An electric vehicle (almost) without dependence on charging stations — that sounds like dreams of the future, but the first steps towards it are being taken right now. The consortium of the “Street” research project, in close cooperation with Continental Engineering Services, has now put a prototype of a light commercial vehicle on the road that is equipped with highly efficient vehicle integrated photovoltaics (VIPV). What’s special about it is that the energy converted from sunlight can be fed into the high-voltage vehicle electrical system and thus used directly to extend the range.
Photovoltaic modules convert sunlight into electrical energy. Modern battery-electric vehicles always have two power storage units on board: a small 12 V battery that can supply electrical consumers, lights and power steering, and a large traction battery that operates at a higher voltage of 400 V and supplies the electric drive with energy. In order for the energy generated by VIPV to be fed into the large traction battery and thus contribute to extending the range, it is necessary to couple the PV modules to the high-voltage vehicle electrical system. This is technically very demanding, as it requires a conversion from 12 V to 400 V and is linked to many safety aspects. It is precisely this challenge that the Street Consortium has now successfully addressed. The basis for this was the combination of different competences: The conversion of solar energy into electrical energy takes place in PV modules developed by a2-solar for automotive use. These are based on highly efficient silicon heterojunction solar cells from Meyer Burger, which were interconnected at the ISFH using Smartwire interconnection technology. This technology, developed in Europe, not only enables maximum cell and module efficiencies, but also maximum module yields due to a lower temperature coefficient. Control to the point with maximum power is provided by electronics from Vitesco Technologies, which has also developed the DC/DC converter from 12 V to 400 V as a central innovation. Continental Engineering Services was responsible for the integration of all components and their integration into the vehicle electrical system.
The “WORK L” light commercial vehicle from the StreetScooter company used as a demonstrator offers ideal conditions for VIPV: a total area of 15 m² is available for the 10 PV modules. In contrast to integration on passenger cars, the modules did not have to be curved or coloured. Their nominal total output is 2180 Wp. At the same time, the energy requirement for driving, at approx. 19 kWh / 100 km, is similarly low to that of passenger cars.
“We expect an annual range extension of about 5200 km for trips in Lower Saxony, and significantly more in more southern regions. This would save more than one in four grid-based charging stops,” says Prof. Robby Peibst, coordinator of the Street project. “Our results will show the attractiveness of vehicle-integrated photovoltaics first for such light commercial vehicles. In addition, however, they also provide important insights into the transfer of VIPV to other vehicle classes.”
The demonstrator vehicle has road approval in accordance with the German Road Traffic Licensing Regulations (StVZO) and has completed initial tests. It is equipped with numerous sensors to accurately track energy flows. By the end of the project, all components will have been put through their paces in test drives at different times of the day and year and under different weather conditions. In the near future, the vehicle will therefore often be seen on the roads of the Weserbergland, the Hannover region and in the state capital itself. The number plate “HM-PV-30E” refers to the potential for solar energy in Lower Saxony: studies by the ISFH show that in a cost-optimized sustainable energy system in Lower Saxony, up to 30 % of the final energy demand can be provided by PV.
The research project “Street” is funded by the German Federal Ministry for Economic Affairs and Energy (funding code 01183157). The results of the project also flow into the international working group “Task 17 — PV for Transport” in the Photovoltaic Power Systems Programme of the International Energy Agency (IEA). There, experts from all over the world exchange ideas on how to reduce CO2 emissions in the transport sector by means of photovoltaics.
Vehicle integrated photovoltaics (VIPV) was already conceived in the sixties. However, for many years the main application was in the niche of competitions of special streamlined lightweight solar vehicles. For some years now, various manufacturers have also been offering car models with solar roofs or PV modules integrated on truck refrigerator boxes. In this case, the PV-converted energy is used for “additional functions” such as air conditioning or cooling. These applications run on a low voltage level of typically 12 V, the systems available on the market are not suitable for charging the high voltage traction battery of an electric vehicle.
With currently 155 employees in two departments, the ISFH develops innovative technologies for the use of solar energy. The photovoltaics department develops new industry-oriented solar cell technologies, highly efficient photovoltaic modules that can be industrialized and, as in this case, researches the integration of PV into innovative systems. The ISFH is a member of the Forschungsverbund Erneuerbare Energien (FVEE) and the Zuse-Gemeinschaft as well as an affiliated institute of the Leibniz Universität Hannover.