Advantages PV-insertion system: The better choice for photovoltaic systems

Since the beginning of commercial photovoltaic installation, most rooftopPV systems have been installed with a conventional clamping system. This means that two aluminium clamps are screwed to the long or short module side with a rail underneath. Nowadays, however, PV insertion systems with insertion rails are also increasingly used for module installation. Increasingly seen especially on commercial photovoltaic systems with sheet steel roofing and private houses with tile roofing.

Thermal Expansion of PV Systems

While the aesthetic aspect of photovoltaic integration systems plays the primary role on private tile roofs, the technical advantages take center stage on roofs with steel roofing. In addition to the individual benefits of a PV integration system, it is essential to address simple yet critical physical conditions as effectively as possible. This involves the thermal expansion of the roof and the mounting system. On a steel roof—for example, a trapezoidal roof with photovoltaics—this results in significant stresses between the steel roof and the aluminum PV mounting system, since aluminum’s coefficient of linear expansion is approximately twice that of steel. This means that if the photovoltaic system was installed in the summer, the roof will contract twice as much as the aluminum in the mounting system during the winter; conversely, if installed in the winter, the roof will expand twice as much as the aluminum in the mounting system during the summer. Added to this is thermal expansion caused by fluctuations in day and night temperatures.

Problems with conventional clamping 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 fixing 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.

1. Tension between roof and mounting system

   The stresses can negatively affect 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 gives way. In a static comparison with riveted connections, screw connections in particular have a higher risk here, as rivets can withstand significantly higher shear and suction forces due to the expansion on the inside of the steel roof and can thus better ensure the tightness of the connection.

2. Tensions between clamp connection and solar 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, voltages can discharge onto the PV module, which can lead to glass breakage or micro-cracks in the cells as a long-term consequence.

Advantages of the PV insertion system

The floating mounting of the PV insertion system not only avoids damage to the PV system due to thermal expansion, but also enables the complete use of roof areas due to this property, as thermal separation of module fields (e.g. after every 12 metres) is no longer necessary. In our example, we show the photovoltaic installation on a roof with trapezoidal sheet metal covering.

1. Separate expansion of the materials possible

   The PV insertion system TRI-STAND can be attached to the trapezoidal roof using either a riveted or screwed connection, although the riveted connection is generally preferred. In this case, a aluminum plate (SafeClick) with a rail mount on the top serves as the roof mounting. Here, a screwless, floating connection is created by snapping the module profile (insert profile) into place. This allows steel and aluminum to expand at different rates independently of one another, significantly reducing the stress on the riveted or screwed connection.

   

2. Floating storage of the solar modules

   In contrast to a clamping system, in an insertion system the PV module is not fixed 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 floating. This allows the horizontal rails sufficient room for thermal expansion, and the modules remain completely unaffected.

   

3. Enormous savings in assembly time

   Depending on the type of roof, the installation system can result in significant savings in installation time. The TRITEC installation system makes this possible through the simple click connection between the module rail and the SafeClick, as well as the screwless installation of the PV modules into the module rail.

   

4. Great optics due to a closed module surface

   Especially in private homes, aesthetics often play a primary role alongside performance. Since there are no clamps on the four sides of the modules in 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.

   

Video: Insertion system for tiled roof

→ Learn more about the TRI-STAND mounting system