven by a horizontal working turntable. The second is to track the altitude of the sun. Another servo motor can convert circular motion into linear motion through pulleys and lead screws, and change the inclination of the collector to align with the sun.