An electrolyser is a device that passes an electric current through water to split it into hydrogen and oxygen. When the electricity comes from renewable sources, the result is called green or electrolytic hydrogen, and no carbon dioxide is released in making it.
How it works
Each electrolyser cell has two electrodes separated by an electrolyte, a material that lets charged particles pass but keeps the two gases apart. Hydrogen forms at one electrode and oxygen at the other. Cells are stacked together to reach industrial scale.
| Type | Electrolyte | Main features |
|---|---|---|
| Alkaline | Liquid potassium hydroxide solution | The oldest and most widely used design; cheaper materials, slower to follow changes in power |
| PEM (proton exchange membrane) | Solid polymer membrane | Compact, responds quickly to variable wind and solar output; uses platinum-group metals |
| Solid oxide | Ceramic, running at high temperature | Can be more efficient, especially using waste heat from industry; less mature |
UK projects
The government supports electrolytic hydrogen through Hydrogen Allocation Rounds, which pair a long-term revenue contract (the Hydrogen Production Business Model) with capital grants. In December 2023 the first round (HAR1) selected 11 projects with a combined capacity of about 125 MW, spread across England, Scotland and Wales, at an average strike price of £241/MWh. By July 2025, 10 of them had signed contracts and could begin construction. A second round shortlisted 27 projects in April 2025; shortlisting does not guarantee funding.
Why it matters
Hydrogen made this way can replace natural gas or grey hydrogen in industries that are hard to run on electricity directly, such as chemicals, refining and some high-temperature processes. Electrolysers can also use surplus wind power that would otherwise be curtailed. Against that, a lot of energy is lost in conversion, so for heating homes and running cars, using the electricity directly is usually more efficient.
Read more: Green hydrogen: how it is made and what the UK plans to use it for.