Toyota to test solar panels for electric cars

Toyota to test solar panels for electric cars
Credit: Toyota

What's not to like about this concept: high-efficiency solar cells gifting electric cars with mileage.

Bertel Schmitt, The Drive, said, "The solar roof could morph from mostly a marketing-device to a helpful feature." He noted that, referring to plug-ins, "On a fair-weather day, the juice would be provided by the sun, a big improvement especially for people who don't have their own garage."

Toyota has ambitions over the concept and is to start testing an onboard solar recharging system where the hood, the roof, and back are covered with cells. The solar roof can charge while the car is on the move.

It did not escape Interesting Engineering's notice that the new solar battery cell can fit a larger surface. "The solar battery cell is a thin film about 0.03 mm thick. Because it is so thin, it can fit the curves of the vehicle including the roof, hood , and rear hatch door," said the report.

Darrell Etherington, TechCrunch, said at center stage was the new and improved version of the solar cells previously launched on the Japan-exclusive Prius PHV.

The Toyota news release said "the demo car employs a system that charges the driving battery while the vehicle is parked and also while it's being driven." This was seen as an interesting development expected to lead to improvements in the electric car's cruising range and fuel efficiency.

"Previously, the Prius PHV charged the driving battery only while the vehicle was parked. However, with improvements in power generation output, the demo car employs a system that charges while the vehicle is being driven. This is expected to boost the BEV-mode cruising range and significantly," said Toyota.

Toyota to test solar panels for electric cars
Credit: Toyota

NEDO, which is a national research and development organization, Sharp and Toyota are to start some road trials where the will be equipped with solar batteries. NEDO and Sharp will share a selection of trial data results, said Toyota.

Those presiding over the tests are going to see the power generation output of the solar panel. Toyota City, Aichi Prefecture, Tokyo, and other areas are the sites planned for the test, where weather and driving conditions will vary.

Etherington commented that the car's prototype cells being able to convert at 34 percent and up was better than the existing commercial version's numbers.

Reports noted the solar cells were extremely efficient. According to The Drive, the solar Sharp-made solar cells are of the triple-junction compound type, sporting a conversion efficiency of 34 percent, and occasionally more.

Etherington: "The new system will provide up to 44.5 km (27.7 miles) of additional range per day while parked and soaking up sun, and can add up to 56.3 km (35 miles) of power to both the driving system and the auxiliary power battery on board, which runs the AC, navigation and more."

All in all, Elektrek offered its take on the news:

"As we always like to point out with these solar car efforts, a car's roof is not the most ideal place to install solar cells. They would most likely be more efficient installed on the rooftop of a home and then, you can use the power to charge your vehicle. However, there's something appealing about your producing its own energy and it is starting to get more attractive with the specs Toyota is talking about now."

Explore further

Sono Motors to put its electric car in production mode 2019

More information:

© 2019 Science X Network

Citation: Toyota to test solar panels for electric cars (2019, July 6) retrieved 19 September 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Jul 06, 2019
The new system will provide up to 44.5 km (27.7 miles) of additional range per day while parked and soaking up sun

That number is highly suspect. Even with high efficiency cells, the orientation of the panels is not optimal and the coefficient of production will be very low.

Toyota claims 860 W peak output. If you assume the CoP of an average rooftop solar panel without any special care for orientation or shade, the peak-to-average ratio is about 10:1 and the average daily energy production would be no more than 2 kWh realistically.

The driving range is estimated according to the JC08 driving cycle for light duty vehicles, which exaggerates the driving range (average speed 34 km/h), but still it does not explain how a car can go 44 km on 2 kWh (45 Wh/km) while existing real electric cars take up 3-5 times the energy (150 - 240 Wh/km)

It's seems they've forgotten that solar panels don't crank out full power 24/7 and they need to angle towards the sun.

Jul 06, 2019
Theoretically, if you put a flat solar panel on flat ground with no shadows or clouds, the highest attainable average power over a day is the root mean square of a sine function divided by 2 (because half the time it's night), which gives you 0.35 times the peak rating of the panel.

But this only work on the equator. Obviously, because the sun is not directly overhead anywhere else. At 45 degrees north (Europe, US, Russia), the power is diminished again to about 0.25 the peak rating.

This is why the absolute minimum peak-to-average ratio of fixed solar panels in the US, Europe, Russia, etc. is about 4:1 and when you account for shade and cloud coverage, dust and weather etc. it grows to about 8:1 for rooftop panels. For a car, it's going to be much worse because cars are preferably parked next to buildings and in the shade of trees etc. Indirect radiation even with the best panels produces only a tiny fraction of the power.

Jul 06, 2019
For example on cloud coverage, New York LaGuardia airport reports 96 clear days over a year, 117 "partially cloudy" days, and 213 days overall with some sunshine. Over many years, the average amount of time that the sun reaches the ground during daylight hours is 58%

So in practice, the geometric effects reduce the peak power by a factor of 4, and the weather effects by a factor of 2, approximately, hence the rule of thumb that solar panels make about 8 times less power on average than the rated power output.

It gets better if you happen to live in Abu Dhabi, but most people prefer to live in more temperate climates.

Jul 06, 2019
A step in the right direction as styling is paramount

Styling is why we choose a car for its goods looks
These solar panels do nothing the on this automobile catwalk
If this aspiring model wishes to attract human drivers
It needs to spruce up its panels a shade

As with all things in life
Beauty is more than skin deep
These panels serve a purpose
As this purpose has not to be sullied with shady marketing
As shady is this key for these are solarpanels
These solarpanels are curved
Curved away from the sun
A sun that never shines directly at these curved solarpanels
For these solarpanels never give this theoretical output

This comes full circle to this shady marketing
For these inquisitive aspiring customers
Will see through this shady hype of these stylish lines this car once had
Before it had to drag these solarpanels through this wind, rain and hail
Of this typical English summer

For all this weight of tech drags this fuel consumption down the drain of this English Summer

Jul 06, 2019
Electric cars and electric power hungry tech

These large tablet screens
While dangerous to safe driving consume electricity
Electric cars need only
A speedometer
A fuel consumption meter
Even the fuel consumption meter can flatten an electric battery stone dead
You should have to press a button to see this battery level
There should be no USB charging points as this is further unnecessary battery drain
There are plenty of mobile mini chargers to charge up at home to bring into the car

These batteries of today are only capable of driving
These electric cars electric motors, their brakes and their lights
There is no capacity to heat this car in the cold and cool it in the heat

Leave these battery draining power hungry techs where they belong on the drawing board
Give us the maximum mileage from these electric cars now!

Jul 06, 2019
Eikka's right on power. 2kw hours will be like 6 min drive time. However, one major issue I ran into last time on a road trip during a heat wave was that it got so hot in car when left parked, numerous things in my luggage were destroyed, pull bottles melted, etc. It will be on ongoing crisis as global warming increases. Solar panels on cars could generate enough juice to run ac while parked, keeping groceries cool, even preventing cars from being death traps when they break down due to heat.

Jul 07, 2019
I can't believe it's taken this long to get to this point.

Jul 07, 2019
The Solar Constant is 1300 Watts per square meter. With ineffficiencies, one horsepower per square meter is vulgar and easily remembered (745 Watts = 1 horsepower).

The roof of a car is generously 3 square meters.

In re automobile AC; 1 Air Conditioning Ton is 3,500 Watts, the power of the smallest household unit and a typical automobile system. Automotive AC must also deal with solar heating.

Jul 07, 2019
The Solar Constant is 1300 Watts per square meter. With ineffficiencies, one horsepower per square meter is vulgar and easily remembered (745 Watts = 1 horsepower).

The average figure is actually about 350 w/m2 at the surface, in ideal conditions. There is no way solar panels on a small car are going to run the AC. There simply isn't enough energy available.

Sad to see Toyota has decided to exploit the global hysteria. I used to think it was above such shenanigans.

People who think electric cars are going to save the planet: "fossil" fuels supply 95% of nonhydroelectric power. You are simply engaged in self-deception if you think a Tesla is ecologically justified; its CO2 emissions are masked but no less impactful than any other automobile's.

Meanwhile, adding the burden of car charging to a stressed-out grid, whose stability is already being undermined by fickle renewables, will result in higher costs, shortages and blackouts.

Jul 07, 2019
"1 Air Conditioning Ton is 3,500 Watts, the power of the smallest household unit and a typical automobile system."

Never heard of that unit. I ran a 1000 watt unit to cool a room through summer and it was fine, much larger space than a little car interior, though maybe less heated by hot sun than car. I bet a couple hundred watts would go a long way to prevent catastrophic heat in a small space.


Jul 08, 2019
Never heard of that unit.

It's literally the cooling power of a block of ice that weighs a short ton, over 24 hours. That's 907 kg of ice melted over a day. It comes from the time when people would literally put blocks of ice in a cooling cabinet to keep their groceries, before mechanical refrigeration was invented.

But yeah, AC takes a lot of power, and even with the best solar panels available, you still have about 4-5 times as much heat radiation coming at the car than what you can capture by solar panels, which are black, which collect the heat and make your car hotter. Couple hundred watts doesn't even begin to do anything about it.

It's best just to leave the car in a shade.

At high sun, you get around 1000 Watts of energy per square meter, over the whole car. Suppose it's 2x5 meters: 10 000 watts.

Jul 08, 2019
Some carmakers have put "solar AC" on their cars though. What they really do is just run some small fans, which keeps the heat down by circulating air through the car.

It has about the same effect as cracking a window open slightly. Your steering wheel is still going to burn your hands.

Jul 08, 2019
@Eikka, Note the magic weasel words "up to". These results are achievable at noon between the tropics of Capricorn & Cancer (+- 23.44 degrees latitude) on one of the two days/year when the sun is directly overhead. In most of North America, they are achieved on a closed course (east-west road) with a professional driver who can drive on two wheels. ;)

Even with all the inefficiencies, a vehicle that can generate some power on its own is attractive. It can keep itself cool on hot, sunny days. If totally away from power, it will, given some sun, generate some charge that might allow it to limp to a place with power available. If cars with solar panels became popular, I can see where sloped, solar aligned parking spaces might also become popular.

Jul 08, 2019
I've always thought those boxy Grumman LLV US postal delivery vehicles would be ideal for at least hybridization if not outright electric conversion due to their constant stops and starts. Electric running gear would probably stand up to the constant starts and stops better than conventional brakes and transmission. As I understand it, a typical postal vehicle does less than 20 miles a day, so solar panels providing several miles of extra energy would be significant. They'd probably be fully charged on Mondays due to collection over the weekend. Fleet vehicles like this seem like lower hanging fruit than consumer vehicles.

Jul 09, 2019
People who think electric cars are going to save the planet: "fossil" fuels supply 95% of nonhydroelectric power.

That a bad generalization or a lie. This is a graph from europe's energy production: https://ec.europa...tion.png

Over 50 % comes from nuclear and renewables.

Jul 10, 2019
It can keep itself cool on hot, sunny days.

A stationary car without the air convection from driving is a solar oven. The body panels soak up the sunlight, and the windows act like solar collectors. Unless your AC can top the solar heat coming in, it's still going to get almost as hot because the net power input is still very much positive. It's just going to take a little longer to reach the temperature.

"Keeping cool" means that you pump out just as much heat as is coming in. If you can't do that - and 860 W isn't nearly enough - then you have a surplus which keeps accumulating until the car is hot enough to radiate it out.

Jul 10, 2019
People who think electric cars are going to save the planet: "fossil" fuels supply 95% of nonhydroelectric power.

"That a bad generalization or a lie."

It is a little bit bad generalization. (I forgot nuclear.) But your figures are for Europe, not the US. In the US, wind and solar power account for 8% of total energy production (;t=3).

So I restate my claim: electric cars mostly rely on fossil fuels + nuclear; sun and wind won't/can't save the planet. (Not that it needs saving -- the planet has been accustomed to much warmer temps than now).

Jul 10, 2019
But your figures are for Europe, not the US. In the US, wind and solar power account for 8% of total energy production

8% electricity, not total energy. This is an often confused figure, because people forget to mention that more energy is consumed NOT as electricity, but directly as chemicals and fuels. If you count all energy, then the share of power is much worse. It's roughly in the 1-2% even in the areas which have most invested in them.

For "Renewable" power, the figures are higher because burning wood and other biomass, and hydroelectric dams both count as "renewable", which lets you post numbers in the low 20%.

In fact, for all the hoopla and money spent, nothing of note has actually been accomplished with wind and solar power in the last 30 years. On the contrary, with rising electricity prices, people have started to use more natural gas to power their homes instead.

Jul 10, 2019
Though you might complain, "What about Denmark?" etc.

But the reason why places like Denmark can post high percentages of renewable power on their grids is because they're a 5 million people country in a 500 million customer European synchronous grid. They have no integration issues because their wind power is nothing on the scale of the system. The rest is just a numbers game: you count everything produced as used and ignore the power exports and imports.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more