What is a solar tracker? How is it structured and how does tracking work? What different tracking systems are there for photovoltaics and what advantages and disadvantages do they have?
Solar trackers (also called solar trackers and sun trackers) are technical devices that allow a photovoltaic system to automatically adjust to the current position of the sun. Hence the German name tracking system, the English “to track” means something like: “follow”, “track”, “follow up”. The tracking ensures that the solar modules are always optimally aligned to the sun, so that they absorb the maximum amount of solar energy and convert it into solar power. With a solar tracking system, above-average solar yields can be achieved in both small and large solar systems. However, they also need their own electricity for tracking, which in turn reduces the net yield. In this article we explain the functional principle of solar trackers.
Differentiation from solar tracker systems
The sun moves from east to west in the course of a day . With a fixed solar cell, the rays of the sun come in at a different angle at any time of the day . The illuminated area can assume all values between 0% and 100% of the actual module area.
Horizontal and vertical tracking
In order to increase the electricity yield, it makes sense to track the sun’s solar cells using a solar tracker. By rotating around the horizontal axis , the module points east towards sunrise in the morning and west towards sunset in the evening .
In addition, the solar cell can be tracked around the horizontal or vertical axis . This tracking takes into account that the sun is higher in the sky at noon than in the morning .
Single and dual axis trackers
In addition, solar trackers are differentiated according to the number of axes used for tracking . A uniaxial tracking means that the solar modules either only follow the sun’s angle of incidence (elevation) horizontally , i.e. horizontally, or only vertically , i.e. vertically, the sun’s path (azimuth) .
Two-axis tracking means that the module is tracking both the angle of attack and the azimuth . Since the two-axis tracking solar trackers can turn to any point in the sky, their solar energy yield is currently the highest .
The DEGER tracking system D100 has an enlarged elevation angle of 10 ° to 90 °, so that higher yields can be achieved especially with flat solar radiation at sunrise and sunset. (Photo: DEGERenergie GmbH & Co. KG)
Special tracker solutions
Trackers don’t necessarily have to be based on a single stand. In the meantime, there are also special solutions that allow the angle of the modules to be varied, which are placed on a substructure table typical of open spaces . As a rule, the azimuth angle is varied over an axis .
There are also so-called revolving halls, in which the entire building stands on a kind of raceway. Your tracking control always turns the solar roof with the modules towards the sun. Alternative devices keep the building in place and only turn the roof towards the sun . In addition to solar tracking, such rotating buildings are also used to optimize heat and thermal insulation.
Typical structure of a stand system
The most frequently used type of solar tracker consists of a stand or mast to which a frame is attached, which in turn serves as a substructure for the solar modules . The construction of a photovoltaic system with solar tracker technology is quite straightforward. These components are needed:
- Stand made of welded steel tubes,
- Frame made of aluminum,
- one or two gear motors that move the frame,
- Control unit
- and inverters for every solar tracker.
In the case of a sensor- controlled system, the sensor would also be added.
Very important: the anemometer . It helps to operate the system as damage-free as possible – because according to the manufacturer’s instructions , most systems have a maximum wind force that they can withstand. If the wind is stronger, you have to take the modules out of the wind in the manner prescribed by the manufacturer so that they create as little resistance as possible.
Two-axis tracking PV systems can ideally follow almost any position of the sun thanks to their vertical and horizontal alignment and thus maximize the solar yield.
Astronomical solar tracker
If a solar tracker is controlled astronomically , the location-specific daily course of the sun is stored in advance within a year . The tracking system then controls the specified position of the sun without being influenced by clouds that may be pushed in front of the sun.
Sensory solar tracker
With a sensory control, the system always tracks the brightest point in the sky , which, mind you, does not always have to correspond to the position of the sun. For example, it is brighter at the edges of a cloud that is pushed in front of the sun, because the sun’s rays are reflected there than at the point of the cloud behind which the sun is also located. The reflected sun rays also hit a different point on the earth’s surface than unreflected rays. The sensor even takes into account reflections from bright surfaces such as facades or snow. It automatically searches for the brightest point and the solar modules are aligned accordingly .
Comparison of tracker controls
The difference between astronomical and sensory control of the solar trackers becomes particularly clear when the sky is completely overcast . The astronomical control locates the sun based on the values found in the memory and controls the location, regardless of whether the thickest clouds are hanging there (little light) or not. The sensory control, on the other hand, aligns its solar modules perfectly horizontally so that the angle is 180 degrees. All the light that penetrates the cloud cover hits the modules almost perpendicularly, which can maintain this position for most of the day. With the help of sensor-controlled solar trackers, even on days with extreme weather and constantly changing cloud cover, up to two thirds or more additional yields can be “harvested” than with a permanently installed photovoltaic system.
Deployment according to the control mode
The previous explanations also provide knowledge for the optimal use of the differently controlled solar trackers: In regions where the weather is rather changeable, sensor-controlled solar trackers achieve significantly better yields by far . The area of the Federal Republic is one of these regions with changeable weather. If you want to track the course of the sun efficiently here, you should use sensory control.
For photovoltaic systems that are installed closer to the equator, for example in the countries bordering the Mediterranean, where the weather is much more constant than here and the sun usually shines all day without clouds in front of it, astronomical control is more profitable than that more expensive sensory control – even if the latter would also bring in a higher yield there.
Electromotive tracker drive
The module table of a solar tracker is tracked by one or more electric motors . In a simple variant, the electric motor drives a worm gear that transfers the rotation to the corresponding axis. In this way, the module table can be precisely adjusted. Alternatively, electric cylinders are sometimes used in solar trackers, which take over the drive by means of a trapezoidal thread spindle and DC motor.
With several solar trackers, each works independently of one another. In contrast, there are also drive technologies in which one motor controls several trackers. The force is then transmitted, for example, with the help of a wire rope which is placed around the individual tracking frames. The tracker motor receives actuating impulses from an electronic control system. These are transmitted to a rotating spindle via a planetary gear. The turning spindle in turn moves the wire rope which then deflects the individual frames.
Thermohydraulic tracker drive
An alternative to the electric motor drive of solar trackers is passively tracked photovoltaic systems based on thermohydraulic tracking. The thermohydraulic drive (THA) is simple, reliable, self-sufficient in terms of energy and self-regulating, ie it does not require a power supply or control electronics. It draws its drive energy directly from the sun and aligns itself automatically with it. There are two types of thermal-hydraulic solar tracking. One works according to the principle of gravity – weight shift through the thermohydraulic displacement of a column of liquid, the other according to the hydrostatic principle – Thermohydraulic movement of an actuating cylinder.
Yield, costs and profitability of solar trackers
By combining horizontal and vertical tracking techniques, the illuminated area of the solar module can be kept almost constant at 100% . The sun is always at right angles to the solar cell and sees it directly from above. In this way, solar power production can be increased considerably .
Compared to a permanently installed photovoltaic system that faces south, a single-axis tracking system generates up to 30 percent more solar yield . And a two-axis tracker system tops the additional yield by up to a further 15 percent , so that there is a gross yield increase of up to 45 percent compared to the permanently installed solar system. All values mentioned are annual mean values.
Tracked tracking systems can only be of interest if they deliver a significantly higher yield than fixed systems. An important point is therefore the power consumption that is consumed by the tracking drive . A further complicating factor is that a solar tracker can only achieve high energy yields if the tracking systems follow the course of the sun sufficiently quickly , which usually results in higher power consumption.
If one considers the costs of tracking systems, the highest costs usually result for complex computer-controlled solar trackers . However, the operational data analysis “tracked and stationary photovoltaic systems with crystalline, amorphous and CIS modules” by the electrical engineering department at the Gelsenkirchen University of Applied Sciences suggests that the yield-cost ratio of complex solar trackers is worse than the simply designed solar tracker such as B. thermohydraulic tracking systems.
Advantages and disadvantages of solar tracking in comparison
If you want to compare the advantages and disadvantages of solar tracking, the following picture emerges:
Benefits of solar trackers
- Solar trackers deliver higher yields than rigid photovoltaic systems.
- Thanks to the typical mounting on masts, there are no problems with shading .
- The mast construction also ensures optimal rear ventilation of the solar modules.
- With a solar tracker on the mast, your own roof remains untouched .
- The mast construction is easily accessible for maintenance, troubleshooting or repair .
Disadvantages of solar trackers
- Tracking photovoltaic systems on masts are considered to be open-air systems – you only get a lower feed-in tariff for this.
- The need for installation space is higher than that of rigid open-air systems, especially if several masts are to be erected: These need a large distance to prevent mutual shading throughout the day.
- Tracking systems are more expensive than rigid systems.
- The maintenance and repair cost more than rigidly installed equipment. The reason: the components that ensure mobility are usually more susceptible to failure.
- You need inverters that are suitable and approved for use outside.
- Suitable anti-theft devices are required for outdoor systems.
- More material is needed to cope with the high wind loads.
- The cost of connecting to the power grid is comparatively higher.
- The procurement of spare parts over the life of the system, we are talking about 20 years and longer can be problematic.
Comparison of rigid vs. movable PV systems
In a comparison of the two types of systems – more rigid and more flexible – the advantage with regard to the service life of the rigid systems can hardly be seen today , which resulted from their immobility for a long time. The tracking systems have long since followed suit and will also function for a long time . However, you have to accept that the system is put through its paces every year.
Solar trackers that are equipped with system monitoring and thus provide the manufacturer with system data have an advantage here. The same goes for the operators who have opted for a full maintenance contract that enables a warranty period that extends beyond the usual two years.