Photobiological hydrogen production at pilot scale: Integrating bioprocess optimization and techno-economic modeling

Microalgal hydrogen production offers a carbon-neutral route for solar fuel generation, yet adoption remains limited by low efficiency and biomass degradation. We demonstrate stable, days-long H 2 production at pilot scale using the Chlamydomonas reinhardtii pgr5 mutant under nutrient-replete, non-destructive conditions. Direct volumetric measurements show a 6-fold scale-up compared to our previous laboratory benchmarks, achieved through engineering optimization of photobioreactor design. The resulting biomass retained 47 % protein with balanced amino acids, lipids, and carotenoids. Having established a functional platform that preserves both productivity and biomass integrity, we next performed a techno-economic analysis, asking: what would the cost of hydrogen be if such a system were integrated into an existing, profitable algae facility? Applying our experimentally measured rates yielded a production cost of $13–19 kg H 2 −1 . Modeled improvements identified milestones toward economic viability, showing that sustained H 2 production at higher biomass densities could reduce costs to ∼$2–3 kg H 2 −1 . Together, these findings map the development path toward an economically viable “green-coin” platform linking energy and protein production.