Thermodynamic and economic analysis of an off–grid photovoltaic hydrogen production system hybrid with organic Rankine cycle

Water electrolysis technology is a potential approach for green hydrogen production and photovoltaic power consumption. However, due to the volatility and uncertainty of the solar energy, supplying photovoltaic power directly to the water electrolysis auxiliary system is instable. An innovative off–grid photovoltaic proton exchange membrane electrolytic cells hydrogen production system is proposed to address that issue. The system integrates an organic Rankine cycle system with evacuated tube collector modules to supply power for the auxiliary system. The electrical power generated by the photovoltaic module is directly supplied to the proton exchange membrane electrolytic cells. The matching of the organic Rankine cycle system output power and auxiliary system power demand has been conducted by comparing the temperature control methods and parameters. The thermodynamic and economic performances of the photovoltaic hydrogen production system have been investigated with the meteorological data of Nanjing. The results demonstrate the organic Rankine cycle system can completely satisfy the power demand of the auxiliary system operation. The annual hydrogen production of the system can reach 26.07 tons (316203.0 Nm³) and the hydrogen average electricity consumption is 4.75 kWh/Nm³. The system has a maximum energy and exergy efficiency of 8.8 % and 9.1 %, respectively. This system is suitable for retrofitting photovoltaic plants, the payback period of the retrofit project is 12 years, which shows higher profitability than that of grid-supplied hydrogen production.