Solar Cars: Fuel up with Sunlight
Author: Joachim Geiger
The issue of the best fuel for greater sustainability is playing an increasingly important role in electromobility. It is true that from a physical perspective, electricity for the electric motor is simply electricity. But it is crucial that this energy is fed from renewable resources. The ideal solution would be to use solar energy, with solar cells on the roof of the car converting the sun’s energy into traction current for the engine or to charge the battery – solar energy doesn’t cost a cent and emits no CO2. Could this be the future? Just putting a few dozen powerful solar cells on the roof, and the solar car is ready? And if it works, why does every electric car not already have a photovoltaic module on its roof for extra energy?
Manufacturers like Toyota and Hyundai at least have the idea on their radar. The Japanese offer a solar roof with an output of 180 watts as an optional extra for their brand-new Toyota bZ4X. The South Koreans make a similar offer for their Ioniq 5 SUV. In both cases, the solar cells supposedly increase the electric range by five kilometers a day on sunny days. Mercedes-Benz also has its sights set on reducing energy requirements with solar cells in its VISION EQXX concept car – apparently, the current prototype achieves up to 25 kilometers of extra range per day under ideal conditions.
Scientists are already driving solar vehicles around the world
At this point, the question arises whether the use of solar cells from the accessories shelf turns an electric car into a solar vehicle. In any case, the ranges gained this way are limited. Strictly speaking, a solar car only becomes a reality when there is no more need for external charging. The fact that the technology for this approach works in principle is demonstrated by the solar wagons that race through the Australian outback on solar power alone every two years, as part of the World Solar Challenge.
A permanent fixture at this event is Bochum University, which has so far built almost a dozen solar cars. One highlight in the portfolio is the “SolarWorld Gran Turismo” – the Bochum solar car team has succeeded in driving the small sedan almost 30,000 kilometers around the world through Australia, New Zealand, the USA, France, and Luxembourg. The truth is, however, that the trips in the World Solar Challenge are all made with experimental vehicles and usually take place in ideal weather. These vehicles are a long way from being used in everyday electromobility.
Stumbling block is the modest efficiency of solar cells
So where can the journey of solar electromobility take us? It is clear that in the future, solar cars will feature customized energy systems with very high efficiency – a key parameter for the performance of a solar cell. It determines how much solar energy the cells convert into electricity. The more energy the cell converts, the better the balance in terms of resource consumption during cell production.
But the efficiency of current solar panels is still expandable, knows Andreas Richter, an engineer at DEKRA’s Electromobility Competence Center. “Cells for photovoltaic systems today usually achieve efficiencies of between 18 and 24 percent. In particular, with the comparatively small solar surface on the vehicle, only relatively little solar energy can actually be used to generate electricity.“ On the other hand, scientists have long been working on technologies that promise higher yields. Germany’s Fraunhofer Institute for Solar Energy Systems recently developed a high-efficiency solar cell that achieves nearly 50 percent efficiency under laboratory conditions. Such an energy performance would certainly spur solar mobility. But even without supercells, solar cars for everyday use are no longer science fiction.
The first solar electric cars will be on the market this year
The pacemakers for solar technology are young and ambitious companies that are rethinking the electric car in terms of sustainability, lightweight construction, and aerodynamics. The first vehicles are about to be launched – not yet true solar cars, but electric cars with a high level of integration of solar technology into the vehicle concept.
Munich-based start-up Sono Motors, for example, has developed a van in which the solar cells are fully integrated into the body. Dutch start-up Lightyear from Helmond near Eindhoven will be launching a spectacular sedan that sets new standards in terms of efficiency and range at the end of the year. Automotive company Aptera Motors from San Diego, California, on the other hand, is working on a solar vehicle that is in a league of its own in terms of design.
Profile: Solar electric mobility
Sono Motors Sion
The Munich-based start-up’s concept for the Sion comes close to the aspirations of an electric everyday car that realizes part of its propulsion with solar technology. The electric powertrain features a 54 kWh lithium iron phosphate battery that apparently works without the use of problematic materials such as cobalt, manganese, and nickel. The electric motor produces 120 kW and allows a range of around 300 kilometers. A closer look at the box-shaped body reveals that the vehicle is lavishly equipped with solar technology. According to the manufacturer, they’ve installed 248 solar cells. The flexible injection-molded panels sit in the roof, on the front hood, at the rear, and stretch along both sides of the vehicle. The cells’ output supposedly reaches between 250 and 300 watts under favorable conditions. In weather conditions such as those typical in southern Germany, this equipment should be able to generate traction current for a range of around 110 kilometers per week. In constant sunlight, 245 kilometers are possible. The Munich-based company is currently working on the Sion’s start of series production. The first vehicles are scheduled to roll off the production line at contract manufacturer Valmet in Finland in mid-2023. The company plans to produce 43,000 vehicles per year.
The Lightyear 0
After six years of development work, start-up Lightyear, which emerged from a solar car project at TU Eindhoven, presented its first electric production vehicle at the beginning of June 2022. The Lightyear 0 sets standards in terms of efficiency. The carbon fiber body and aluminum chassis together weigh just under 1,600 kilograms. With a Cd value of 0.19, the five-seater boasts a record-breaking drag coefficient. Drive is provided by efficient wheel hub motors on all wheels with a total output of 100 kW. The installed battery has a capacity of 60 kWh. Lightyear puts the WLTP range of its vehicle at 625 kilometers, and energy consumption is around 10.5 kWh per 100 kilometers at speed 110. The energy concept is rounded off by the integration of solar technology, which also harnesses the power of the sun while driving. To this end, the manufacturer has installed around 800 solar cells over an area of five square meters on the roof and hood of the five-meter-long sedan, which generate electricity for a range of around 70 kilometers on summer days with enough sunlight. The sleek coupe will initially be delivered to customers in a run of just under 1,000 units starting in November.
Solar car Aptera Sol
The futuristic-looking Aptera Sol electric car has its commitment to efficiency and range literally written all over its face. The body has a teardrop-shaped profile with an extremely low Cd value of 0.13. With materials such as carbon, Kevlar, and hemp, the three-wheeled two-seater is trimmed for lightweight construction. According to media reports, the vehicle, which weighs between 800 and 1,000 kilograms depending on the battery installed, will essentially consist of four components that can be printed with a 3D printer. The small car’s solar equipment depends on the vehicle features. In the basic configuration, solar panels on the roof shall provide up to 25 kilometers of range per day. A more complex version with up to 180 solar cells distributed over the entire body should be able to cover up to 65 kilometers a day. Several packages are also available for the electric drive – including a 100 kW motor for the front axle or a 150 kW motor for the all-wheel drive variant. The battery size depends on the desired range. The range includes batteries with capacities between 25 kWh and 100 kWh. In the most powerful version, around 1,600 kilometers should be possible in combination with the installed solar cells. The vehicle appears to be popular with customers on both sides of the Atlantic. So far, the manufacturer has received more than 22,000 advance orders for the design. Deliveries are scheduled to start at the end of the year.