Drive systems of the future

The fuel cell also requires an expensive and scarce raw material: platinum. "About 20 grams for an SUV", says Ulf Groos. He heads the Fuel Cell Systems department at the Freiburg Fraunhofer Institute for Solar Energy Systems (ISE). "That is roughly twice the amount of platinum that a modern exhaust catalytic converter contains, which is then no longer necessary in fuel cell cars." But he is not only focusing on the development of fuel cells for passenger cars: "In the next five years we will see trucks, buses and trains powered by fuel cells." In Northern Germany, for example, two prototypes of a fuel cell train have been in operation since the fall of 2018. "The potential on the railways is great because about 40 percent of the rail network in Germany is not electrified," says Ulf Groos. Synthetic fuels are also suitable for the same purpose. "Diesel locomotives can be operated with them," says Thomas Koch. The KIT engine expert has been researching the "reFuels" project since the beginning of the year.

Its goal is to produce synthetic fuels with the help of renewable energies. Initially, however, Thomas Koch and his team are interested in a transitional strategy: By 2030, 15 to 20 percent of reFuels are to be added to the fuel of conventional combustion engines, thereby reducing emissions. As with batteries and fuel cells, there is also a debate on resources for synthetic fuels: "The regenerative part of biodiesel used to be obtained mainly from rape. There was a tank-or-dish debate," says Thomas Koch, alluding to the controversial question of whether agricultural land should only be used for food production or also for the production of power plants for mobility. "In the future, we will have to find alternative sources of carbon, possible are biogenic residues such as straw or the recycling of food leftovers and waste fats". The key advantage of his reFuels is that the vehicle population could be preserved. Only the liquid that is burned for propulsion changes. And: "Even if a combustion process continues to take place, we no longer have a particle problem thanks to modern filter systems," says Thomas Koch. Another argument in favor of the refuels is the existing infrastructure for refuelling. Filling stations, decentralized generation and logistics - nothing has to be changed.

However, for hydrogen or electric vehicles, the whole country will have to be covered by a new infrastructure, which will be very expensive. "A sufficient network of hydrogen filling stations would probably have to comprise 1,000 filling stations," says Ulf Groos from Fraunhofer ISE. According to the operator of the hydrogen infrastructure in Germany, 75 filling stations are currently in operation, but mainly in urban areas. By the end of the year, there should be 100. In addition, refuelling with a gaseous fuel is also very costly. "To ensure that the hydrogen flows quickly from the gas pump to the vehicle, the hydrogen is cooled to minus 40 degrees in the filling stations and compressed to 800 bar," says Ulf Groos. Although the user does not notice much of this, the procedure is technologically complex. Maximilian Fichtner is particularly critical of the efficiency, i.e. the ratio of the energy used to the usable energy: "If hydrogen is compressed for transport, a 20 percent loss in efficiency must be expected; if it is liquefied, the loss is as high as 50 percent. The costly refuelling process would result in a further considerable loss.

However, charging is also an obstacle to battery-powered mobility - despite private ade stations. "We have far too few quick-charge stations, especially for long-distance travel," he says. "For more power at the gas pumps, a medium-voltage network must be established throughout Germany that makes several thousand volts possible. Otherwise, travel will in future include half-hour charging stops." Last year, Research Centre Jülich calculated the costs of connecting both supply networks: If 20 million vehicles each had to be supplied in Germany - according to the Federal Motor Transport Authority, almost 57 million vehicles are currently licensed - the costs for an adequate infrastructure would amount to 40 billion euros for hydrogen vehicles and 51 billion euros for battery-powered ones.