Fixing system for solar panels for use on principally flat roofs, consisting of a base and a roof penetration, which base can be anchored to the existing steel structure of the roof, which base is further suitable to be connected to the specified roof penetration, which roof penetration is equipped above with fixings for the attachment of the further structure of the solar panels, where the roof penetration includes an inner tube and an outer tube formed from principally rectangular tubes fitting one inside the other without contacting one another, at an angle of 45° so that rubber profiles can be pressed into the spaces between the inner tube and the outer tube, serving to provide thermal gaps and functioning as a mechanical connection between the inner tube and the outer tube.