Techno-economic and environmental assessment of power-to-liquid processes

The Power-to-X (PtX) concept enables the 'infusion' of renewable energies into economic sectors that will present a challenge in terms of direct electrification. In particular, Power-to-Liquid (PtL) processes utilising captured carbon dioxide and electrolytic hydrogen, enable the production of synthetic high-density energy carriers, fuels and chemicals independent from an exploitation of fossil resources. In the present cumulative dissertation, PtX and in particular PtL concepts are evaluated from both a techno-economic and an environmental perspective. The overview chapter sets a frame for the scientific publications by defining the general concept and required process steps as well as the necessity of PtX and PtL for highly defossilised energy systems. The chapter is complemented by analyses of future land requirements for dedicated renewable energy plants and a demand for imported PtX energy carriers. The scientific publications are the result of specific case studies conducted over the past four years. The aim was to analyse certain PtX and PtL scenarios in detail and thus gain new insights into the techno-economic performance of individual components and their respective influence on the concepts overall ecological footprints. On the other hand, more general conclusions were to be drawn, which would allow for a better understanding of the ecology and economy of PtX processes as an important part of integrated energy systems. Results show that at greenhouse gas reduction targets beyond 80 %, the PtX concept will become an important element of global economies. PtX is expected to reach installed capacities in the Terawatt hour range within this decade. However, as the cradle-to-grave assessments show, PtX processes require significant amounts of dedicated renewable energy capacities to enable products with clearly reduced greenhouse gas footprints. Additionally, the analysis of further environmental impacts highlighted an importance of a holistic transformation of global product systems towards a reduced consumption of fossil resources. Otherwise, minor shares of fossil based energy generation and resources will drive the indirect environmental impact of PtX products. The use of concentrated fossil carbon dioxide sources can be seen as an intermediate solution for the production of synthetic energy carriers, which in turn substitute the production of fossil-based energy carriers. However, in order to contribute to closing the global carbon cycle in the long term, the use of atmospheric carbon dioxide, whether through the use of biomass or through atmospheric capture is seen as a central objective for carbon based PtX processes. In terms of economic efficiency, PtX pathways depend on the availability of low-cost electricity supplied at increased full load hours. For PtX scenarios located in Germany, fully renewable electricity based pathways show clearly elevated production costs in comparison to their cheap fossil reference products. However, a steady increase in the TRL of central PtX components will benefit overall PtX pathway efficiencies. Furthermore, the cost-reducing economies of scale effect in combination with a further market ramp-up of hydrogen technologies promise a significant reduction in PtX production costs for the coming decades. An assessment on the energy and cost-efficiency of synthetic energy carriers produced in Morocco and transported via ship to Europe serves as a general example for a PtX production in countries with promising renewable energy potential. The results show that the technical feasibility is already promising today with clearly reduced production costs compared to PtX plants located in central Europe. Cost parity of PtX products with cheap fossil based energy carriers and fuels will not be achieved as long as the external environmental costs of fossil fuels are not reflected in their production costs. Further research is necessary to enable more dynamic synthesis processes which can in turn save cost-intensive hydrogen storage capacities. Additionally, environmental datasets should be updated to better reflect the progressive defossilisation efforts of global economies.