Why don't electric car manufacurers put solar panels on the car roofs?

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.

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.

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

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.

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.

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/

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.

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.

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.

Popsci article.

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

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.

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.

Wouldn't it better to just build more solars to power the chargers? It scales independently.

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.

For range it doesn't add much in most cases. But it also depends on how long between journeys you have. If you're traveling in a van and you are going to be stationary for a few weeks at a time then it can start to make sense, maybe with an extra fold out.

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.

The new Prius Prime has an optional rooftop solar panel.

According to an article in Slash Gear you can get about 4 miles of range after 9 hours in the sun.

So it has the potential to marginally increase your range on the scale of a short commute under ideal circumstances, but it's not much apparently.

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.

The Dutch have been working on this for ages : https://lightyear.one/

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.

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.

https://en.wikipedia.org/wiki/Sono_Motors_Sion

It would increase the cost and also complicate the manufacturing process.

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.

Thanks for posting the question! Whole point of the community.

I think we'll see more of this in the future as they continue to make progress on inexpensive "solar paints" and the like. It's not a bad idea, it's just that the tech level doesn't show much bang for the buck...yet.

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.

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.

Also where I live, most cars spend a long time in underground (or at least covered) garages

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

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.

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 same could be asked with smartphones.

Why don't smartphones include solar panels on the back side of the phone?

This guy heard you:

https://youtu.be/qPENum9DFFA

It would be cool if they were built into the highway and could charge your car as you drive over it. That might make toll roads almost worth it.