NOVELTY - A hydrogen production system comprises a first heat recovery steam generator to produce steam using heat from first working fluid heated by a geothermal energy source, and an electrolyzer to receive steam produced by the first heat recovery steam generator and to produce hydrogen and oxygen from the steam.    USE - For producing hydrogen.    ADVANTAGE - The inventive system enables efficient and inexpensive production of hydrogen.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a combined hydrogen and power generation system comprising a hydrogen production system including a first heat recovery steam generator and an electrolyzer; and a power generation system including a second heat recovery system to transfer heat from first working fluid to second working fluid, an electric generator, and a turbine coupled to the electric generator and driven by the second working fluid to power the electric generator to produce electricity;    (2) a method of utilizing heat from a geothermal energy source to produce hydrogen, by extracting heat generated from a geothermal energy source to produce steam in a first heat recovery steam generator, directing the steam to an electrolyzer to undergo electrolysis to produce hydrogen and oxygen, and recycling heat within hydrogen and oxygen produced by electrolyzer; and    (3) a method of utilizing heat from a geothermal energy source for combined hydrogen and power generation system, by extracting first part of heat from a geothermal energy source to produce steam in a first heat recovery steam generator, directing the steam to an electrolyzer for electrolysis to produce hydrogen and oxygen, extracting second part of heat from the geothermal energy source and transferring the heat to a second working fluid in a second heat recovery system, applying the second working fluid to a turbine coupled to an electric generator for producing electricity, and recycling the heat within hydrogen and oxygen produced by the electrolyzer in a first heat exchanger and a second heat exchanger.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram of a method for producing hydrogen by electrolysis of steam produced by heat from working fluid heated by a geothermal energy source.