Such a roof is generally known. The solar cells are generally arranged directly under the external roof or incorporated into it. This means that maintaining or repairing the solar cells implies removing the concerned part of the external roof.

As the inner roof is not generally water tight, this means some risk for the building as it is necessary to wait until the weather situation is fine before carrying out the expensive maintaining/ repairing operation.

The object of the invention is to provide a roof structure of the above-mentioned type alleviating this problem.

This aim is reached, according to the invention, by providing between the external roof and the inner roof a number of guiding members along which oblong panels provided with solar cells can be slid between the external roof and the inner roof.

Thereby, the solar cells can be maintained and/or repaired without having to remove the inner roof. Moreover, a direct contact between the external roof and the solar cells is prevented, thereby reducing any damaging risks for the solar cells.

Preferably, the roof structure is built in such a way that the space between the inner roof and

the external roof can be closed so as to prevent essentially any air exchange with the environment.

Consequently, the solar cells cannot get dirty because, with the external air, dust particles and similar can also penetrate within the space and settle therein.

In a preferred embodiment according to the invention, the inner roof, the external roof, the guiding members and the panels together form a number of channels, a first part of which extend on top of the panels and another part of which extend under the panels.

Thereby, an air stream may circulate around the solar cells, so ensuring a good cooling of the latter.

Others features and advantages of the invention will become clear from the following description in which reference is made to the accompanying drawings, in which : Fig. 1 is a schematic cross-section of a roof structure according to the invention, Fig. 2 is a cross-section along the line II- II in Fig. 1, Fig. 3 is a cross-section as illustrated in Fig. 2 of a modified embodiment of the roof structure according to the invention, and Fig. 4 is a cross-section as illustrated in Fig. 2 of a third embodiment of a roof structure according to the invention.

Fig. 1 schematically illustrates a roof structure according to the invention, comprising an

inner roof 5 and an external roof 6 between which panels 7 provided with solar cells are arranged. Such a roof structure is sloping in the illustrated embodiment, which generally is advantageous for increasing the solar cell yield and is preferably oriented as far as possible southwards.

The energy generated by the sun can be used for numerous purposes, for example for heating a building having such a roof structure, for producing electricity, etc.

The inner roof 5 can be a common thermal isolating layer as already generally used in the building of houses. The external roof 6 should be at least partially transparent in order to allow the sun radiation to reach the solar cells. Additionally, the external roof 6 may comprise separate members, for instance members in the form of roof tiles, but others forms are also possible.

As illustrated in Fig. 2, the inner roof 5 is provided with a layer comprising a number of oblong ridges 10 forming the rooftop, wherein each ridge 10 is provided, lengthwise, i. e. in the direction vertical to the surface of Fig. 2, on both sides with a plate 11, respectively 12, on which a panel 7 provided with solar cells can lie.

The external roof 6 with a shape equal to that of the roof tiles is made of a transparent material, for example, glass and rests on the upper sides 13 of the ridges 10.

As it is obvious from Fig. 2, two channels 15 and 16 are thereby formed between each pair of adjacent

ridges 10, wherein each channel 15 extends between the external roof 6 and the panel 7 and each channel 16 extends between the panel 7 and the inner roof 5.

The panel lies proximate to the lower end of the roof structure on retaining members which are mounted on the plates, with the structure being such that each panel 7 can be slid, from the side 20 and the space between external and inner roofs, onto the plates 11 and 12 until their lower end is slid onto the retaining members and, therefore, the panel can be maintained on its place.

The opening adjacent to the side 20 between external and inner roofs can be subsequently closed, such as by means of a cover 21 for each panel, which cover being adjusted in the space between each pair of ridges 10. This way, there is some free space between the cover 21 and the lower end of the panel 7 so that the channels 15 and 16 there are connected to each other.

Proximate to the upper end, the panel 7 does not completely extend as far as in the ridge and a free space 24 is formed which extends transversally over all the panels. A heat exchanger 25 is arranged in said space, which makes it possible to exchange heat between the air being present in the channels 15,16 and the space 24 and another medium, for example, water.

Moreover, a fan 26 is provided making it possible to cause the air to flow through the channels 15,16.

Upon flowing, the air flow is heated on the one hand directly by the solar heat and on the other hand by the cooling of the members limiting the

channels 15,16, more particularly the panels 7 provided with the solar cells. This heat is transferred in the heat exchanger 25 at least partially to another medium, for example water, which can be used in a house warm water circuit.