With solar power - From student project to competition for Tesla?

Electric cars are no longer anything unusual, and two start-ups have dusted off a long-forgotten idea: vehicles powered by the sun.

The future of driving is electric. So why not build a car that uses its exterior surface to fill up on free energy? The five-seater Lightyear One does just that, generating its own electricity to travel from A to B. Even on gray days, the energy flows. To this end, all possible surfaces are covered with photovoltaic panels: the roof, the hood and the trunk. The surface totals five square meters and is enclosed in safety glass, similar to the familiar panels on domestic rooftops. Former students from Eindhoven started their own business, and after spending two years on development they have now unveiled their first prototype. The Dutch engineers have plenty of practical experience. The core team has won the World Solar Challenge three times, in which students from all over the world compete in experimental vehicles that are powered solely by the sun. The participating solar cars have to cover a route of about 3,000 kilometers in Australia. That inspires investor confidence. 

The most aerodynamic series vehicle in the world

The road trip can be completed without a charging infrastructure. Yet what technology is needed? According to the developers, the solar car is one to three times more energy-efficient than current electric cars such as a Tesla or an Audi e-tron. The makers say that depending on the size of the battery, the vehicle can travel up to 725 kilometers on a full charge, and on ideal sunny days the solar cells should be able to extend the range by twelve kilometers every hour – so the total range would be 200 kilometers more than the current Model S. Over a whole year Lightyear promises to produce electricity equivalent to 20,000 kilometers. Its standard consumption should be as little as 8.3 kWh over 100 kilometers. The chassis, drive train and aerodynamics have been designed specifically with this in mind. Tried-and-tested solutions such as wheel covers and side cameras instead of exterior mirrors are used to reduce the drag coefficient (Cd), which is given as below 0.20, making the car the most aerodynamic series vehicle in the world. By comparison, the Porsche Taycan and the current Mercedes-Benz CLA start on 0.22.


In addition, the car boasts lightweight components made of carbon fiber, and four-wheel drive with four hub motors. This means there is a small electric motor in each wheel. If the sun is not shining and the battery is about to give up, Lightyear One can simply be connected to a domestic power outlet or recharged by a charging pillar or fast charging system. And when parked, Lightyear One becomes a power plant. After all, a private car remains unused on average for around 22 to 23 hours a day. The principle is Vehicle-to-Grid – V2G for short. The car either feeds stored energy back into the local grid, or else supplies energy directly to the home. In 2021 construction will commence of an initial series of 1,000 Lightyear One per year. However, the price tag is a problem… at well over 100,000 euros. Yet in the long term Lightyear’s makers want to develop solar electric cars for the mass market.

Sion prototype at Trollhättan – Sono Motors GmbH © 2020

The German competitor

Lightyear’s somewhat more compact competitor is the Sion from Sono Motors. The Munich start-up gathered its seed money together via community-funding platforms in order to build the compact van. After five years of development, the prototype is ready to go. The exterior is completely covered by 248 solar cells that deliver up to 1.2 kilowatts. The production process adapts the solar modules to the exact shape of the vehicle. They enable the car to produce its own electrical energy. In fine weather it can generate enough power for an additional 34 kilometers in one day, or up to 5,800 kilometers over a whole year. Unlike conventional solar modules, these cells have a polymer coating instead of being embedded in glass. This makes the system lighter than other similar approaches to automotive solar integration.

The founders team: Jona Christians, Navina Pernsteiner, Laurin Hahn – Sono Motors GmbH © 2020

The electric car has a 35 kWh battery supplying enough energy for a range of 255 kilometers and is driven by a 120 kW electric motor on the front axle. Its consumption is 14 kWh over 100 kilometers. Series production is scheduled to include an integrated electric axle drive from Vitesco Technologies. “Fully integrated” means that the new drivetrain combines the electric motor, power electronics and reduction gearing inside a single housing. The intelligent combination of components renders many cable connections and connectors, for instance, unnecessary. The technology was developed in a process of continuous dialog with a community that came up with the ideas and wishes, such as bidirectional charging, which enables the Sion to store energy and deliver up to 11 kW for use by other electric cars or appliances. The first generation of the Sion is expected to be built in the Swedish town of Trollhättan. The plant used to house the production lines of the Swedish car maker Saab.

NEVS plant at Trollhättan – Sono Motors GmbH © 2020

A long way from series production

The idea of a solar-powered car is not new. In the past there have been many attempts by companies and inventors. The first solar-powered car was developed by the US engineer Charles Alexander Escoffery in 1958. He installed over 10,000 solar cells with an output of 200 Watts on the roof of an old Baker electric car. After charging for ten hours, the car was able to operate for around 60 minutes with a top speed of 32 km/h. In 1991 Mercedes-presented its futuristic F 100 concept car with solar cells on the roof. Eleven years later the Maybach 62 was sporting a panoramic roof with solar cells, which generated electricity for the air-conditioning when parked. VW’s (now discontinued) Phaeton flagship also had a solar sliding roof. In 2014, Mercedes-Benz presented the G-Code design study, whose paintwork functioned like a gigantic solar cell. And if the sun happens to be hidden, the paint can be charged up electrostatically by the airstream while the vehicle is in motion, thus supplying energy for producing hydrogen on board. But this car, too, never made it past the prototype.

Mercedes-Benz’ F 100 concept car from 1991 with solar cells

The F 100 concept car from Mercedes-Benz from 1991 with solar cells

In excellent company

The direct competitor Toyota has made more progress. Three years ago the Japanese launched the Prius Plug-in Solar onto the roads as a series vehicle with solar modules. However, the energy they generate is only sufficient to extend the range by six kilometers – and the technology comes as a special edition with a hefty price tag. Previously, the photovoltaic cells had only been able to top the battery up when the car was parked. When it is in motion, the 12-Volt battery on the solar roof relieves the on-board system. Last year Toyota’s engineers unveiled a demo vehicle based on the Prius, but covered (like the Lightyear One) from the hood to the trunk with solar cells that also charge the batteries while the car is being driven. The efficiency of the triple-junction solar cell module is reported to reach 34 percent. In contrast, modules for home rooftop units achieve an efficiency of 20 to 25 percent, and Sono Motors’ technology comes in at 24 percent. This enables the prototype to travel 56 kilometers daily on its own solar power. The two newcomers cannot match that.

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