Dual Axis Solar Trackers: How They Work

How the two axes work

A dual axis tracker holds solar panels on two independent pivots. The first axis, usually called the azimuth axis, allows the array to rotate horizontally. The second axis, the elevation axis, tilts the panels up and down. Together, these two movements let the array follow the sun’s position in the sky with high precision.

The azimuth axis handles the east to west movement of the sun. The elevation axis compensates for the sun’s height above the horizon. At sunrise and sunset, the panels face low angles. At midday, the elevation axis tilts the panels to face the sun more directly. The result is a continuous adjustment of panel orientation.

This dual movement differs from single axis tracking. A single axis tracker rotates only around a horizontal axis. It can follow the sun’s horizontal movement but cannot fully adjust to the sun’s changing height. A dual axis system adds the vertical tilt, which captures more light when the single axis design would be misaligned.

The mechanical structure

The core of any dual axis tracker is its mechanical frame. The frame must hold the solar panels securely while allowing smooth movement on both axes. Most designs use a central mast or post that supports the upper assembly. The azimuth rotation happens at the base or at a mid-height pivot. The elevation rotation happens above that, holding the panel array.

Materials matter for both strength and weight. Aluminum is common for the moving parts because it offers a good balance of strength and low weight. Steel may be used for the base or mast to handle heavier loads. The joints and bearings must resist wear and allow free movement. Grease or dry lubricant is often applied to these points during installation and maintenance.

The panel mounting surface is usually a flat or slightly tilted structure. It holds the solar modules with rails or frames. The mounting system must distribute the load evenly across the elevation axis. Uneven loading can create stress points that reduce the lifespan of the bearings or the frame.

The sun tracking logic

The tracker needs to know where the sun is. The control system uses sun position algorithms or sensor feedback to determine the correct azimuth and elevation angles. Many systems use a combination of time, location data, and sensor inputs. Some rely on light sensors mounted on the array to detect the direction of incoming sunlight. Others use encoders on the motors to track the axis positions.

The control logic calculates the target angles based on the sun’s position. The motors then move the axes to those positions. The system updates the angles continuously, often every few minutes or every few seconds. The speed of movement is controlled to avoid sudden jerks that could damage the panels or the structure.

Sensor accuracy is a key factor. If the system relies on light sensors, it must handle shading, clouds, and reflections. Clouds can cause rapid changes in light intensity, which may confuse the sensors. For this reason, many systems use a hybrid approach. They use sun position algorithms as the primary guide and sensor data as a secondary check.

Drive mechanisms and motors

The motors that drive the axes are central to the tracker’s performance. Each axis usually has its own motor. The azimuth motor is often larger because it must rotate the entire upper assembly. The elevation motor may be smaller but must handle the tilt loads, especially when the panels are exposed to wind.

Motor types vary. Gear motors are common because they provide high torque at low speeds. This is useful for moving the heavy array smoothly. The gear ratio is selected to match the required speed and torque. A lower gear ratio gives more torque but slower movement. A higher gear ratio gives faster movement but less torque.

The control system sends signals to the motors based on the calculated target angles. The motors move until the encoders confirm the axes are at the correct positions. If the system detects a mismatch between the target and the actual position, it corrects the movement. This closed loop control helps maintain accuracy over time.

Wind loads and safety

Wind is a major design consideration for any solar tracking system. A dual axis tracker presents a large surface area to the wind. The panels can act like sails, creating high forces on the axes and the mast. The structure must be able to handle these loads without failure.

The tracker has safety modes for high wind conditions. When wind speeds exceed a set threshold, the system stops tracking and moves to a safe position. This is usually a low azimuth angle or a flat position that reduces the wind load. The system may also lock the axes to prevent movement.

The design must account for gusts as well as steady wind. Gusts can cause sudden spikes in load. The bearings and motors must be rated to handle these transient forces. The control system should also be able to detect abnormal movement and shut down if necessary.

Sourcing and specification considerations

When sourcing a dual axis tracker, buyers need to evaluate several factors. The first is the axis geometry. The design of the two axes affects the range of motion and the structural loads. A well designed axis geometry allows the panels to cover the full range of sun positions without excessive mechanical stress.

The second factor is the drive mechanism. The type of motor and gear ratio influences the speed and torque available for tracking. A system with high torque can handle heavier panels and stronger winds. A system with high speed can adjust more quickly, which may be useful in rapidly changing light conditions.

The third factor is the control logic. The accuracy and reliability of the tracking logic determine how well the array follows the sun. A system with precise sensors and robust algorithms will capture more energy. The control system should also include safety features for high wind, fault detection, and manual override.

The fourth factor is the structural materials and construction. The frame and mast must be strong enough to handle the loads. The materials should resist corrosion and wear. The joints and bearings should be designed for long term durability.

A worked example

Consider a site with a flat roof and a dual axis tracker installed on a central mast. The tracker has two axes. The azimuth axis rotates the array from east to west. The elevation axis tilts the panels up and down. The system uses a gear motor for each axis. The control system uses sun position algorithms and light sensors to determine the correct angles.

During the morning, the sun is low in the east. The azimuth axis points the panels toward the east. The elevation axis tilts the panels to face the low sun. As the sun rises, the elevation angle increases. The azimuth angle shifts slowly toward the south. At midday, the sun is high and near the south. The panels face south with a high elevation angle. In the afternoon, the azimuth axis rotates toward the west. The elevation axis tilts the panels down to follow the setting sun.

The system updates the angles continuously. If clouds pass over the sun, the light sensors may detect a change in intensity. The control logic adjusts the angles to maintain the best possible orientation. If the wind picks up, the system moves to a safe position. The panels are tilted flat and the azimuth axis is locked. This reduces the wind load on the structure.

Common design challenges

Dual axis trackers face several design challenges. The first is maintaining mechanical precision over time. Bearings and joints can wear, causing misalignment. Regular inspection and maintenance are needed to keep the system accurate.

The second challenge is managing wind loads. The large surface area of the panels can create high forces. The structure must be designed to handle these loads without failure. The control system must also be able to detect high wind conditions and move to a safe position.

The third challenge is the complexity of the control system. A dual axis tracker has two axes to control. The control logic must manage both axes simultaneously and ensure they move in coordination. Any error in the control logic can cause the panels to miss the optimal position.

Comparison with single axis tracking

A single axis tracker rotates around one horizontal axis. It follows the sun’s east to west movement but cannot fully adjust to the sun’s height. This design is simpler and less expensive than a dual axis tracker. It also has fewer moving parts and lower maintenance costs.

A dual axis tracker offers higher energy capture because it follows the sun more closely. The additional elevation axis allows the panels to face the sun more directly throughout the day. This is especially useful in locations with high latitude or in cloudy regions where the sun’s path changes significantly.

The trade off is complexity. A dual axis tracker has more parts, more motors, and a more complex control system. It also requires more precise installation and maintenance. The cost of a dual axis tracker is generally higher than a single axis tracker. The choice between the two depends on the site conditions, the energy goals, and the budget.

Maintenance and inspection

Regular maintenance is essential for the long term performance of a dual axis tracker. The bearings and joints should be inspected for wear and lubricated as needed. The motors and gears should be checked for proper function. The control system should be tested to ensure it responds correctly to sensor inputs.

The structure should be checked for corrosion and damage. The mast and frame should be secure. The panel mounting surface should be clean and free of debris. The electrical connections should be tight and free of corrosion.

The control system software should be updated as needed. The sun position algorithms should be accurate for the site location. The sensor calibration should be checked periodically. The safety modes should be tested to ensure they activate correctly in high wind conditions.

Final considerations

A dual axis tracker is a sophisticated solar mounting system. It uses two independent axes to follow the sun’s path across the sky. The mechanical structure, drive mechanisms, and control logic work together to maintain optimal panel orientation. The system offers higher energy capture than single axis tracking but comes with greater complexity and cost.

Buyers should evaluate the axis geometry, drive mechanisms, control logic, and structural materials when sourcing a dual axis tracker. The system must be designed to handle the site conditions, including wind loads and temperature variations. Regular maintenance is needed to keep the system accurate and reliable.

The dual axis tracker is a powerful tool for maximizing solar energy capture. It requires careful selection and installation to perform well. Understanding the mechanical and operational principles helps buyers make informed decisions. The system can deliver high performance when it is well designed and well maintained.