Power-to-X and Alternative Fuels for the Maritime Industry

Maritime transport emits about 1 billion tons of CO_2e annually and is responsible for about 3% of annual global greenhouse gas emissions. One of the most promising options to reduce the climate impact of the shipping industry is to replace the fossil fuels used for propulsion by alternative fuels having lower global carbon emissions. Various alternative fuels could be used, such as biofuels derived from biomass, electro-fuels derived from electricity and hydrogen produced from renewables, bio-e-fuels combining the use of biomass and renewable hydrogen, or blue fuels produced like conventional fossil fuels but using carbon capture and storage technologies during the process. The aim of the thesis is to provide fuel transition pathways for the maritime industry taking in account fuel production costs and associated greenhouse gas emissions, fuel availability and the shipping fleet changes needed. The work of this thesis presents an in-depth analysis of various alternative fuels production pathways and proposes open access tools and methods for the techno-economic assessment of power-to-X plants producing electrolytic hydrogen based fuels. The modeling aspect related to input power profile simulations is tested using experimental data. The initial methodology used for techno-economic assessment of power-to-X plants is further developed to consider the renewable power profile uncertainties. Finally, the e-fuels techno-assessments are supplemented by an analysis of life-cycle greenhouse gas emissions associated with e-fuel production while considering the influence of regulations and incentives related to renewable fuel certification. This in-depth analysis of electrolytic hydrogen-based fuel production serves as a basis to derive fuel transition pathways for the maritime industry. Various other considerations are studied in order to derive fuel transition road-maps such as: fuel availability (constrained by the amount of sustainable CO₂/biomass available globally and production capacities); the current state of the shipping fleet; cost, timing and production capacity of new build ships and engines adapted to alternative fuels; future transport demand; carbon budget for the shipping industry. All these parameters are combined in a fuel transition pathway ("SeaMaps") model that provides initial inputs and indications about what is needed to keep the maritime industry in line with the Paris agreement. The potential drivers for the "green" transition of the shipping sector presented in this thesis include a global carbon budget that must be respected or a combination of a CO₂ tax on fossil fuels and fuel consumption reduction.

Results demonstrate that achieving a carbon-neutral transition in the maritime sector aligned with the 1.5 °C target of the Paris Agreement demands an urgent and substantial increase in renewable fuel production capacities. The recommendation is for a minimum of 5 GW of electrolysis capacities installed by 2026, escalating by 50% annually until 2040. Caution is urged against uncontrolled grid- connected e-fuel production, which poses the risk of delaying emissions reduction which is not an option to respect the 1.5 °C target. The fuel consumption must decrease early on, and has to be lower by 16% in average between 2026 and 2035 compared to the current global fuel consumption. The preferred transition pathways involve renewable ammonia or bio-e-fuels depending on the sustainable biomass availability. Achieving the well below 2°C carbon budget is feasible without early fuel consumption reduction.
Initiating the transition could involve implementing a progressive CO_2e tax, increasing linearly from the current 50 €/tCO_2e to at least 650 €/tCO_2e in 2050. Even with a high CO_2e tax, significant fuel consumption reduction or negative CO_2e emissions are necessary to stay within a carbon budget aligned with the 1.5 °C target of the Paris Agreement. We advocate for early demonstration plants, affordable capital access, and technology development to expedite the adoption of low-emission fuels. The large-scale production of e-fuels will necessitate massive resources and land requirements, thus warranting careful consideration of environmental and land use change concerns. The thesis results have been derived using open-source tools developed for this purpose. These tools and the data used as input will be made freely available, hopefully as an online tool one day, enabling potential re-use and allowing others to validate and replicate the results.