A solar tracker is a mechanical device - automatic act to guide favorably with respect to the sun's rays from a photovoltaic panel, a solar thermal panel or a solar concentrator. The solar tracker causes an increase in the power of the captured solar energy and, therefore, the actual performance of the renewable energy device. One type of solar tracker is the heliostat. Historically, the first solar tracking systems were those in orbit on artificial satellites in the respective solar panels.
The main objective of a tracker is to maximize the efficiency of the device housed on board. In the photovoltaic field, modules mounted on a tracker are generally arranged geometrically on a single panel, a practice that avoids the use of a tracker for each individual module.
In the field of solar concentration, a solar tracker is useful to keep the fire point generated by the paraboloid constant in the channeling element of the liquid to be heated. The greater the perpendicular alignment with the sun's rays, the greater the efficiency of thermodynamic conversion and the thermal energy produced for the same surface, the lower the surface of the solar panel required for the same required power, the lower the installation costs .
Advantages and disadvantages of the solar tracker
In all the aforementioned cases, the negative sides of the solar trackers are manifested in mechanical problems that inevitably encounter the wear and tear of time, with the consequent closure of the plant caused. Tracer servomechanisms are poorly stressed organs, but by their nature they are subject to adverse weather conditions for at least 20 years. These limits must be met by preparing a prudent maintenance program both on time and after the surveys that will be carried out together with each phase of cleaning the system.
The electricity consumption of electronic components is negligible in a modern system designed properly
Ordinary maintenance is generally simple, and in the field of photovoltaic energy you benefit from a lower sensitivity of the photovoltaic effect to dust deposited on the surface of the modules, thanks to the better average angle of incidence of solar radiation.
The case studies available to date attest to the fact that the most profitable field of use for solar trackers is that of large land plants.
Classification of solar trackers
According to their construction characteristics, solar trackers are divided according to:
- Degrees of freedom offered. Solar trackers can offer the panel a freedom of mono or biaxial movement.
- Power supplied to the orientation mechanism;
- Type of electronic control.
Trackers to a degree of freedom
Tilt trackers are the simplest to make and rotate around the east - west axis. The solar panel rises or falls (usually manually twice a year) towards the horizon, so that the angle to the ground is statistically optimal according to seasonality. In practice, a tilt follower is made using telescopic mechanical profiles to raise or lower the photovoltaic panel with respect to the horizon. Conceptually similar to the liftable shelf of a school desk, these trackers offer an increase in production of less than 10%, to rarely justify a servomechanism.
The trackers aim to follow the sun throughout the sky on their daily journey, regardless of the season of use. In this case, the axis of rotation is north-south, while the height of the Sun above the horizon is ignored. These trackers are particularly suitable for low-latitude countries, where the sun's path is, on average, wider during the year. The rotation required for these structures is wider than the inclination, sometimes up to ± 60 °.
These followers make each row of photovoltaic modules look like a grill facing the equator. This type of tracker manages to have a higher performance than the trackers along the X axis, and allows to increase energy production by approximately 15%, compared to a fixed photovoltaic system.
An advanced feature of these followers is called recoil and solves the problem of shading that the rows of photovoltaic modules inevitably cause at sunrise and sunset rising to the horizon. This technique requires that the servomechanisms orient the modules according to the sun's rays only in the central band of the day, but reverse tracking near sunrise and sunset.
The nocturnal position of a photovoltaic field with recoil is perfectly horizontal with respect to the ground, and after dawn, the misalignment of the modules orthogonal to the sun's rays is progressively reduced as the shadows allow. A similar procedure is performed before sunset, returning the photovoltaic field to a horizontal position during the night period.
Azimuth (or yaw) followers have a degree of freedom with a zenith axis - nadir. To achieve this, the panel is mounted on a servo-assisted rotating base, flush with the ground. The resulting increase in electricity production is approximately 25%.
The polar axis trackers move on a single axis inclined with respect to the ground and approximately parallel to the axis of rotation of the earth. This axis is similar to the one around which the sun draws its path in the sky. The axis is similar but not the same due to the variations in the height of the path of the sun with respect to the ground in the different seasons. Therefore, this system of rotation of the photovoltaic panel around a single axis manages to keep the panel perpendicular to the sun throughout the day (always neglecting the summer-winter oscillations of the sun's path) and provides the maximum efficiency that can be obtained with a single axis of rotation.
Solar trackers with two degrees of freedom
The most sophisticated solar trackers have two degrees of freedom, with the aim of perfectly aligning the orthogonal photovoltaic panels with the sun's rays in real time. The cheapest, but not the only, way to do them is to mount one tracker on another. With these solar trackers there are increases in the production of electricity that reach up to 35% -40%, but with greater constructive complexity.
Based on the power necessary for the persecutors movement, we can divide them into:
- Active trackers, if activated by gearmotors;
- Passive trackers, if they are set in motion by autonomous physical phenomena, such as thermal expansion of gas or whatever.