The safe, sufficient, affordable and environmentally sound supply of energy is a major challenge – last but not least with regard to the goal pursued by German politics of achieving a high degree of climate neutrality by 2050. To be able to achieve this goal, energy consumption in the transport sector plays a decisive role. Overall, transport accounts for about one fifth of Germany's total greenhouse gas emissions with road haulage by trucks accounting for about 35 %. Heavy trucks with high mileages represent a potentially large lever for making a significant contribution to reducing greenhouse gas emissions originating from transport by modifying comparatively few vehicles. Since algae can be processed into fuels that can be used – in pure form or mixed with diesel – as diesel substitutes in trucks without a need for major modifications of the infrastructure, this could open up interesting possibilities for reducing the current dependency of truck traffic on fossil fuels.

The report prepared within the framework of the TAB monitoring called »Sustainability potentials of bioeconomy – 3^rd generation biofuels« focuses on the potential of algae-based fuels for truck traffic. Notwithstanding this focus, other fuels and their respective propulsion systems are also dealt with in order to be able to evaluate the potential role of algae-based fuels for trucks with regard to reducing greenhouse gas emissions from transport in relation to these other technology paths.

Key results

Algae biomass can be processed into biofuels in various ways. The most thoroughly investigated fuel path is the use of the oils or lipids contained in the algae, which can be processed into fuel in conventional refineries. In order to obtain the algae oils, the algae biomass must first be collected and dried. Various processes have been developed for harvesting, drying and oil extraction which are technically demanding and very energy-intensive. This means that the energy required for fuel production can exceed the energy content of the fuel obtained. Moreover, depending on the production system used, the production costs for algae biomass are estimated to be 500 to even 100,000 EUR/t, which represents a large obstacle regarding the competitiveness of algae-based biofuels. In comparison, the producer price levels for rapeseed (approx. 330 EUR/t) and wheat (approx. 170 EUR/t) are significantly lower. Generally, however, the costs for further processing algae oils into fuels are similar to those of other biofuels based on vegetable oils.

One the one hand, considering the potential of algae-based biofuels with regard to a decarbonisation of road haulage, the theoretical advantages of this technology become evident. The higher productivity per unit area compared to the production of plant-based resources as well as the possibility of producing on sites that do not compete with food production or nature conservation help to mitigate undesirable side effects of biofuels. On the other hand, it is also obvious that algae-based biofuels cannot make a contribution to climate-neutral transport in the short and medium term under the production options currently assumed to be plausible. Thus, it can be stated that a noticeable contribution to improving the GHG balance of road haulage by 2050 probably cannot be expected from algae-based biofuels. This would require scientific and technological breakthroughs and process innovations that are not yet foreseeable. If algae-based fuels are to be produced on an industrial scale and in a way that makes sense from a sustainability perspective, significant progress is needed – particularly with regard to their energy balance. For this, a more targeted selection of algae species as well as process innovations with regard to the extraction of algae oils and their further processing into fuels are possible approaches.

A comparison with other fuels shows that the main challenges consist in the production of algae biomass. From a technical point of view, however, there is still a need for specific development in fuel production, but the real bottleneck is the mass production of algae required for this purpose. In order to approach the theoretical potentials of algae technology in practice in an appropriate way, some effort and intensive research is currently being made to utilise algae biomass as comprehensively as possible in biorefineries. For this, the focus is on producing highly priced algae-based products with a high marketing potential (e. g. food supplements, cosmetics, chemical compounds). This approach – in which fuel production is a secondary aspect – could possibly reduce the cost of producing algae biomass to a marketable level.

As a second possibility, the use of waste water as a nutrient medium for algae cultivation is an interesting approach. The resulting synergies between nutrient supply and waste water treatment could be an option to reduce the costs of algae fuel production in the long term. However, there are still numerous research questions resulting from the complex and multi-link process chain that ranges from the cultivation of algae biomass to the production of algae-based products. To answer these questions, the funding of pilot plants seems to be appropriate in order to support the available model-theoretic considerations in scientific literature with real operating data.