Fig. 6: Sensitivity of import volume on total system cost and composition.

a Solid lines show the total system cost as a function of enforced import volumes for higher (brown scale) or lower (blue scale) import costs. The dashed lines indicate the corresponding shares of the domestic system cost. The red markers denote the maximum cost reductions and cost-optimal import volume for given import cost levels (extreme points of the curves). The cost alterations are uniformly applied to all import options but direct electricity imports. Steel is included in energy terms, applying 2.1 kWh kg⁻¹ as released by the oxidation of iron. b shows the composition of the total system cost as a function of enforced import volumes for the central import cost estimate. The dashed line splits the system costs into costs for imports and the domestic system. All shown scenarios use technology assumptions for 2040 and allow relocation of crude steel and ammonia production within Europe. Cost compositions for the alternative import cost scenarios are presented in Supplementary Figs. 15–18. Source data are provided as a Source Data file. HBI = hot briquetted iron; HVDC = high-voltage direct current.