Abstract: An apparatus and a method for using geothermal energy include the use of at least a first conduit, through which a working substance is carried downward into the interior of the Earth, at least one second conduit, through which the working substance is carried upward, in the direction of the surface of the Earth, with the first and second conduits form a closed system relative to the soil, wherein the working substance is carried downward into the interior of the Earth, and the throttling region throttles the largely liquid working substance upstream, in the flow direction, of the throttling region to a vaporization pressure, so that downstream of the throttling region the working substance is largely completely vaporizable.