E-fuels are synthetic, liquid fuels. They are produced from water (H2O) and carbon dioxide (CO2). The electricity needed for their production should be obtained from renewable energies (solar and wind power). Porsche is conducting intensive research into these fuels: e-fuels allow practically carbon-neutral operation of combustion engines because the CO2 emissions correspond to the amount of CO2 that was previously taken from the atmosphere for e-fuel production. This is known as a closed cycle.
E-fuels reduce CO2 emissions immediately because they can replace fossil fuels. Depending on availability, e-fuels can also be initially added to conventional fuel. Other advantages include the possibility of storage and transport using the existing infrastructure. In addition, the potential of green electricity, which is found in abundance in some regions of the world, can be stored in e-fuels and transported over long distances.
In this way, e-fuels can contribute to reducing CO2 emissions and are an important element in the drive strategy pursued by Porsche: the sports car manufacturer will offer a trio of drive systems in the medium term. Alongside the electric models, this still includes emotive, optimised combustion engines and plug-in hybrids with zero local emissions. E-fuels substantially reduce the CO2 footprint of combustion engines and plug-in hybrids.
Raw materials: water and carbon dioxide
E-fuels require only the two raw materials, water and carbon dioxide, for their production. The hydrogen that is needed is extracted from water by electrolysis. For this purpose, a direct current is passed through water, whereby hydrogen is split off and collected at the negative pole (cathode). The energy efficiency of this process is around 70 per cent. In order to protect drinking water supplies, sustainable concepts provide for the construction of production installations close to the sea and the use of desalinated seawater where possible. Two litres of water are required per litre of re-fuel within the process chain.
The carbon dioxide is extracted straight from the air using the Direct Air Capture process. Large fans blow ambient air through filters in which the carbon dioxide contained in the atmosphere is deposited. Depending on the process, the filters are treated with different substances from which the CO2 is separated during further processing. Such facilities are already in operation, for example in Canada and in Switzerland. The reduction and recovery of CO2 from the ambient air can become a key technology for climate protection in the future. It is therefore crucial to further industrialise these technologies and make them economically viable.
Green electricity in windy and sunny regions for local production of e-fuels
The economically and ecologically optimum regions for production of electricity from wind and solar energy are located mainly close to the coast where there is plenty of wind or intensive solar radiation. Such regions can be found, for example, in Morocco, the United Arab Emirates (UAE) or South Africa, in Chile in South America or in Australia. It is currently estimated that electricity can be produced there with a three to four times higher degree of utilisation of the power generation plants compared to Central Europe. The transmission of this energy in electric form over long distances to consumers would result in great losses while being expensive. It therefore makes sense to produce e-fuels locally at energy-rich sites with renewable power generation set up specifically for this purpose. For this reason, a wind farm or a solar park is integrated directly in the chemical plant to produce e-fuels. As expensive and complex transport via cables is therefore not necessary, electricity cost benefits that far exceed a factor of four can be achieved. In addition, the advantages of liquid fuels, such as storage and transport capability, can be used to the full. The whole world can thus be supplied with CO2-neutral energy sources by pipeline or by ship. The situation is different in Central Europe. Here, electricity produced from wind power or photovoltaic systems can be used more efficiently if it remains as electricity. Distribution via power lines, storage in batteries and use in electric vehicles is much more efficient than via e-fuels. Depending on the geographical distance between energy production and demand, different approaches are therefore possible.
Via e-methanol to a low-emission fuel suitable for universal use
The manufacturing process of e-fuels starts with the production of e-methanol; from hydrogen and CO2. Various processes are used for this, including some that utilise a catalyst. This e-methanol can be used directly in many industrial sectors worldwide as a green substitute for methanol made from fossil crude oil or natural gas. In only one synthesis step, known as the methanol-to-gasoline (MtG) process, e-methanol can be further processed into e-fuel (e-petrol). Through further refinement, this fuel achieves an octane rating comparable to that of super-unleaded petrol and can then be used in all conventional petrol engines.
If e-fuels are produced using only renewable energy, emissions of fossil CO2 from pure combustion vehicles and plug-in hybrids in operation can be substantially reduced. This is something that applies to the entire vehicle pool. Depending on initial availability, it can be mixed with conventional fuel, and later used in pure e-fuel form. In addition, the existing infrastructure for storage and distribution of fuel can still be used. Manufacturing e-fuels synthetically also makes it possible to develop a fuel with properties that reduce emissions and increase efficiency. For example, e-fuels produce less pollutant and fine dust emissions than petroleum-based fuels as they contain no contamination and therefore result in cleaner combustion. This means that the raw emissions – of particles, for example – from many existing engines can be significantly reduced simply by using e-fuels.