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There is much written about hydrogen in the press and media, but if like the author, you are just starting out along your hydrogen journey and you are perhaps suffering colour confusion, then this little blog guide to deciphering the colours of hydrogen will hopefully brighten your day.
Whilst Hydrogen itself is a colourless gas, a colour name is often attributed to it to denote how that hydrogen is produced. Hydrogen occurs naturally in nature, but it is quite rare and is sometimes known as white hydrogen. On an industrial scale hydrogen is generated using another fuel/process and this gives the hydrogen its colour name.
A T-rainbow of hydrogen colour
| Colour | Fuel | Process | Products | |
|---|---|---|---|---|
| Brown/Black | Coal | Steam reforming or gasification | H2 + CO2 (released) | |
| White | N/A | Naturally occurring | H2 | |
| Grey | Natural Gas | Steam reforming | H2 + CO2 (released) | |
| Blue | Natural Gas | Steam reforming | H2 + CO2 (% captured and stored) | |
| Turquoise | Natural Gas | Pyrolysis | H2 + C (solid) | |
| Red | Nuclear Power | Catalytic splitting | H2 + O2 | |
| Purple/Pink | Nuclear Power | Electrolysis | H2 + O2 | |
| Yellow | Solar Power | Electrolysis | H2 + O2 | |
| Green | Renewable Electricity | Electrolysis | H2 + O2 |
As the hydrogen economy evolves and technology develops and matures other processes and colours may be utilised. It must also be noted that not everyone around the world agrees on the naming scheme, so local variations may exist. However, the information above is the most generally accepted view at the current time (late 2021). Often colours are grouped together, and we explore why and how in more detail below.
Colour grouping
Often for "simplicity" (but perhaps confusing to those new to hydrogen), colours are grouped together under one colour banner as they share many attributes.
Brown hydrogen
Brown is used by many in industry to cover Brown, Black and Grey hydrogen all under one banner. All 3 processes take a fossil fuel from the ground and turn it into Hydrogen gas, releasing CO2 to the atmosphere. Generating hydrogen this always carbon positive.
Blue Hydrogen
Blue hydrogen similarly can be expanded to encompass any fossil fuels used as the energy source (rather than just natural gas) and just like Brown it too generates CO2. The key difference with Blue Hydrogen is that developing technologies are then used to capture a proportion of the generated CO2 and store it, often underground. The carbon intensity of this process can vary significantly and capture technologies at larger scales are an area of significant development. Blue hydrogen does have the potential to be a low carbon fuel.
Green Hydrogen
Green hydrogen uses a renewable energy source (wind, solar, tidal etc) to generate electricity. This electricity is used to split water (H2O) via electrolysis into Hydrogen and Oxygen gases (H2 and O2). This process generally results in a low carbon fuel.
I hope that this brief high-level tour of the hydrogen colour spectrum gives you a greater appreciation of some of the potential sources of hydrogen to power your projects.
If you'd like to discuss a possible hydrogen project, then please get in touch and we'll put you on the right track.
