Managing intermittency of renewable power in sustainable production of methanol, coupled with direct air capture

Abstract

Coupling direct air capture (DAC) with methanol production is a technically attainable opportunity for CO₂ capture and utilisation (CCU). The process, known as power-to-methanol (PtM), consumes large amounts of renewable electricity for water electrolysis and DAC. However, the time-variability of renewable power remains a major challenge. Here, we consider erecting a wind farm as part of a PtM facility and propose using four parallel reactors to adjust the methanol production according to daily wind power generation, which we model for 90 onshore and offshore locations with real-world data. Batteries and reserve storage of compressed H₂ and CO₂ allow methanol production during near-zero availability of wind power. We investigate different operation strategies, aiming to either minimise the reserve storage or maximise production, ultimately finding minimised storage as more cost-effective. The resulting selling price of methanol from a plant powered by an onshore wind farm is $1400 per tonne, rising to $2200 for offshore wind power because of higher farm installation costs. However, with a well-located wind farm, coupled with improvements to DAC, electrolysis, and catalysts, the selling price falls as low as $300 per tonne of methanol, reaching parity with fossil fuel-derived methanol. Purchasing stable grid power for PtM avoids issues of intermittency, and results in a lower methanol selling price of $960 per tonne, falling to $340 with process improvements. However, life cycle assessment (LCA) shows the global warming potential (GWP) of the grid-based cases is no better than producing methanol from natural gas; whereas, wind-powered DAC-PtM delivers net-negative GWP between −760 and −1240 kg_CO2eq. per t_MeOH, demonstrating successful CCU.