Why are so few green hydrogen projects actually getting built?
The biggest gap is between ambition and reality. A 2025 study tracking 190 projects over three years found that only 7% of global capacity announcements were finished on schedule, revealing a wide 'implementation gap' [2]. Even though the total announced pipeline nearly tripled to 422 GW, the authors estimate that realizing all these projects would require global subsidies of $1.3 trillion (with a range of $0.8–$2.6 trillion), far exceeding what has been announced [2]. This means that without a massive increase in government support or carbon pricing, most green hydrogen will remain too expensive to compete with fossil-based hydrogen.
The cost problem is especially acute in sectors like aviation. A 2021 study modeled hydrogen-powered aircraft and found that total operating costs could increase by 10–70% for short-range flights and 15–102% for medium-range flights, depending on the cost of green liquid hydrogen [6]. The authors stress that the entire economy of hydrogen aviation depends on low-cost supply infrastructure, which barely exists today [6].
What technical problems still need solving for storing and moving hydrogen?
Storing hydrogen underground in unlined rock caverns is a promising option for large-scale storage (over 100 GWh), but major knowledge gaps remain. A 2024 review identifies critical unknowns: how hydrogen reacts with rock materials at typical storage conditions (below 100°C and 15 MPa), how to design hydraulic containment systems to prevent leaks, and whether fracture-sealing materials will hold up over decades [4]. The authors call for more experimental and numerical studies before this technology can be deployed.
Transporting hydrogen via pipelines faces similar gaps. A 2025 review notes that hydrogen degrades the mechanical properties of steel, affecting pipeline integrity, and that key unknowns include how to use high-strength materials safely, how to design pipelines for hydrogen (versus natural gas), and whether existing natural gas pipelines can be repurposed [5]. The authors emphasize that economic viability and safety are the two key challenges, and current standards are insufficient [5].
Are there gaps in the people and materials needed to scale up?
Yes, and they are often overlooked. A 2023 survey of 41 Australian hydrogen industry participants found widespread agreement that training and skilling are 'very important' but 'under-provisioned' across the sector [7]. The authors argue that without urgent cross-sector attention to skill development, the promise of green hydrogen will not be realized [7]. This is a concrete evidence gap: we don't have enough trained engineers, technicians, and operators to build and run the facilities.
On the materials side, porous electrodes for water electrolysis are a key area of innovation, but a 2026 review identifies persistent gaps in structural reproducibility, long-term mechanical robustness, scalability, and standardized performance benchmarking [3]. Similarly, silicon-based photocatalysts for solar-driven hydrogen production face challenges in balancing performance with economic and environmental costs, and the optimal synthesis methods are still unclear [1]. For seawater splitting, a 2026 review highlights that stability under realistic conditions (with biofouling, corrosion, and multivalent ions) remains unproven, and mass-transport management at device scale is a critical knowledge gap [8].
About These Sources
This answer is built on 8 peer-reviewed studies — published from 2021 to 2026, 6 from 2024 or later, 7 in Q1 journals, collectively cited 600 times — selected as the most relevant from 11 studies that passed quality screening, drawn from 64 papers retrieved from a database of over 500 million.
Sources used in this answer
Progress in silicon-based materials for emerging solar-powered green hydrogen (H2) production
Silicon-based photocatalysts show promise for solar hydrogen production, but balancing performance with economic and environmental costs remains a key challenge, and optimal synthesis methods are still unclear.
The green hydrogen ambition and implementation gap
Tracking 190 projects over 3 years, only 7% of global capacity announcements were completed on schedule; meeting 2030 climate goals would require up to $2.6 trillion in subsidies, far exceeding current commitments.
Fabrication of Porous Electrodes for Green Hydrogen Evolution: A Review of Additive Manufacturing, Laser Texturing, Dynamic Hydrogen Bubble Templating, Powder Metallurgy, Lithography, and Nano-Ink Printing
Porous electrodes improve hydrogen evolution reaction efficiency, but key gaps remain in structural reproducibility, long-term robustness, scalability, and standardized benchmarking.
Hydrogen storage in unlined rock caverns: An insight on opportunities and challenges
Unlined rock caverns could store hydrogen at >100 GWh scale, but knowledge gaps exist in hydrogen reactivity with rock, hydraulic containment design, and fracture-sealing material integrity.
State-of-the-art and knowledge gaps in gaseous hydrogen pipelines: from the perspective of materials, design, and integrity management
Hydrogen pipelines face gaps in high-strength material use, pipeline design, hydrogen velocity determination, and repurposing natural gas pipelines; economic viability and safety are key challenges.
Hydrogen-powered aviation and its reliance on green hydrogen infrastructure – Review and research gaps
Hydrogen-powered aviation costs could increase 10–102% depending on liquid hydrogen cost; the entire economy depends on low-cost green hydrogen supply infrastructure.
Skilling the green hydrogen economy: A case study from Australia
A survey of 41 Australian industry participants found training and skilling are seen as very important but under-provisioned; urgent cross-sector attention is needed.
Photoelectrocatalytic seawater splitting for sustainable hydrogen production: Catalysts, challenges and future directions
Photoelectrochemical seawater splitting is promising but constrained by chloride corrosion, biofouling, and precipitation; stability under realistic conditions and mass-transport management are key gaps.