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

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.

kinttach ,
@kinttach@lemm.ee avatar

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.

Upsidedownturtle ,

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.

daq ,

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.

mortalic ,

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.

eyeon ,

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

TheFriar ,

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?

joostjakob ,

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.

ryathal ,

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.

Cryophilia ,

All newer cars do this. It's called regenerative braking.

COASTER1921 ,

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.

mortalic ,

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

Boozilla ,
@Boozilla@lemmy.world avatar

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.

snooggums ,
@snooggums@midwest.social avatar

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.

Blubber28 OP ,

That does indeed make sense, thank you (and many others) for the answers!

bobburger ,

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.

dgriffith ,
@dgriffith@aussie.zone avatar

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.

hungover_pilot ,

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/

DaddleDew ,

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.

CookieOfFortune ,

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!

stsquad ,

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.

ramble81 ,

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.

Successful_Try543 ,

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.

OhmsLawn ,

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.

BombOmOm ,

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.

SomeoneSomewhere ,

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.

Fedizen ,

such as parked at work or in a summer traffic jam?

SomeoneSomewhere ,

You're better off putting the panel somewhere where it always gets sun, and isn't extra weight you have to haul around.

forgrytaboutit ,

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.

whodatdair ,

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.

https://youtu.be/DDmeqLEB9c0

Edit: oops, I’m combining two of his vids in my head, this one is just solar not pedals.

NABDad ,

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).

whodatdair ,

Ah crap, you’re right - that’s another video of his, apologies

Bigfish ,

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.

BlameThePeacock ,

What kind of ev are you driving? That's insanely high energy usage.

My EV gets about 6km per kwh (around 4 miles)

Guest_User ,

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.

Phil_in_here ,

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

Guest_User ,

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

doughless ,

I'm still a little confused, wouldn't 6kwh provide roughly 12 to 24 miles of driving range?

Guest_User ,

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.

doughless ,

Right, which is why people are confused. Fish likely meant 3.3 miles / kWh, but that comes out to 20 miles for one hour of charge. But the fact they said just under 2 miles of range actually correlates with their 3.3kWh/mile statement, but no one has ever heard of an EV with efficiency that terrible.

Deestan ,

Spot on.

Rough summary of when it is energy and effort efficient: https://xkcd.com/1924/

setsneedtofeed ,
@setsneedtofeed@lemmy.world avatar

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.

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