NOVELTY - A method for gasifying carbon compounds (I) to produce synthesis gas (II) involves: (A) pyrolyzing (I) to give carbon (III) and gas (IV) in a solar-microwave reactor (1), using thermal energy from (i) heating of the reactor wall (1a) by solar radiation and (ii) 1-300 GHz microwaves; and (B) converting (III) and (IV) into (II) by oxidoreductive reactions in a cyclone reactor, with superimposed or nested cyclone units, heated directly by microwaves.    USE - For producing synthesis gas (II) (mainly carbon monoxide and hydrogen), specifically from biomass (including e.g. animal manure or paper pulp) or coal. (II) may be converted into hydrocarbon fuels (e.g. using Fischer-Tropsch synthesis) and/or used as a source of hydrogen (also useful as fuel).    ADVANTAGE - A combination of solar energy and plasma (obtainable using electricity from solar panels or wind farms) is used to form synthesis gas for conversion into fuels. A low-pollution energy source, avoiding petroleum sources, is thus provided.    DETAILED DESCRIPTION - A method for gasifying carbon compounds (I) to produce synthesis gas (II) involves: (A) pyrolyzing (I) to give carbon (III) and gas (IV) in a solar-microwave reactor (1), using a synergistic combination of thermal energy from (i) heating of the reactor wall (1a) by solar radiation concentrated, by convergence or reflection, onto the wall surfaces and (ii) 1-300 GHz microwaves directed into the reactor interior and (I); and (B) converting (III) and (IV) into (II) by oxidoreductive reactions in a cyclone reactor, with at least two superimposed or nested cyclone units, in which (i) a gaseous vortex entrains and oxidizes particles of (III) utilizing combustion of (IV) or an additional gas, (ii) heated gas (or gaseous mixture) is injected into the cyclone components and (iii) gas present in the reactor is heated by microwaves directed into the reactor.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of the solar-microwave reactor part of a synthesis gas production plant.    Tubes of solar-microwave furnace (1)    Wall of solar furnace (1a)    Vacuum or insulating gas, e.g. argon (1b)    Transparent wall of containing vessel (1c)    Quantum particles of containing vessel wall, for converting solar UV radiation into visible and infrared radiation (1d)    Endless screw (2)    Mirror system (3)    Mirror within containing vessel (3a)    Mirrors (4)    Convergent or Fresnel lenses (5)    Magnetron (6)    Wave guide (7)