A binary geothermal system comprising: —an organic Rankine cycle having at least one supply pump for feeding an organic working fluid, in liquid phase, of at least one heat exchanger for heating the organic working fluid until its transformation vapor phase and to its eventual overheating, an expansion turbine to expand the organic working fluid vapor, a condenser bringing in a liquid phase the organic working fluid, —a geothermal source comprising a geothermal liquid and a geothermal vapor, the organic working fluid is vaporized directly or indirectly through a flow of geothermal vapor in the heat exchanger and is preheated by a flow of geothermal liquid in a first pre-heater, and the organic working fluid is preheated also in a second pre-heater which exploits the thermal energy contained in a flow rate formed by the gas mixture and by the geothermal vapor fraction which is not condensed.