In a previous article, we discussed what hydrogen is and why everyone's talking about it. We covered how hydrogen is the most abundant element in the universe, present in 75% of all matter. It's light, can be stored, and doesn't generate any pollution by itself — making it a strong candidate as a fuel source. However, hydrogen doesn't begin as an energy source; it's an energy vector. It needs a chemical process to extract it and turn it into fuel. There are many ways to complete this process, but not all of them are sustainable.

This is where the colour classification of hydrogen comes in. Hydrogen is a colourless gas, but each colour corresponds to a different production process.

The three most common types of hydrogen are grey, blue, and green.

Grey Hydrogen

Grey hydrogen is currently the most common and cheapest form of hydrogen production. It's created from natural gas using steam reforming, which separates the hydrogen from the natural gas. However, the technologies used don't capture the carbon emissions produced — these are released directly into the atmosphere.

Blue Hydrogen

Blue hydrogen is also extracted using steam reforming, but differs from grey in that the carbon emissions are captured and stored — reducing atmospheric emissions, though not eliminating them. Blue hydrogen is sometimes called 'low-carbon hydrogen' because the process doesn't prevent greenhouse gas creation, it simply stores it.

Green Hydrogen

Green hydrogen generates no emissions across its entire life cycle. It uses renewable energy — from wind and solar — to electrolyse water, splitting it into hydrogen and oxygen with no carbon emissions released. It's the most sustainable option, though the main challenge remains reducing production costs to make it broadly viable. Find out more about clean energy at ACCIONA.

Black and Brown Hydrogen

Black and brown hydrogen is produced using coal through a process called gasification — the opposite end of the spectrum from electrolysis. Carbon-rich materials are converted into hydrogen and carbon dioxide, with emissions released into the atmosphere. This makes it the most harmful hydrogen for the environment.

Pink Hydrogen

Pink hydrogen is extracted through electrolysis powered by nuclear energy. You may also hear it referred to as purple or red hydrogen.

Turquoise Hydrogen

Turquoise hydrogen is still emerging and being assessed for large-scale viability. It's produced using methane pyrolysis, which uses heat to break down methane into hydrogen and solid carbon — with no carbon released into the air. If the solid carbon can be stored safely, turquoise may eventually be considered a 'low-carbon' option alongside blue hydrogen.

Yellow Hydrogen

Yellow hydrogen is made through electrolysis using solar power specifically — similar to green hydrogen, but produced solely from solar energy.

White Hydrogen

White hydrogen occurs naturally in underground geological deposits and is extracted through fracking. There are currently no active plans to develop it as an energy source at scale.

As a leading provider of green energy infrastructure, ACCIONA's goal is to advance a truly sustainable energy industry — championing renewable energy options and processes, including green hydrogen.

Find out more about ACCIONA Energía's hydrogen and other renewable energy projects globally and locally.