Also Mount Signal Solar had a 29.7%(average 2015–2017) capacity factor from it’s solar panels. That’s 2.85kWh per day from a single 400W panel. https://en.wikipedia.org/wiki/Mount_Signal_Solar

Obviously most cars never approach that but buyers are going to self select for better areas. How effective this would be in Alaska is irrelevant if nobody buys it in Alaska. California has both lots of sun, high electricity prices, and many people parking outside of shade. Hawaii doesn’t get quite as much sun, but is paying 45.4c/kWh right now.

Because a 400W solar panel is basically the size of a car (~1mX2m). And under IDEAL CONDITIONS, you're looking at a 250 hour charge [1] ... and you're not going to get ideal conditions most of the time.

>Cars are large 3D objects, you aren’t going to get nearly as much power from side panels or the dashboard as the roof ...

You're guaranteed to get 0 power from the sides that aren't facing the sun. So now you're horribly complicating manufacturing for an approach that would provide, at best, miniscule improvement to range.

>How effective this would be in Alaska is irrelevant if nobody buys it in Alaska.

It won't work in California either.

But let's try something else ... with EV manufacturers being obsessed with squeezing out every km of range, why do you think approximately 0 of them are actually building an EV with built-in solar panels? What do you know, that they don't?

[1] Assuming a 100kWh battery -> 100000Wh/400W = 250h

RVs are often parked in full sun at least, but even then. I think I'd be lucky to get more than 5kwhh a day. Which is great for me as long as I'm not running the ACs. But that would not even remotely account for the extra drag it put on an EV to trailer it ten miles.

There've been attempts to make "solar paint" for cars, which would be lovely if possible, but even then I think the economic argument will essentially never work out when you factor in time value of money. As the original article said, the economics will likely always be much better for putting the solar panels on your house and charging at home.

Here’s a random 2.6 kW example which still has a great deal of wasted space. https://youtu.be/Ekoh_QhiJJI

5th wheel with 3kW and still a significant amount of wasted space. https://youtu.be/BPTfkocNEu4

Did you watch that video? The solar panels are not even able to fully handle their appliances and AC, and they still use a generator to supplement. They aren't used for charging a car battery at all.

>but this discussion is about what happens if you optimize the vehicle for solar at the design phase

It still doesn't change the equation because you're not looking at a order of magnitude difference. In the case of RVs and the YouTube videos you posted, you don't need to worry about what happens if you 'optimize' a vehicle for solar during a design phase - just do a back-of-the-napkin calculation by doubling the output and ... nothing changes. The challenges are the same. The use-cases are still the same (namely, hope for sunny days to generate power to run some appliances). You're still not making any meaningful progress towards extending EV range - and that's assuming double output (and you're not going to get double in the real world).

Clearly a camper that people live in has different demands for things like AC and a microwave than a car that’s just sitting around empty most of the day. A 15.5 foot long car is half the length and nearly the same with so downscaling a 3kW system to ~1kW seems perfectly reasonable.

Toyota built a demo by sticking solar panels on a stock Prius and says it added roughly 25 miles per day of range. That would cover the majority of what the average American drives per year. Yes most people would still need to charge their cars, but suddenly using a normal outlet at home rather than paying for a level 2 charger looks reasonable. So not only are you saving on electricity but also instillation costs.

I'm not sure where I've said that because I'm not against solar panels on campers or solar panels in general. Solar panels make a lot of sense in a lot situations. For example, I don't think it's a bad idea for an RV that is frequently off-grid to have them built-in to provide whatever power they can - after all, some power is better than no power. Solar panels on outside parking lots, that makes a ton of sense to me.

Solar panels for EV range extension does not make any sense.

>Toyota built a demo by sticking solar panels on a stock Prius and says it added roughly 25 miles per day of range.

Again, this is under ideal conditions, and it wasn't meant for range extension[0] (i.e. to charge the car while it's moving). But let's go with that for argument's sake .. so you're looking at a day of charging for 25 miles of range. 25 miles is approximately a 30 mins charge connected to the grid. That makes no sense. If you really want to use solar to power your EV just get regular rooftop solar and charge your car from your mains.

[0]https://www.torquenews.com/8113/toyota-prius-solar-game-chan...

And as the original article points out, when Toyota says they add 25 miles per day, they are doing so under nothing even remotely like real world conditions. They’re surely counting on full sun, flat driving with no air conditioning running, etc. An actual user likely wouldn’t even get half of that.

You can approximate aerodynamic curves with multiple flat segments, cyber truck being an over the top example. It requires extra panels to cover this 3D shape. However, those extra panels also collect more light than a simple flat panel would over the course of the days. In effect the amount of direct sunlight you collect is limited by the minimum flat panel which would cast the same shadow.

Uh huh. Do you want to put some numbers behind your assumptions. How much do you actually think you can generate that would make a difference to a Tesla 60kWh-100kWh battery? How much extra range do you think solar panels would provide?

And finally, what aren't EV manufacturers seeing that you are seeing? It's not like solar panels on an EV are such a novel idea. In fact, it's the very first (naive) idea that everyone has as a potential solution to EV range and charging.

So, assuming 4miles per kWh that Prius was expected to hit over 6kWh per day. That might not look like much vs a 100kWh battery pack but it’s 9,000 miles per year when the majority of Americans are only driving 13,000 or less.

Their design doesn’t look practical, but 5kW/day in sunny areas seem to be a reasonable real world goal.

I checked your link after reading your math, above. Coming from the RV solar world I found these numbers surprising. I think your comment about the 100 kWh battery pack threw me off. The normal battery in a Prius is 8.8 kWh with a 25 mile all-electric range [0].

Toyota is saying that the panels they used generate approximately 860 watts of power. The normal rule of thumb in the RV world (which I am familiar with) is to multiply panel wattage by 5 for kilowatt hours per day in good sun, so I would assume 5 kWh total per day for 860 watts of panels, in real life. So their numbers look optimistic to me, but aren't crazy - I would have said 15 miles under ideal conditions (5 kWh of their 8.8 kWh 25 mile battery), they said 44.5 km. They used a 34% efficient panel to get these numbers, something normally only available to the likes of NASA at this time.

Only people in places like Arizona and Texas would get most of that power output, others not so much. I don't think people realize how much impact clouds, shade (even partial shade, even a bunch of bird crap), and optimal panel angle towards the sun have on solar power output. For example, in 2021 Germany had 58728 MW of solar panels generating 49011 GW of power per year [1], which is 134.2 GW per day, which is only 2.3 times their panel capacity, and this is due to clouds. So instead of 25 miles or 15 miles that car in Germany may only get 7-12 miles of extra solar powered range, and perhaps a good bit less because the car panels are not oriented towards the sun like fixed panel installations usually are, and people park in shade under trees or next to buildings sometimes, winter when it's below freezing and cloudy and the battery needs to warm itself to safely be charged, etc.

The only other thing I would add to this discussion is that panels fixed to the surface of a car may have problems with heat. Normal rigid solar panels are in frames and elevated, allowing air to flow under the panels and cool them. Panels loose efficiency with heat. Flexible solar panels, which don't need a frame and can be attached to curved surfaces, typically fail in a year or three, they are nowhere near as reliable as rigid panels. There's a lot of discussion about this in the RV and boat communities.

If the numbers work out on this idea, then that's great. Reliability would be my biggest concern, these panels need to last to pay for themselves.

[0] https://getjerry.com/car-repair/toyota-prius-plug-in-hybrid-...

[1] https://en.wikipedia.org/wiki/Solar_power_in_Germany#Generat...

You mean in 2019.

>or dashboard which they say adds 25miles of range per day.

They made a prototype. They didn't say how much extra cost it would add to the car (and how it affects reliability, maintenance and safety). The cost of those panels has to be balanced by the fact that 25 miles is 30-60 min charge from your mains vs a day of charging from solar?

They also made a point to state this wasn't for range extension - i.e. when you're driving, that solar panel isn't contributing meaningfully to your range.

>Their design doesn’t look practical, but 5kW/day in sunny areas seem to be a reasonable real world goal.

You and I have different definition of 'reasonable'. Like I said, there's a cost to putting these panels on the car and the benefit is so effin small (even sunny areas have cloudy days and/or your car is frequently parked in the shade or indoors) that it's much more reasonable just to plug the darn thing into your mains and charge that way.

Did you bother looking up panel sizes? One large panel (5.4'x3.25') is most of usable car area. Sure, maybe you can put 2 or 3 - at vastly lower return due to being tilted towards the sun.

Do you really think that you can get more power over the entire surface of a car, when most of it will be tilted to the sun, as you can get from an entire panel optimally placed?

Go ahead and demonstrate.

>Mount Signal Solar had a 29.7%(average 2015–2017)....

Did you bother to check any of the math?

For example, the single 400W panel is a First Solar Series 6 440W, 80"x49", that and they use trackers to make them align to perfectly to the sun. Want to estimate what you'd expect from a car? I don't think you're putting an 80 x49" large flat surface on it, unless you want to drag losses to vastly outweigh anything else. Other panels in later phases are even worse when you think they apply to cars.

I'll never understand how people think the most ideal, large scale installation at ideal location, with moving trackers, will yield the same on a car with nearly zero surface at ideal angles.

>buyers are going to self select for better areas

How well are these solar cars selling in these best places? That might give you more insight.

Solar options on EV’s will always be niche. Probably less than 20% of people would see significant benefits. However, as the percentage of EV owners increases that ratio should stay the same. 5% of EV buyers (themselves 5% of car buyers) the market isn’t very many people. However if EV’s made up 75% of new cars then 5% of that is a more significant market segment.

For now I suspect cars with an extreme focus on solar will flop. But, a base model with modest styling compromises and 2 levels of solar options roof vs every surface could be quite popular. In the short term a solar on a van seems to be the obvious option with the smallest compromise. It’s stick with large nearly flat surfaces to maximize internal volume, so why not toss in solar.

????

By approximate you mean lose signifcant energy?

A car is a closed manifold. Take the area it casts a shadow on - that is the area a solar tracker would get ~100% of the sun's flux. A general closed manifold (which is prefect for a car since the car and sun will move) will get ~50% of that energy. That's pretty massive.

A simple way to compute exactly 50% loss is for the area of a shadow from a sphere - a tracking disk with that area would get pi * r^2 of the energy. A sphere with the same shadow would get 50% of that (set up, integrate).

Do you even check these claims?

Of course you'll fixate on a sphere vs a car, but make any closed manifold, let the sun move throughout the day, and you will end up with pretty much the same result (via theorems on total curvatures on closed manifolds stuff).

I recommend sketching this out for yourself.

So go ahead and demonstrate my lack of reality. Post your panel stats and math. I did.

Have you looked at the size of solar panels per watt and the flat area available on a car?

I have solar panels on a boat and the area is approximately (don't have measurements here with me) about the size of the roof of a regular sedan. All I could fit there was 110W worth of panels. If you have a long, wide SUV you can do more but only so much more.

In practice, those 110W worth of panels really only deliver 40W-50W to the batteries on a good sunny afternoon in California. The angle isn't perfect just like it won't be on a car which reduces output quite a bit.

It's worth it on a boat because I'm only charging the batteries to power the electronics so it's borderline enough. On an EV which uses tens of kW to move, it would be a microscopic contribution.

On a car or small truck there just isn't enough sunlight to make a difference even at 100% efficiency (last I heard labs were getting in the low 40% range using tricks that probably don't apply in the real world). However for large motor homes (and possibly semi trucks) there is enough roof space to make a difference. Motorhomes often stop for a few days at a time so can get some useful range (or at least not use the batteries running the stuff inside).

In no case though is anyone thinking about saving money with solor on a moving vehicle. The large ones can possibly get enough range to be worth the extra costs even though it's costs more money.

What I'm seeing on this topic is a lot of folks that I can only assume have never spec'ed out and used a solar installation. Go throw some panels on the roof of your house and RV, and then we can talk about how "all we have to do" is put panels on a passenger car. Not one of the "all ya have to do" crowd has mentioned how efficient their solar installation is, how the math works. Nope, it assumes a spherical cow, yada, yada, yada, and the sun is always pointing at a direct 90 degree angle to the panel.

The 410W on our RV, for example, is good for recharging the house battery after running the microwave to make breakfast. If it's cloudy, you won't get to run the microwave for supper, but at least the lights can stay on.

With some quick-and-dirty visual estimates from the charts, I'm coming up with about .85kWh/day. Yeah, I know, but I looked at it twice. I went back and looked at some other time periods as a sanity check. And <1kWh/day is what we get. In the summer. Right now the RV is sitting in the drive with the panels uncovered, and the driveway is sloped and slightly angling the panels to that sad little January-in-Seattle sun. Yesterday the panels cranked out a massive 0.1kWh. That's right: enough to run a 100W light bulb for an hour.

Despite all that, it's enough to run the microwave a couple of times a day (which is really the only large draw the RV has), watch some TV, run the lights at night. And if the panels can't keep up, that's what the giant-ass 300ah lithium house battery is for.