Emmerthal/Nuremberg: 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, consisting of the coordinating Institute for Solar Energy Research Hamelin (ISFH), the companies Vitesco Technologies, a2-solar and Meyer Burger, and the research institutions Forschungszentrum Jülich, the Helmholtz-Zentrum Berlin and the MBE Institute of Leibniz University Hannover, has now in close cooperation with Continental Engineering Services put a prototype of a light commercial vehicle on the road that is equipped with highly efficient vehicle integrated photovoltaics (VIPV). What makes it special is that the energy converted from sunlight can be fed into the high-voltage vehicle electrical system and thus used directly to extend the vehicle’s range.
Prof. Robby Peibst
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Driving on Sunshine – VIPV prototype on the road in the Weser uplands near Hamelin
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 energy to the electric powertrain. In order for the energy generated by VIPV to be fed into the large traction battery and thus contribute to range extension, 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 from a2-solar developed for automotive use. These are based on highly efficient silicon heterojunction solar cells from Meyer Burger, which were interconnected at 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 the lower temperature coefficient. Regulation to the point with maximum power is provided by electronics from Vitesco Technologies, which also developed the DC/DC converter from 12 V to 400 V as a key innovation. Continental Engineering Services handled 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 colored. Their nominal total output is 2180 Wp. At the same time, the energy requirement for driving is similar to that of passenger cars at around 19 kWh / 100 km.
“We expect an annual range extension of about 5200 km for driving 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, project coordinator of the Street project. “Our results will demonstrate the attractiveness of vehicle-integrated photovoltaics first for such light commercial vehicles. But beyond that, they will also provide important insights for transferring VIPV to other vehicle classes.”
The demonstrator vehicle has road approval in accordance with the German StVZO and has completed initial tests. It is equipped with numerous sensors to enable the energy flows to be tracked precisely. Until the end of the project, all components will be put through their paces in test drives at different times of the day and year and in different weather conditions. The vehicle will therefore be seen frequently in the near future on the roads of the Weserbergland region, the Hannover region and in the state capital itself. The license 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 “Street” research project is funded by the German Federal Ministry for Economic Affairs and Energy (grant number 01183157). The results of the project also flow into the international working group “Task 17 – PV for Transport” in the Photovoltaic Power Systems Program of the International Energy Agency (IEA). There, experts from around the world exchange ideas on how to use photovoltaics to reduce CO2 emissions in the transportation sector.
Vehicle-integrated photovoltaics (VIPV) was already developed in the 1960s. For many years, however, 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 passenger car models with solar roofs or PV modules integrated on truck refrigerated cases. In these cases, the PV-converted energy is used for “auxiliary functions” such as air conditioning or refrigeration. These applications run on low-voltage levels of typically 12 V; the systems available on the market are not suitable for charging the high-voltage traction battery of an electric vehicle.
The ISFH currently has 155 employees in two departments developing innovative technologies for 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, conducts research on the integration of PV into innovative systems. The ISFH is a member of the German Renewable Energy Research Association (FVEE) and the Zuse-Gemeinschaft and an associated research institute of the Leibniz Universität Hannover.