Hyundai Sonata EV with solar panels on the roof, for sale in Korea
Hyundai
Once again, we see great buzz around the idea of an electric car with a solar panel on it, in this case a new Hyundai Sonata (not yet available in the USA.) Sadly, it is necessary to point out the realities behind this, because it’s a pretty stupid idea.
Hyundai says their solar panel will provide enough electricity to power 808 miles of driving per year, or 2.2 per day — if you leave the car out in the sun. That’s not nothing, but it’s close to nothing, so close as to not justify the cost. You also give up the opportunity for things like Tesla’s panoramic roof or sunroofs. This low amount of energy is shown in the history of cars. An early Prius with a solar panel only used it to power a fan to keep the car cool on hot days.
The question of hot days is an important one. You only drive 1-2 hours/day typically. To gain this power, you must park the car in the sun. Not everybody can do that and not everybody wants to do that, for in warm places it means the car is baking, and would easily consume all the power it generated from sitting out in the sun, and sometimes more, with the extra air conditioning needed to cool the sun-baked car down. (The AC draws about 1kw and would use up a hour of solar power if it runs for 5 extra minutes.) The panels will also add a small amount of weight.
Putting solar panels on cars can actually be anti-green. That’s because if you’re going to spend some money on solar panels, you want to use their full potential. That means mounting them in a sunny place, tilted at an angle to best catch the sun, and most importantly, connected to the power grid. Leaving them flat can lose 30% of the energy they generate. Parking in the shade of course loses almost all of it.
In fact, like the older Prius, it could be the best use of the solar panel could be to keep the car cool when you’re forced to park in the sun, not to have you deliberately park in the sun to charge. The reality is that a car solar panel, which has to be shaped to the car roof, protected and robust against vibration, is much more expensive than a regular panel. If want 2 miles of extra range a day, your best bet would be to (if you could) buy a slightly bigger battery, and pay for solar power from your electric company.
Being connected to the grid is also important. Once your car is charged, the power has nowhere to go, and you simply discard it. Connected to the grid, all the power gets used, powering your house or offsetting fossil fuel burning on the grid. To be fair, the solar panel on a car produces so little power that it would take a long time for the panel to restore the car to your desired charge level. And most people don’t charge their car to full, so it can tolerate a little extra power from the panel to avoid wasting it. You can program your car to not take your normal charge if you know it’s going to be sitting out in the sun all day. But there will still be times when you throw away that power.
It is possible to operate a vehicle on solar panel. The annual World Solar Challenge pits specially designed, small, low-slung, super-aerodynamic vehicles made of ultra-lightweight materials and carrying a small and lightweight driver. They drive a long route through a sunny desert in vehicles that are 15 to 20 times more efficient than consumer electric cars. It’s impressive, but far from practical.
If solar panels become so cheap that we can throw them anywhere, or much more efficient, they would make sense on cars, as long as you don’t overheat the car by parking it in the sun. If you cover the roof and hood they could do better. They can make sense on motorhomes which have a much larger roof surface and stay put for long times. Otherwise, put your solar power money into panels on your roof, or better, using a power company that is 100% renewables.
