[kwakubiney]

Might be a noob question, but why can't EVs have solar panels on them directly so they can get charged just by moving around? Or why can't we have SVs(Solar Vehicles)? Why do we have to use solar panels on EV stations rather than just having them on the vehicles themselves?

[snowchaser]

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

[Jedd]

> 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%.

[6510]

There is a tiny image hidden at the bottom on one of the race team pages which represents an interesting effort towards a road legal solar car.

https://en.wikipedia.org/wiki/UNSW_Sunswift#/media/File:Suns...

They are now working on the sunswift 8 which is to be a combination of solar battery and hydrogen.

They are not calling it a solar car anymore apparently.

https://www.unsw.edu.au/challeng/vertically-integrated-proje...

Pure solar is indeed to much of a constraint, it make it more challenging than propelling humans over roads in an enclosure needs to be.

A big problem is sharing the road with conventional vehicles. Many could probably drive straight though it, a Tesla could probably drive straight though it.

If the car must be a strong metal container the choices quickly reduce to the things on the market right now.

[snowchaser]

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.

[Jedd]

It was the fact you started using units the world knows - albeit misspelling metre - but in the next sentence, comparing that same dimension, you used an apostrophe to allude to a unit that only 5% of the planet uses.

[majoe]

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]

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]

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]

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.

[SideburnsOfDoom]

> 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.

[JKCalhoun]

I would point out this guy: https://youtu.be/ZDByoLRS9QA

[defrost]

You absolutely can .. but in order to be self sustaining vehicles need to look somewhat like the builds that appear in Australian multi day solar races - ultra lightweight, extreme streamlining, zero driver comfort, no extras like cargo space and automatic rear doors, etc.

Maybe in time efficiencies will get there.

* https://worldsolarchallenge.org/

* https://www.youtube.com/watch?v=4K0FD9Hh6XY

* https://www.youtube.com/watch?v=R_lVdrHnbYo

Addendum: addressing the [dead] comment below

> With 100% efficiency the area of the car is too small to produce enough electricity to drive.

is false - Australia has been racing solar powered cars for a good many years now, clearly they generate sufficient power to drive, just not especially fast, with any reserve energy, or at night, with any real comfort, etc.

[embedding-shape]

Ok, so lets say we didn't want 100% of the energy to come from those "self-sustainable panels on the car", but rather N%, so we keep most everything as-is, except switching all the outside body/chassi panels for solar panels, how much N% could we recover from that? Could it change so someone goes from needing to charge once every 3 days to once every 2 weeks lets say? Together with re-generative breaking, maybe it could at least have some impact.

[thechao]

You're off by an order of magnitude. It's a few hundred watts; an EV is consuming 10s of kilowatts. (Ignore the watt-watt/hour sloppiness, pls.) To charge my car 60% would take about 2 months. Ambient needs (battery cooling) would eat up more than I'd get back. At best it extends idle sit time.

[embedding-shape]

> You're off by an order of magnitude.

How can a question be "off"? :D I literally used N% as to avoid replies like this, but seems you managed anyways...

> To charge my car 60% would take about 2 months.

Depends heavily on where you park and where in the world you live, wouldn't it? I use my car maybe 2-3 hours per week, most of the time it's just standing outside in sunny Spain, would that change the calculation anything?

[functional_dev]

consumer car needs hundreds of pounds of reinforcement... just to pass side impact test

[shepherdjerred]

Hyundai had this https://techcrunch.com/2022/03/23/hyundai-sonata-hybrid-roof...

> After baking in the sun all day, the car can add 3-4 miles to its range.

[thinkcontext]

The amount of power that can be generated from the surface area of a car is pretty small compared to how much a car consumes. And the cost hasn't been low enough compared to the value of the electricity it could produce.

Maybe someday the price will get so low it will be a no-brainer.

[SideburnsOfDoom]

> Maybe someday the price will get so low it will be a no-brainer.

The cost of solar panels is already low, that's why it's booming. This cost isn't the main constraint any more.

Panels on a vehicle have stronger requirements for low weight, and vibration tolerance than those on a fixed structure. They contribute to the complexity of the vehicle's power systems. They have to be designed with vehicle aerodynamics in mind.

And of course the limited surface area means that you do all of that, for a component that's it's barely able to keep the vehicles' aircon running. The physics of that will remain the same. Even of the total costs are low (and factors such as the vehicle weighing more are an unavoidable cost), the benefits are lower.

At any price point, including free solar panels, there are good arguments to put the panels on a fixed structure instead.

So maybe it will happen when we have run out of non-moving surfaces to put the panels on. i.e. don't hold your breath.

[nirolo]

Aptera has this planned but not sure if they ever reach market maturity.

There also was a project car from the Nordics I think. Can't recall the name though.

Main problem is the large amount of energy a car needs vs what kind of surface area you have and efficiency we get.

An ideal (100% effiwncy) solar cell of 5m² would still need 20 hours to charge a 100kWh battery. And we are way off on area an efficiency in reality.

[SideburnsOfDoom]

> Aptera has this planned but not sure if they ever reach market maturity.

Yes, Aptera does not have a shipping product, and if they ship the current design it might not have a large market for it. The have been promising delivery for a long time now, so it certainly looks a lot like vapourware.

[amunozo]

Well but that would be a problem for keeping the car infinitely running with only solar power. But what about just passively charging it while idle? Cars sit idle most of the time.

[Moldoteck]

you get too little energy vs the cost of integrating it. It gets worse considering as a driver you want to park your car in shade/garage/multistory parkings

[GoToRO]

My understanding is that when buying a car you are dealing with an oligopoly. You might think that you have a lot of options, but they all come from the same source. Furthermore, big money control not only car production, but oil too. If they allow the ceo of a car company to come with such a car, they loose billions in the oil industry. So they have no incentive to do that.

New options do appear on the market like the new toyota prius with solar panel, but if you look at it you will see that they didn't even try to maximize the solar panel size. Still it gets 2 km extra range in bad conditions. Triple that and you have 6 km, in real conditions. If you use your car every other day, you will never charge it, ever. If you get average or above sun, you can drive it daily and not charge it ever. A big problem if you sell oil.

The problem with green energy is that it is very democratic and hard to control. Nobody with big money is interested in that.

To understand who controls your life, see all the draconian measures taken against electric scooters: cheap, not poluting, democratic, don't need a lot of space and so on. Everyone with money said: we can't allow that. Write defamatory articles in the media they control, pass laws against it and so on.

[SideburnsOfDoom]

> The problem with green energy is that it is very democratic and hard to control.

It's not that I totally disagree with this - there is some truth to it. But it has no bearing at all on the question "can I put the panels on the car instead?" Which has been debunked in this thread and elsewhere many, many times.

The counterargument to what you say is that Solar is in fact booming. It is coming - oil money can slow it, but not stop it. They have more success in some countries than others. It's not a coincidence that China, which course desires energy independence but doesn't have access to a lot of oil, is leading the way. Sorry USA, you're laggards now.

But solar + battery is on an exponential ramp-up and getting big now. Each shock like the current Hormoz idiocy makes the case for it even more to the rest of the world. It's coming, fast.

Just, it's not useful on car roofs. That's a poor choice of panel location.

[bryanlarsen]

> China doesn't have access to a lot of oil

Just an aside, but China is the 5th largest oil producer. They have a lot of oil. The problem is that they're the 2nd largest oil consumer, so are still importing. Their current course is sufficient to achieve energy independence.

It's kind of unfortunate they don't need to further decarbonize to achieve that independence. There are some other fields that aren't yet economically valid to decarbonize. If China had a non-economic reason to decarbonize jet fuel, steel, plastic etc they might drive enough volume to make them economic.

[GoToRO]

As a personal challenge, you should refrain from using the word "debunked" for a full year.

[SideburnsOfDoom]

Thank you for the suggestion, and I will give it all due consideration.

[arjonagelhout]

There was a production car planned called the Lightyear One [0], originating from a Dutch student team, but if I recall correctly it was quite difficult and expensive to manufacture.

[0] https://en.wikipedia.org/wiki/Lightyear_0

[embedding-shape]

> but if I recall correctly it was quite difficult and expensive to manufacture

More importantly, seems they stopped manufacture it because they made a new version, that was supposed to be available in 2025, but I don't think I've seen it anywhere.

> However, in January 2023 Lightyear announced that it was halting production of the 0 model, redirecting their efforts towards production of Lightyear 2; Atlas Technologies B.V., the subsidiary responsible for the manufacture of the Lightyear 0, would be allowed to go bankrupt. As of 2023, the replacement, Lightyear 2, is slated to be US$40,000 and available in both Europe and North America, and to start production in 2025.

[SideburnsOfDoom]

> Might be a noob question, but why can't EVs have solar panels on them directly

This is 100% a very common noob question. The answers are therefor easy to find if you try.

https://www.forbes.com/sites/billroberson/2022/11/30/why-doe...

https://octopusev.com/ev-hub/why-dont-electric-cars-have-sol...

https://www.youtube.com/watch?v=7L1_zvqg73Q&t=590s

A much better idea is to 20x the surface area of solar panels, get ones that aren't as weight sensitive (and therefor expensive), mount them on your house or garage roof instead, and charge the EV off that when it's parked adjacent. Maybe add a battery as buffer for when the car's not there.

And it in fact has been an option on some cars, but not a popular one. It has been described as "worthless"

https://www.reddit.com/r/Hyundai/comments/tayavo/what_happen...

https://news.ycombinator.com/item?id=46456963

Have a look at this, which is a (semi) serious hacker attempt to make it a bit more practical.

https://www.dartsolar.com/ https://www.reddit.com/r/TeslaLounge/comments/194ajsm/my_tes...

He came up with a design where the panels can can unfolded for a larger surface area. But you can only do that when the car is at rest. And it's permanently like having a loaded roof-rack. Its's still less practical than mounting solar panels on the roof of a house or other fixed structure.