A NOVEL DESIGN OF A LOW COST, ROBUST, EFFICIENT AND DYNAMIC ELECTROLYSER OPTIMISED FOR FLUCTUATING AND INTERMITTENT RENEWABLE ENERGY POWERED OPERATION

The renewable energy powered hydrogen energy system has been designed and installed by Loughborough University, UK and Beacon energy. This HARI (Hydrogen and Renewable Integration) project has been operating since November 2003 at the West Beacon Farm, Leicestershire, UK. A new electrolyser has been designed based on the simulation modelling and operating experience with present electrolyser technology. The stack-design of the new electrolyser is based on in-depth modeling by incorporating the thermodynamic, electrochemistry, heat and mass transfer of the electrolyser in the context of fluctuating and intermittent renewable energy powered operation. The operation of current electrolysers with dynamic renewable energy sources faces more challenges compared to the grid connected steady state operation. This problem is aggravated for pressurised electrolysers than atmospheric electrolysers, especially when powered by the off-grid renewable energy supply without any back-up. During periods at standby, the temperature and pressure within the system drop due to inevitable gas venting, thus diminishing efficiency of pressurised systems. The complexities of control systems, depending on the operating pressure of the electrolyser, introduce some delay to follow the dynamic power supplies, with the result that some of the available energy remains un-captured. The simulation suggests that the novel electrolyser will have much faster dynamic response due to optimised double layer capacitance and current density of the stack with efficient gas bubble removal mechanism. The on-off cycling and the time spent in the stand-by mode, without a protective current, cause corrosion in the electrodes of standard industrial electrolysers when powered by renewable energy sources. This problem can be resolved using a new technique of voltage protection facilitating unlimited on-off cycle rather than a protective current. The differential pressure across the membrane would be self controlled due to different cell structure within the stack of the new electrolyser, which is normally done by controlled venting using motorized valves in the standard industrial electrolysers. The heat capacity of the stack is optimised for enhancing the overall efficiency and minimizing the restriction on input current at low temperature. This helps in reducing the cooling demand of the stack as well. This paper also describes the compatibility of pressurised and atmospheric electrolysers when integrated with renewable energy sources on the basis of energy efficiency, gas loss, corrosion, gas purity and on-off cycling.