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Comment by snowchaser

8 hours ago

It’s a good question, but the reality is the energy required to power a car is far larger than what you can collect.

The solar energy you can collect is about 750W/sq meter.

A car roof is about 5’x5’, and if we are generous and include a trunk and hood area, maybe you are getting 60 sqft?

Best case if the sun is right over the car you can illuminate about 5 square meters. That’s about 3.75KW.

To convert that to a more familiar car power measurement that’s about 5 horsepower.

Hopefully it’s clear why a realtime solar car is hard.

This is not to say it’s impossible, they have been built. They’re just not super practical for everyday use.

https://en.wikipedia.org/wiki/Solar_car

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snowchaser

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Jedd  8 hours ago

> The solar energy you can collect is about 750W/sq meter.

> A car roof is about 5’x5’, and if we are generous and include a trunk and hood area, maybe you are getting 60 sqft?

We must think metric, every inch of the way!

Anyway, PVCs currently max out at about 300W / square metre - and that's in ideal conditions.

I believe theoretical maximum energy per square metre (when light actually arrives at the planet surface) is conveniently pretty close to 1000W, assuming you're in the right place, but maximum efficiency of contemporary panels is only about 30%.

  • snowchaser  8 hours ago

    Totally agree, SI units for the win!

    I was just trying to use “familiar” units. I could have led with 1 HP per square yard, and then you’d totally have license to call me out!

    And yeah, I was just talking about solar flux, there’s a whole lot of real world losses to consider but my point was that none of this matters, it’s orders of magnitude away from ICE engine output.

majoe  4 hours ago

I recently read about Aptera, a company building a commercial solar car:

https://aptera.us/first-vehicle-off-validation-line/

I think it is quite interesting, because it also tries to be maximal efficient, which increases the "reach" that the panels provide.

Don't get me wrong, this is a enthusiast car, but I think the economics could actually work for a small city car. Currently here in Europe, buying a electric car makes sense for home owners, which can charge their vehicle for cheap at home (especially if you PV). But a lot of people living in cities don't have a cheap charging spot. A car with solar panels, which gains a few percents of charge each day (instead of losing some), e.g. enough for the daily commute to work, may be interesting for such people.

I would love to see a ultra cheap take on this. Maybe an electric tuktuk like someone else suggested, with some solar panels slapped on it.

  • SideburnsOfDoom  3 hours ago

    Aptera have been promising this product for a long time now. I'll be surprised if they ever ship.

    > Don't get me wrong, this is a enthusiast car

    Right, it's about as commercially appealing as a Sinclair C5.

JKCalhoun  6 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.

  • BobaFloutist  3 hours ago

    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.