What Is Green Hydrogen? How Electrolysis Turns Power Into Fuel

Hydrogen has been used in industry for more than a century, so the interest in “green hydrogen” is not about a new gas — it is about a new way of making an old one. The question that matters is how you produce the hydrogen, and what that production does to the climate. Get that framing right and most of the confusion around the topic disappears.

What is green hydrogen, and why the colour?

Green hydrogen is hydrogen produced by electrolysis using electricity from renewable sources such as wind, solar or hydro. The word “green” describes the production pathway, not the molecule: a hydrogen atom made from renewable electricity is indistinguishable from one made from natural gas. The industry uses a spectrum of colour labels precisely because the gas gives no clue to its origins, so a shorthand is needed to talk about how clean — or not — a given batch of hydrogen is.

That shorthand is worth learning, because a large share of hydrogen produced today is not green at all.

The colours are informal and sometimes contested, but they capture the key point: emissions depend entirely on the production method, and “green” specifically means renewable-powered electrolysis.

How electrolysis works

Electrolysis is the reverse of the reaction that powers a fuel cell. An electrolyser is fed water and electricity. Inside, two electrodes sit in or against an electrolyte. When current flows, water molecules are split: hydrogen gas forms at the cathode (the negative electrode) and oxygen forms at the anode (the positive electrode). The two gases are kept apart, collected, and the hydrogen is dried and compressed for use or storage. The only direct by-product is oxygen. If the electricity driving the reaction is renewable, the whole process carries very low carbon emissions — which is the entire point.

The main electrolyser technologies

Not all electrolysers are the same, and the differences shape where each is used. Alkaline electrolysers are the most mature and generally the lowest-cost, using a liquid alkaline electrolyte; they are well proven but respond more slowly to changing power input. Proton-exchange membrane (PEM) electrolysers use a solid polymer membrane, are compact and responsive, and cope well with the variable output of wind and solar — a valuable trait when the power source itself fluctuates. Solid-oxide electrolysers operate at high temperature and can be very efficient, especially where waste heat is available, but are at an earlier stage of commercial deployment. The choice between them is a trade-off between cost, flexibility, efficiency and maturity.

The green hydrogen value chain

Producing hydrogen is only the first link. A workable green hydrogen system involves several connected stages, each with its own participants and challenges.

Two of these stages — storage and transport — are where much of the practical difficulty lies. Hydrogen is the lightest element, with a low energy density by volume, so storing and moving it is harder than for conventional fuels. That is why one common strategy is to convert hydrogen into carriers such as ammonia or methanol, which are easier to handle, and reconvert them at the destination.

What green hydrogen is actually good for

Green hydrogen is not a universal energy solution, and the honest case for it is specific. Where electricity can do a job directly — lighting, most road transport, low-temperature heat — using it to make hydrogen first is usually less efficient. Hydrogen’s real value is in the “hard-to-electrify” corners of the economy. It is already an essential industrial feedstock for making ammonia (and therefore fertiliser) and for oil refining, and replacing today’s grey hydrogen in those uses with green hydrogen is a direct emissions win. It can deliver the high-temperature heat that heavy industry needs, offers a route to lower-carbon steelmaking, and is a candidate for heavy transport, shipping fuels and long-duration energy storage. Public analysis from bodies such as the IEA and IRENA tends to emphasise these targeted roles rather than a hydrogen-for-everything vision.

Drivers and headwinds

The drivers are decarbonisation policy, industrial emissions targets, the falling cost of renewable electricity, and support schemes and standards that reward low-carbon hydrogen. The headwinds are equally concrete. Green hydrogen needs large volumes of cheap renewable power to be competitive, and that power is itself in demand elsewhere. Electrolyser manufacturing has to scale up. Storage, pipelines and refuelling infrastructure barely exist in most places. And efficiency losses along the chain mean the end product carries a cost premium over incumbent fuels and over grey hydrogen. None of these are chemistry problems — they are questions of cost, infrastructure and scale.

How analysts frame the sector

Because green hydrogen sits at the intersection of power, industry and transport, analysts avoid treating it as one monolithic market. They segment by production route (electrolyser type and power source), by end-use sector (industry, mobility, power, buildings), and by value-chain stage (equipment makers, project developers, gas handlers, off-takers). That discipline keeps the analysis honest and avoids conflating a mature use like ammonia feedstock with a speculative one. If you want to see how sectors like this are structured into defensible segments, our market research guide and market sizing explainer walk through the method, and how to read a market report helps you separate grounded figures from hype. For neighbouring topics, see our explainers on the solar PV value chain and battery energy storage in the energy & power hub.

Stripped of hype, green hydrogen is a clear idea: use clean electricity to split water, and deploy the resulting gas where direct electrification cannot reach. The chemistry is settled; the story of the next decade is whether the cost, power supply and infrastructure can be built to match the ambition.