Control and energy efficiency of PEM water electrolyzers in renewable energy systems.

The practical dynamic properties and operational limitations of a commercial differential pressure 1 Nm 3 h −1 proton exchange membrane (PEM) water electrolyzer are studied from the viewpoint of renewable power production. Measured values from a 5 kW p solar photovoltaic (PV) power plant and PEM electrolyzer are analyzed to study factors affecting the control of PEM water electrolyzers operating as a part of renewable power production systems. Specific energy consumption of the PEM stack as a function of stack hydrogen outlet pressure is estimated based on measured values from two different measurement systems. Electrical energy consumption of the stack does not show any notable increase as the hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. However, the stack specific energy consumption increases by a maximum of 0.2 kWh/Nm 3 when hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. The increase in specific energy consumption at high differential pressure operation is due to a decrease in Faraday efficiency. Selection and control of the hydrogen outlet pressure can minimize the specific energy consumption and maximize the real hydrogen production in dynamic PEM water electrolyzer operation. [ABSTRACT FROM AUTHOR]