Environmental and economic sustainability assessment of solar thermochemical hydrogen production technologies in China

The environmental and economic sustainability of solar thermochemical (STC) hydrogen production in China has not yet been comprehensively assessed. This study conducts a cradle-to-grave life cycle assessment combined with life cycle costing for five STC cycles in China using a unified methodological framework. Results show that STC reduces the climate change impact by 59-96 % compared to conventional hydrogen and has lower values in most other impacts. The four-step copper-chlorine (Cu-Cl) and hybrid sulphur cycles (HyS) exhibit the lowest environmental impacts and costs. However, STC remains economically uncompetitive, with levelised cost of hydrogen (LCOH) 2.3-4.6 times higher than that of conventional hydrogen. Improving system efficiency, capacity factor, and systems lifetime would render the LCOH of HyS, four-step Cu-Cl and three-step magnesium-chlorine (Mg-Cl) competitive with conventional hydrogen (1672-1934 vs 1180-2380 $/t), while oxygen co-product utilisation would lead to a net-negative LCOH (profit) for these three cycles. These findings highlight key environmental and economic trade-offs and support decision-making for sustainable hydrogen deployment.