Comparing hydrogen color codes
Hydrogen is often categorized by color labels that indicate how it was produced and its carbon footprint:
- Grey hydrogen: produced from natural gas via steam methane reforming without capturing CO2. It is the most common and highest in emissions.
- Blue hydrogen: produced similarly to grey hydrogen but paired with carbon capture and storage (CCS) to reduce CO2 emissions, though some emissions usually remain.
- Green hydrogen: produced by electrolysis using renewable electricity and has the lowest lifecycle emissions when renewables are the source.
Key differences
- Carbon intensity: green is lowest, blue can be low but depends on capture rates and methane leakage, grey is high.
- Cost: currently grey is cheapest, blue adds CCS costs, and green tends to be more expensive due to electrolyzer and renewable energy costs; however, falling renewable prices and scaling electrolyzer manufacturing are narrowing the gap.
- Scalability and supply: grey hydrogen is widely available via existing fossil infrastructure; green depends on renewable power build-out; blue needs CCS infrastructure and low methane leakage in the gas supply.
Considerations beyond color
- Lifecycle assessment: the real emissions depend on electricity source, methane leakage in gas supply chains, and the effectiveness of CO2 storage. Labels can oversimplify.
- Policy and market demand: incentives, carbon pricing, and industrial decarbonization targets affect which types are prioritized.
- Use cases: green hydrogen is favored for long-term low-carbon strategies, while blue hydrogen is sometimes proposed as a transitional solution where CCS is feasible.
Conclusion
Green, blue, and grey describe production pathways with different emissions profiles, costs, and infrastructure needs. Green hydrogen offers the clearest route to deep decarbonization when powered by renewables, while blue may play a transitional role depending on local resources, policy, and CCS capability.