NOVELTY - The method for operating a solid fermentation plant (10) with a discontinuously operable garage-like solid fermenter (12) for the fermentation of organic solids to produce biogas e.g. methane, comprises flowing-through the solid fermenter from top to bottom with a percolate (18), obtaining and collecting the biogas from the fermenter, and then subjecting to a cleaning process for carbon dioxide derivatives in such a way that the carbon dioxide content of the obtained methane gas is lowered under 45 vol.%. The carbon dioxide content is depleted less than 40 vol.%.    USE - Method for operating a solid fermentation plant with a discontinuously operable garage-like solid fermenter for the fermentation of organic solids to produce biogas e.g. methane, which is useful in gas engines.    ADVANTAGE - The method is capable of simply and safely operating the solid fermentation plant with less investment costs and low maintenance cost without clogging nozzles in environmental-friendly manner thus producing high quality biogas with less effort and high yield.    DETAILED DESCRIPTION - The method for operating a solid fermentation plant (10) with a discontinuously operable garage-like solid fermenter (12) for the fermentation of organic solids to produce biogas e.g. methane, comprises flowing-through the solid fermenter from top to bottom with a percolate (18), obtaining and collecting the biogas from the fermenter, and then subjecting to a cleaning process for carbon dioxide derivatives in such a way that the carbon dioxide content of the obtained methane gas is lowered under 45 vol.%. The carbon dioxide content is depleted less than 40 vol.%. Two discontinuously and temporally displaceable and operable garage-like solid fermenters are used. The biogas of the fermenters is obtained and mixed. The effluent percolate of the solid fermenters is gathered in a percolate container (16) operating as continuous regeneration fermenter and again supplied to the solid fermenters. The cleaning process is carried out before storing the biogas. The obtained and cleaned biogas is already supplied to an energetical utilization during inserting methane formation in the solid fermenter. An INDEPENDENT CLAIM is included for a solid fermenter plant.    DESCRIPTION OF DRAWING(S) - The diagram shows a solid fermentation plant.    Solid fermentation plant (10)    Solid fermenter (12)    Percolate container (16)    Percolate (18)    Pipeline. (20)