Optimal hydrogen production in a stand-alone renewable energy system

A stand-alone renewable wind-photovoltaic energy system can be used to meet the energy requirements of off-grid remote area applications. Such a system has been developed and successfully tested at the Hydrogen Research Institute (HRI). In the HRI's system the excess electrical energy with respect to load demand, is transformed and stored as hydrogen gas via an electrolyzer. The stored hydrogen represents a long-term ecological and transportable form of energy. The renewable energy (RE) system components have subs tantially different voltage-current characteristics and their operation must be well understood and coordinated to allow an optimal power management in the system. Wind turbine generator, DC-DC buck converter and electrolyzer play key roles in the hydrogen production process. Accurate knowing of operating characteristics of these components is necessary to develop an effective power flow control for the hydrogen production. This paper investigates operational characteristics of the wind turbine, the electrolyzer and the buck converter in order to develop an energy management strategy that will increase the hydrogen production efficiency in the RE system. Wind turbine model is developed and simulation results are compared with experimental measurements. The electrolyzer is characterized and its optimal operating range is defined. The multiphase control principle of the designed buck converter is presented and the efficiency curve is provided. An energy management strategy is proposed to increase the overall efficiency of the hydrogen production process.