NOVELTY - The method comprises stripping, from hydrocarbon gas, most of gaseous impurities consisting of hydrogen sulfide, siloxanes, volatile organic compounds other than hydrocarbons and halogenated volatile organic compounds to provide stripped hydrocarbon gas including carbon dioxide, compressing the stripped hydrocarbon gas to provide compressed stripped biogas, and reacting the stripped hydrocarbon gas in a solar radiation receiving reactor having a catalyst that is heated by concentrated solar radiation impinging for providing an output gas mixture comprising hydrogen gas and carbon monoxide.    USE - The method is useful for reforming a hydrocarbon gas (claimed) such as a biogas including ethane, propane and butane, where the reformed gas is useful: for processing liquid fuels such as methanol or biodiesel; as a feed gas for a gas turbine, a turbo generator, a furnace, or a natural gas pipeline; and for producing green hydrogen for fuel cell powered cars.    ADVANTAGE - The method is capable increasing a calorific value of the hydrocarbon gas without coking in an economical and energy efficient manner.    DETAILED DESCRIPTION - The method comprises stripping, from hydrocarbon gas, most of gaseous impurities consisting of hydrogen sulfide, siloxanes, volatile organic compounds other than hydrocarbons and halogenated volatile organic compounds to provide stripped hydrocarbon gas including carbon dioxide, compressing the stripped hydrocarbon gas to provide compressed stripped biogas, reacting the stripped hydrocarbon gas in a solar radiation receiving reactor having a catalyst that is heated by concentrated solar radiation impinging for providing an output gas mixture comprising hydrogen gas and carbon monoxide, and adding steam and/or carbon dioxide to the stripped hydrocarbon gas, when as molar ratio of carbon dioxide to hydrocarbon gas in the stripped hydrocarbon gas is below a preferred molar ratio, to provide oxygen-enhanced stripped hydrocarbon gas for supply to the solar radiation receiving reactor. The solar radiation receiving reactor includes a solar radiation transparent window for allowing the solar radiation to impinge on the catalyst. The method further comprises cooling the solar radiation transparent window to help prevent deposition of carbon, stripping excess water and carbon dioxide from the output gas mixture, and ascertaining a composition of the output gas mixture and controlling a flow rate of the output gas mixture. The stripping step includes adsorption of the gaseous impurities on a material comprising activated carbon, alumina, clay, zinc oxide nanoparticles, molecular sieves and polymer beds, and is performed using water or a liquid catalyst and a cold trap. An INDEPENDENT CLAIM is included for a system for reforming hydrocarbon gas.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a system for reforming biogas.    Biogas stripping unit (102)    Biogas supply source (104)    Sensor (106)    Gas compressor (108)    Tank. (110)