It sounds like a dream of the future: vehicles that can produce their own green energy. And the visual impression of cars with the dark, reflective photovoltaic surfaces on their roofs also make them seem like something out of a science fiction film. But the technology is in fact a reality and is already being used in practice. So does this mean that car drivers will soon no longer have to go to a charging station? ‘Unfortunately, we haven’t quite got that far yet and that is simply not what today's vehicle-integrated photovoltaics in cars are designed to do,’ says Dr Martin Heinrich, Coordinator of PV mobility at the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg. However, when it comes to extending driving performance or supplying the air conditioning or the entertainment system with power, vehicle-integrated photovoltaics (VIPV) can make a significant contribution. The vehicle industry is slowly realising that VIPV technology can bring huge benefits, particularly given political stipulations in regard to the energy and drive revolution,’ says Heinrich.
Vehicle-integrated solar energy generation is actually nothing new. Even twenty years ago there were commercial cars with a sliding solar sunroof that could power the air conditioning, such as the Fisker Karma, plus Audi and Toyota models. However, mass-produced versions of the technology have not yet taken off. ‘It used to be simply too expensive,’ explains Heinrich, adding: ‘Over the past few years, however, the photovoltaic industry has taken a huge step forward in reducing costs because of the high levels of demand and mass production for ground-mounted solar power plants and properties.’ One watt generated by solar power would have cost around ten euros 20 years ago, he says, but now costs just 30 cents
Solar technology is developing at a rapid pace
Robert Händel, CEO of the company OPES Solutions, which is based in Berlin and specialises in vehicle-integrated photovoltaics, confirms the rapid improvement in technology. OPES Solutions has just been awarded the Sustainability Award in Automotive 2022 for its flexible and robust photovoltaic modules for vehicles (SOLFLEX). ‘Solar cell technology is developing incredibly quickly. With the SOLFLEX, we are already achieving an efficiency of 22 per cent, and more technological development is likely to increase this value still further in future,’ says Händel. Efficiency refers to the ratio of theoretically available energy and the amount that can actually be used as electricity in the end. By way of comparison: a light bulb has an efficiency of 5 per cent, a modern diesel engine 45 per cent. The major difference between photovoltaics and fossil fuels is that the sun's clean energy is available almost free of charge from the sun and does not have to be generated by combustion first.
The ever increasing efficiency and falling costs mean that photovoltaic plants on house roofs are now almost commonplace – but are such plants a sensible option in the vehicle segment? ‘With commercial vehicles such as lorries or buses, there is a lot of roof space available, which is ideal for large solar panels and they could in principle generate as much as electricity as a solar plant on a family home,’ says Fraunhofer expert Heinrich. Furthermore, aesthetics do not play as important a role in commercial vehicles as they do in cars. With refrigerated trucks, for example, the energy generated can be used to power the cooling system, regardless of whether the vehicle itself is driven by electricity or fossil fuels. ‘However, the full potential of the technology will only really be seen in electric vehicles as the large volumes of energy generated will be stored in powerful high-voltage batteries and used to run the engine.’
Pilot project with 18-tonner
Last year, Fraunhofer ISE undertook a pilot project in collaboration with specialist companies, taking an electric 18t lorry equipped with a powerful photovoltaic system on the roof that is now out on the road in the Freiburg region for the electrical wholesaler Alexander Bürkle GmbH. ‘The 3.5 kilowatt system with integrated high-voltage PV system and feed-in to the 800 volt traction battery generates up to ten per cent of the vehicle's entire energy requirements,’ says Heinrich. As a safety precaution, a disconnection device was especially developed for use in road traffic, which automatically cuts the power connection of the PV modules in milliseconds in the event of an accident, leaving the vehicle with only a harmless low voltage current.
The PV modules themselves must also possess different qualities than those used on house roofs, explains OPES Solutions CEO Händel. ‘Normal PV modules cannot withstand vibrations particularly well, and this is a huge factor when it comes to vehicles. Robustness, pliability and a low weight are also extremely important. Our SOLFLEX module, developed together with the Fraunhofer Centre for Silicon Photovoltaics, therefore uses scratch-proof plastic and is the first to combine extreme resistance to environmental influences and damage with a special diode technology. This makes it ideal for use in the automotive market,’ he explains. The special diode technology is associated with a natural enemy of photovoltaics: shade. With normal PV modules, solar cells are connected in series. This means that if one is in the shade, the performance of all the others is reduced.
Innovation pays off
On house roofs, this is not such an issue as the whole solar panel is usually either in the sun or the shade. ‘However, vehicles often sit in the shade of trees or buildings, which is why the SOLFLEX module is designed to ensure that only the affected cells are impacted,’ says Händel. Innovation like this pays off: OPES Solutions is commercially successful and has been able to capture a high market share in many areas, such as in the motorhome segment, where the manufacturer Westfalia integrates them directly into the roof, and also the solar-powered cargo bike segment. In Asia, OPES Solutions is the market leader in small solar modules in Sharebikes.
With commercial vehicles or cargo bikes, the mobility PV experts Händel and Heinrich think that, at today's electricity prices, the additional costs incurred on vehicle-integrated photovoltaics would pay for themselves in just a few years. The situation in the car segment, however, is unfortunately rather different as VIPV is still very much in the shadows. A solar roof is an option on very few models. The best-known one is the Hyundai's electric car, the IONIQ 5, where a 205 watt solar roof is available for a surcharge of just 1300 euros. According to the manufacturer, this can – provided there is an average of five hours of sun a day directly on the roof – provide to up to 2000 kilometres of additional range per year generated by the vehicle itself. However, at current electricity prices, the solar roof will pay for itself only after ten years.
Huge potential for cars too
Despite this, the VIPV experts are optimistic that the technology will also become ever more important in the car segment in the near future. ‘Up to now, electric engines in commercial cars have not been optimised for efficiency. Instead of the more than 18 kilowatt hours at 100 kilometres or more that is currently the norm, optimisation could bring consumption down to the one-figure kilowatt range,’ says Heinrich. Händel thinks it possible that even small cars will also be able to avail themselves of more powerful systems thanks to further improvements in PV modules and the utilisation of larger areas: ‘Alongside the roof, the bonnet is well suited as a solar surface. At some point, solar cells will be integrated directly into the body of the vehicle. These methods will considerably increase the performance of PV systems on small cars.’
There is actually a great deal of activity in the car segment at the moment. The Dutch manufacturer Lightyear, for example, is building the ‘Lightyear 0’, a futuristic long-range electric car (1000-plus kilometres) that is aerodynamically optimised for efficiency and uses a large solar roof plus a solar bonnet to generate solar electricity. According to the manufacturer, the ‘Lightyear 0’ can achieve a 70-kilometre range with its vehicle-integrated photovoltaics. However, at a price of around 250,000 euros, the model is not suitable for the mass market. The recently launched model ‘Sion’ by the Munich company Sono Motors is a different matter. This novel but practical electric car is almost completely covered in solar cells and for short trips, it can be operated almost solely with self-generated solar energy (an average of a 112 up to 245 kilometre range per week with vehicle-generated solar energy) and is affordable for average earners at a price of just 30,000 euros. However, it will only be evident whether this revolutionary-sounding vehicle can keep its promises once the planned production has started in 2023. In the motorhome sector, too, this technology could be used much more often in future than it is now, as the experimental test vehicle ‘Stella Vita’ made by the Technical University of Eindhoven shows. This futuristic electric vehicle with a generous 17 square metres for solar power generation can in principle cover its entire energy requirements itself, including the electric engine, refrigerator and induction hob.
The future of VIPV is thus very promising, and PV experts Heinrich and Händel also very much believe this to be the case. If you only drive short distances under 50 kilometres, you could cover your own energy requirements fully in the spring and summer in Germany – and even all year round in regions that have more sunshine. Only with longer trips of several hundred kilometres would you still need to visit a charging station. ‘The aim of VIPV must be that we only visit the charging station an average of once a month instead of ten times a month. This would be an important contribution to the energy revolution,’ says OPES Solutions CEO Händel. Fraunhofer expert Heinrich adds: ‘The potential of the technology is huge and has not yet been fully exploited. However in order to do so, we need the right signals from politicians and industry.’
‘Our vision is to create a world without fossil fuels by integrating solar cells into all vehicles. We're convinced that today, freedom from energy suppliers, functionality and the consistent reduction in emissions will play a much greater role than automotive status symbols. For us, one thing is clear: the traditional combustion engine is already a thing of the past, while classic electric cars are the present and the future is solar electric cars (SEV). The “Sion” is a family-friendly, affordable electric car that has over 400 integrated solar cells, which provide an additional range of an average of 112 kilometres per week. The “Sion” is expected to be on the road by the second half of 2023. Until then, we and our partners will show just how versatile our solar technology can be: we are already saving CO2 emissions on commercial vehicles and public transport, for example on Munich transport company buses.’
‘“Stella Vita” generates energy via solar cells on its roof and uses this energy for driving and living purposes. The energy is used for the journey and daily requirements such as cooking, showering and watching TV. With “Stella Vita” you are completely self-sufficient and do not have to rely on a charging infrastructure. It is inspiring today’s caravan market to think differently about vehicle construction and use lightweight materials, and it also shows that it is possible to drive even a larger vehicle using solar energy.’
‚Lightyear is the Dutch high-tech company developing the world's first solar car, Lightyear 0. With production slated for this fall, our timing couldn't be more suitable as the auto industry is currently transitioning to more sustainable forms of fuel and mobility. The more electric mobility continues to grow at a global scale, the higher the demand is for charging infrastructure, batteries, and rare earth materials. Solar electric vehicles (SEV) are a viable solution to reduce dependency on infrastructure because they are intrinsically highly efficient. In Europe, we have established the ASOM (Alliance for Solar Mobility) to represent relevant industry players in the solar mobility value chain. Today, Europe is outpacing the US and China in developing solar mobility, effectively allowing us to become a global leader in this swiftly rising industry. Lightyear launched its production-intent vehicle, Lightyear 0, in June of this year, and the first ones will be on the roads by the end of the year. Vehicles like Lightyear 0, and upcoming Lightyear models, optimize the necessary high energy efficiency of an electric vehicle with on-vehicle solar generation. This translates to clear values for Lightyear customers: more range, less time spent charging, and an added 6,000 to 11,000 kilometers per year of 'solar kilometers.'
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