Trade-Offs between Grid Connectivity and Operational Flexibility in Reducing the Cost and Carbon Footprint of Green Ammonia

Ammonia is essential for fertilizer production and industrial applications, but conventional synthesis is highly carbon-intensive due to reliance on fossil-based hydrogen. Producing "green ammonia" with renewables-based electrolytic hydrogen offers lower emissions and greater resilience to fossil fuel market volatility, though at a higher cost. To reduce infrastructure overbuilding and associated costs, two main strategies have been proposed: (1) grid connection under emission caps and (2) increased operational flexibility. Yet, their relative benefits remain location-specific and uncertain. Here, we evaluate these strategies across a wide range of European Union (EU) weather patterns using the levelized cost of ammonia (LCOA) and life-cycle greenhouse gas emissions as benchmarks. We find that grid-connected plants achieve greater cost reductions but are more sensitive to regulatory uncertainty, particularly emission caps, while operational flexibility achieves larger emission cuts. On average, grid-connected plants lower LCOA by 42% (1569 EUR/t NH3; range: 999-2772) and emissions by 25% (0.66 t CO2e/t; range: 0.39-1.15), while flexible off-grid plants reduce costs by 39% (1593 EUR/t; range: 1168-2573) and emissions by 45% (0.49 t CO2e/t; range: 0.31-0.94) compared to baseline off-grid, nonflexible green ammonia systems. Benefits are most pronounced in regions with limited renewable resources, though plants in those regions may face competitiveness challenges, potentially making relocation more attractive. Combining both strategies yields only modest additional benefits, except in wind-rich regions. These findings provide robust guidance for selecting cost- and emission-effective strategies, supporting targeted deployment and sector decarbonization.