Optimal sizing of renewable generation and storage for grid-connected CO₂ electrolysis

Abstract

Co-electrolysis of CO₂ (CO₂E) and water enables the production of syngas for sustainable aviation fuels (SAF) that are compliant with European RFNBO (renewable fuels of non-biological origin) regulations. However, a mismatch exists between the intermittent renewable electricity supply and the continuous operation of the downstream Fischer–Tropsch plants. To address this, we developed a two-stage linear optimization model to optimize the operation of a 540 MW electrolysis plant, alongside the sizing and operation of the connected renewable generation, battery storage, and syngas storage. Applying this model to a Dutch case study, we explored grid integration with an electrolyzer across future scenarios with global warming potentials (GWPs) ranging between 35 and 370 g CO₂-eq per kWh. For generation, the preferred renewable mix is onshore wind combined with PV. When grid mix electricity consumption is restricted, the electrolyzer has an optimal capacity factor of 78% but requires a battery of comparable capacity to the electrolyzer and multi-kilotonne syngas storage to ensure continuous output. Crucially, we found that producing RFNBO-compliant syngas for SAF is impossible with the 2025 Dutch grid mix. Even at a reduced grid intensity of 205 g CO₂-eq per kWh, RFNBO compliance limits grid consumption to just 1% of grid mix electricity per hour. This results in a levelized cost of 2350 EUR₂₀₁₉ per tonne syngas. Unrestricted grid electricity consumption becomes feasible when emissions drop below 36 g CO₂-eq per kWh, reducing production costs by 43% (1344 EUR₂₀₁₉ per tonne syngas). Consequently, we demonstrate that grid composition intensity is a bottleneck for the short-term economic viability and regulatory compliance of CO₂E-based SAF in the Netherlands.