Where are All the Solar-Powered Cars?

One of the most common questions I have received as a solar engineer is this - “Why don’t we have electric cars powered entirely with solar so you could drive infinite miles without having to recharge or refuel?” One amusing friend even went as far as saying the governments were controlling the companies and not allowing them to come up with such technologies.

Fortunately or unfortunately, the reality is different, and of course, less dramatic than that. Here’s the truth, and this is one of the very few times you’ll find me praising fossil fuels for something - petroleum-based fuels are incredibly good at storing large amounts of energy in small spaces. A full tank of a mid-size car weighs less than 2 solar panels and can take you hundreds of miles.

Problems Encountered in Powering a Car with Solar

In comparison, solar panels face two physical problems. Unlike gasoline, solar panels need to collect energy from sunlight, which means they cannot be densely packed into a 75-pound structure somewhere inside the car. Since it is the vertically exposed surface area in question and not volume, the car’s surface area itself sets the limit on how large your solar panel can be (unless you want to have solar panels larger than the car and mess everything from aerodynamics to safety).

The second problem is the problem of efficiency. While there is only a limited amount of sunlight that can be captured, there’s a further limit on how much of it can be converted into electricity. Currently, the best solar panels still operate at efficiencies lower than 25%, meaning only a fourth of the incident solar radiation can be utilized at the most. Of course, there are technologies such as perovskites and multi-junction cells that have achieved over 40% efficiency in labs, but these are still not close to being commercially available.

Let’s do a simple calculation using Tesla’s model 3 and its solar panels:

The Model 3 has at least a 50 kWh battery in it. To charge this fully, we will need a product of power and time (kW x h) to reach the number 50.

The car’s dimensions are 184” x 76” x 56”, and the dimensions of Tesla’s solar panels are 68.5" x 40.6" x 1.57", which means we can fit roughly 4 panels on the car (let us ignore the windshield and rear glass for the moment). Each of Tesla’s panel has a maximum power rating of 340W, which means, from the 4 panels we’d get 340 x 4 = 1360W = 1.36 kW.

If we think of charging the battery fully, the time required will be as follows:

1.36 kW x hours required = 50 kWh

Thus, hours required = 50/1.36 = 36.76! If we take into account other limiting factors such as angle of incidence of the sunrays, available sunlight intensity, etc., this number easily jumps to over 50 hours.

And that, ladies and gentlemen, is why electric cars don’t run on solar.

Now if the panels generated far more, say 4 kW instead of 1.36 kW, then we might have been able to charge the car in around 15 hours, but it is still quite high.

One frugal YouTuber even tried to set up a rig behind a Tesla with a bunch of solar panels to see if it works. Check out his interesting experiment.

Existing Solar-Powered Vehicles

Despite the above-mentioned problems, it doesn’t mean solar cars are totally impossible. There are several national and international solar car races happening every year (well, every normal, non-pandemic year), where hundreds of solar cars participate, built mostly in universities by tech geeks (definitely some young Elon Musks in there).

Image of a solar racing car

Take a look at the solar car above. I know, it looks weird, and the reason is that the makers have tried to, quite cleverly, maximize the solar absorption area while reducing the size and weight of everything else. The lighter and more aerodynamic the car, the better it is suited for solar.

One thing is clear - at this point, such a car is not truly ready for the market, for more than one reasons. But does that mean solar panels and mobility can never be connected?

Ways to Use Solar for EVs

The good news is, for a car to be powered by solar, the solar panels don’t have to necessarily sit on the car. Even for cars with integrated solar panels, there needs to be a battery in the car (or you’d have to avoid driving in shade all day, good luck in winters!).

Your car does not have a 1000 sq. ft. surface area, but your home does! EV owners are increasingly getting solar panels on their roofs to charge their EVs, which essentially makes their travel free of cost.

And although it is still not as fast as filling gasoline in a tank, it is cheap, it is clean, and it makes you seriously cool!