Navigation | Page content | Additional information

Page content

Regenerative fuels –
a possible solution for public transport?

Guest article by:

Der Rote Renner

The EU Directive 2019/1161, also known as the Clean Vehicles Directive (CVD), requires that public transport companies successively convert their vehicle fleets to alternative drivetrains. In addition to cost-intensive vehicle purchases, switching from the internal combustion engine means that companies have to establish a new technological infrastructure, with new expertise and lots of capital – all in more or less record time. For small companies in particular the challenges of the CVD would seem too great. Thus, powering conventional diesel engines with regenerative fuels offers a potential solution for an industry that must fulfil its responsibilities in the effort to meet climate targets.

Regenerative fuels as contributors to carbon-neutral mobility

Public transport companies are facing massive change. On the one hand, this is due to the pandemic, which since early 2020 has led to huge cuts in public transport and has given rise to and accelerated far-reaching socio-economic change. On the other hand, the industry is subject to regulatory measures by the state due to the growing problems caused by climate change.

Thus, on 15 June of this year a Clean Vehicle Procurement Act (SaubFahrzeugBeschG) came into force. It lays down the rules for implementing the EU Directive (EU) 2019/1161, known as the Clean Vehicles Directive (CVD) in Germany, as well as for funding of clean and energy-efficient road vehicles.

Since 2 August 2021 this act, which envisages full implementation of the CVD, for the first time lays down minimum legal requirements for procuring low and zero-emissions heavy-duty utility vehicles.

By 2025, at least 45 per cent of procured public transport buses, rising to 65 per cent by 2030, must employ alternative drivetrains, powered by electricity, fuel cells, natural gas, synthetic fuels or biofuels. At least half of these base targets must be met with zero-emissions vehicles.

Regenerative fuels as contributors to carbon-neutral mobility (source: KIT)
Regenerative fuels as contributors to carbon-neutral mobility (source: KIT), *Methane, biogas, PtG, *Regenerative Fuels, *Fuel cells *Electromobility

Regenerative fuels as an interim technology

The EU Commission regards synthetic fuels and biofuels, i.e. regenerative fuels, as an interim technology. Regarding their use, EU Commission expert Laure Chapuis said: “During an interim phase various forms of low-emissions hydrogen power and other fuels will be needed to initiate the departure from fossil fuels.“ Regenerative fuels are sourced from either Biomass-to-Liquid (BtL) or Power-to-Liquid (PtL) production.

In targeting carbon-neutral mobility and in the face of the massive challenges posed by the CVD, public transport companies will likely welcome the use of regenerative fuels on various levels. For public transport companies the implementation of the new CVD with its considerable extra costs represents a huge challenge, financially, organisationally and in terms of operations.

Thus the electrification of a bus fleet, in addition to being 2.5 times the cost of diesel buses, brings other considerable obstacles with it, namely the need for a new charging and transport infrastructure. Installing a charging point that provides the necessary energy is often a problem, particularly for companies in rural areas. Other challenges are changes needed to operations and workshops, retraining personnel, and the additional space required by a new technology. For smaller companies in particular, apart from not knowing which investment in zero-emissions drivetrain technology is right for them, running two or three drivetrains in parallel is hard to manage. These are just some of the aspects worth noting in the context of a switch by public transport to zero-emissions drivetrains.

Aside from these aspects, current scenarios of the energy transition in the transport sector indicate that a full changeover cannot be achieved by 2050 with electromobility alone. Therefore, electrification alternatives such as fuel cell drivetrains are initially unavoidable.

As an interim technology, regenerative fuels have an advantage in that diesel buses do not require a new infrastructure for refuelling and can thus remain in service. Existing infrastructures and other technologies can also remain in use.

Demands for quicker progress

However, to date no substantial moves have been made to establish a supply of regenerative fuels. Despite a noticeable increase in electric buses, regenerative fuel technology has yet to emerge from the starting blocks. This sentiment is echoed by Baden-Württemberg, by its own description the only federal state to have formulated a roadmap for building supplies of regenerative fuels. Only last October, the state’s transport minister Winfried Herrmann criticised protracted proceedings at EU and federal level, and demanded that the European Union and German government step up efforts and the availability of funds for regenerative fuel projects.

Regenerative fuels are needed very soon in order to meet climate targets, says Winfried Herrmann. These fuels have been sufficiently researched and tested for practical use. According to him, it is high time to switch from a research environment to industrial mass-scale production.

“We have been waiting for almost two years for the Federal Ministry of Transport and Digital Infrastructure to issue a call for tender for the development of systems capable of producing more than 10,000 tons annually.“ On the other hand, in Berlin they are waiting for the publication of the Delegated Act on the Certification of Green Hydrogen from the EU, so that 42 to 48 months could elapse before a funding project begins, he said. At the very least, pending a final decision, a certificate of non-objection needs to be issued to clear the way forward, Herrmann said at a session of the state parliament.

In addition to this demand, the states of Baden-Württemberg, Brandenburg and Hamburg have applied to amend the Federal Immission Control Act to be able to market undiluted synthetic (PtL) fuels at petrol stations. The Federal Association of German Bus Operators supports this move.

Energy Lab 2.0 – source: KIT
Energy Lab 2.0 – source: KIT

Regenerative fuels project at the Karlsruhe Institute of Technology (KIT)

Since 2019, as part of its roadmap to build supplies of regenerative fuels, Baden-Württemberg has invested five million euros in the project ’ReFuels – Rethinking Fuels’ at the Karlsruhe Institut of Technology (KIT). The automotive industry, supply industry and mineral oil industry have also funded the project with 15 million euros.

To date, as part of the project, two test facilities have been set up to produce and test fuels. According to the KIT, the bioliq® and Energy Lab 2.0 have already produced several thousand litres of regenerative fuels. Tests have also been conducted on internal combustion engines. The goal is to optimise the synthesising process for creating regenerative fuels to reduce primary emissions.

Researchers have now reached a point where they consider synthetic fuels to be ready for wide-scale use in the transport sector. “If they are blended and prepared to meet current fuel standards then they can be used in all internal combustion applications.“ That was the assessment reached following vehicle and fleet tests.

“The regenerative fuel blends tested in our facility to date satisfy the current standards for petrol and diesel fuels. In tests conducted on an existing car fleet we were unable to identify any negative characteristics in regenerative fuels. In certain cases, pollutant levels were slightly improved – both in diesel and petrol-driven vehicles“, said Uwe Wagner of the Institute of Piston-driven Engines (IFKM) of the KIT. Tests were also conducted on a fleet of six HGVs. The results there also demonstrated no problems in practical use.

However, in order to fully exploit the potential of regenerative fuels to reduce greenhouse gases, the electricity used must be 100 per cent from renewable sources. The CO2 required for the synthesising process is extracted from the atmosphere or from biogas and waste treatment plants. In order for this technology to be effective PtX systems must operate sufficient hours under full load.

Prof. Roland Dittmeyer, an expert at the KIT, predicts synthetic fuels will be market-ready in 2026.

Using regenerative fuels would also have another benefit. They could replace diesel fuel reserves in order to supply vehicles, the police and emergency services in the event of natural disasters.

The graphic shows the efficiency of various drivetrain technologies in a car. Source: Agora Verkehrswende und Agora Energiewende (2018) (Agora Transport and Energy Transition), graphic 2, based on aca
The graphic shows the efficiency of various drivetrain technologies in a car. Source: Agora Verkehrswende und Agora Energiewende (2018) (Agora Transport and Energy Transition), graphic 2, based on acatech et al. (2017), graphic 5.

The obstacles to wide-scale use of regenerative fuels

Nevertheless, there are obstacles and risks involved with this interim technology. Currently its efficiency ranks well below that of electric motors.

A battery-electric vehicle achieves an efficiency of 69 per cent, while PtL achieves only 13 per cent. The costs that regenerative fuels save initially due to new infrastructures not being required must at least be partially re-invested in the production of this new and currently still expensive technology. Already there are scenarios projecting the cost of regenerative fuels. However, they vary depending on electricity prices and production volumes. What direction the cost of regenerative fuels will take by 2030 is unclear. That was the conclusion reached by an assessment of the federal government.

At the same time, any wide-scale use of regenerative fuels is currently tied to production uncertainties. Industrial production facilities have yet to be established. These include making electricity available from what are necessarily renewable sources. A 2019 study by the Öko-Institut came to the conclusion that using electricity-based fuels only makes sense if renewable sources account for 80 per cent of that electricity. Against this backdrop, any widespread use of synthetic fuels is unlikely before the year 2030.

Text: Vera Wendlandt-Meeser, CEO Der Rote Renner


acatech et al. (2017a): acatech, Leopoldina, Akademienunion. „Sektorkopplung“ – Optionen für die nächste Phase der Energiewende. Stellungnahme, November 2017 die-naechste-phase-der-energiewende.html


Agora Verkehrswende and Agora Energiewende (2018): The Future Cost of Electricity- Based Synthetic Fuels: Conclusions Drawn by Agora Verkehrswende and Agora


Energiewende. In: Agora Verkehrswende, Agora Energiewende and Frontier Economics (2018): The Future Cost of Electricity-Based Synthetic Fuels.

Bundesministerium für Verkehr und Infrastruktur:

Bundesverband Deutscher Omnibusunternehmen e.V.: SN41 Positionspapier - Nationale Umsetzung der Clean Vehicle Directive

Karlsruher Institut für Technologie (KIT):,

Öko-Institut: eMobil 2050 Szenarien zum möglichen Beitrag des elektrischen Verkehrs zum langfristigen Klimaschutz

Share this article