Solar energy is one of the renewable energy sources with great potential to meet the world’s energy demands while reducing greenhouse gas (GHG) emissions. As a result, several technologies have been developed over the years to harness solar energy to generate heat and electricity.

However, because the sun’s position in the sky changes throughout the day and varies with the seasons, most of these solar devices are designed to track the sun’s movement to maximize their efficiency in capturing solar energy. An essential component helping solar collectors achieve this desirable operation is called a solar tracking device (or solar tracker).

In order to understand how solar tracking devices work, it is important to cover some basic concepts and factors that influence the amount of solar energy that a solar collector can absorb.

## Understanding how solar tracking devices work

Studies have shown that the power incident on a solar collector or photovoltaic (PV) module depends not only on the solar irradiance but also on the angle at which the sunlight strikes the collector. This angle is called the angle of incidence, and it is the angle measured between the beam radiation on the surface and the normal to that surface.

A solar collector that is perpendicular to the sunlight (so that the angle of incidence is very small or close to 0°) produces more power than collectors with a large angle of incidence under the same operating conditions. At smaller angles of incidence, the solar rays are concentrated over a minimal area, maximizing the power density.

Solar tracking devices align the solar collector with the sun rays, thereby maintaining the optimal angle of incidence between them. These tracking devices typically feature sensors and operate based on complex algorithms that allow them to determine the sun’s relative position depending on the location’s latitude and longitude, time of the day and orientation of the collector.

## Types of solar tracking devices

Solar tracking systems are classified based on their motions into:

1. single-axis rotation
2. double-axis rotation

### Single-axis tracking devices

As its name implies, a single-axis solar tracker rotates around one axis. For instance, these trackers are typically aligned in the north-south direction, allowing them to follow the sun’s east-to-west movement. Alternatively, they may be aligned with the east-west direction to track the sun’s movement along the north-south direction.

Each of these orientations has its own advantages and suitability for different application requirements. For instance, solar collectors that are aligned along the north-south direction and track the sun’s east-to-west movement are quite efficient in capturing solar energy in higher latitudes where the sun’s path is more horizontally spread. In contrast, the east-west aligned single-axis tracking devices are commonly used in regions close to the equator where the sun’s elevation angle changes significantly throughout the year.

For instance, consider a solar collector rotated about a horizontal east-west axis with continuous adjustment to minimize the angle of incidence. In such a scenario, the angle of incidence can be calculated using:

The declination and hour angles help to describe the position of the sun for its daily path. In addition, the required surface slope (angle between the plane of the collector surface and the horizontal) can then be calculated using:

### Double-axis tracking devices

The double-axis tracking devices have two degrees of freedom that act in the azimuth and elevation directions. They follow the sun’s path more precisely, accounting for its daily and seasonal movements.

## Conclusion

Solar PV modules and concentrating solar power (CSP) systems equipped with tracking devices are contributing to meeting energy demands while reducing GHG emissions. While this article presents the basics of solar tracking devices, engineers and designers must consider several other factors when choosing one for an application, such as the efficiency and power requirements of the solar tracker. Therefore, it is recommended to reach out to manufacturers of solar trackers to discuss application requirements.