[giobox]

Not really, as we know the max theoretical power output of solar on earth. Given we know that generally best sun can do is approximately 1kw/square meter, Assuming you had 100 percent efficient conversion (we aren't close to that even with best solar panels today), we know its never going to be great for charging cars who have large energy requirements.

Even in the best possible case, very few people are going to charge a car directly from their own private solar source unless no other choices, it's just not remotely time efficient and likely never will be. To charge an empty 75kwh car battery in roughly 1 hr today you would need approximately 225 square meters of solar panel, assuming a pretty good ~30 percent efficiency rate and strong sun. In reality it will likely need even more panels, and this is all before you contend with shade, weather, night storage and so forth. For a car, private solar will likely never work well enough to become mainstream due to aforementioned solar energy transmission limits.

[FullyFunctional]

Citing the time to charge an empty car is such a disingenuous argument; if you have ever lived with an EV you'd know that's very rarely what you do. Instead you top off what you consumed earlier, typically once daily. So unless you are counting the very atypical cross-county drive, you don't need nearly that much.

That said, I don't believe carrying panels around to be a very practical nor attractive option.

[ravi-delia]

> Citing the time to charge an empty car is such a disingenuous argument; if you have ever lived with an EV you'd know that's very rarely what you do.

I've been very annoyed by online discourse that ignores that simple fact, but in this case the primary utility of a portable option would be on that cross-country drive. If you're just making small trips and topping it up, you're no better off than if you just charged overnight at home.

[FullyFunctional]

Fair point; still impractical for most situations.

I _have_ seen non-EV RVs with mounted panels (charging while driving) and more to be unfolded while parked for both shade and more power. They used the power for fridges etc, but not for locomotion. Seemed totally reasonable to me.

[ben_w]

> To charge an empty 75kwh car battery in roughly 1 hr today you would need approximately 225 square meters of solar panel

Yes, though most people don’t need to do that. Average miles driven in the USA per year is 13500, and this car (“in a desert”) would generate 12,000.

Yes shade, climate, etc. is relevant, but it’s also true that a significant minority of people just won’t drive the way you’re talking about. (Such people shouldn’t be spending 100k on a car, but that’s a separate issue).

[_ph_]

If you have the solar cells with your car, you don't need to charge the whole battery in one hour. You have to recharge during one day what you are using in your daily driving. Which is of course much less. In Germany a car drives less than 50 kilometers per day on average, so that is less than 10 kWh per day.

[giobox]

12 hours of sun, the best you can hope for any time soon is about 3kwh put back into the car. In other words, a few miles of range can be restored.

There is a reason no car manufacturer is currently seriously pursuing solar roofs - it's just too small a surface area to generate meaningful energy in a car context. The math doesn't work.

We might see systems (as we've seen in past) where solar helps power accessories on the 12v system (AC/in car entertainment etc), but its not going to meaningfully affect range of the vehicle or help top up the traction battery.

[ben_w]

> 12 hours of sun, the best you can hope for any time soon is about 3kwh put back into the car. In other words, a few miles of range can be restored.

Horizontal solar radiation is 3 kWh/m^2/day, in Germany. 5 m^2 of PV on the car in the article I linked to. 0.25-ish wH/mile is roughly what Teslas get. That works out as 60 miles times the cell efficiency per day, call it 12-24 miles in practice with 20-40% efficient cells. Matches the article pretty well, considering how far north Germany is.

> no car manufacturer is currently seriously pursuing solar roofs

I literally linked to a car manufacturer doing just that :P

[giobox]

> I literally linked to a car manufacturer doing just that :P

You literally linked to a car tech startup whose unproven prototype technology has shipped in exactly zero production cars, yes ;) There is no car manufacturer doing this meaningfully today, and again likely won't be soon.