Solar-thermal hydrogen production: an engineering review of advances, challenges, and perspectives

Hydrogen is widely recognized as a cornerstone energy vector for deep decarbonization across hard-to-electrify sectors, but its sustainability and cost depend strongly on the primary energy source and system integration. Solar-driven hydrogen production offers a pathway to convert abundant solar resources into a storable chemical fuel. However, in most solar-to-hydrogen routes a significant fraction of captured solar energy ultimately appears as heat, and the ability to manage, upgrade, and valorize this heat often determines overall efficiency, capacity factor, and levelized cost of hydrogen (LCOH). Key limitations across pathways include solar intermittency, thermal cycling, limited availability high-temperature thermal storage, receiver/reactor material durability, energy losses, and feedstock handling and logistics. This review provides an engineering-oriented assessment of solar thermal hydrogen production technologies, emphasizing developments over the last decade and the key barriers to scale-up. Distinct from prior reviews, we synthesize the literature using eight decision-relevant criteria that capture the dominant feasibility and cost drivers (collector/receiver, storage, temperature feasibility, hybridization, feedstock/products, integration scenario, demonstrated scale, and techno-economics). Finally, we identify the pathway combinations most likely to achieve high solar share and competitive hydrogen cost. We further outline research priorities in system design, thermal storage, materials, and system-level integration to accelerate industrial deployment.