Since the beginning of commercial photovoltaic installation, most rooftop PV systems have been installed with a conventional clamp system. I.e. two aluminium clamps are screwed to the long or short module side with a rail underneath. Nowadays, however, insertion rails are also increasingly used for module mounting. This is increasingly seen on commercial photovoltaic systems with sheet steel roofing.
Advantages of a PV insertion system
While the aesthetic aspect of insertion systems play a great role on private tiled roofs, the technical advantages of roofs with steel roofing are in the foreground. In addition to the individual advantages of an insertion system, simple but essential physical conditions must be met in the best possible way.
Thermal expansion – an important factor
This is about the thermal expansion of the roof and the mounting system. On a steel roof, e.g. a trapezoidal roof with photovoltaics, this causes great tension between the steel roof and the aluminium PV mounting system, as the coefficient of linear expansion of aluminium is approximately twice as high as that of steel. This means that if the photovoltaic system was built in summer, the roof will contract twice as much in winter as the aluminium of the mounting system, or if installed in winter, it will expand twice as much in summer. In addition, there is thermal expansion due to day and night temperatures.
Caution with firmly screwed mounting systems
A mounting system that is firmly screwed to the roof, where the rails are firmly connected to the roof, therefore has no chance of yielding to or compensating for thermal expansion in any way and thus generates enormous stress points. On the one hand, at the roof fixation points where the mounting system is connected to the roof, and on the other hand, at the module clamps with which the PV module is screwed to the mounting system.
What are the risks?
- Tension between the roof and the mounting system: The stresses can negatively influence the holding force of a screw or rivet over a longer period of time, as screw or drill holes can experience permanent deformations, so that in the worst case the connection gets loose. Screw connections in particular have a higher risk here in a static comparison with riveted connections, as rivets can withstand significantly higher shear and suction forces due to the expansion on the inside of the steel roof and can therefore better ensure the tightness of the connection.
- Tension between clamp connection and solar module: Tension in the clamp connection with the PV module: There are several risks here. On the one hand, in extreme cases, the clamp can loosen from the module and thus no longer guarantee the fixation of the module. On the other hand, tension can discharge onto the PV module, which can lead to glass breakage or micro-cracks in the cells as a long-term consequence.
The TRITEC insert system solves these problems
Safeclick enables separated expansion
The TRITEC TRI-STAND insertion system can be connected to the trapezoidal roof with a rivet or screw connection, whereby the rivet connection is usually used primarily. In this case, an aluminium plate (Safeclick) with a rail receptacle on the upper side serves as the roof fixation. Here, by clicking in the module profile (insert profile), a screwless, floating connection is created. This allows the different expansion of steel and aluminium to take place independently of each other. This puts much less strain on the riveted or screwed connection.
With an insertion system, the solar module is mounted floatingly
In contrast to a clamping system, with an insertion system the PV module is not permanently connected to the mounting system by means of a clamping device, but, as the name already suggests, is only inserted into the horizontal rail and is thus also only supported in a floating manner. This allows the horizontal rails sufficient room for thermal expansion, and the modules remain completely unaffected.
The floating mounting of the insertion system not only avoids damage to the PV system due to thermal expansion, but also enables the complete use of roof areas, as thermal separation of module fields (e.g. after every 12 metres) is no longer necessary.
Enormous savings in installation time
Depending on the type of roof, enormous savings in installation time are possible with the insertion system. The TRITEC insertion system makes this possible through the simple click connection of the horizontal rail with the Safeclick and through the screwless installation of the PV modules in turn in the horizontal rail.
Great aesthetics thanks to a closed and homogeneous module surface.
Especially in private homes, aesthetics often play a primary role alongside performance. Since there are no clamps on the four module sides of the insertion system, there are no gaps between each module, which can be up to 2 cm depending on the clamping system. This means that with the insertion system, you have a closed, homogeneous module surface which, depending on the size of the roof, allows you space for additional modules due to the saved clamping distances.
You can find an overview of the system’s applications here: PV mounting systems from TRITEC