HYDROGEN FUNDAMENTALS
What do the colors of hydrogen mean?
Hydrogen is colorless. The industry uses color names as shorthand for how hydrogen is produced, which energy source is used, and whether carbon emissions are captured.
A USEFUL SHORTHAND — NOT A UNIVERSAL STANDARD
The production pathway matters more than the label
Color names can make hydrogen easier to discuss, but definitions are not globally standardized. The most meaningful comparison considers lifecycle greenhouse-gas emissions, electricity source, feedstock, carbon capture performance, water use and delivery requirements.
COMMONLY USED CATEGORIES
The hydrogen color spectrum
The descriptions below reflect common industry usage. Some organizations may use the terms differently.
Renewable electrolysis
Water is split into hydrogen and oxygen using electricity from renewable sources such as solar, wind or hydropower.
Solar or grid electrolysis
Often used for solar-powered electrolysis. In some markets it refers more broadly to electrolysis using grid electricity, so the definition should always be stated.
Nuclear-powered electrolysis
Hydrogen is produced using nuclear electricity, and sometimes nuclear heat. It may be low-emission, although the terminology varies.
Fossil fuel with carbon capture
Usually produced from natural gas, with a portion of the carbon dioxide captured and stored. Actual emissions depend on methane leakage and capture performance.
Natural gas without carbon capture
Typically produced by steam methane reforming. The resulting carbon dioxide is released rather than captured.
Bituminous-coal gasification
Hydrogen is produced from black coal without capturing the associated carbon emissions.
Lignite gasification
Produced from brown coal or lignite, generally without carbon capture. It is typically a high-emission pathway.
Methane pyrolysis
Methane is converted into hydrogen and solid carbon. Its footprint depends on the heat source, methane supply and how the solid carbon is managed.
Geologic hydrogen
Naturally occurring hydrogen found underground. Environmental performance depends on extraction, processing and transport.
On-site hydrogen from water electrolysis
Efena systems generate hydrogen and oxygen on demand through water electrolysis, close to the point of use. When the electricity supplied to the system is verified renewable, the hydrogen can be classified as green. When grid electricity is used, its emissions profile depends on the local generation mix.
For technical accuracy, Efena describes the output as on-site electrolytic hydrogen unless the renewable origin of the electricity has been confirmed.
Why this distinction matters
- It avoids unsupported environmental claims.
- It lets customers evaluate the actual energy source at each installation.
- It supports credible reporting and future certification.
- It focuses attention on measured lifecycle emissions rather than a color alone.
POTENTIAL ENVIRONMENTAL BENEFITS
Benefits when powered responsibly
Renewable-powered, on-site electrolysis can offer environmental advantages, but results depend on the complete installation and operating conditions.
REFERENCES
Learn from authoritative sources
International Energy Agency: Why clearer hydrogen terminology matters — explains that color definitions are not standardized and may conceal important differences in emissions.
International Energy Agency: Electrolysers — describes electrolysis as a key pathway for low-emission hydrogen when paired with low-emission electricity.
International Renewable Energy Agency: Policies for green hydrogen — defines green hydrogen around renewable energy and water electrolysis.
Which pathway fits your application?
Efena evaluates the host equipment, energy source, operating profile and project objectives before recommending a system.