Comment by JKCalhoun
4 hours ago
I would love to see this laid out practically.
For example, if you had an electric golf cart with a solar roof, on a sunny day…
With two adults, a speed of 35 MPH, an LLM suggested a ratio of 10:1—that is, the power demands of the golf cart were 10x what the solar could deliver in real time. (LLM considered also aerodynamic drag, rolling resistance of golf cart tires…). When I suggest a speed of 25 MPH, the ratio came down to 5:1.
Regardless, assuming batteries to store energy on the cart, it suggests a 10 minute drive to your neighborhood grocery store would require the golf cart to sit in the parking lot for close to an hour before it will have caught the batteries back up to their charge before you left home. (And this is at the rather impatient 25 MPH drive.)
To get to a better ratio you would have to engineer like hell to start squeezing the numerator. Make it radically aerodynamic, low-rolling resistance tires (probably the lowest hanging fruit), cut the weight significantly…
I do love the idea of something like an electric rickshaw or tuk-tuk. Maybe not streamlined, but you could get much better rolling resistance with something like bicycle tires—and weight could be kept in check.
To make the math more complicated, you could theoretically have an unfoldable solar roof. Say you have cute, tiny one-person car with trunkspace for two bags of groceries, call that 1/9 the footprint of a "normal" car, and give it an expanding roof that can fill up a typical parking space. So you get to multiply the numbers by 9, which would mean a 10-minute drive to the neighborhood grocery store would require 60/9 roughly 7 minute charging? That's getting really close to useable, so we must have cheated a little too much with some of the "simple" math. Also probably the unfoldable solar panel ideal really just doesn't work for some reason that's extremely obvious to engineers.
> To make the math more complicated, you could theoretically have an unfoldable solar roof.
This is not completely theoretical, this guy did it on his Tesla:
https://www.dartsolar.com/
https://www.reddit.com/r/TeslaLounge/comments/194ajsm/my_tes...
I doubt that it will go mainstream, since you can only unfold it when the car is at rest. And it's permanently like having a loaded roof-rack for aerodynamics and weight. You'd always be asking - why not get put the panels on the roof of a house or other fixed structure? Easier and you can add even more of them.