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Should be the first affordable solar electric car: The Sion from Sono Motors
Photo: Sono Motors
The idea is as charming as it is obvious: solar cells in the car roof, on the front hood or on the doors produce electricity while parking and driving and make some charging stops superfluous - depending on how strong the sun is shining.
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The technology could reverse the summer parking behavior of many electric car drivers.
A shady parking lot would suddenly no longer be the ultimate when it comes to a trip to the lake.
The idea is not entirely new; the “World Solar Challenge”, a race for special solar cars, has existed since the late 1980s.
But it should get new momentum in 2021, starting with the entertainment trade fair CES.
Start-ups want to use the power of the sun
There, the German start-up Sono Motors is presenting the prototype of the Sion, with solar modules integrated into the entire body.
The car is intended to be the first solar electric car "for everyone", as Sono co-founder Laurin Hahn explained in advance.
Under ideal conditions, solar energy should bring an additional range of up to 34 kilometers per day.
Sono Motors is not alone with the idea of using the sun for more range.
The Lightyear One, an e-car from the Netherlands, which, according to the company, will come onto the market at the end of 2021, should generate up to 70 kilometers of additional range every day thanks to five square meters of solar panels in the outer skin.
But do solar cells in electric cars even make sense in view of the high energy consumption of a car?
So why does a technology that at first glance seem like a marketing gag get a new boost?
“Solar modules on the car are no gimmick,” says Martin Heinrich from the Fraunhofer Institute for Solar Energy Systems (ISE).
In the past, solar roofs on cars were just a gimmick that never paid off economically for the customer.
That has changed - today solar cells are much cheaper and more efficient, the scientist argues.
Small contribution with amazing results
"A very good solar module creates 200 watts per square meter," says Heinrich.
If you equip a car roof of around two square meters with it, you could generate two kilowatt hours a day in summer, "that's a range of almost ten kilometers".
It doesn't feel like much, Heinrich admits.
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Car in solar dress: The Lightyear One
Photo: Lightyear
The difference to the information from Sion and Lightyear is due to their concept.
The roof area of the Lightyear is significantly larger at five square meters, while the Sion has solar modules throughout the body - and both promise more output per square meter: Lightyear 215 watts, Sono Motors 200 to 220 watts.
As with saving money, small, regular contributions like Heinrich's calculated two kilowatt hours per day have a big effect.
Calculated over the course of a year, he calculates "like adding 2,000 additional kilometers."
With an average mileage of 15,000 kilometers per year, this saves ten to 15 percent charging current.
A study by Fraunhofer ISE shows how much potential there is in the roofs of popular e-cars:
A Renault Zoe with a roof area of 1.7 square meters and a module output of 200 watts per square meter could produce 366 kilowatt hours of energy in one year in Freiburg and thus generate an additional range of 2068 kilometers - provided that there is no shadow of trees or houses on it Automobile.
A Hyundai Ioniq Electric with a roof area of 2.2 square meters would even have 473 kilowatt hours and a range of 3428 kilometers.
The 2.3 square meter roof area of an Audi e-tron even enables 495 kilowatt hours per year, but the achieved range would only be 2063 kilometers because the heavy vehicle consumes a lot of energy.
According to Heinrich, a module output of 200 watts per square meter has so far been rare.
Hyundai is equipping the Sonata with such solar cells.
For the hybrid version of this model, which is not available in Europe, the Korean manufacturer - like Toyota for the Prius plug-in hybrid - offers a solar roof.
With a daily charging time of 5.8 hours, this should bring 1,300 additional kilometers per year.
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Hardly recognizable at first glance: the solar roof of the Hyundai Sonata Hybrid
Photo: Drew Phillips / Hyundai
According to Heinrich, the solar cells on such a roof cost less than 150 euros, plus electronics and integration into the vehicle.
"A selling price below 1000 euros is realistic," the scientist calculates.
At an electricity price of 30 cents per kilowatt hour, a solar roof would pay for itself after seven to eight years.
Volkswagen currently sees no benefit in solar panels
However, this period is not yet enough for some automakers to become more involved in the field.
For example, Volkswagen currently sees little point in the panels.
The combination of area and efficiency does not currently allow use to extend the range of series vehicles, said a VW spokesman.
Photovoltaics are space-consuming and cost-intensive, which limits their use as a range extender.
However, the company is constantly re-evaluating the technology and may use it in the future.
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The solar roof available for the plug-in hybrid version of the Toyota Prius increases the electric range by five kilometers per day, according to the manufacturer
Photo: Toyota
In fact, several factors make it difficult to use solar technology in cars.
Many car roofs are slightly curved, and the resulting poorer solar radiation results in losses in the single-digit percentage range, explains ISE researcher Heinrich.
20 percent loss due to shadowing
A much bigger problem, however, is shade from trees or houses.
"An office worker in Freiburg who parks in the underground car park at home but outdoors during work hours loses around 20 percent of the ideal range," admits Heinrich.
It is also difficult to actually harness the energy.
For a longer range, the energy has to be fed into the high-voltage battery in the car - but its operation itself costs energy, for example to maintain the temperature, explains Heinrich.
The low-voltage battery, which provides electricity for numerous components, is usually too small - solar energy generated is wasted.
"That's why," says Heinrich, "many manufacturers are still hesitant here."
Start-ups such as Sono Motors or Lightyear would weight the positive effects of additional range and saved costs more heavily than corporations, and they would also optimize the entire vehicle for harnessing solar energy, argues the scientist.
According to the manufacturer, the electronics of the Sion are explicitly designed for charging with solar power.
Short-distance commuters and city buses are ideal applications
However, other types of vehicles would actually be best suited for the installation of solar modules: buses and trucks - they have large, straight roofs and tower above other vehicles, so they are rarely out in the shade.
"Even with a lower module efficiency of eight percent, a truck in Central Europe with an annual mileage of 100,000 kilometers could cover 5000 to 7000 kilometers with solar power," Heinrich calculates.
The highest proportion of the energy required by photovoltaics is naturally achieved by those who drive little and park a lot.
Solar car drivers are also motivated to leave the car parked more often - ideally in the blazing sun.
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