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
Spot on.
Rough summary of when it is energy and effort efficient: https://xkcd.com/1924/
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.
And more weight means less range.
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.
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.
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.
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
I think they should put windmills on the roof. If you’re going down the freeway that would charge the battery real quick! /s
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.
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.
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.
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
I remember looking at the Prius and it had a solar roof option. I remember reading a MotorTrend article about it. They had to make a lot of assumptions like 12 hours of sun everyday no exceptions and just to break even from the cost of the roof option it would take 5+ years. So not really worth it. You’d be better off just paying for the electricity or putting solar on your house and charging with that.
Edit…words missing
the solar panel was just to run a 12V fan to keep the car cool in the sun. it didn’t charge any batteries.
The title of the article I linked and its subtext is
“The 2023 Toyota Prius Prime Could Take 3 Weeks to Recharge—Without Plugging In
Or, put another way, you can get more than 1,000 miles of free range in a year.”
It most definitely charges the battery.
ah, they’ve gone back to the idea! Sorry, yeah, the only-runs-a-fan was an older model of Prius. Circa 2014.
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.
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!
The math doesn’t work out unless it’s an ultra light car. Check Aging Wheels video on the Aptera for more. The first few minutes, he covers the technical stuff on car mounted pv.
In addition to the other points about efficiency, there is also the maintenance and added weight in a high location on the car that would impact stability and safety. Keeping that slab or solar cells from majing a crash worse would be a large undertaking for example.
Solar panels now are like tube tvs. If we make a breakthrough on paintable or extremely thin and flexible solar cells like we did with the leap to flatscreen tvs then it would be much more likely as the costs come down even if they still provided only a small charge.
That does indeed make sense, thank you (and many others) for the answers!
Wouldn’t it better to just build more solars to power the chargers? It scales independently.
