Why are neither hydrogen nor e-fuels a solution for road transport?

It is primarily a matter of energy efficiency. Road transport is the mode of transport with the highest final energy consumption. That is why there needs to be a decarbonisation process that always opts for renewable energies.

Transport is the sector with the highest final energy consumption both in the European Union and in Spain. In 2020, according to data provided by the Ministry of Transport, Mobility and Urban Agenda (MITMA), in the EU as a whole, transport accounted for 28.4% of total consumption, while in Spain it was as much as 36.0%. The predominant mode is road transport, with almost 95% of final consumption in the transport sector.

Given that road transport nowadays is mostly dependent on fossil fuels, especially petroleum derivatives (petrol and diesel), it is not surprising that it alone is the main culprit for greenhouse gas (GHG) emissions in the EU and also in Spain, where it accounted for 27.8% of total greenhouse gas emissions in 2021, according to data provided by the "National Inventory of Greenhouse Gas Emissions: 1990-2021 series", published in March 2023 by the Ministry of Ecological Transition and the Demographic Challenge (MITECO).

 

Efficient decarbonisation of road transport

Fortunately, there are alternatives to fossil fuels to undertake the necessary process of decarbonising transport. But, for the energy transition towards decarbonisation to be plausible, it needs to be energy efficient. And of course it should always be based on the use of renewable energies.

Decarbonising transport by using renewable electricity is a major challenge. There is no way we can be using renewable electricity inefficiently. Allowing the use of synthetic hydrocarbons (also known as e-fuels, electro-fuels or synthetic fuels) in road transport, when there are much more efficient technical alternatives such as the direct use of electricity (battery electric vehicles), entails a huge energy penalty and risks derailing the entire decarbonisation effort.

The figures show that if we use renewable electricity (such as wind or solar energy) and feed it directly into a car battery, a total energy efficiency of 77% is obtained, in other words, 77% of the initial energy is what powers the vehicle. In the case of e-fuels, it is only 20% for electro-diesel and 16% for electro-petrol, (see graphs below).

In other words, moving a road vehicle (car, van, bus, lorry) using green hydrogen in a fuel cell or using electro-fuels is respectively, about 2.5 times, in the first case, and between 3.5 to 5 times, in the second, more energetically expensive than using renewable electricity directly in battery-driven vehicles.   

Cars: Direct electrification is by far the most efficient

From the well to the tank. 100% renewable electricity.

Electrolysis. Hydrogen 2020 - 76%; electro-diesel 2020 - 76%; Electro-Petrol 2020 - 76%.

Capturing CO2 directly from the air and FT synthesis. Electro-diesel 2020 - 72%; Electro-petrol 2020 - 72%.

Transport, storage and distribution: Direct electrification 2020 - 94%; hydrogen 2020 - 89%.

Overall efficiency. Direct electrification 94%. Hydrogen 89% Electro-diesel 55%. Electro-petrol 55%. 

 

From the tank to the wheel. 100% renewable electricity.

Charging equipment. Direct electrification 2020 - 95%.

Battery charging efficiency. Direct electrification 2020 - 95%.

Converting H2 into electricity. Hydrogen 2020 - 54%.

DC/AC inversion. Direct electrification 2020 - 95%. Hydrogen 2020 - 95%.

Engine efficiency. Direct electrification 2020 - 95%. Hydrogen 2020 - 95%. Electro-diesel 2020 - 36%. Electro-petrol - 30%.

Overall efficiency. Direct electrification 2020/2050 77%/81%. Hydrogen 2020/2050 33%/42%. Electro-diesel 2020/2050 20%/22%. Electro-petrol 2020/2050 16%/18%.

 

Notes: These should be understood as approximate average values taking into account the different production methods. Hydrogen includes compression of the fuel on board. Mechanical losses are excluded.

Source: Wrokbank (2014) Apotolaki-losifidou et al. (2017), Peters et al. (2017), Larmanie et al. (2012), Unweltbundesamt (2019), National Research Council (2013), Ricardo Energy & Environment (2020), DOE (undated), ACEA (2016)

Lorries: Direct electrification is by far the most efficient

From the well to the tank. 100% renewable electricity.

Electrolysis. Hydrogen 2020 - 76%; electro-diesel 2020 - 76%; Electro-Petrol 2020 - 76%.

Capturing CO2 directly from the air and FT synthesis/methanation. Electro-diesel 2020 - 72%; Electro-petrol 2020 - 73%.

Transport, storage and distribution: Direct electrification 2020 - 94%; hydrogen 2020 - 89%; electro-petrol 93%.

Overall efficiency. Direct electrification 94%. Hydrogen 68% Electro-diesel 55%. Electro-petrol 55%. 

 

From the tank to the wheel. 100% renewable electricity.

Charging equipment. Direct electrification 2020 - 95%.

Battery charging efficiency. Direct electrification 2020 - 95%.

Converting H2 into electricity. Hydrogen 2020 - 54%.

DC/AC inversion. Direct electrification 2020 - 95%. Hydrogen 2020 - 95%.

Engine efficiency. Direct electrification 2020 - 95%. Hydrogen 2020 - 95%. Electro-diesel 2020 - 42%. Electro-petrol - 42%.

Overall efficiency. Direct electrification 2020/2050 77%/81%. Hydrogen 2020/2050 33%/42%. Electro-diesel 2020/2050 23%/29%. Electro-petrol 2020/2050 22%/28%.

 

Notes: Efficiency indices for heavy goods vehicles for long-distance transport should be understood to be approximate average values taking the different production methods into account. Direct electricity represents both battery-electric vehicles that run on batteries and/or overhead catenaries. Hydrogen includes the compression of the fuel on board, while the conversion of energies into methane includes the liquefaction of the fuel. The same engine efficiency is assumed for both diesel vehicles and those with HDPI fuel engines.

Source: Wrokbank (2014) Apotolaki-losifidou et al. (2017), Peters et al. (2017), Larmanie et al. (2012), Unweltbundesamt (2019), National Research Council (2013), Ricardo Energy & Environment (2020), Delgado et al. (2017)

Manufacturing e-fuels for road transport would be a waste of renewable electricity

If we promote the use of green hydrogen or that of e-fuels for road transport, a large amount of additional renewable electricity would need to be generated to produce them, which would require the installation of a significant number of extra renewable energy plants, with the consequent impact on the territory and potentially on biodiversity.

In a study by Transport & Environment (T&E), it was estimated that to power only 10% of cars, vans and small lorries with green hydrogen and another 10% with e-diesel in 2050 would require 41% more renewable energy than if these were battery-electric vehicles. And if half of heavy-duty lorries ran on hydrogen and the other half on e-diesel, they would consume 151% more renewable resources in 2050 than in the case of directly electrified vehicles.

Giving direct electrification priority over e-fuels in road transport has an added advantage. Because battery electric vehicles are in fact "batteries on wheels", the possibility of intelligent charging (e.g. with the V2G, vehicle-to-grid option) for these vehicles will help to reduce the restriction of the high shares of wind and solar energy needed in European grids by 2030, and this will potentially reduce the additional renewable electricity needed by almost 10%. By 2050, this potential could be even greater with an almost 100% electrified vehicle fleet and a very high proportion of renewable energies throughout the EU. 

 

Disadvantages of using e-fuels in road transport

In theory, when burned in an internal combustion engine, e-petrol and e-diesel emit exactly the same amount of CO₂ from the exhaust pipe as their respective conventional fuels, as they have the same chemical composition. However, the only way to make them theoretically CO2 neutral is for them to be produced using green hydrogen, produced from additional renewable electricity, and for the carbon to be obtained by direct capture of CO2 from the air.

However, the use of renewable e-petrol or e-diesel in vehicles is not climate neutral. In tests conducted by T&E, it was found that burning e-petrol in a combustion engine produces two more powerful greenhouse gases: Methane (CH4) and nitrous oxide (N2O). Similarly, it was also discovered that these gases were emitted by e-diesel in test conducted by CONCAWE. Those proposing e-fuels do not take these emissions into account when they claim "climate neutrality". According to the study by T&E, if all new petrol and diesel cars sold in 2020 ran on e-petrol or e-diesel, the additional CO2-eq emissions (from methane and nitrous oxides) would be equivalent to those of about 50,000 more fossil-fuel cars on EU roads in just one year.

Cars powered by e-fuels emit as many nitrogen oxides (NOx) as engines that burn fossil fuels. NOx is a toxic substance responsible for poor air quality in our cities. The use of e-fuels also increases emissions of toxic carbon monoxide, also harmful for our health.

The transport sector is one of the main culprits for the poor quality of the air we breathe. According to the latest AEMA estimates, at least 238,000 people died prematurely in the EU in 2020 due to exposure to PM2.5 pollution above the WHO guidance level of 5 μg/m³. 49,000 premature deaths were caused by nitrogen dioxide pollution in the EU and 24,000 by exposure to ozone.

The production of e-fuels is expensive. That is why they will be sold at a high price. Even with an optimistic approach, a driver with a synthetic petrol car in 2030 would spend €10,000 more than one with a battery-electric car over 5 years. Most Europeans would not be able to afford this.

E-fuels could not power even 2% of the number cars expected to be on the road in 2035. The industry's own analysis shows that the volume of e-fuels expected to be available in 2035 would only power five million cars out of a fleet expected to be 287 million in the EU. Even the industry does not see e-fuels as a viable alternative to fossil fuels. 

 

The role of e-fuels in the decarbonisation of the transport sector

The EU can meet the demand of the road transport sector with the direct use of renewable electricity (i.e. through battery electric vehicles), and should therefore concentrate the use of green hydrogen and synthetic electro-fuels derived from it to decarbonise sectors that cannot easily achieve this through direct electrification, as is the case with air transport, a large proportion of maritime transport and certain industrial uses.

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