New study rethinks cost of renewables in green ammonia production

A new study from the department is challenging assumptions about how best to use renewable electricity in green ammonia production, offering a practical way to design more cost-effective systems.

Led by Dr Collin Smith and Professor Laura Torrente-Murciano in the Catalysis and Process Integration Group (CaPI), the work introduces a new metric – the Levelised Cost of Utilisation (LCOU) – to assess the cost of using intermittent renewable energy in Power-to-X processes. These processes use electricity to drive chemical reactions, such as producing ammonia from water and air, but it can be extrapolated to other electrified processes.

The paper is published in Nature Chemical Engineering today.

While renewable electricity is often cheaper than fossil-based energy, its variability makes it difficult to run industrial processes efficiently. Plants need additional infrastructure – particularly for hydrogen storage – to keep operating when wind or solar generation drops, and this adds significant cost.

To investigate this, the team modelled green ammonia production at over 4,500 locations across Europe using real solar and wind data. They found that aiming to use all available renewable energy increases costs due to the need for excessively oversized equipment and storage. In nearly all cases, curtailing a portion of the energy – deliberately leaving some unused – results in a lower overall cost.

“To many people, curtailing energy sounds wasteful,” said Dr Smith. “But when you look at the full system costs, it’s sometimes the smarter and cheaper option. Our work helps define that balance.”

The study also introduces the Levelised Apparent Energy Cost (LAEC), which combines the cost of generating renewable electricity with the cost of using it. The team show that combining solar and wind, or designing energy plants to run more flexibly, can reduce both energy waste and production costs. The approach could make green ammonia commercially viable in parts of Europe with high penetration of renewable resources in the grid, such as Spain and Norway, or even the UK in the near future.

According to the editorial team at Nature Chemical Engineering, the research stands out for its comprehensive geographic analysis, its investigation of renewable intermittency, and its design framework for off-grid production systems.

“We believe this analysis will inspire future design, optimisation and scale-up of off-grid green ammonia production,” the editors noted.