Why don't electric cars have solar panels?

Given the move to a greener future with electric cars and solar panels, a lot of people wonder why don't electric cars have solar panels. The answer is rooted in practicality rather than science. Fundamentally, the concept would work, but the benefit would be so small as to be not worth the effort.

Solar panels mounted on electric cars sound like a match made in heaven. Whether it’s a fully electric vehicle or a plug in hybrid, the idea of a solar panel charging the car’s battery pack while the car is parked has all sorts of appeal. Unfortunately, even though modern solar panels are a lot more efficient than they ever were, the relatively small surface area a car offers means that the panels’ contribution would be a drop in the bucket compared with plugging the same car into the grid to recharge. In fact, it’s reckoned that you’d need about 90 hours (nearly four days) to recharge an electric vehicle from panels fitted to the car. And that’s in full sunlight.

Solar panels work by converting the sun’s energy (photons) into electricity by using the photons to knock an electron off the solar panel’s cells, thereby creating an electric current. It’s free power and completely renewable and it’s all thanks to that giant nuclear reactor we call the sun. The best way to take advantage of this is to have a huge array of solar panels – the more the better – to multiply the effect. Simply, an electric car’s body is too small to fit enough panels to charge its batteries in a timely way. That may well change as solar tech becomes more developed, but for now, that’s the reality.

The concept of solar panels on cars does have one real-world application, though. And that’s when it comes to 4X4 camping vehicles which often have a solar panel mounted on the roof. That panel can trickle charge the vehicle’s battery (or batteries, many off-road 4X4s have an extra 12-volt battery) keeping the on-board fridge running longer for extended stays at a camping site. Some owners prefer to use a portable solar panel for this, enabling them to move the panel into direct sunlight as the sun crosses the sky. While these panels are good at what they do, in terms of charging an electric vehicle, they’d take even longer than those 90 hours, compared with the few hours or even minutes that a high-voltage charging station can achieve.

Some car owners have fitted smaller panels to their cars to trickle-charge the battery while the car is parked. As soon as you park in a garage or the shade or on a cloudy day, however, the benefit is lost.

There’s one other application of solar panels for cars, and that’s the vehicles that compete in the Solar Challenge that runs from Adelaide to Darwin, 3000km through the Australia outback every second year (Covid permitting). These vehicles must run purely on power gained through solar panels, so their bodies are completely covered in panels while the rest of the vehicle is aimed at reducing drag, friction and maximising efficiency. Practical they are not, but they do point to a future where 'solar panels on car roof' might be an option-box you tick when you order you new electric car.