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Public Transport and Alternative Fuels: Fuelling Change

Echoing one of the most talked about news in recent days regarding the agreement reached between the EU and Germany on eliminating the ban on the sale of combustion cars (those using petrol, diesel or gas, including hybrids) beyond 2035, under the condition that they are modified to use only synthetic fuels in the future, this post discusses what alternative energy sources are currently driving public transport worldwide and what the future outlook is for e-fuels in passenger transport.

As a starting point it is worth mentioning that there are several fuels that are used in passenger transport, among them:

  • Petrol: although considered a fossil fuel that produces greenhouse gas emissions, petrol is still a widely used fuel in public transport in many countries.
  • Diesel: Another petroleum derivative and therefore a fossil fuel used especially in buses and trucks.
  • Natural gas: This is a fossil fuel that emits less carbon dioxide than petrol or diesel, which is why it has been used in some public transport systems for some years.
  • Biofuels: These are produced from renewable raw materials, such as corn, sugar cane or sugar beet, and can be a more sustainable alternative to fossil fuels.
  • Electricity: Electric buses, for example, use rechargeable batteries to power their engines; these vehicles emit no exhaust fumes and are considered a cleaner alternative to internal combustion engine vehicles.
  • Hydrogen: In some vehicles hydrogen is used as a fuel, which has the advantage that it only emits water as a by-product of its operation.
  • Hybrid systems: Hybrid vehicles combine an electric motor with an internal combustion engine. They use electric power when they can, which reduces their fuel consumption and exhaust emissions.
Alternative fuels are gaining ground in Public Transport

From this perspective it can be seen that there are a variety of alternative fuels, the choice of which depends on many factors such as cost, availability, infrastructure and local legislation.

However, there is a growing interest in the use of more sustainable alternative fuels, i.e. fuels that seek to reduce greenhouse gas emissions and improve air quality in cities. In this line, the United States and Germany announced an agreement to promote the use of e-fuels, with the aim of establishing a roadmap for their production and use in both countries, which could have significant implications in the global fight against climate change.

But what are e-fuels? Also known as electrofuels, or synthetic fuels, the term refers to any technology that converts electrical energy (renewable energy such as photovoltaic, hydro or wind) into a gaseous or liquid energy carrier. There are different taxonomies that refer to e-fuels: liquid renewable fuels (Power-to-liquid or PtL) or gaseous renewable fuels (Power-to-Gas or PtG) of non-biological origin. In addition, there are also hydrogen-derived synthetic renewable fuels, which include liquid and gaseous varieties based on (renewable) hydrogen and (captured) carbon. Examples of these are those derived from the reaction of these two elements to produce methane or to obtain diesel or petrol by Fischer-Tropschs synthesis.

E-fuels convert electrical energy (renewable photovoltaic, hydro or wind) into a gaseous or liquid energy carrier.

This set of fuels has the particularity of being able to be used in conventional engines without the need to modify them, which is why they have become increasingly attractive, as they are projected as a solution to reduce emissions, especially in those sectors where complete electrification (which use electricity exclusively as an energy vector) is not feasible, such as air or maritime transport.

According to specialised literature, systems can be electrified either directly or indirectly. Specifically, direct electrification in transport involves the use of battery electric vehicles, whose main use is in road transport and includes the implementation of contact technologies such as pantographs for trains.

Indirect electrification is mainly concerned with making use of PtL or PtG technologies to generate e-fuels such as hydrogen, e-methanol and ammonia. These fuels could be used directly through e-methanol-to-gasoline conversion processes, such as hydrogen fuel cells (HFCs) or direct methanol fuel cells (DMFCs), and also cover maritime and air transport.

It is worth noting that there has been a great deal of interest in direct electrification of transport in recent years due to the increase in energy density (storage capacity) of batteries and their consequent decrease in procurement costs (lithium-ion battery prices have decreased by around 89 % between 2010 and 2020).

Energy pathway for sustainable mobility based on e-fuels (Own elaboration, 2023)

However, as in the case of direct electrification, there are limitations to the use of e-fuels on a mass scale. In particular, they require large amounts of renewable electricity for electrolysis and inherently have a low well-to-wheel efficiency (around 13% compared to 73% achieved by direct electrification).

Despite this, experts in the field agree that by being obtained from renewable energy, these fuels can help to drastically reduce greenhouse gas emissions, while at the same time helping to stabilise the electricity grid, as the surplus obtained from wind or photovoltaic generation can be used to produce these fuels. Thus, e-fuels are emerging as a more sustainable solution to meet the energy demand of a growing global economy, even in the future, as technological progress and cost reductions in wind and solar power, as well as electrolysers, have been significant in recent years.

Synfuels thus offer the opportunity to be used in all sectors and in almost all available applications. They complement the direct use of renewable energies, especially where direct electrification is not possible or economical. Furthermore, e-fuels can be fully or partially integrated into the existing liquid and gaseous fuel

E-fuels help reduce greenhouse gas emissions.

Specifically, e-fuels offer many advantages: they help to reduce carbon emissions, they are carbon neutral, they have a high energy content per mass, they can be moved, they can be stored long-term in liquid or gaseous form without energy losses; or in large volumes to be used in case of a blackout or any other supply problem with other energy carriers, they bring security and reliability to the energy system, they facilitate the use of existing infrastructure and most importantly, they can be used by the existing vehicle fleet. Moreover, with their production, countries with few natural resources but good solar and wind conditions will have the opportunity to improve their own energy supply and become a new player in the global energy market.

There is no doubt that e-fuels represent an opportunity to mitigate the impacts of fossil fuel use, but the extent of the benefits will largely depend on a combination of factors such as the right choice of feedstock and technologies, including the carbon source, the efficiency of electrolysers and the input of electricity from decarbonised grids.

It is on this last aspect that experts agree that the obvious solution to the decarbonisation of the energy sector is extensive electrification of passenger vehicles. With an increasing share of renewable energies in the electricity sector, this would automatically mitigate CO2 emissions in the transport sector without, of course, taking into account the emissions related to battery production.

In this way, with technological advances in fuel production and the supply chain, as well as the decarbonisation of the European electricity mix, the net impact is expected to decrease in the future. However, a strict climate policy with high rates of decarbonisation of the sector in Europe, and the world in general, is needed to make e-fuels clearly more environmentally friendly than fossil fuel.

Johanna Diaz – Architect & Urban Planner at Vectio

 

 

References:

 

Abid, H., Kany, M. S., Mathiesen, B. V., Nielsen, S., & Maya-Drysdale, D. W. (2021). Transport electrification scenarios for decarbonization of the European transport sector by 2050. Eceee 2021 Digital Summer Study: Energy efficiency in the new reality, 751-759.

Ausfelder, F., & Wagemann, K. (2020). Power-to-Fuels: E-Fuels as an Important Option for a Climate-Friendly Mobility of the Future. Chemie Ingenieur Technik, 1-2(92), 21-30.

Ballal, V., Cavalett, O., Cherubini, F., & Barbosa Watanabe, M. D. (2023). Climate change impacts of e-fuels for aviation in Europe under present-day conditions and future policy scenarios. Fuel(338), 1-11.

Freire Ordóñez, D., Halfdanarson, T., Ganzer, C., Shah, N., Mac Dowell, N., & Guillén-Gosálbez, G. (2022). Evaluation of the potential use of e-fuels in the European aviation sector: a comprehensive economic and environmental assessment including externalities. Sustainable Energy & Fuels(6), 4749-4764.

Hombach, L., Doré, L., Heidgen, K., Maas, H., Wallington, T., & Walther, G. (2019). Economic and environmental assessment of current (2015) and future (2030) use of E-fuels in light-duty vehicles in Germany. Journal of Cleaner Production, 207, 153-162.

Kramer, U., Goericke, D., & Thee, R. (2019). Energy Paths for Road Transport in the Future. MTZ worldwide, 5(80), 18-25.

Pütz, R. (2021). Towards zero emission: Are e-fuels a promising option? Mobility & Vehicle mechanics, 47(2), 1-14.

Pasini, G., Lutzemberger, G., & Ferrari, L. (2023). Renewable Electricity for Decarbonisation of Road Transport: Batteries or E-Fuels? Batteries, 2(9), 135.

Viscardi, R., Bassano, C., Nigliaccio, G., & Deiana, P. (2021). The potential of E-fuels as future fuels . (1), 112-116.

 

(i) The European Union’s target is to reduce greenhouse gas emissions by 80 % by 2050 compared to 1990 levels.

(ii) Under the EU Clean Vehicles Directive buses with highly sophisticated diesel engines would still be allowed as “clean” vehicles in the medium term if they run on sustainable biofuels or e-fuels. Therefore, PtL, GtL and even CtL (coal-to-liquids) fuels would be allowed, the latter regardless of their high CO2 intensity.

(iii)  Data published in 2022 by Eurostat reveal that in advanced countries, transport has an even greater impact than other individual sectors with almost 30% of final energy consumption.

(iv) On average energy consumption increases by approximately 1-2% per year, transport accounts for around 25% of global energy demand and over 60% of total oil consumption for the same period. In addition, the transport sector is responsible for about 20% of the world’s carbon emissions.

(v)  In the energy policy debate on specific driving and fuel concepts, electromobility is seen and promoted almost exclusively as a sustainable option. This ignores the fact that modern internal combustion engines of the Euro VI (for commercial vehicles) and Euro 6d (for passenger cars) stages already have a local level of emissions close to zero and only renewable fuels are needed to achieve a very significant reduction in greenhouse gas emissions.

(vi)  The German Federal Government’s climate protection plan sets ambitious targets for the overall reduction of CO2: by 2050 it aims for a reduction of 80-95% compared to 1990 levels. Within the transport sector, in particular, the target is a 40% reduction in final energy use, however, no specific CO2 emission reduction target is set.

 

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