NOVELTY - Clamping rail system for at least one film present as a roof on a fermentation container of a biogas plant, comprises a lower rail chain (8) and an upper rail chain vertically arranged above the lower rail chain, respectively comprising several rail elements (10). The rail elements are formed straight, and exhibit a convex curvature at one end, and an associated complementary concave curvature at other end. The mutually associated complementary curvatures and the horizontally adjacent rail elements engage into each other such that a relative pivotal movement around a pivoting angle is allowed.    USE - The clamping rail system is useful for at least one film present as a roof on a fermentation container of a biogas plant (claimed).    ADVANTAGE - The clamping rail system can be manufactured and assembled in a cost-effective manner.    DETAILED DESCRIPTION - Clamping rail system for at least one film present as a roof on a fermentation container of a biogas plant, comprises a lower rail chain (8) and an upper rail chain which is vertically arranged above the lower rail chain, respectively comprising several rail elements (10). The fermentation container comprises a container wall surrounding a container inner chamber in a cylindrical tubular manner. The container wall on its upper side is fixed with the clamping rail system. The film is clamped between the lower- and the upper rail chains in a force-fit manner, and is optionally fixed in a form-fit manner by holding elements. The rail elements are formed straight, and exhibit a convex curvature at one end, and an associated complementary concave curvature at other end. The mutually associated complementary curvatures and the horizontally adjacent rail elements engage into each other such that a relative pivotal movement around a pivoting angle is allowed. An INDEPENDENT CLAIM is also included for the rail element for the above clamping rail system, exhibiting in the region of the concave curvature, a width which decreases in the direction of the concave curvature, preferably an end side extends in a pointed manner having a tip angle of 1-5 degrees , and in the region of the convex curvature, a reduced width in which the edges of the concave curvature of the horizontally adjacent rail element, move around the pivoting angle during pivoting, where the convex curvature is formed as a semicircle having an angle of 180 degrees , and the concave curvature is formed less than a semicircle, preferably as a partial circle having an angle of 90-135 degrees .    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic top view of a partial section of the container wall of the fermenter container with the lower rail chain of the clamping rail system.    Average diameter of the tubular cylindrical container wall (5)    Lower rail chain (8)    Rail elements (10)    Sealant (19)    Thickness of the container wall (34)