NOVELTY - The method comprises introducing biomass in a fermentation container (2), which is gas-tightly closed against the atmosphere and aerobically fermenting over a period of 5 years. The biomass remains in the fermentation container during the total operation time of the fermentation container after the shutdown of the container. A free area of the fermentation container is filled with fresh biomass during fermentation through reduction of the volume of the introduced biomass. The filling of the biomass is continuously and/or discontinuously carried out.    USE - Method useful for producing biogas.    ADVANTAGE - The method ensures safe and economical production of biogas with high yield.    DETAILED DESCRIPTION - The method comprises introducing biomass in a fermentation container (2), which is gas-tightly closed against the atmosphere and aerobically fermenting over a period of 5 years. The biomass remains in the fermentation container during the total operation time of the fermentation container after the shutdown of the container. A free area of the fermentation container is filled with fresh biomass during fermentation through reduction of the volume of the introduced biomass. The filling of the biomass is continuously and/or discontinuously carried out. The portion of water in the biomass is adjusted before or directly after the introduction into the fermentation container to 50-90 wt.%. The pH value of water contained in the biomass is adjusted to 6.5-7.5. The biomass is crushed before introducing into the container. The decomposition process of the biomass is aerobically carried out in the fermentation container. Oxygen is supplied into the fermentation container. The process temperature is adjusted to 33-38 degrees C. The adjusting of the process temperature is carried out through the supply of oxygen, where geothermal energy is utilized for adjusting the process temperature and is taken away from a depth of 300 m. Process water or biogas is used as heat exchanging fluid for utilizing the geothermal energy. The remaining residual volume is filled with non-decomposable solid materials for the shutdown of the fermentation container, which is lidded with soil after its finalization. The fermentation container remains durably in the soil. An INDEPENDENT CLAIM is included for a plant for producing biogas.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a plant for producing energy under simultaneous reduction of the emission of greenhouse gases into the atmosphere.    Fermentation container (2)    Biosphere (4)    Lignite-opencast mines (5)    Tube line system (6)    Tapping line. (7)