The RES2H2 wind-hydrogen pilot plant in Keratea, Greece, has been in operation for over two years now, in order to study and optimise the production of “green” hydrogen. The system is composed of a 25 kW water electrolyzer, metal hydride tanks filled with a LaNi5-type alloy and a hydrogen compressor for filling hydrogen cylinders, all powered by a 500 kW synchronous wind turbine.
The advanced alkaline electrolyzer produces 0.45 kg/h hydrogen directly at 2 MPa pressure, which is compressed up to 22 MPa in a single stage, with an additional 10% energy loss. A small hydrogen buffer accommodates the flow variations between the electrolyser and the compressor. The electrolytic hydrogen may be also stored in six metal hydride tanks with a total capacity of 3.6 kg hydrogen. The utilities comprise an air compressor and drier to supply instrument air to the pneumatic valves, a water boiler to supply hot water to the metal hydride tanks for hydrogen desorption and a water chiller for the cooling water circuit, all supplied by wind energy.
Only the electrolyzer, among the plant’s components, can withstand the rapid variations of wind power. The efficiency of the system, from wind power to the high heating value of the hydrogen stored varies from 50% to 70%, according to the operating conditions. The different operating modes and the subsequent system efficiency will be presented. The performance of the metal hydride tanks under real conditions and their potential for the purification of electrolytic hydrogen will be discussed.