Photovoltaics on a trapezoidal sheet metal roof: an excellent alternative to asbestos roofing
When it comes to renovating the roof of warehouses or production halls, many owners are faced with the question of what is the best future alternative for their pitched roof. If a rooftop photovoltaic system is also planned, there is a roofing alternative which is very well suited for this purpose. This is the trapezoidal sheet metal roof, which is both inexpensive and weatherproof.
As photovoltaic installations on asbestos roofing are not approved, the experts at STEAG Solar Energy Solutions generally recommend renovation. The harmful asbestos cement roofs which can still be found are usually replaced by trapezoidal sheet metal before the solar panels are mounted. In order to be able to offer our customers an all-round carefree package, our engineers work together with reliable, highly qualified manufacturers and service providers who take care of both the construction of the new roof and the subsequent installation of the solar system.
Thanks to comparatively low material costs, trapezoidal sheet metal roofs are particularly suitable for basic roofs such as warehouses that don't require special insulation. If there are special requirements and the roof also needs to be equipped with an insulating function, the so-called “sandwich roof” is available as a special form. In this case an insulating core, for example made of PIR (polyisocyanurates), is located between two thin layers of sheet metal to provide the desired insulation. Sandwich panels are also the right choice for roof cladding in terms of energy efficiency.
How many solar modules does a roof made of trapezoidal sheet metal support?
Due to its distinctive trapezoidal shape, the sheet metal roof doesn’t bend under loads and thus guarantees the necessary stability required for the installation of solar panels on the roof. The minimum sheet thickness for the installation of a roof-mounted system is 0.75 millimetres. Trapezoidal roofs belong to the traditional pitched roofs and feature a roof pitch of more than 5°. This angle of inclination distinguishes them from flat roofs.
As a first step our team from the Energy Systems division calculates how many solar modules the trapezoidal sheet metal roof will support. This calculation also provides information about the output of the finished PV roof system, how much electricity can be produced per year and the future CO2 savings. A particular challenge when planning a photovoltaic system on trapezoidal sheet metal is the angle of inclination to be considered. If this is exactly the same as the roof, we refer to the mounting as “parallel to the roof”. This makes the additional raising of the solar modules to increase the yield unnecessary, and generally makes sense for roof inclinations of more than 12°. Roofs with an east-west orientation are also advantageous, as the yield is usually highest here.
The substructure of the PV system is decisive for mounting on the trapezoidal sheet metal
In designing the photovoltaic system, the solar experts at SENS work together with various premium service providers. Aluminium rails from the manufacturer K2 Systems, based in Renningen near Stuttgart, serve as the substructure for the solar panels and are screwed directly onto the roof. These rails are unique in their design and can only be obtained from this supplier. For the PV mounting systems we differentiate between short-rail and long-rail systems. Long rails are often used for mounting because they offer a decisive advantage: compared to short rails, they can be grounded better and integrated into the external lightning conductor system.
When choosing the substructure, the durability of the material must also be taken into account in every case. It should be both corrosion-proof and UV-resistant, and comply with the generally accepted rules of technology.
Strong temperature fluctuations can cause different expansion levels. A plastic element therefore serves as a buffer between the steel and the aluminium. In this case, the PV module is then referred to as having "floating" mountings. Depending on the manufacturer the solar panels are fixed to the rail with module clamps. During the planning, maintenance walkways must also be taken into account. These also serve as protection against thermal expansion. Since a system life of 25 to 30 years is assumed, our solar experts attach great importance to high-quality planning and documentation of the project. For this purpose, SENS offers a complete package: after completion and commissioning of the PV system, customers can also engage SENS as a service provider for maintenance and servicing.
The statics of the system plays an important role in the installation of PV on trapezoidal roofs
The statics of the system also plays an important role in the planning of the roof and subsequent installation of the photovoltaic system. The following roof parameters have to be considered: building height, roof pitch, location of the site (exposed position), wind load, snow load, sheet thickness and bead spacing, type of roofing material and use of the building. These factors are decisive when calculating the necessary number of mounting points which penetrate the roof.
To ensure the durability of the construction, the fitters use stainless steel screws and self-tapping screws with sealing washers. In addition to the substructure, optimum cable management must also be taken into account during the mounting of the PV system. In the best case, the cables are not laid directly on the roof, but float above the trapezoidal sheet metal. In particular the plug connections (module plugs) must not be routed in the water-bearing layer. Any water penetrating the plug and cable would lead to an insulation fault in the long term.
If all the factors mentioned above have been taken into account, SENS customers will on completion receive a quality product that will produce green electricity on their own roof for the next 25 to 30 years. As an alternative to trapezoidal sheet metal, during the renovation work it is possible to construct a roof made of corrugated fibre cement. Our experts will be happy to advise you on making your decision!
Photos: Sascha Link