Efficiency Enhancement for Alkaline Water Electrolyzers Directly Driven by Fluctuating PV Power

Hydrogen production from photovoltaic arrays is a promising way to fully utilize the solar energy and to relieve consumption pressure of the power system. The low-cost and mature alkaline water electrolysis is suitable for large-scale hydrogen production. However, the low-load inefficiency of alkaline water electrolyzers greatly limits their operation range (usually 40%∼100% of rated load). Hence, alkaline water electrolyzers are hard to follow the fluctuating photovoltaic power in full range. Focusing on this problem, this paper analyzes the inefficiency mechanism of low-load alkaline water electrolyzers. It is found that through modifying the excitation electric field, the low-load performance of alkaline water electrolyzers can be greatly enhanced. Based on this, an optimal current pulse-width modulation control strategy and the corresponding prototype converter are proposed to regulate alkaline water electrolyzers directly driven by photovoltaic arrays. The effectiveness of the proposed method is verified by a 2 Nm ³ /h commercial alkaline water electrolyzer. Experimental results show that compared to the conventional dc power supply, 1) the maximum efficiency improvement can exceed two times, 2) the alkaline water electrolyzer can follow the fluctuating photovoltaic power well.