Resumen de Prospective assessment of alternative fuel production technologies for decarbonising road transport in Spain
Road transport is one of the main sources of greenhouse (GHG) emissions due to the current dependence on fossil fuels such as diesel and gasoline. Thus, governments work on the development and prospective planning of decarbonisation strategies oriented towards sustainable transport. In this regard, it is necessary to eliminate fossil fuels and instead implement alternative fuels and vehicles such as biofuels, electric vehicles (EV), and fuel cell electric vehicles (FCEV) fuelled by hydrogen. Nevertheless, the environmental suitability of alternative fuels is conditioned by how they are produced. In this context, through the case study of Spain, this thesis prospectively assesses –from a techno-economic and carbon footprint perspective– the production technology mix of alternative fuels including biofuels, electricity, and hydrogen from 2020 to 2050. Here, an energy systems optimisation model was built considering a wide range of production technologies (all of them techno-economically and environmentally characterised) to optimise the production technology mix. Additionally, carbon footprint indicator was integrated in the models. This integration of a life-cycle sustainability indicator enriches the analysis of the prospective performance of the energy system while making possible the definition of constraints on this life-cycle indicator. The models include a large number of production technologies regarding biofuels (divided into bioethanol, biodiesel, synthetic diesel/gasoline, and hydrotreated vegetable oil, also known as HVO), electricity, and hydrogen.
Obtaining robust techno-economic data of production pathways for alternative fuels is still a challenge for energy planners, modellers, analysts and policy-makers when building their prospective models to support decision-making processes. That is the reason why the techno-economic data presented in this thesis are expected to be especially useful to those energy actors interested in performing long-term studies on the transition to a sustainable transport system. The combined study of the alternative fuels productions models provides a relevant framework to discuss the targets established for the road transport sector with a high level of detail not only regarding fuel types but also technology breakdown.
Alternative fuels such as bioethanol and biodiesel are usually blended with conventional fuels in different proportions. In Spain, bioethanol is commonly used for blending with gasoline, and currently could suppose around 10% (v/v) of the total blend. Assuming a scenario with gasoline vehicles retirement in the long term, the total bioethanol demand would also have a direct reduction. According to the production technology mix, first-generation bioethanol would partly contribute to meeting the bioethanol demand but second-generation bioethanol from biomass fermentation would be the main production technology during the whole time frame. Biodiesel has a similar behaviour since it is typically blended with diesel (around 7% (v/v)) and it would disappear in the long term. First-generation biodiesel would be produced through oil esterification in the short term. However, for the evaluated period, the fulfilment of the biodiesel demand would be led by second-generation biodiesel from oil esterification. The synthetic diesel and gasoline biofuels would be met by pyrolysis in the short and medium term and then pyrolysis would be gradually substituted by gasification according to the techno-economic progress achieved by the gasification pathway. Finally, HVO demand would be satisfied by second-generation biomass hydrogenation.
The results show the relevance of second-generation biofuel production technologies in fulfilling the future biofuel demand. At the same time, the penetration of EV seems to be a forthcoming reality in the transport sector worldwide, involving an increase in electricity demand. When compared to a business-as-usual situation, this work evaluates the optimisation of production technologies for the increased electricity demand linked to the Spanish road transport until 2050. This is done under three alternative scenarios based on the low, medium, or high penetration rate of EV. In all cases, EV deployment was found to involve a relatively small percentage (<9%) of the final electricity demand in Spain. The increased electricity demand associated with EV penetration compared to a case when EV deployment does not take place would be met by renewable power plants, in particular by solar (photovoltaic and thermoelectric) and wind plants.
Regarding FCEV, they could contribute to decarbonising the transport system because they have no direct CO2 emissions during the use phase. In fact, the life-cycle environmental performance of hydrogen as a transportation fuel highly depends on its production pathway. In order to avoid relying on fossil resources as the main feedstock, an alternative scenario characterised by carbon footprint restrictions with respect to a fossil-based scenario dominated by steam methane reforming was evaluated. In this scenario, the steam reforming of natural gas (NG) still arises as the key hydrogen production technology in the short term, whereas water electrolysis is the main technology in the medium and long term.
These findings are expected to be relevant not only to the specific case study of Spain but also to analysts and decision-makers in many countries facing similar concerns. Analysing the carbon footprint of each fuel (including production and combustion), it was concluded that the retirement of fossil fuels and the penetration of alternative fuels would lead to significant GHG emission reductions in the medium and long term. In particular, the GHG emissions related to fossil diesel and gasoline would decrease more than 90% in the evaluated period at the expense of a slight increase in the GHG emissions associated with alternative fuels. Overall, this integrated approach to the long-term production technology mix of alternative fuels for road transport is expected to be relevant to a wide range of decision-makers willing to prospectively assess road transport systems from a technology perspective.
