I always try to park in the shade on a sunny day so the inside of my car won’t get so hot.

If solar cars become practical, I’ll want to park in the sunniest place I can find.

When will electric cars with solar panels on the roof be available?

Two very different ideas are currently under development. Toyota is putting solar panels on its Prius hybrid. Other established car companies have a similar concept in development. Tesla likewise wants to offer a solar option.

On the other hand, a team of Dutch students has designed an entirely new solar car that generates more energy than it uses. It has no gas motor. And the only reason to plug it in is to use the car to power something in the house or contribute excess electricity to the grid.

Solar hybrid cars

In 2010, when Toyota launched the Prius, it included the option of a rooftop solar panel to operate the air conditioner.

The 2017 Prius Prime has a larger solar panel that can charge the battery pack while the car is parked.

It enables the car to operate about 10% longer in electric-only driving.

The Prius Prime solar option operates on an advanced system from Panasonic. The earliest rooftop solar cells only provided tens of watts. Panasonic’s latest system, with three-dimensional curved glass, puts out 180 watts.

It can add about four miles of range to the Prius in electric mode on a sunny day. That figure represents a substantial fraction of many people’s daily commute. A fully charged battery has a range of about 25 miles before the driver has to use the gasoline engine.

So far the curved glass doesn’t meet US rollover standards. The Tesla Model S, on the other hand, has an all-glass roof that earns a five-star rating in rollover tests. Panasonic contributed expertise to Tesla’s Gigafactory. Toyota can probably learn enough from Tesla’s glass roof to improve its solar panels.

Tesla and  Ford also plan to offer electric cars with solar  panels on the roof.

A new company, Sono Motors, has introduced a solar-assisted plug-in electric car that costs about $18,800—without the battery.

Owners can either rent a battery pack from Sono or buy one for an extra $4,800. The Sono costs much less than such established brands as the Tesla, Prius, or Chevy Volt, but it has a smaller battery and therefore shorter range.

These companies essentially put solar panels on the roof of more conventional cars. They are solar-assisted electric vehicles or solar-assisted hybrids. They don’t qualify as solar cars.

The World Solar Challenge

In 1982, Hans Tholstrup and Larry Perkins had a dream of a car that could run only on sunlight. They built a solar car they called Quiet Achiever and drove it across Australia. In order to encourage further research into solar cars, they inaugurated the World Solar Challenge.

It celebrates its 30th anniversary this year. Every two years since 1987, teams of students have accepted the challenge of building a solar-powered car and driving it from Darwin to Adelaide in Australia. In other words, the car must travel 3,000 km through the Australian Outback using only solar power.

Something completely different in a solar-powered car

A team from the Technical University of Eindhoven in the Netherlands has entered the challenge with three different solar cars, beginning with Stella.

They claim Stella is the world’s first family car to operate on solar power. It won the 2013 competition.

The prototype had enough room for the driver and three passengers. It met all the standards for electric vehicles to drive on public roads. The team also claimed that Stella generated more energy than it consumed in a year of driving.

So the battery can add power to the grid—or take excess electricity from it. A critical mass of electric vehicles can help stabilize the grid.

Solar Team Eindhoven introduced improvements in its winning 2015 entry, Stella Lux, It was comparable in size to a 2015 Toyota Corolla. It was somewhat shorter, but weighed only about a quarter as much.

Its solar cells could generate about 1500 watts in direct sunlight. They charged a 15 KWH lithium-ion battery. The car operated on two in-wheel axial flux motors.

Electric motors operate efficiently at both slow and fast speeds. Therefore, they don’t need a transmission. And so the car doesn’t carry a transmission’s weight. Not only is it lighter, it’s less complicated to maintain.

Its innovations include more than the solar array. Stella Lux was synchronized with a smart phone. Among other things, that meant it could collect weather data and suggest optimal routes. It also locked or unlocked the car, depending on whether it detected the phone.

Stella Vie, their 2017 entry in the World Solar Challenge, has a smaller battery and solar array than Stella Lux. Its roomier interior seats five people. But it is 9% more aerodynamically efficient. It can go 1000 kilometers on a sunny day in the summer. It even helps find the sunniest parking space at destination.

Can it work in the marketplace?

Alumni of Solar Team Eindhoven have launched a startup, called Lightyear, for commercial production cars based on the Stella series. (One lightyear is approximately the distance that humans travel every year in fossil-fuel vehicles.) They plan to make 10 cars in 2019 and 100 in 2020.

With such a small production, the cars will retail at about $136,000. Can they add full-size tires and all the features regulators and customers insist on?

Tesla’s quick success with a battery-operated car surprised nearly everyone. If the Lightyear succeeds in marketing a true solar-powered car, it will have a revolutionary effect on automobile transportation.

Sources:
Net-positive solar EV goes 600 miles on a charge and carries four passengers / Tom Lombardo, engineering.com. July 12, 2015
Solar Team Eindhoven
Toyota brings back the solar panel on the Plug-In Prius Prime – but now it powers the car / Fred Lambert, electrek. June 20, 2016
Will electric cars soon have solar roofs? Toyota and Tesla say yes / Joe Romm, Think Progress. March 7, 2017

Photo credits:
Solar Prius. Public domain from Wikimedia Commons
Stella Lux and Stella Vie. TU Eindhoven, photos by Bart van Overbeeke