Serial connection of 48-cell alkaline electrolysis stacks

Power supply cost significantly impacts the economic feasibility and the balance of plant in alkaline electrolysis, and since these costs are mainly driven by the rated current, increasing system voltage can improve cost efficiency. Voltage can be raised by using longer stacks or connecting shorter stacks in series; however, stack length is limited by stray currents and mechanical constraints, making serial connection of short stacks a promising approach. This study experimentally investigates a 200 V alkaline water electrolysis (AWE) system comprising two 48-cell stacks, tested individually and in series, focusing on current efficiency, specific energy consumption (SEC), and stray current behavior under different operating conditions and DC grounding schemes. The adoption of a serial connection was operationally feasible: individual stacks reached current efficiencies above 95 %, while the series configuration showed a modest reduction, with SEC increasing by less than 5 % once current exceeded 50 % of nominal load. At low currents, however, external stray currents accounted for up to 30 % of the supply current, leading to efficiency losses of around 10%–20% compared to single-stack operation. Grounding the second stack increased stray current magnitude due to the elevated potential gradient between the first stack and ground. Higher electrolyte flow improved gas removal and reduced cell voltages by about 1 %, but also slightly increased stray currents through outlet hoses. Theoretical estimates of gas-induced conductivity losses underestimated actual stray current magnitudes, likely due to faster gas removal than assumed. • Serial connection of two 48-cell AWE stacks validated at 200 V. • Serial operation shows minimal loss vs. single stack operation. • External stray currents cause main losses at low operating currents. • Higher temperature improves current efficiency and lowers SEC. • Grounding and hose design critical for stray current reduction.