NOVELTY - The device has a rail (2) including a sole plate (21) with an inner face supported on a support (1). Another rail (3) comprises a sole plate (31) with an inner face supported on a support and another sole plate (32) arranged parallel to the former sole plate. A fixing unit (14) fixes the rails at juxtaposition on the support by the sole plates such that an inner face of a wing (22) of the former rail and an upper face of the latter sole plate of the latter rail are arranged remotely so as to allow interlocking of solar panels (5) between the faces.    USE - Device for fixing a roof cover (claimed) on a support e.g. facade, framework, rafter, frame, and terrace, or on an installation e.g. thermal or photovoltaic solar panel installation, of a building such as industrial building e.g. workshop. Can also be used to fix the roof cover on a wall or slab.    ADVANTAGE - The fixing device ensures rapid fixation of the solar panels in landscape or portrait mode along slopes ranging from 0 to 90 degrees for assuring sealing function, thermal insulation function, wind resistance function and resistance to concentrated and distributed loads regardless of nature of the supports. The fixing device reduces overload imposed to the roof structure by the presence of solar panels installation. The fixing device assures ventilation of an air space between the panels and assures mounting inviolability of the roof cover. The fixing device ensures rapid assembling of the solar panel installation. The fixing device prevents access to rear side of the panels for avoiding accidental or malicious tearing of the panels.    DETAILED DESCRIPTION - The transparent solar panels are made of Lexan Thermoclear (RTM: structured polycarbonate sheet) and Tedlar (RTM: polyvinyl fluoride film). An INDEPENDENT CLAIM is also included for a roof cover comprising a flat plate reinforced under solar panels.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a fixing device in which rails are combined to form U-shape.    Support (1)    Rails (2, 3)    Solar panels (5)    Fixing unit (14)    Sole plates (21, 31, 32)    Wing (22)