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.
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.
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.
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.
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.
All newer cars do this. It’s called regenerative braking.
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.
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.
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.
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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.
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!
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.
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.
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.
