Thermodynamic analysis and exergy based cost formation of hydrogen production by a water electrolysis process powered by a binary geothermal power plant is performed. The exergetic cost formation process is developed applying the specific exergy cost method (SPECO). For a geothermal resource temperature of 160 degrees C and a geothermal flow rate of 100 kg/s, hydrogen gas can be produced at a rate of 0.0253 kg/s in the electrolyzer. This corresponds to 0.253 g of hydrogen production per kilogram of geothermal water. Thermoeconomic cost analysis reveals that the unit exergetic costs of electricity and hydrogen produced in the system are 6.495 $/GJ (or 0.0234 $/kWh) and 19.7 $/GJ (or 2.366$/kg H-2), respectively. (C) 2015 Elsevier Ltd. All rights reserved.