Here, the challenges for tomorrow's mobility are identified and concrete solutions are jointly developed. The results contribute to a sustainable transport system in Germany and Europe that benefits society and the economy in equal measure. In the Energy and Transport research programmes, DLR is investigating the optimisation of energy flows, especially between the energy grid and vehicles with alternative drive concepts.
The skilful networking of the energy supply and mobility sectors is important for the success of the energy and transport transition. Vehicles powered by batteries and fuel cells can feed electricity and heat into stationary distribution grids when required or be used as a mobile power source or heating system, for example on campsites or at events. In emergencies, after earthquakes or floods, a local power supply could also be generated in this way. The interactive DLR model shows how sector coupling can work in everyday life using the state of charge of a battery-powered car: the charging stations at home recharge the vehicle batteries or feed electricity back into the grid as required. An intelligent charging management system controls the individual charging currents. This ensures that the power grid is not overloaded. Fast charging is an important aspect on the road: for example, along motorways when electric vehicles are travelling long distances. In cities, a large number of electric vehicles can be charged in a short time at fast-charging stations with high charging capacities. Mobile charging stations allow electric vehicles to be charged at locations without their own power connection. This allows the charging infrastructure for battery electric vehicles to be improved across the board. Rural areas in particular can benefit from this.
Driving and heating with hydrogen cars
By coupling a fuel cell vehicle with a building energy system/grid, the utilisation time of the fuel cell system can be increased. The vehicle is no longer just used as a means of transport, but also as a supplier of electrical and thermal energy, which increases the added value of the investment. In order to feed electricity and/or heat from the vehicle into a building, the interfaces for this must be available on both sides and both sides must also communicate with each other. For example, the vehicle must tell the building how much energy it can supply so that it can make the next journey without any problems. The car park and the building must be in close proximity for the energy to be fed back. For example, fuel cell vehicles are charged with hydrogen and can feed back electrical energy in the event of grid bottlenecks.
Thermoelectric sector coupling
Thermoelectric sector coupling describes a new, CO2-neutral and economical technology that has the potential to ensure a cross-sector energy supply in winter. The technology is based on the integration of thermoelectric generators (TEGs) in heat generators such as pellet boilers: The heat generated during pellet combustion is channelled through the TEGs into the heating water and the TEGs convert part of the heat into electricity through a solid-state effect. The simultaneous utilisation of heat and electricity maintains the high overall efficiency of the system and, in particular, the utilisation of the calorific value.
In the current "PellTEG" project, the high economic efficiency of the technology is being demonstrated in typical detached houses and apartment blocks, thus enabling development close to the market. The target values set for this are 600 W nominal electrical output and thus 1000 kWh/a electrical energy supply per year. In addition, a very short amortisation period should be achieved and no additional maintenance should be necessary. The system can be integrated into various heat generators and thus generate electricity for electromobility at home in a cost-effective and largely climate-neutral way.
Inductive charging
Inductive charging makes it possible to park the electric car on the charging coil and the battery then charges itself. This makes the charging process much more convenient and practical. Users no longer have to carry cables and plugs with them and connect them manually. The tripping hazard caused by the cable is eliminated, especially at public charging stations, and dirty or damaged cables will no longer be an issue in future. Inductive charging can therefore help to increase consumer acceptance of alternative battery-based drive concepts. The technology is also interesting in the context of automated driving: if the driver becomes a passenger and uses a service such as a taxi, they do not want to worry about how and where a vehicle is charged. The automated vehicle finds the charging coil by itself and parks itself automatically on the coil, as is already technically possible today.
Intelligent charging management
The eLISA-BW project (intelligent control and connection of electric charging infrastructure in Baden-Württemberg) was funded as part of the INPUT (intelligent network connection of car parks and underground car parks) funding call. The existing charging infrastructure in the Waldhornstraße underground car park of Parkraumgesellschaft Baden-Württemberg was expanded by eight charging points and an intelligent charging management system was implemented. This charging management system provides an interface to the booking system of the Karlsruhe regional council and to the backend of the charging points. The current load status is recognised via measurement technology on the building's main and sub-distribution boards, transmitted to the system and the available charging capacity for the vehicles is calculated. The intelligent algorithm developed distributes the available power to the vehicles according to demand so that they are as fully charged as possible at the time of use. This means that the almost fully electrified vehicle fleet of the Karlsruhe Regional Council (RPK), which largely consists of plug-in hybrid vehicles (PHEV) and battery electric vehicles (BEV), can be charged as required in future without having to invest in new grid infrastructure. An analysis of the journey data also revealed that the majority of journeys would be suitable for battery electric vehicles, although PHEVs are also used. The results of the project were published in a guide, among other things:
Fast charging
Range and charging capacity are key factors in determining the long-distance capability of an electric vehicle. Users who are used to the combustion engine are only used to making short refuelling stops. A further reduction in the current charging times of 20 to 30 minutes is therefore desirable.
Reducing the charging time is the key to success, especially with a limited number of charging points and high charging volumes. DC charging stations currently provide charging capacities of up to 350 kW - and the trend is rising. Both the grid infrastructure and the battery systems in the electric vehicles are heavily stressed by fast charging. DLR is therefore working on the development of powerful, efficient and compact temperature control systems for the rapid charging of electric vehicles.
Mobile charging stations
Until now, electric cars have only been able to charge their batteries at fixed charging stations. The mobile charging station developed at the German Aerospace Centre (DLR) provides more flexibility. The electricity is supplied by a fuel cell system with a hydrogen tank. It is so compact that it fits on a car trailer. In the L3-BW research project ("Charging, up and down the country for Baden-Württemberg"), the DLR Institute of Vehicle Concepts and the company Vector are building a functional demonstrator. During a test phase, the DLR researchers are trialling the charging trailer in real-life use.
Mobile charging stations can be used to improve the charging infrastructure for battery-powered electric vehicles across the board. Electric cars, e-bikes and even cargo bikes can be charged at the charging trailers. Rural areas in particular can benefit from this. "Mobile charging stations can be used in car parks for hikers and seasonal parking spaces, for example, where a powerful grid connection is not possible or too expensive. The charging trailers can also be used on campsites, in ski resorts or at large events," explains Markus Kordel, head of the L3-BW project at the DLR Institute of Vehicle Concepts in Stuttgart.
H2 expansion machine
In the future, heavy construction site vehicles will be able to handle longer jobs without refuelling using hydrogen. This will be made possible by a hydrogen expansion machine. This machine takes the high pressure of the hydrogen from the storage tank and reduces it for the fuel cell. The energy released during this expansion is converted into electricity by a generator on board the vehicle. The electricity can in turn be used in an electric motor to drive the hydrogen vehicle. Existing systems use pressure reducers to reduce the hydrogen pressure. However, these do not allow the energy from the expansion process to be recovered. The use of an H2 expansion engine increases the efficiency, operating time and maximum system performance of the vehicles. Construction site vehicles are particularly suitable for the use of the expansion machine due to their high power requirements.
DLR has honoured the "H2 expansion machine" innovation idea for the mobility of the future with the DLR.IDEA AWARD, which promotes application-oriented ideas and creative solutions for technology transfer.