Stick a panel on the bloody roof of a house or building and use that to charge the car. It'll do orders of magnitude more good.
Only thing holding off my EV purchase is that I want proper V2G support. If I'm paying for 100kWh of lithium battery capacity I damn well want to use it as a backup for my house.
Why exactly do you want a backup? If you're looking to maintain a few key appliances or internet during a grid outage a vehicle with V2L like an MG4 or BYD might be sufficient.
You probably already know this, but for the sake of providing context to other readers: V2G - vehicle to grid, providing power to the grid from your car battery like is common for home solar batteries; V2L - vehicle to load, a power outlet using energy from your car battery.
I have a 13kW array on the roof and live in a place where ice storms make power outages a thing most years. My solar inverter is grid following. Even if I can't get grid forming from a car I'd only have to pay for a small battery and grid forming inverter to cold start the whole operation rather than $10K of extra batteries for them to do the grid forming. Then I can let the solar and vehicle do their thing and follow the islanded grid during the outage.
I assume this means that no one is using open standards or else you could conceivably just use the Ford Lightning equipment with any other vehicle.
The Quasar 2 bi-directional charger has been on the verge of coming out for years now but still isn't ready to just go out and buy it.
I agree with you though. I work from home and so my EV sits in front of my house for the vast majority of the time, and the battery is more than 2x my total usage during high cost hours. I don't have solar, but I do have time of use rating, so if I could use the giant battery to demand shift, that would save me a ton of money every year.
Specifically, without the neutral, the car can already generate that with the onboard charger. A bidirectional charger costs no more than a unidirectional one if you are designing it.
But generating that neutral is expensive. You either need a hundred lbs of transformer, or some expensive power electronics.
I always find this argument strange and it just feels like an excuse people use to sound informed while also dumping on EVs.
Do you have frequent enough power outages that you need a backup power solution? Why don't you have that solution already? Did the lack of ability to use an ICE vehicle as a generator for your home stop you from purchasing ICE vehicles? What's your definition of "proper V2G support" and why don't current EVs with V2G suffice?
V2G has a number of downsides. The most glaring is that you're stranded at home during a power outage or your house is without power while you go out. It requires to your EV to be plugged in, and won't automatically kick in when the power fails.
The power needs of a home are minimal compared to an EV, if having power during power outages is important then you're far better off investing in a whole home battery backup system. They're significantly cheaper than an EV because they aren't optimized for density and portability.
My last EV used 22 MWh over 6.5 years. That works out to 390W.
My solar array is located at high latitudes (northern Minnesota), the mounting angle isn't great, it's occasionally covered in snow, etc. In these conditions, I need 6.3 solar panels to produce 22 MWh over 6.5 years.
The area used by 6.3 solar panels -- enough PV to cover _all_ my EV's energy needs -- works out to be a parking spot large enough to fit the vehicle but not large enough to fully open any of the doors.
That's so much real estate available that would lower electricity costs, decrease the amount of AC used to cool cars down, and make going to malls and similar places a little nicer for everyone.
In high sun areas there’s a positive ROI
I have solar panels at home and can charge a car .. but I'm mostly parked elsewhere when the sun is shining the most.
You add a lot of complexity for marginal gains. Peak time you get maybe 500W which doesn't go very far.
I haven't made video about solar yet, but I am sharing what I know on https://www.youtube.com/@foxev-content
61 kWh per month in the best month of the year (August)
39 kWh per month in the worst month of the year (December)
As you can see from this, the kWh per day is quite minuscule, not enough to charge a car to go any appreciable distance.
Like everyone else has said - there just isn't enough area on the top surfaces of a car to do any noticeable charging.
(61kWh/month) / (270Wh/mile) / (31day/month) = 7.3mile/day =~ 11.7km/day
(39kWh/month) / (270Wh/mile) / (31day/month) = 4.7mile/day =~ 7.5km/day
My conmute is like 3 or 7 miles (4 or 11 km), depending on where I have to go.
Anyway, I expect that a rooftop installation is much more efficient.
On an actual car that parks under trees, in parking garages, beside buildings in the shade, etc, the actual production would be much less. Not to mention the panel would be 'flat' on the roof and rarely if ever angled facing south, unless you happened to park on a hill with the roof of the car angled south...
It's also not possible to say that a theoretical 39kWh can be turned into so many miles at 270Wh/mile because it's not a perfectly efficient system, I'd guess at least 15-20% would be lost to heat in charging the battery and DC-DC conversion.
You'd get enough surface to get ~4kW
The math does not really work out to a viable product with this bus, but it is not too far off. A city bus that has been purpose-built for low speed in urban areas without other traffic may work as it can make some sacrifices. For instance, since it runs much slower on average it would need smaller engines. It could also use more light-weight material since it won't need to handle high speed collisions. If it is just used for short distances within a city center it could also do away with seats. Lower speed should also lead to lower consumption.
The Solaris Urbino 18 weighs 17.5 tons curb weight. Assuming fuel consumption is pretty linearly related with weight and you could get it down to less than half, you could get a bus with a range of 10 miles per hour of charging. If it drove for 6 hours a day, but got charged for 12, 20 miles on average per hour is possible.
I imagine that could be viable in, say, Dubai or some other extremely sunny place ?
Trams use fixed infrastructure, including overhead power lines. I'm sure they must exist somewhere, but battery-powered trams are not popular.
Yes, they do exist. The Alstom Citadis at Rio de Janeiro, which I take often, uses a supercapacitor for small pieces of its route (mostly crossings where the third rail would be damaged too often by vehicle traffic, or be impractical); according to the Wikipedia article (https://en.wikipedia.org/wiki/Alstom_Citadis), the Alstom Citadis at Nice uses batteries for parts of its route (https://www.railway-technology.com/projects/nice-trams/). I'm sure there are others.
I think it can help calibrate people's intuitions about what you can expect out a pure-solar car.
You also need to remember that inside those shells is basically nothing but a driver. No AC, no seats for people beyond the bare minimum. And that's broad daylight. So you need to look at them doing 20-30mph and bear in mind that it's still not comparable to a street-legal sedan of a similar size doing 20-30mph... those cars are essentially as close to "a mobile cardboard box" as the competitors can make them.
You might be able to build something that people would agree is "a bus" that moves with a couple of people on board, but it probably will stop moving once it enters shadow. Anything that we'd call "a bus" is going to need a lot more physical material per unit solar input than those cars have. I'm not sure that even "moves with a couple of people on board" will necessarily end up being faster than those couple of people walking, either. It's effectively impossible to power a vehicle with its own solar footprint in real time. It also ends up difficult to use them to power batteries because having to move the additional mass of the batteries eats up the advantages of being able to gather power for larger periods of time. It's possible, because of course you can hook a car up to solar panels and eventually charge it, but you don't get very many miles-per-day out of it for what fits on the car itself alone if you work the math.
Commenting here to encourage other HNers to go watch it. Right now it has under 400 views and no comments.
And even those IIRC don't drive continuously. They drive for part of the day, then park them angled into the sun for the other part of the day to top up the batteries.
It's pretty hard to beat fixed panels + fast charging + parking your vehicle in a garage where it doesn't see the sun anyway (or get super hot).
Then you can reduce rolling resistance by using steel tracks and steel wheels ...
... and oh, you have invented the tram/light rail ;)
(But even with solar you need to finance the construction and maintenance, even the slow vehicle need some ... thus either tax finance or charge fares or mix income)
Very location specific, might do wonders in Cancun or San Francisco or Vegas, not so much in Gatlinburg or Seattle or anywhere where there is not a lot of tourism or where there is a lot of rain or that has a long snowy season.
The newest (2023+) Prius brought back the solar roof as an option - and this time it charges the battery (albeit marginally / but not bad for those that drive minimally).
If solar tech gets more efficient or cheaper, I think it starts becoming a much more attractive option in some areas. If you get into the 10+ miles per day range, that would cover a lot of peoples commutes in certain areas.
ETA: and the fact that this option is tied to the significantly less efficient 19" wheel package, instead of the standard 17" wheels, means that this will never, ever be a net benefit.
If this quoted number comes from the manufacturer itself, then I think the answer is "no".
If you’re suggesting it wouldn’t work in a garage, that’s obviously true (and another factor in whether car solar makes sense) but many (most?) people park their cars outside during the day anyway. I for one can’t remember the last time I parked under cover
Most cars are already sitting in the sun all day.
In the old days, they used duty cycle to adapt to the changing load. Modern ones do things like varying compressor displacement or compressor speed to adapt to the load. Variable frequency inverters are used to efficiently drive electric compressors.
The variable displacement trick is used in ones mechanically linked to internal combustion engines. It can vary the compression stroke to account for different load as well as different engine speed.
2.86 miles of charge, but only if left outside, uncovered, in full sun, on a fully sunny day, for a full 8 hours, in a place that gets effectively the maximum amount of solar radiation per day out of anywhere in the entire country.
Now, do the same experiment anywhere else in the country, that doesn't get max solar radiation, or that can't get full sunlight for full 8 hours, or where it's cloudy at all, or rainy at all.
2.86 miles per day is the practical MAXIMUM, given perfect conditions. For the average scenario it'd be some fraction of that.
The 6 miles figure is what they said you'd get if, in addition to perfect conditions, "if the sun shifted its orbit" (?) and gave perfect sunlight for 12 hours straight. Which is a number which should obviously not be thrown around as if it's obtainable.
The fact that they're quoting numbers about what range you'd get if the solar system was constructed differently also makes me doubt the impartiality of their experiment and the numbers they provided.
[0] https://www.motortrend.com/features/the-2023-toyota-prius-pr...
I'm hooking it up via starlink specifically so it works in remote areas with no cell coverage too.
Monitoring and proxying everything via an RPI as well. Victron DC-DC inverter to keep the bluetti battery pack charged with bluetooth relay boards so we can turn loads (camera/starlink/others) on/off programmatically (it only turns the starlink on when there's no good/known wifi for example).
Fun project, combines software dev (which I'm fairly good at) with hardware work (which I'm less) and my dogs (which I'm a big fan of).
But!
That's a practical consideration at the level of "should a government require EV makers to design the roof, bonnet, doors etc. to be tiled in PV in order to reduce, but not eliminate, the induced extra demand on the grid" and definitely not "should I personally bolt a small, fixed, PV panel and inverter into my EV as an aftermarket DIY job?"
The former gets wind-tunnel tests for efficiency, QA, designed around all the other safety concerns cars have e.g. crash safety.
The latter, doesn't.
Compare to a fast charger which will be several hundred mph.
Could be "%/minute" maybe, but that is less useful if you know you need to go 45 miles, you would want to know how many hours (or fraction there of) that would take.
Can't remember how long it took, think a couple weeks at least?
Those are a very small share of car owners, and EVs are nowhere close to the market penetration to care abut them. But it will eventually make sense.
- The panel sits at open-circuit voltage of 48V
- That then needs to be converted/boosted to 400V (conversion loss)
- The converter needs to talk to the BMS to make sure batteries can be charged at this moment (component that is live all the time and is a current draw)
- Need to think about it, but you want another set of contactors between panel and HV-Bus where the battery sits (current draw)
1km of driving is 150Wh so 1kWh gets you 6.6km or 4.1 mi
Let's be generous and say you have a 500W panel(punchy) for 8 hours at full blast (doesn't happen), you get 500W x 8 hrs = 4kWh. Lets say isolated converter loses you 10% so you are at 3.6kWh Thats 24km or 15mi of driving in perfect conditions.
2x Gigavac contactors, keep them closed costs you 24W, so that lowers the input further to 476W * 8hrs = 3.8kWh, less 10% = 3.42kWh ...
Someone who studied EE might be able to make this more accurate. Back of the napkin math, not totally impossible, but not worth adding it for a trickle charge. Adding components that can break, adding weight etc.
There are interesting solar cars out there where you reduce the weight heavily and fold out big solar sails. Then you are getting somewhere, for a city car you don't have enough surface. For an SUV or American Style Flatbed truck you have so much weight it's not worth it either.
I don't drive 24km per day, and don't have a good way to get to the train station other than by car. The bus is too tight, they miss each other often. Cycling isn't safe between towns, you have to basically go on a highway without any separation (yes that's legal in Germany to cycle on, as there is no other way than perhaps a farmer's grass path to go between towns, so they don't call them highways but cars drive highway speeds - or more, if they don't stick to the limit). I also don't have charging infrastructure or a driveway. A vehicle that does those couple km a few times per week without needing to drive elsewhere to charge gets me a long way. Charge me up, Scotty
I've looked into this and the moment the Aptera ships (probably never but here's for hoping) I'm buying my first car. I've looked critically at the range they assume you get at my latitude and it would keep topped up for enough months of the year that it's totally worth it (maybe it was even year-round because they're so efficient, I don't remember now, but I'm also okay charging it thrice a year)
Unless you own a big American pickup truck, it's hard to see where those panels fit on the car. And if you do own a big American pickup truck, you will not achieve the 150 Wh/km assumed by the GP (it will be more like double that). GP also used quite optimistic loss figures for conversion.
It begs the question: Why not a Nissan Leaf and solar panels on your (home) roof?
[1] Only 1000 W of solar energy falls on each square meter of the earth's surface at noon. The best commercially available solar panels have about 25% efficiency converting light to low voltage DC. This means you need a flat surface of about 2 square meters directly facing the sun to collect 2000 W of light, which will achieve 500 W of electrical power.
Maybe it's interesting if you live in a city and drive once a week.
RV panels make sense for the boondocking use case, where you want to charge computers or power a satellite internet terminal or something, but I can't imagine actually trying to drive on that trickle of juice.
https://www.youtube.com/watch?v=BmbH-TAM2Wk&list=PLQp8FoQ4t-...
So you’ll be charging at 2~5mi/h, if the sun is shining straight overhead.
It’ll count for something if you park the RV in the sun for a week as you camp somewhere, but on the road it gives you some limping ability and that’s about it. The main benefit is not running the AC off of the engine.
It has larger surface area, doesn't weight the vehicle down at all even if it's built in a less weight-efficient way, and the vehicle doesn't need to be exposed to the elements.
I put 1800W on my RV and that's covering the roof end to end. I'd guess it'd be enough for something like 1-2 miles a day on an electric drive train, assuming you don't use power for anything else.
Anyway, one could also set up the panel to output a much higher voltage by having the factory wire cells in series (though how well that trades off with partial shading for a car roof I have no idea, and I have no idea the minimum quantity required to get that).
... but I agree, even with all that, it seems like a stretch to make it work.
The complexity should not be overlooked. The PV panels add a lot of things that can fail: An additional layer that must be adhered or fastened the roof. Transparent panel covers that can become damaged in ways that aren’t as easy to repair as a rock chip in paint. Extra wiring that runs into the vehicle. A charging regulator. Systems to monitor that it’s all working and give the appropriate diagnostic codes if it fails.
Having worked on a lot of older and newer cars when I was younger, I’ve come to appreciate a degree of simplicity in vehicles. Modern electronics and vehicle systems are more reliable, but when the number of motors, sensors, and functions in a car goes up by 10X with all of the new features, a lot of little things start to fail in annoying ways as cars age out.
With solar I imagine old car owners would just ignore the system when it stopped working, but you’re still hauling all of that extra weight around for the lifetime of the car. That extra weight subtracts from your efficiency.
If you get 400W watt performance for a few hours per day, that's maybe a couple of kwh per day. 2 would be alright. 4 would be amazing. 6 probably not that likely unless you live in a very sunny place. Most decent EVs do at least 3 miles per kwh. So, you get maybe 6-12 "free" miles per day. Maybe more with an efficient one. Up to 20 miles even.
Most commute round trips aren't that long. You are might need more power than that. But not a lot. You could be cutting how often you charge by some meaningful percentage. It's not going to be that useful on a long journey. But most people don't do those all the time but they drive small distances on a daily basis. Imagine you drive to work, and back maybe covering 20 miles. You go to sleep, and the car is back at 100% charge. Because you only used a few kwh driving there and back and the car had plenty of time parked to collect those back because the weather is nice. Or maybe it got to 95%. The difference is meaningless because you only use a few percent on a given day. Basically you'd be charging a bit less often and stretch existing charges a bit longer.
If you have a 60kwh battery and you get 2kwh per day from the sun, that's 1 full charge per month. Most people would charge maybe 2-4 times per month. So that's a meaningful amount. Cutting them amount of power that you have to pay for by 25 or more percent can be interesting. I think for most the savings aren't going to be dramatic. But it's nice that the car just sits there slowly topping its battery up without you having to worry about it. That's convenient.
They are nice gimmicks like that newer model of Prius but far from being economic reality.
For most of my own commutes, this would mean I’d almost never have to plug the vehicle in. While abundant stationary chargers without stupid mobile app requirements would be preferable, this sounds like a perfectly fine plan B.
I’d miss the sun roof though.
From an economic standpoint solar panels on vehicles are a gimmick.
What would have been a poor investment 10 years ago, or even 5, might well be net-positive today, potentially even in suboptimal weather conditions.
If you can guarantee that, in moderately sunny weather, the solar panel on your car's roof can provide enough power to keep the car going at, say, 30mph indefinitely, that's no longer just a fun toy.
Now, that level of utility may still be a long way off—or may even never be possible!—but I'm not willing to write it off for good, given solar's curve.
ETA: sorry, realized I should unpack a bit why I think this is worth mentioning: Your GP post was expressing confusion over why people would study this; I think it's very valuable to continue studying it as solar continues to improve, so that we can understand just where we are in relation to that utility curve.
I guess it’s a testament to the Netherlands being very compact.
Something to keep in mind: A full EV doesn't require oil changes, which you still need to do with a plugin hybrid.
If you're able to do all your daily driving on battery only, then why bother with a gas engine that you aren't using? High speed charging works very well for the occasional road trip; it's at the point where if you take your bathroom breaks at high-speed chargers, you don't even need to "think" about charging.
A friend of my family is a carpenter who came from a very bad family situation, and is just climbing out of poverty. He has an old Chevy K1500 that gets him to and from work, with all his tools.
His transmission went, but he was able to find one at a local junkyard and swap it in over the course of a day and be back on the road for a few hundred dollars.
If you proposed this guy get a F-150 Lightning (or god forbid, a Cybertruck) to reduce his carbon emissions, he'd keel over laughing.
They did come around in later years, changing their tune to be more pro-EV. A lot of the damage was done, though.
Good reminder with respect to the CAFE standards (rip) that sometimes engineering doesn't trend towards what is "good" with respect to SWaP-C but rather what games the current regulatory environment best.
I'm not trying to say solar roofs on cars make sense as a default option, but focusing on "percentage of battery charged" is the wrong metric. Most Americans would get by just fine on a relatively modest amount of charge per day, especially if we got over our range anxiety of insisting on massively oversized batteries for the average EV, which drastically increases weight and decreases efficiency.
Electrical engineers in 2025 have so many little power drains that any car left undriven for a few months has a dead battery.
A small book sized solar panel is enough to counteract that.
You can literally leave it plugged in charging for a month and come home to find it dead.
Interestingly enough, the quiescent current drain of my 2020s era vehicle is lower than either of my past 2000s era vehicles when I measured it.
The phenomenon of batteries being drained after a few months of being left unattended is not new.
Older cars had this too - I had a bunch of cars which would kill their own batteries if not locked - the engineers assumed that all owners lock the car when walking away, which often isn't the case in your own garage.
[1] this is the switch I got https://a.co/d/90K0QiH
A truck departs NY at the crack of dawn on the longest day of the year and cannonball-runs west at 100mph without hitting a single red light. The sun covers 15 degrees per hr. Denver is 30 degrees west of NY. The truck doesn't quite make it to Denver though, the sun sets on it somewhere in the middle of Nebraska. By chasing the sun, instead of 1700 miles, it gained a whole 1hr40mins of extra sunlight. That 20kW array turns that into 36kWh of extra power. By doing this chasing the sun instead of west-to-east, our truck turned a 1700 mile trip into something like 1718 miles.
On any 'typical' daily long-haul of 600 miles, we're looking at something more like an extra 3000-4000 feet. On something not as perfectly east-to-west like 900 miles NY to Atlanta, we're in the extra 100-200 feet, as long as it's not overcast.
This is nonsense and would easily be proven false except that the article's technical content is paywalled. But common sense says that, if the claim were true, simple economics would make it a reality.
The publishing journal, the "SAE International Journal of Alternative Powertrains", appears to be one of thousands of online-only journals meant to provide a fee-based publication opportunity for authors who have no chance to publish in a reputable journal. In short, the authors pay, then the readers pay -- quite a system.
How large does a solar panel array have to be on a solar laser crop weeder, and how much acreage can it cover on a sunny day?
Is there potential to optimize solar beyond the perceived limits?
torginus•7h ago
nordsieck•7h ago
I want to see a picture of that.
Apparently 1 kw fits on an extended box van [1]. But I don't now how you'd do it on a wagon without making it look like some sort of Burning Man art car.
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1. https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_any...
Veliladon•7h ago
A purpose built EV gets something like 270Wh/mile in near perfect conditions little alone in a colder climate like Sweden.
12.5 * 270 = 3,375
So we've made absolutely every assumption greatly in his favor and we're already 750Wh short.
The math ain't mathing.
taneq•7h ago
Edit: Never mind, “hybrid station wagon”.
IAmBroom•6h ago
pchew•6h ago
Even then, he said hybrid.
nielsole•6h ago
torginus•6h ago
You can play around with assumptions, like what if it was driven in stop-and-go traffic at very low speeds? Then your quoted 270Wh figure might be lower.
But anyways, with these general conditions, with the numbers you quoted, and with a 10 kwh battery (aspull), you'd be looking at a net loss of 775Wh/day, which means you could go 13 days between charges.
The point I tried to make, is that solar panels on hybrids/EVs add a lot of practical value to people who can't charge at home/work, and it's not just meaningless greenwashing.
Also that 2.6kWh figure is a yearly average probably, sunlight varies greatly over the year.
sigio•6h ago
(Driving a full EV, but needing to charge 30+kwh/week, and my small (but larger than a car could fit) home-solar only provides max 20kwh/week in spring/summer.