Economic consequences of undefined durability in water electrolysis: on extending use beyond the performance drop threshold

Electrolyzer durability remains undefined by international standards, despite its importance in the techno-economic viability of hydrogen production. Existing benchmarks define end-of-life (EoL) through a performance threshold (PT), typically based on voltage degradation. These thresholds often trigger stack replacement, although stacks may continue operating beyond such limits at a reduced efficiency. This work estimates the economic lifetime of an electrolyzer, defined as the operational period that minimizes the levelized cost of hydrogen (LCOH), comparing it with conventional PT-based lifetimes. Two stack management strategies are evaluated using an LCOH model that incorporates degradation rates, electricity costs, and capacity factors (CF): replacing the entire stack, or extending its operation while supplementing production losses with smaller stacks to maintain hydrogen production. Results show that the economically optimal lifetime often diverges from PT lifetimes, particularly in low CF and low-cost energy contexts, where lifetime extension proves advantageous. The economically optimal strategy is highly context dependent.