This work is devoted to thermodynamic interpretations and electrical network analyses for the operational considerations of electrolyser cell (EC) systems composed of low/high-temperature electrolysers and heat engines. Detailed trajectories of current density, required power, and practice heat have been addressed to demonstrate the optimal operation mode of the systems in terms of hydrogen production rate and efficiency, as well as power consumption. Suitable simulations exhibit a boundary current path at the thermal neutral (TN) modes between heat addition and heat removal (occurring after heat addition). Results indicate that the integration of high-temperature electrolysers with renewable energy from solar or geothermal to optimize the hydrogen production efficiency and reduce power consumption is of high interest. It is more important to understand that heat removal can further increase hydrogen production rate over thermoneutral path at constant temperature. The analyses also demonstrates that adding renewable heat and minimizing area specific resistance (ASR) would be highly desirable for further developing high-efficient and low-consumption EC systems.