Electrolyser choice is one of the first big decisions in a green hydrogen project. Alkaline and proton exchange membrane (PEM) electrolysers are both commercially available, but they suit different operating profiles.
Key takeaways
- Alkaline is mature and usually lower in capital cost.
- PEM responds faster to variable renewable power and is more compact.
- Balance of plant often decides the overall business case.
| Factor | Alkaline | PEM |
|---|---|---|
| Technology maturity | Very mature | Mature, scaling fast |
| Response to variable power | Moderate | Fast |
| Footprint | Larger | Compact |
| Critical materials | Nickel-based | Platinum-group metals |
| Output pressure | Typically lower | Typically higher |
Look beyond the stack
Water treatment, power conversion, cooling, compression and storage can make up a large share of total cost. Comparing complete plants rather than stacks alone gives a fair result.
Matching the power profile
Solar- or wind-driven plants with large swings in power may favour fast-responding technology, while plants with firm grid power may favour lower capital cost. A feasibility study should test both against the real power profile.