NOVELTY - Combined use of raw biogas containing carbon dioxide and a usable gas, preferably methane, comprises (i) providing usable gas comprising (1a) providing alkali carbonate, (1b) removing carbon dioxide from raw biogas, (1c) separating alkali hydrogen carbonate and providing usable gas, and (ii) generating electricity comprising (2a) combusting the raw biogas in a heat engine for producing electrical energy and waste heat, (2b) using the waste heat for regeneration of alkali hydrogen carbonate, and (2c) recycling the resulting alkali carbonate in step (1a).    USE - The method is useful for combined use of raw biogas containing carbon dioxide and a usable gas, preferably methane.    ADVANTAGE - The method is carried out with high efficiency; and is flexibly carried out to external conditions, preferably energy demand.    DETAILED DESCRIPTION - Combined use of raw biogas containing carbon dioxide and a usable gas, preferably methane, comprises (i) providing usable gas comprising (1a) providing alkali carbonate, (1b) removing carbon dioxide from raw biogas by reacting carbon dioxide with alkali carbonate in the presence of water to alkali hydrogen carbonate according to a reaction comprising reacting usable gas with alkali carbonate, water and carbon dioxide to obtain usable gas and alkali hydrogen carbonate, (1c) separating alkali hydrogen carbonate and providing usable gas, and (ii) generating electricity comprising (2a) combusting the raw biogas in a heat engine for producing electrical energy in a generator, which is driven by the heat engine, and waste heat, (2b) using the waste heat for regeneration of alkali hydrogen carbonate according to a reaction comprising converting alkali hydrogen carbonate to alkali carbonate, water and carbon dioxide, and (2c) recycling the resulting alkali carbonate in step (1a).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic block diagram of part of the method for providing usable gas (Drawing includes non-English language text).    Biogas reactor (1)    Biogas discharge (2)    Carbon dioxide absorber (3)    Gas network (4)