The carbon footprint of hydrogen production is often assessed based on direct emissions from the process itself, such as CO2 released during steam methane reforming or the electricity source for electrolysis. However, indirect emissions from supporting infrastructure—pipelines, compression stations, and storage facilities—play a significant but understudied role in the overall environmental impact. These contributions arise from material extraction, manufacturing, construction, and maintenance, all of which carry embedded carbon costs that can influence the sustainability of hydrogen as an energy carrier.
Pipeline networks are a critical component of hydrogen distribution, and their construction involves substantial material use. Traditional pipelines are made of steel, a material with high embodied energy due to mining, refining, and manufacturing processes. The carbon intensity of steel varies depending on production methods, with blast furnace steel emitting approximately 1.8 to 2.2 metric tons of CO2 per ton of steel, while electric arc furnace steel, which uses recycled scrap, emits closer to 0.5 to 0.7 metric tons. Hydrogen pipelines require higher-grade steels or composites to prevent embrittlement and leakage, further increasing material-related emissions. Composite materials, such as fiber-reinforced polymers, offer weight savings and corrosion resistance but also have their own carbon footprint from resin production and curing processes.
Compression stations, necessary to maintain gas flow in pipelines, contribute additional emissions through energy consumption and infrastructure. Compressors typically run on electricity or natural gas, and their efficiency varies widely. Electrically driven compressors tied to renewable grids have lower operational emissions, but the embedded carbon from manufacturing compressors, valves, and control systems must still be accounted for. Natural gas-driven compressors introduce direct methane emissions, a potent greenhouse gas, alongside CO2 from combustion. The choice of compressor type and power source thus indirectly affects the overall carbon footprint of hydrogen delivery.
Storage facilities, whether for compressed gas, liquid hydrogen, or solid-state storage like metal hydrides, also add to indirect emissions. Compressed gas storage relies on high-pressure vessels, often constructed from carbon-intensive materials like chromium-molybdenum steel. Liquid hydrogen storage demands cryogenic tanks with multi-layered insulation, requiring significant energy for cooling and materials like stainless steel or aluminum with high production emissions. Underground storage in salt caverns or depleted aquifers has lower material demands but involves energy-intensive drilling and site preparation. Each storage method carries trade-offs between energy efficiency, material use, and lifecycle emissions.
Construction-phase emissions are frequently overlooked in carbon accounting. Building pipelines, storage sites, and compression stations involves heavy machinery, transportation of materials, and land modification, all of which generate CO2. For example, laying a kilometer of hydrogen pipeline can emit between 50 to 150 metric tons of CO2, depending on terrain and construction practices. Similarly, preparing a salt cavern for hydrogen storage may require thousands of megawatt-hours of electricity for solution mining, with emissions varying by grid carbon intensity.
Maintenance and leakage further contribute to indirect emissions. Hydrogen’s small molecular size increases the risk of permeation through materials, leading to fugitive emissions. While hydrogen itself is not a greenhouse gas, its leakage indirectly affects climate by extending the atmospheric lifetime of methane through hydroxyl radical depletion. Pipeline integrity management, including inspections and repairs, adds to operational emissions over time.
Material choices play a pivotal role in mitigating these indirect emissions. Advanced high-strength steels with lower alloy content can reduce embodied carbon while maintaining performance. Composites, though carbon-intensive to produce, may offer longer lifespans and reduced maintenance needs. Alternative materials like thermoplastic-lined pipes are being explored for their balance of durability and lower production emissions. Similarly, modular construction techniques for compression stations and storage units can minimize on-site energy use and waste.
Indirect emissions from hydrogen infrastructure are not yet standardized in lifecycle assessments, leading to gaps in carbon accounting. Current methodologies often focus narrowly on production emissions, neglecting the full value chain. A comprehensive approach would include infrastructure-related emissions as part of the hydrogen economy’s environmental impact, enabling more accurate comparisons between production methods and distribution pathways.
The push for low-carbon hydrogen must therefore address not only how hydrogen is made but also how it is moved and stored. As infrastructure scales up to meet growing demand, the cumulative effect of material choices, construction practices, and operational emissions will become increasingly significant. Policymakers and industry stakeholders must prioritize transparency in carbon accounting to ensure that hydrogen’s role in decarbonization is based on a complete understanding of its environmental footprint.
Future research should focus on quantifying these indirect emissions with greater precision, developing low-carbon materials for hydrogen infrastructure, and optimizing designs to minimize embedded energy. Only by addressing the hidden carbon costs of pipelines, storage, and compression can hydrogen truly fulfill its potential as a clean energy solution.