# Can an electric car be usefully powered (or at least supported) by solar energy?

There are cars on the road that run on electricity instead of gasoline. And that's great, it really is. But you have to charge them, which is a problem if there are no charging stations in your area.

But what if your car could charge itself with the sun? It would be refuelling while you parked, or even while you're driving. My question: would it be practical? More specifically, let's assume the following:

• The car's feature set, weight, and charging time are comparable to that of a Tesla Model 3
• The car can still be charged with conventional charging stations
• The car can be designed around solar panels (as opposed to haphazardly grafting them on)

Given this, can an electric car be powered with solar energy in a manner that is practical, either as a primary source or as a supplement?

• Without any more limit the answers to this is a 'yes. E.g. add solar panels, charge for a week. Drive your alternate Tesla to the shop 1km away. For longer distances or shorter charging times things get more interesting. – Hennes Sep 11 '17 at 16:57
• Have a look here: physics.stackexchange.com/questions/460430/… – james Feb 12 at 21:56

As far as I know, this is your current state of solar-powered cars:

(See Wikipedia: Solar Car)

They're designed completely around the solar panel, and they're not really sedans.

• I think this image is a few years old, but yeah. The solar car engineering competition is a thing and the cars they make are definitely laboratory kit rather than production models. – dmckee Sep 11 '17 at 17:30

what if your car could charge itself with the sun?

It would take a long time to charge. My plug-in hybrid (Cheverolet Volt) requires a modest 3.8 kilowatts for charging, and it can go about ten miles for every hour that it spends on the charger.

I'm not totally up-to-date with the efficiency of modern solar cells, but even if they were 100% efficient (they're not), and even if I covered every non-glass square inch of the car with solar cells, and even if I lived in the tropics; the best I could hope for would be maybe two or three hundred Watts of power at mid-day.

A Tesla, "standard" charger requires almost ten thousand Watts, and the "fast" charger needs even more.

You can charge a car from solar power, you just can't carry the charging station around with the car itself.

• I felt like there are a few things to add. Solar panels tend to heat up fast. During a sunny day the surface of a panel reaches 50-60 °C in a few tens of minutes. On a roof panels are usually isolated from the roof itself by a layer of air, but on a car all this heat can enter inside quite easily, so you'd need AC, that consumes the precious charge accumulated by the panels. Moreover, hot panels produce less because their resistivity increases, so the efficiency of the panel decreases in time. And you'd have to be careful to always have your car clean. It simply isn't worth the cost, sadly. – GRB Sep 11 '17 at 17:15
• BTW, the "standard" solar irradiance is shown as $1 \frac {kW}{m^2}$ on Wikipedia, so your optimistic estimate of a a couple hundred W peak in ideal conditions might be closer to a realistic output. – JMac Sep 11 '17 at 17:44
• So given that the power offered by solar panels is two orders of magnitude less than a dedicated charger, it won't even make a useful supplement? – JesseTG Sep 11 '17 at 18:30
• @JesseTG, depends on what you mean by "useful." On a sunny, summer day at my lattitude, solar panels that I could install on the exterior of my car might put two or three miles-worth of charge on the battery while it sits in the parking lot all day long outside of the building where I work. That could be "useful" if it saves me from having to get out and push the car two or three miles. It would be that much more energy that I did not have to draw from the grid. But, it would not anywhere near enough to get me home every day if it was my only source of energy. – Solomon Slow Sep 11 '17 at 18:52
• Average solar energy for Earth works out to two to three horsepower per square foot. If you had 100% efficient panels a 10x20 foot car would have around about 200 hp to play with, which would be be sufficient as long as you were someplace where the sunshine wasn't too far below average. 100% efficient panels would be hard to see though and roughly equivalent to painting your vehicle with nannyblack... Not really a wise choice on the road. – Perkins Oct 11 '18 at 0:20