Best Practise - Mounting System
Best Practise - Mounting System. Do-It-Yourself Installation
Best Practise Mounting System

Proper installation of  photovoltaic modules requires the correct selection and sizing of the mounting system. We provide below few basic considerations for the design of roof-top installations.

What Mounting System to choose

Essential is to choose the right type of mounting system fitting to your roof. In most cases, three types of mounting systems are considered for a roof-parallel mounting:

a/ Brick and tile roofs: Roof hooks

Dachhaken - Roof Hooks

Roof hooks are used for tile or pan roofs. Shown on the left is a stainless steel standard roof hook.

The standard thickness is usually 5 mm. For higher loads, are also reinforced roof hooks with 6mm or 7mm thickness available.

To consider for  installing:

  • Select appropriate shape. Different shapes are available up on the roof type.
  • The roof hook must fully sit on the battens. Also hooks must not rest on the brick or pan. If necessary.
  • Ensure proper design and sizing.

    Rule of thumb: When using standard roof hooks use 2 pieces per square meter (module) area. This results in placing about 12 hooks per peak kilowatt when using poly crystalline standard modules.

    Depending on the snow and wind load maybe even more or stronger roof hooks may be necessary.

b/ Corrugated eternit or corrugated sheet metal: Mounting with Hanger Bolts


For Corrugated eternit or corrugated sheet metal, the solar rails are fastened with hanger bolts as seen on the left hand site.
Hanger bolts are available in various lengths and thicknesses. Commonly used are M10 bolts with a total length of 200 or 250mm.
Bolts are provided with a seal to prevent fungal growth and water penetration into the roof structure.

An adapter plate connect the hanger bolt with the mounting rails.

To consider when installing:

  • Choose appropriate length and diameter.
  • Screw depth need to be 8 times the diameter of the screw. Bearing width need to be 3 times of the diameter .

c/ Trapezoidal Metal Sheet: Mounting with trapezoidal sheet metal bridge


For trapezoidal steel sheets, so-called trapezoidal metal bridges are used as seen on the left hand site.
Trapezoidal bridges are a quite economic methos, because little material is required and installation is very quick.
Trapezoidal bridges are connected to the metal sheet either with certified screws or certified rivets.
It is important that the trapezoidal sheet has a minimum thickness of 0.5 mm.

Usually these bridges can not be used for aluminium roofs because aluminum is too brittle for a permanent connection.

To consider for the installing:

  • Minimum thickness of the trapezoidal sheet must be given. Get manufacture permission to use the bridge for the trapezoidal sheet.
  • Use only certified rivets or screws.
  • Usually not suitable for metal sandwich panels
Once the right type of the connectors has been selected and installed, the suitable rails and modules need to choose and installed. Standard rails have a cross section of 40mm and can typically overspan a width up to 1.50 - 1.80 m. However, a smaller distance is advisable. Furthermore, wind and snow loads can make stronger rails neccessary.

Mounting of the Modules:

Klemmabstand Module


Not only the right number of roof hooks or hanger bolts is important, also the distance of the module clamps is crucial to avoid long term damages.

Modules should never be clamped on the short side. It implies for standard roof type an upright installation of the modules.

If you you want to install the modules horizontally, a so called cross conecction need to be used as a substructure. A cross connection is a two-layer system in which both track rail layers are perpendicular to one another.

Check always the manufacture manual to find out the allowed ranges of clamping dictances. A typical range is 1/8 to 1/4 of the module length. Also the mounting holes in the module frames indicates the right range for clamps - clamps should be attached between the inner and the outer mounting hole.

Also ensure an expansion gap between the modules of 1 to 2 cm after installation on the vertical side.








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