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).
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
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
The first generation Hyundai Ioniq 5 had solar roof (at least some models).
The first gen ioniq 5 also had a very low payload capacity, with stories of families who couldn't legally be in the car at the same time without being over the capacity.
The reason, I'm told, is that supporting the solar roof reduced the payload capacity a lot.
Also, solar cells on a car doesn't make much sense like others have already said.
Assumption:
Someone crams a 300 watt solar panel onto the roof of their EV and manages to integrate it into the charging system so that it's pretty efficient to use that power.
Numbers:
One hour of good sunshine on the 300 watt panel = 300 watt-hours (Wh).
Average EV energy usage : 200Wh per kilometre these days. Maybe a little more, maybe a little less, depends on how and where you're driving.
Result:
One hour of perfect sunshine hitting the roof of your car equals 1.5 kilometres of extra range, or you can drive your car in a steady-state fashion at a 3-5 kilometres per hour because an EV is more efficient than the average usage at lower speeds.
Conclusion:
Probably better off increasing the storage capacity of the battery as a full day's sunshine will get you about 10 kilometres of range.
Look at the Fisker Ocean, it adds almost no range or energy, and leaves horrible and distracting shadows on the passengers. Youat as well ask why you can't charge a car with a D battery.
The amount of power you could pull from a single square metre of solar on the roof wouldn't increase your range meaningfully.
What it would do, is that you could possibly keep your starter-battery from going dead-flat if you left your car alone for a 1/2 month, in the summer ( snow would cover it, obviously ), & since bringing a lead-acid battery to dead-flat permanently-damages it, this would prevent costly problems for the car-owners.
( this happened to a friend with a Prius: had to replace the battery, and the damned thing was inside the rear wheel-well??? in a little compartment.
Origami-engineering's .. simultaneously incredible & stupidly-frustrating )
I've held for years that they should be doing it to keep the starter-battery trickle-charging, but .. why make the customers have fewer costly/frustrating problems?
on the roof doesn't make much sense. What I did see the CSIRO testing was a portable solar array that you could roll up and store in the boot. IIRC they drove a Tesla across a large swath of Australia stopping and only charing on the portable array as needed
I don't remember what car it was but an ex's car had this. It was only really used for keeping the car from getting way too hot while it was off in the summer.
They have them on some international models of Hyundai electric cars. It's not nearly enough to power the car or charge the battery, though. It's more to just slow the battery down while it powers low-power things and look cool (it's part of the trim package). Solar panels need to be way more efficient than they are now for them to really make a difference with such a relatively small surface area.
Even on ideal conditions (close to the Equator, no clouds) like in Northeast Brazil, you only get 5.5 to 6.0 kWh/m^2 of Solar energy, which means the roof of a small car, with 1 m^2 of solar panels, would only generate that amount of electricity if they were 100% efficient. That's just 10% of the battery capacity of a small EV, like a BYD Dolphin.
My point is, even if solar panels doubled their efficiency, they would still only capture about half the energy of the Sun (currently, the best panels are at 24% efficiency), which means only about 2.5 to 3.0 kWh per day.
I have a very vague memory of watching a video where someone calculated the amount of energy produced, which was minimal. The benefit vs the cost is very poor.
Solar cells on a car have no real use. You would have to leave the car out in the sun for weeks to months to charge it up just once.
The materials are more expensive and heavy than what car roofs are normally made of, and the charge they would generate is miniscule. It may not even offset the added energy needed to move the car because of the added weight. Particularly if you live far from the equator, or somewhere cloudy, it's probably not worth it.
When I was a kid (in the early 00's) there were solar cars on TV and they were always these absurdly shaped pancakes made of ultralight materials and couldn't even reach road speeds. I'm sure the tech has improved since then, but the real innovation that made electric cars possible was batteries. It's hard to generate enough energy on the same platform you need to move without it being too heavy.
There are some, but as mentioned several times, the traditional car is too heavy for solar panels to be effective. There are some vehicles that are essentially enclosed motorcycles like the Aptera where it can be effectively used, though. Aptera can use solar panels effectively because even at their largest battery capacity, it's still significantly lighter than an EV sedan.
While that might not be economically feasible, I've always wondered why plug-in electrics couldn't send power back into the grid. No solar? Send energy onto the grid during the day from the car and recharge during the off-hours at night. Solar? Recharge during the day and send energy onto the grid at night. Just make sure to set a minimum charge that will get you to a charging station.
Some do, but to do this, the point of entry to the grid needs to be set up in such a way as to support this, with an automatic transfer switch for when the grid disconnects, and a meter that reads energy use as both incoming and outgoing, rather than the default of all incoming.
Source: am electrician who has installed batteries on peoples houses
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