Honestly it seems like a no-brainer to me to put a solar panel on the roof of electric cars to increase their action radius, so I figured there’s probably one or more good reasons why they don’t.
Also, I acknowledge that a quick google could answer the question, but with the current state of google I don’t want to read AI bullshit. I want an actual answer, and I bet there will be some engineers eager to explain the issues.
What I have seen previously is that the amount of energy you get from the solar cells that you could fit on the top of the car is really small compared to what it takes to charge the battery.
Since there is minimal benefit, and it’s costly to include them and wire them to the battery, it hasn’t been viewed as worthwhile.
Yeah this is what I’ve heard as well. Aging Wheels goes into it a bit in this review of a concept car, kinda neat - it has pedals like a bicycle but the energy they add is a tiny fraction of what the thing needs to move.
Edit: oops, I’m combining two of his vids in my head, this one is just solar not pedals.
it has pedals like a bicycle
Are you taking about the Aptera from the video you linked?
If so, the Aptera doesn’t have pedals like a bicycle. It’s a fully electric vehicle (or it will be if it reaches production).
Ah crap, you’re right - that’s another video of his, apologies
For comparison, my rooftop solar array, with around 16 full-sized panels (~6kwp) produces just under 2 miles per hour in my electric car (around 3.3kwh/mi). Or in real life, takes about 2 fully sunny days to produce the power to charge the car.
What kind of ev are you driving? That’s insanely high energy usage.
My EV gets about 6km per kwh (around 4 miles)
You get 4 miles per kwh and they get 3.3 and you call that insanely high? The 2.5-4 mile to kwh is really standard for EVs. I don’t think the 3.3 is outside of the norm at all.
I don’t know anything about EV efficiency, but the rates are inverse, so they are drastically different.
Fish gets 3.3kwh/mile
Peacock gets 4 miles/kwh or 0.25kwh/mile
Oh I see that error now. I guess I just assumed from context his 6kwh panels generated 2 miles per hour. I get the confusion though
I’m still a little confused, wouldn’t 6kwh provide roughly 12 to 24 miles of driving range?
They mentioned their car uses 3.3 kwh per mile. With their solar setup they can generate around 6hwh per hour. Meaning they can generate roughly 2 miles every hour of sunlight.
Fish reversed the numbers. It should have been miles per kWh
Spot on.
Rough summary of when it is energy and effort efficient: https://xkcd.com/1924/
A few of them have. The core issue is it doesn’t add much range, while at the same time adding more cost, weight, and complexity. On a sunny summer day you can expect to get single digit kilometers added to the range, while on a cloudy winter day you won’t get even a full kilometer added.
They do make some sense on hybrids, as they are lighter so the range increase is a bit more and people are less likely to charge a hybrid. But, they still suffer from not adding much range, while adding cost, weight, and complexity.
Edit: Auto Focus did a re-review of the Fisker Ocean, which has solar panels. Linked to the timestamp where he is talking about them.
Bear in mind also that the extra weight and possibly aerodynamic compromises actually reduce range. In some cases, particularly at night, in poor weather, and at high speed, the panels would be a net negative.
They would only be useful if your car sat around in the sun for long periods without access to a charger.
such as parked at work or in a summer traffic jam?
Parked at work it will probably have a building nearby that creates a shadow. In a traffic jam, assuming perfect sun conditions and no shade, a 100W panel will generate around about 500m (or yards) of range per hour. Meanwhile the AC will use about 700W to 1kW of power to prevent your face from melting.
Some tests on YouTube report a realistic addition of 1 mile per day using the car in a typical commute.
Depending on the car and the temperature, AC Is simply not an option (same for heat) in a traffic jam. I drove a 2019 Nissan Leaf (with 12/12 battery bars and normally 80-140 miles in range, depending on the season)for my 19 mile commute for a while, and had an awful time during subzero temperatures (~-20 Celsius) once. I went from fully charged on the work chargers to considering breaking out my reflective emergency blanket in three hour stop-and-go traffic so as not to kill my battery before home. I stopped to charge and it took much longer than usual, to the point that I just gave up and used my hand warmers and hoped on the way home.
I don’t blame the car for that, I was unprepared for the predictable consequences of cold temperatures on electric cars, but it was still super unpleasant.
Leafs have battery packs with no active heating or cooling, which significantly impacts their performance in bad weather and when fast charging. Coupled with very small packs in the early models, and you have a recipe for a bad experience.
You’re better off putting the panel somewhere where it always gets sun, and isn’t extra weight you have to haul around.
Doesn’t provide enough power for the cost of the cells, plus having to clean and upkeep them. And the more material you cover them with (to protect them; solar cells are INCREDIBLY fragile), the less efficient they are. I was on a solar car team in college and the cells are so fragile that to clean them, we had to use new microfiber cloths every time. Any dust would scratch and ruin them (which made it quite tough when I drove across the outback in the thing). We kept our cells completely uncovered because we needed maximum efficiency - but even with a super light carbon fiber solar car that’s got very minimal tire contact patches, specialized tires from Bridgestone, and a very aerodynamic shape (plus no amenities like A/C), I think our car could sustain something like 10-15 km/h on a perfectly sunny day in the middle of the outback. It just doesn’t add enough on a huge, heavy EV
So a solar golf cart might be doable?
A 9v battery powered skateboard is viable if you pick the right combination of weight, speed, and distance. Doesn’t mean it’s going to change the world.
On the other hand: most cars are not moved 23h a day. They just stand around.
A lightweight solar panel could be a worthwhile range extender in at least some climates.
On the other hand: most trips are made to the exact same place, why move solar panels around when you could just leave them in place (especially if the car isn’t moving for 23hr)?
On the other hand: most cars are not moved 23h a day. They just stand around.
It doesn’t take much shade to have a signifigant reduction in the output of a solar panel.
Unless you are parking in an open field with no trees or tall buildings around, your power generation will be signifigantly reduced.
Not that the amount of power generated by a panel the size of a car roof is all that much, even under ideal conditions.
Exactly. And what’s worth remembering is that solar cars tend to be something like 2X longer then normal cars, and cover the entire surface except for windshield with panels. No rear windshield, either.
I’ve seen some prototype solar panels that roll up like a carpet for easy storage. Keep it in the trunk, lay it out when you’re gonna be parked somewhere for a while.
Now THIS is podracing
And more weight means less range.
Having solar cells uncovered by glass is baffling
Yeah, it’s certainly a good thing it doesn’t hail in the outback lmao
The Fisker Ocean has solar panels on its roof. It can add 4 or 5 miles a day if fully exposed to the sun.
Not enough to matter. It’s a gimmick.
If you don’t have an EV, you may think that EV owners are worried about range, and they’d welcome any increase. I have not found this to be true.
It’s more like having a car that starts every day with a full tank. You’re never going to burn through that in a single day. Pretty soon you don’t care about range, efficiency, or pay much attention to the battery meter. It only matters if you’re on a road trip, which for me is a couple times a year.
I would not want to give up a nice full-roof sunroof for a few extra miles a day.
The newest revision of the prius has an option for rooftop solar. The break even point is relatively long, in the 5-8 year time frame iirc. The energy generation isn’t massive; at 185w it won’t substantially extend the range something like 5 miles per day.
For an extra miles a day… if you park in the full sun all day every day. Garage? 0. Driveway? Probably shadow half a day.
if i park in the shade, and therefore don’t have to turn on the ac as soon as I get in, I think that would be about the same, savings wise.
Right. Unless you live in US and have relatives you regularly visit in a different city in the same state only 400km away.
I mean I still don’t care about solar panels on my roof and I’m much happier with a moon roof on my PHEV. Nearly 80km of electric range means I’m driving an electric car 99% of the time and have convenience of 5 minute fill ups when I go further.
Modern EVs such as Teslas have a high power consumption, much higher than some PV panels on the roof could deliver. Thus, it would only increase the weight of the car while not significantly increasing their range.
In addition to weight, there’s cost. They would have to be integrated into the design, not just normal, flat solar panels, so there’s a significant cost increase. It’s no problem on a delivery van, but anything curvy is probably prohibitively expensive to develop and produce.
Aptera is doing this with custom solar cells and they claim it’ll provide up to 40 miles of range per day. https://aptera.us/
I was about to say that. The main reason why they can do it is that Aptera went great lengths to make their vehicle as light and efficient as possible so what little charge they get out of the panels will make a noticeable difference.
This is a stark contrast with the other EVs on the market that are just huge heavy bricks on wheels that compensate for their inefficiency with bigger and heavier batteries.
To put this in perspective… The Aptera claims it with charge at 13mph on level 1 charging. This means if you plug it in the a regular wall socket, you’ll get 13 miles of range per hour.
The full solar package(~2000 dollar add on) get 40 miles of range, per day, under ideal sunlight exposure. That’s roughly a little under 4mph of charging. With a purpose built solar setup, which covers the rear window and even puts solar panels on the dashboard.
The Tesla model 3 gets something like 4-5mph charging on level 1. The full solar package from Aptera might be able to add about 8-10 miles per day in ideal conditions.
Because the aptera is ridiculously efficient and they cover way more than just the roof with the panels. I love the car, but it ain’t something I would consider mass market.
Plus, this again assumes you park it in ideal sun conditions, sun directly overhead (for the panel inclination), no shade anywhere around etc. Famous “up to” values.
I’ve been following them for a while now and hope they can make it into production. Their focus on efficiency and repairability is quite exciting!
Solar panels on cars are thought of the wrong way. The responses in this thread really demonstrate that.
It’s true that they’re kind of pointless on EVs, because they’re never going to supply enough power to not need a proper charge, which makes the panels redundant.
Where they could be useful is hybrids, sold as something that makes the engine 10-20% more efficient.
I vaguely remember reading something about a Prius with solar panel on the roof. It was enough to run a small fan to keep the interior a little cooler. In theory it improved efficiency because the air conditioning had less work to do
While most of the points are covered here, and it’s likely true that the cost to add the panel and micro inverters is high, (I built a small two panel one battery off-grid system for about $4000 to power a chest freezer)… I have a counter point that I feel should be considered.
While it’s true that it isn’t going to extend driving range by much, my thought is that it is still worth it. Take these examples:
Drove to great wolf lodge in the summer, left car in parking lot for 3 days without charge. It lost several %.
Left car in an airport lot for a week lost even more power.
Drove to NorCal, left car at Airbnb driveway, had to find charging despite the car sitting in very bright sunshine for 4 days.
Car camping
Apartment complex parking (literally one of the main negatives about EVs)
All of these would benefit from trickle charging, even if it was just to prevent the drain of sitting.
the question then becomes how much weight are you adding/energy are you consuming by having to carry the weight. I honestly don’t know and considering how heavy batteries are it is likely not that significant, but if you are only getting a few % charge a day then anything eating into that is going to hurt.
I still see some merit in a more utility style vehicle where you do expect to take it out camping, but for a daily commuter I think most people would prefer the sunroof to the trickle charging.
Also as an apartment dweller… I just wish they’d make normal wall outlets more available. Not everyone needs a proper fast charger but only having a few inconveniently located ones to fight for also sucks. But if more spots could just plug in and slow charge that would be a huge improvement
You seem to know what you’re talking about and I want to piggyback off this question to ask why they don’t harvest energy from the brakes or the wheels spinning. I always heard braking once could power a home for a day or something. And I assume if you put a passive spinning wheel power generator on each of the four wheels, you’d also produce a lot of energy. Are all of these things too heavy to have any benefit? Plus the wind passing the car as it drives…it just feels like there are a lot of missed opportunities for new energy production as the car moves that aren’t taken advantage of. What’s holding these ideas back?
Electric cars do charge when braking. Obviously the energy recuperated is less then waht was needed to drive that fast in the first place. Using driving wind would just increase the energy needed to drive that speed and would be net negative.
Most electric cars have regenerative braking. It’s not magic though, it takes more energy to speed the car back up than it recovers. Regenerative braking just makes stopping less bad for range. Sure you can go down a mountain and gain a lot of power, but not enough to go back up the mountain.
All newer cars do this. It’s called regenerative braking.
What car do you have? I worried about this for my Model 3 back in 2021, when it had some vampire drain. But if you don’t open the app on your phone, the car goes into deep sleep and it can be parek for weeks without a single 1% loss.
The problem is that this isn’t really even trickle charging. Customers would absolutely complain and say it’s not working because it couldn’t charge the battery more than 1-2% in an entire day of sun. EV batteries are 60kWh+ yet getting more than 2kWh/sq meter daily from residential panels is hard for much of the US. Add to that the:
- weight of panels
- cost of panels
- heat trapped in the car from having a roof literally designed to absorb solar radiation
- fragility of panels (although all these glass roof EVs have that problem already) And it’s really not worthwhile.
One solution to the apartment street parking problem is adding charging ports to streetlights (they do this in Europe). But for most of US apartments there’s already dedicated parking space so also space for chargers. The unruly size of new vehicles is a much bigger problem in my mind, if there were actual motivation to fix this problem in government it would already be solved through some tax credits.
Replying to my own comment because I just stumbled upon uncle Rich doing exactly this on a cheap chinese EV truck.
It’s kind of a fun take on the crappy truck too. youtube link
Everyone saying how little energy a solar panel will produce in optimum conditions.
I don’t think anyone has mentioned how difficult it would be to get optimum conditions for any significant portion of the day.
If you think about the places you park, how many of them have uninterrupted line of sight to the entire arc of the sun? Right now my car is parked on the street but it’s in the shadow of a building.
Even if you have the option to park directly in the sun, would you?
Being in a car that has been heating up for several hours of direct sun exposure is grueling. Switching on the AC to cool down to acceptable temperatures will probably drain more battery then was gained by the solar panel.
Another really good point.
… a different way of looking at it is that it’s just way more practical to put solar panels in other places, like on the rooves of buildings.
Additionally, there seems to be an assumption amongst middle class suburbanites that everyone should just have roof top solar. Of course, the vast majority of humans to not have any roof space, because they live in an apartment.
I would also point out that my spell checker seems to think that the plural of roof is spelt “roofs” but I’m sure it ought to be “rooves” in the same way the plural of hoof as in part of a horse is hooves.
I would also point out that my spell checker seems to think that the plural of roof is spelt “roofs” but I’m sure it ought to be “rooves” in the same way the plural of hoof as in part of a horse is hooves.
According to Wiktionary, both seem to be correct, but ‘roofs’ is the common variant.
Being in a car that has been heating up for several hours of direct sun exposure is grueling.
Ahh, beach days with mum. I remember the warm sand, cool lake water, and the layers of flesh burned off my young legs when we got into the car. Those days, we got our exercise writhing in place to avoid the worst of the burns until the car got moving enough to cool the seats down. Thankfully seat belts were optional, then.
Yall didn’t just put a towel on the seats?
Bring a wet towel inside the car? Are you mad?!
TLDR solar panels have a lot of inefficiencies, which makes them more of a detriment to mounting on standard commuter cars when you take into account the effects of the added weight.
I think they should put windmills on the roof. If you’re going down the freeway that would charge the battery real quick! /s
Obligatory windmills do not work that way, also that’s exactly how an alternator works.
But… That’s exactly how a windmill works.
Windmills don’t generate electrical energy. For that you need a wind turbine.
Windmills don’t generate electrical energy
What if you used them to grind pizeoelectric materials like quartz? 😌
Nah physics is fake news
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the solar panel was just to run a 12V fan to keep the car cool in the sun. it didn’t charge any batteries.
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ah, they’ve gone back to the idea! Sorry, yeah, the only-runs-a-fan was an older model of Prius. Circa 2014.
Once upon a time Audi had solar panels on the roofs of their car and it could only generate enough power to run the cabin fan to try to cool the car down while you were parked.
To give you an idea of the sheer amount of power that an EV requires to move its bulk, look at the sizes of their batteries vs home battery packs. An EV has battery packs of around 100kWH and that can get you a few hundred miles range at most. Now compare that to the requirements of a home battery. The average use for an entire home is about 30kWH per day, and most home batteries only recommend 10-15kWH.
Looking at that you start to see the massive difference in power usage required. To charge a small home battery like that you usually need multiple panels (10+). They just don’t have the space and power generation to offset the sheer amount of power EVs require.
Because it barely matters. Like putting an extra AA battery in the glove box.
Well now the question is why they don’t put an extra AA battery in the glove box.
Then you can use your glovebox battery to jump your main battery when you leave the light on!
Wouldn’t it better to just build more solars to power the chargers? It scales independently.
