What Is Green Hydrogen?
Green hydrogen is hydrogen gas produced using renewable electricity — typically from solar or wind power — through a process called electrolysis. Water molecules are split into hydrogen and oxygen using an electric current, and because the electricity comes from renewable sources, the entire process produces no direct carbon emissions.
This distinguishes it from grey hydrogen (produced from natural gas, releasing CO₂) and blue hydrogen (also from natural gas, but with carbon capture added). Green hydrogen is the cleanest form, and costs have been falling steadily as renewable energy becomes cheaper.
How Electrolysis Works
The core technology behind green hydrogen is the electrolyser — a device that passes electrical current through water to separate its hydrogen and oxygen atoms. The main types include:
- Alkaline electrolysers — a mature, cost-effective technology widely deployed today.
- PEM (Proton Exchange Membrane) electrolysers — more compact and responsive, ideal for pairing with variable renewable sources like solar.
- Solid oxide electrolysers — highly efficient at high temperatures, still largely at research stage.
Urban Applications of Green Hydrogen
Public Transport
Hydrogen fuel cell buses are already operating in cities across Europe and Asia. Unlike battery-electric buses, hydrogen buses refuel quickly and have a longer range, making them attractive for high-frequency city routes. Cities including London, Hamburg, and Shenzhen have trialled or deployed hydrogen bus fleets.
Heating Buildings
One of the most discussed potential uses for green hydrogen is decarbonising the heating of homes and commercial buildings — currently a major source of urban emissions. Hydrogen can be blended with natural gas in existing pipeline networks or used in dedicated hydrogen boilers, offering a potential pathway for buildings that are difficult to electrify.
Industrial Zones
Cities with industrial areas — steel production, chemicals, heavy manufacturing — face decarbonisation challenges that electrification alone cannot fully address. Green hydrogen offers a high-temperature, carbon-free energy source for these hard-to-abate sectors.
Seasonal Energy Storage
Renewable energy generation is variable — solar peaks in summer, wind varies by season. Green hydrogen can act as a long-duration energy store: surplus renewable electricity generates hydrogen, which is stored and then converted back to electricity or used directly during periods of low generation.
The Current Challenges
Despite its promise, green hydrogen faces significant hurdles before it becomes a mainstream urban energy solution:
- Cost — Green hydrogen is currently more expensive to produce than fossil fuel alternatives, though costs are projected to fall significantly with scale.
- Infrastructure — Distribution networks, refuelling stations, and storage facilities require substantial investment to build out.
- Energy efficiency — Hydrogen production and conversion involves energy losses at each step, making it less efficient than direct electrification for some applications.
- Safety and storage — Hydrogen is highly flammable and requires careful handling and storage, adding complexity to urban deployment.
The Road Ahead
Major economies — including the EU, Japan, South Korea, and Australia — have published national hydrogen strategies, signalling strong policy commitment. The EU's Hydrogen Backbone initiative aims to build a continent-wide pipeline infrastructure. Meanwhile, falling electrolyser costs and scaling renewable capacity are steadily improving green hydrogen's economic case.
For cities, green hydrogen is unlikely to replace electrification as the primary decarbonisation strategy for most end uses. But as a complementary solution — particularly for transport, industrial zones, and seasonal storage — it has real potential to play a meaningful role in the clean energy transition.
Key Takeaway
Green hydrogen is not a silver bullet, but it is a genuinely promising piece of the clean energy puzzle. As technology matures and costs fall, it is increasingly likely to feature in the energy systems of sustainable cities — especially where electrification alone cannot get the job done.