Aptera's First Solar Road Trip. 300 Miles, One Charge

> Even on an overcast day, the team saw over 545 watts of solar input

Let’s (generously) assume that was the minimum they saw, and let’s (generously) say they charged for 14 hours. That’s 7.63 kWh gained over the day, in almost ideal conditions. Flagstaff’s high altitude means stronger sunlight, and they can do regenerative braking as they come down the mountain. In my Nissan leaf, 6 kWh would get me about 20 miles. If they are much more efficient, they maybe got 50 miles from the charging on that day, and the other 250 from the charge they started with.

I’d love to be wrong about any of the above! Solar panels on cars would be so cool! It just doesn’t seem useful. Please correct me if I’m mistaken.

Fully agree. The physics of solar panels on cars just doesn't work. It's bizarre that this is actively pursued by startups and concept cars from large manufacturers when it takes just quick back-of-the-napkin math to see.

A car has about 5 m^2 of flat space on the roof/hood/trunk so that's the maximum surface area that can capture solar energy at any given time.

The total energy to hit the area is 1000 w/m^2.

The panels can't rotate to track the sun so the effective area is the cosine of the angle. So you end up with about half the amount of effective sunlight hours as the actual daylight hours. So in summer you get about 6 hours of effective sunlight.

Good panels in real world conditions can give you 22% efficiency.

So in optimal conditions you get: 5 * 1000 * 6 * 0.22 = 6.6 kwh

That will reflect your best days. It can be dramatically less if it's cloudy, overcast, winter, far from the equator, car is dirty, parked in shade, etc.

6.6 kwh is about one tenth of the battery in my Hyundai Kona EV. With very conservative highway driving, 6.6 kwh can get about 40km of range and about 50km in city driving. It's what I get from plugging into my home charger for 30 min and what you get from a fast charger in about 3 minutes.

So besides some very niche uses, there's no sense in massively increasing the cost and complexity of a car by installing solar panels. Far better to put the panel on the roof of parking and just plug in for a few minutes while you park.