Abstract: Roof structure for transparent roofs with girders (11), each with a solar panel (15, 36). The girders preferably have a height equal to have the distance between each girder. Two trapdoors (13, 14), consisting of thermal insulating material (28), are located between each pair of girders, one on the underside of each girder, which can swing on its pivot axis on the girder between horizontal and vertical positions. In the horizontal position the trapdoors shield against heat loss, in the vertical position they allow all light to enter, and in the intermediate position incoming light is reflected towards the sides of the girders (15) for heat absorbtion.