Is there a scope for solar vehicles

Solar cars: the dream of a perpetual motion machine on four wheels

What do solar power and electric cars have in common? Both technologies have developed enormously in the past few years and in many cases are in no way inferior to their fossil predecessors - coal-fired electricity or internal combustion engines. There are enormous hopes for both: while photovoltaics are supposed to bring about the urgently needed energy transition, nothing less is expected of the electric car than to free private transport from CO2.

What would be more obvious than combining solar power with the electric car and packing cars full of photovoltaic modules? Gone would be the (usually unfounded) fears about insufficient range, overloading of the power grid or the search for a free charging station. The solar car, it would be a perpetual motion machine - not physically, but at least psychologically. Because refueling would be superfluous if the electricity comes from your own roof again and again, free of charge and in an environmentally friendly manner.

Since 1987, freaks from all over the world have been trying to find out what is technically possible at the World Solar Challenge. The approximately 3000 kilometers between the Australian cities of Darwin and Adelaide have to be covered with solar power from their own vehicle alone. The vehicles are - to put it mildly - not exactly suitable for everyday use: Most of them are nothing more than solar panels with wheels in which the driver is squeezed somewhere. It was not until 2013 that new categories were added that also give more practical models a chance.

So far no series production

However, solar cars are not yet in series production. Fittingly, a pioneer comes from the land of the rising sun: the Toyota Prius has also been available in a version with a solar roof since 2017, but the 180 watt photovoltaic panels only provide around five kilometers of additional range per day. During the journey they only feed the on-board electronics.

The Japanese carmaker has therefore been testing a new prototype since 2019, which should bring almost five times as much power and up to 56 free solar kilometers. For this purpose, Toyota has not only papered the roof, but also the hood and the rear with solar modules. It's not really nice to look at: the black modules look like a foreign body on the otherwise well-designed vehicles.

Goodbye, waffle optics

The Fraunhofer Institute for Solar Energy Systems (ISE), among others, is therefore not only working to make mobile solar cells as efficient as possible, but also to make them as invisible as possible. In 2019, the institute presented a car solar roof that can be coated with any color. The typical black "waffle optics" does not exist in the prototype of the ISE. Only if you look very closely can you see that a small solar power plant is working in the car roof. It should deliver up to 300 watts, which could extend the range of a mid-range car by around ten kilometers per day.

Sono Motors wants to equip not just the roof, but the entire body, including doors, with photovoltaics. The German start-up, which was close to bankruptcy at the end of 2019, wants to start production of its Sion model in 2021. The purely solar-electric range should be up to 245 kilometers per week for the small car. The electricity harvest can not only be used for driving, but also for other devices. The car should have a normal Schuko socket - for example for camping trips or construction sites. Blow-drying your hair quickly on the way to work is likely to put a strain on the battery.
Supplement instead of replacement

The Dutch start-up Lightyear even promises full-bodied "months without a shop". Five square meters of photovoltaics are in the streamlined luxury car, which should provide a range of twelve kilometers per hour under sunny conditions. Calculated over the year, that would be 20,000 kilometers, which is more than the 13,000 kilometers that an average Austrian car drives each year. The Lightyear One would come pretty close to the dream of "never recharging" - albeit at a hefty price of around 150,000 euros.

Supplement instead of replacement

In any case, technically complete autonomy is feasible, says Martin Heinrich from ISE. If you cover all of the outside areas with highly efficient solar modules, you can achieve a range of 10,000 to 15,000 kilometers per year in Central Europe using solar power alone. In winter you are of course more dependent on the charging station than in summer. In sunny California, on the other hand, there are 20,000 to 25,000 kilometers in it, Heinrich estimates.
In any case, the ISE sees so-called vehicle-integrated photovoltaics for Germany as having a technical potential of 41 gigawatts of peak output. For comparison: There are currently around 54 gigawatts of solar power installed in Germany.

But wouldn't it be easier and more efficient to first install photovoltaics on house roofs and open spaces instead of laboriously integrating them into vehicles where every gram counts and the yield is probably never optimal? Heinrich sees the vehicle solar systems primarily as a supplement to take pressure off the power grid. If electricity is transported over long distances, part of it is also lost - on the other hand, it is only a short distance from the roof to the battery.

Solar cladding could also be useful for commercial vehicles, for example as a support for refrigerated trucks. To find out how useful, the institute installed measuring systems on trucks to measure solar radiation on typical routes. A 40-ton refrigerated truck could save up to 1900 liters of diesel per year, according to ISE calculations.

It is very clear, but not entirely irrelevant, that the solar vehicle concept only works outside. If the solar roofs were to go into series production, this fact could conflict with some urban transport policies. Nobody wants to have cars on the streets in the city - not even if they generate environmentally friendly electricity. (Philip Pramer, April 29, 2021)