Unlocking the Power of the Sun: Understanding Solar Tracker Axes of Rotation
Solar trackers are devices that track the movement of the sun during the day by rotating the solar panel. They can be powered by various types of engines. Most often, these are electric motors, hydraulics, and pneumatics.
Using solar trackers, which are different from fixed-tilt ground-mount systems because they let the solar panels follow the sun’s direction all day, It is a proven way to boost system output.
A single-axis and a dual-axis solar tracker are the two main types on the market
Coordinate system
For all presentations below, I used the Cartesian coordinate system with XYZ coordinates. There are other ways to analyze data and other types of coordinate systems, but this is the simplest. In our adopted coordinate system, the X-axis is the east-west direction. The Y axis runs south to north. The z axis is vertical – perpendicular to the earth’s surface.
Single axis, 3 types
Single-axle systems are relatively simple to build. Only one drive is needed to follow the movement of the panel. We can have three types of single-axis tracking systems.
We have three types of single axes, depending on the axis position vectors.
Case 1: Reversals of panels around east-west axis
The axis direction is from east to west. This is a very simple panel rotation system that only tracks the altitude angle. It is so simple that it can be manually adjusted monthly (in this case, we do not need a motor). The setup is similar to setting up a beach chair. The panel is adjusted every month with a scissor or similar mechanism to the optimal angle for that month. We can easily see the optimal panel tilt angles in the SPAC application. The altitude angle depends on the geographical latitude. The SPAC application offers a calculation of the profit from the solar panels if we were to adjust them every month. Because it follows only the altitude angle, which is highly dependent on the season, I called it the “seasonal axis of rotation”. The SPAC application has an option to calculate the gain from the seasonal adjustment of the tilt of the solar panels, and it is only 6%.
More about it can be read here
Case 2. Rotation of the panel around a vertical axis
that follows the movement of the sun during the day The axis is normal to the surface of the earth, and from dawn to dusk, the east-to-west axis turns a full 180 degrees following the daily movement of the sun. Given that trajectory, I would call it the “vertical axis of rotation”. This axis is simple, but it is not convenient to place the solar panels vertically. That’s why manufacturers of solar trackers have introduced
Case 3. The rotation axis, which is initially seasonally inclined
and follows the daily movement of the sun. This rotation axis is inclined to the ground surface (XY plane) at the most favorable possible seasonal angle (ideal tilt angle) and rotates during the day following the movement of the sun.
The combined position of one axis of rotation—this system is the closest to the two-axis tracking system in terms of efficiency. It is a combination of the previous two cases. The solar panels are initially tilted at the most favorable average angle for the climate, and then they rotate during the day, starting from the east when it shines in the west until sunset.
The ideal angle of inclination is calculated according to the formula 0.9*altitude. However, testing this corner of the SPAC application, I found that this is not an ideal solution. And that brings us to a new problem, which is:
The ideal tilt angle
is calculated according to the formula 0.9*altitude. However, I have been testing this formula in the SPAC application. I found that this is not an ideal solution. And that brings us to a new problem, which is: Ideal tilt angle This linear formula (0.9* altitude) relies only on the geographical position without taking into account climatic and seasonal changes. In its algorithm, the SPAC application relies on climatic characteristics for each area (larger city) in the world. Therefore, the ideal angle for a year is calculated in a different way using the above mentioned climatic factors, which are not the same all over the world at the same latitude.
The SPAC application does not yet have the ability to calculate single-axis tracking 2 and 3.
Dual axis
This is the most widely used solar tracking system. At any moment in real time, the sun’s rays should fall at the right angle on the panel. Gains in relation to fixed solar panels placed at the most favorable angle are, on average, 32%. The analysis was made with the SPAC application by changing the option axis of rotation. The price of this gain is a complicated design that includes two independent drives, one for each axis of rotation. Depending on the size of the solar panel carrier, servo (electric) motors, hydraulics, or a combination are used for propulsion. For movement along the seasonal axis, hydro cylinder, and for daily movement, hydro motor. Hydromotors are particularly advantageous due to their reliability and high output torque at the expense of low speed (which we don’t even need). The SPAC application has the ability to calculate this option. A special form of dual-axis tracking system is a system with a weather sensor. It contains additional electronics and devices for tracking the movement of the sun. You can see more about it here.
Conclusion
The most favorable way of tracking the sun by rotating the solar panel is the single-axis system variant 3. The panels are initially tilted at the most favorable altitude angle. They require only one drive that rotates the mechanism during the day from east to west.
SPAC application for
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