Amidst the pressing need for urgent action towards a climate-neutral future, it is imperative to produce synthetic fuels from renewable sources in order to decarbonize hard-to-abate sectors. In this context, emerging technologies such as direct air capture (DAC) of atmospheric CO2 and the production of solar fuels through solar processes like the redox cycles are particularly promising. DAC offers a method of capturing CO2 from the atmosphere that circumvents the biophysical limitations and potential conflicts with food production inherent in biogenic carbon sources. However, DAC is still in the early stages of development, with current costs and energy consumption remaining very high. Leading DAC approaches include liquid DAC (L-DAC) and solid DAC (S-DAC), which use liquid solutions and solid sorbents, respectively, to capture atmospheric CO2. Meanwhile, redox cycles offer an attractive pathway for producing synthetic fuels by directly using heat to store chemical energy in hydrogen and carbon monoxide (a mixture commonly referred to as synthesis gas). Due to the high temperatures involved, concentrated solar thermal technologies are the only viable renewable source for this energy-intensive process. While synthesis gas can serve as a fuel directly, it is primarily used as a feedstock for liquid fuels production such as methanol. DAC is often considered as the source of required CO2, yet existing research focuses mainly on DAC development without taking downstream utilization into account, or on solar fuel production without accounting for upstream processes. This study attempts to bridge this knowledge gap by exploring potential integration solutions between DAC and solar fuel production and evaluating them. To this end, this study identifies several integration strategies and groups them into four different scenarios. Models are then developed for the units involved in each scenario, and a case study is established for a solar methanol plant located near Riyadh, Saudi Arabia, with a capacity of 10 kt per year. Using real meteorological data, the performance of each scenario is examined on an hourly basis, facilitating the derivation of key economic and environmental indicators such as levelized cost of fuel and cradle-to-gate climate change impact. The results show that all proposed integrations improve both economic and environmental performance. However, the scenario using S-DAC and utilizing low-temperature waste heat from the solar fuel process emerges as the most favorable. Consequently, the thesis concludes that the integration of DAC with solar fuel production is feasible and desirable, contributing to a more efficient and cost-effective energy transition.
Enric Prats Salvadó (Wed,) studied this question.