Impacts of adding PV solar system to internal combustion engine vehicles
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I have a two complete solar systems on my house the first one was 10.98kW AC installed 4 years ago with the panels facing south. The second was just installed a few days ago and is a 9.9kW AC with the panels facing east/west. Combined the system will produce over 20MWh of power per year. Both systems are grid tied used EnPhase microinverters and are now combined together for monitoring in one site.
I have an EnPhase IQ EV Charger. This has a mode where it communicates with the solar system, understands how much power is being produced and consumed in the house and then adjusts the EV charger output to match the excess solar production.
I have an EV with the largest battery that is available. The Chevy Silverado EV truck has 24 battery modules with a total gross capacity of slightly over 200kWh. The efficiency on road trips at high speeds is about 2.1miles per kWh. I have verified this with a real world road trip of over 400 miles.
The cost of the solar is around 5 cents per kWh over the 25+ year lifespan of the system.
Unless you're consuming a significant portion of that, the payback rate is going to be pretty badly impacted by having such a large system for most people.
I will have overproduction now with the 2nd array. We do have net metering at about 80% of the cost on NEM 2.0. Our bill is split by transmission, generation, distribution and fees. We get 100% on transmission and generation and 25% on distribution.
https://www.energy.nh.gov/sites/g/files/ehbemt551/files/inli...
However, looking at getting an EV - were you able to get bidirectional charging going?
I saw a few places mentioning demos of it over the past 5 years, but I can't find any v2x charger/car configurations I can buy and use in the UK.
Before looking at any of this stuff, I didn't realise how large and cheap the battery in an EV is compared to house batteries. Now I'm struggling to justify getting an EV if I can't do at least V2H bidirectional charging.
Thier max output is only 9.6kW so it can’t do a whole home backup and the car can only run in backup mode when the grid is out.
9.6kW should be enough to backup your entire house, that's 87A... Lots of people only have a 100A supply in general. Depending on your setup you may have to limit what you use at one time but even in a large house that will be more than enough for AC, lights and electronic devices.
Still, 9.6kW should be more than enough to run a fridge, lights, receptacles, sump pump, a 2-3 ton A/C unit, and a furnace fan. It would be challenging to impossible to back up a home with electric (resistive) furnace and electric (resistive) water heater with only 9.6kW.
There's a few places that apparently offered it here, but when I've contacted them, they've all explained it was a tech demo, or trial, or some other PR type thing which means they didn't take it any further and regular humans can't buy it. I think there's some nuance or regulation around the UK power network which is stopping any progress with bidirectional charging here.
Over here though, if you don't have old electric heating, or an electric shower, 9.6kw is very much more than enough for the average household. I have a relatively high usage, and a 6kw inverter can power my house in a powercut, as long as I don't use the electric shower. The various retired people in my life tend to use 2 - 4kwh /day, the peak draw is the kettle which uses 3kw for a minute or so.
As a resident of Alberta, I pay $0.205/kWh for energy and delivery, which I largely attribute to bad decisions made by our provincial government. Even still, my 10 kW rooftop solar install is barely financially viable at those rates.
With that said, it would help if the Canadian government didn't have enormous tariffs on solar panels. Canada levies taxes such that solar panels here cost nearly triple what they cost elsewhere.
This is interesting. While it has the most storage capacity, the range is not good for that much battery.
The Lucid Gravity has a 450 mile range with a 123kWh pack. It’s the only other vehicle with a range close to the GM large packs.
Still, having a 400 mile range also makes this more useful for the middle of the country where there are wide open spaces between towns for charging. Also, having a legitimate truck EV makes it more likely for traditional truck buyers to think of getting an EV.
You still purchase and own the panels, but often a third party maintains them for you and they are installed as part of a large, offsite array. Since they're usually installed at ground level, they can also do more interesting things like follow the sun. The way it works is the power your panels produce is subtracted from your energy usage via an arrangement made with your utility provider.
Like any solar purchase, the cost of your panels can be financed over time and charged against your energy production. So the net effect is your power bill just goes down until the panels are paid for. At that point all the power you generate is deducted from your power bill. To me, it's most all the upside of owning panels on my roof.
The root cause is that they wanted community solar customers to be able to opt-in and opt-out any time. As such it isn’t really what you describe which is owning panels offsite, you are more or less doing a short term rental on them. As such you don’t get the full benefit from them but simply a 15% discount on the current residential rate.
https://www.wabi.tv/2025/02/18/maine-public-advocate-claims-...
I very much think that proper community solar would be a larger upfront investment just like panels on your roof are. With a small monthly cost to maintain the grounds and pay taxes on the real estate where the panels exist. All power generated would be metered for the specific panels you own using microinverters.
I don't now if it's better, but it is different.
The benefit to the utility in this case is much lower capex - it's basically like the restaurant franchise model, but for power.
But like you imply, there's a tradeoff that can be made between capex and opex - in this case, the utility could own everything and consumers could pay for electricity on an ongoing basis. IMO, this model is superior due to reduced principal-agent problems.
I just find this so cool. We have projects like SETI where the solar system tries to communicate with us. Here, you, just one person, have set up a machine talking with outer space and the solar system. Space is talking and we are listening. Amazing. Rock on space cowboy.
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.
I am not an automotive engineer but I doubt that is enough power for a bus that people can ride.
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.
At the low end maybe achievable with a full rooftop covered in solar panels, but probably not adequate at 1kW+.
Manufacturing cost is like $40 cells, $20 electronics and $200 in glass fusion, mounting, etc.
My car eats 200W just being online so it would be useless to charge from solar.
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...
https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-...
EV EPA range historically has been overstated. However, the water is muddied because the EPA doesn't really force the manufacturers to give an accurate number. A manufacturer can choose a highway only test, but then also arbitrarily decide to derate the value (EPA example is 70%). A manufacturer can choose to include city driving in the rating and weigh it accordingly and also derate the value (if they want).
Tesla traditionally (still the vast majority of new and used EV market share) has been the only manufacturer that uses the highway + city driving tests. People then get surprised when the car cannot do the full range at 85 MPH.
All in all, this is the EPAs fault. For EVs they really need two numbers, city driving range and highway driving range. EVs are so much more efficient than ICE that speed makes a huge difference given there substantially smaller energy density.
https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-...
Neither is the voltage when you plug it in at home. The car has a unit specifically to convert the voltage.
If you're saying they didn't connect the right wires for that, that sucks but is easily fixed.
> it's all out the window the second the car starts the ICE side of the hybrid drive system for even an instant
Nah, doing a drive where it's 99% solar power and 1% "burned an ounce of gas to maintain the engine for the month" is fine.
In your particular setup.
A typical car can expose about 3 square meters of lateral area for those same 8 hours, and receive 3 kW of irradiance. multijunction cells can exceed 50% efficiency, so we're talking about a theoretical upper limit of 12 kWh electric per day.
That would require a vehicle totally covered in cells, including the windows, so not very practical, but adding up to 30 miles/50 km per day is nothing to sneeze at.
We could also imagine all sorts of solar receivers that engage during parking and inflate the apparent surface within the limits available, track the sun etc. to maximize energy.
> multijunction cells can exceed 50% efficiency
The maximum demonstrated efficiency of a multijunction cell, in a lab, WITH CONCENTRATION is less than 50%. Commercially available cells are lower.
Concentration is an important caveat for two reasons:
First, it implies that you are collecting light from a larger area than the PV panel itself. Second, efficiency grows with increased irradiance (so efficiency will be lower without concentration).
> 3 square meters of lateral area
Lateral area is meaningless. It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck, there is zero probability that you can put 3 kW of irradiance on your panels. Neither of those vehicles will achieve kWh/mile numbers anywhere close to a Prius.
In practice, you need to halve the efficiency and more than halve the collection area you quoted. You also need to account for conversion losses.
The multijunction theoretical efficiency limit is 87% with infinite junctions, and over 50% with a practical number of junctions. There's nothing stopping you from creating a miniatural concentrating solar device that focuses the light from a 10 cm^2 area onto a 0.5cm^2 cell, we haven't seen such devices because the cost and extra mass exceed what you get from the efficiency gains when you can simply increase area; a very area constrained application with high power requirements might change that.
> It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck
Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the sun, perhaps even unfurl additional area? what about the area of the doors and windows?
Current solar cars can drive 1000 km per day with an average speed approaching 100km/h. It doesn't seem completely out of the realm of the possible to achieve 50km in an hour for a passenger car that can expose similar area while parked.
You replied to (and even quoted) a comment explaining the practical limits, then doubled-down and said multi junction cells can exceed a number which has never been experimentally demonstrated.
And here you are again saying that multifunction cells can achieve 87% efficiency.
An ICE engine can achieve 100% thermal efficiency with the right Th and Tc. That has about as much relevance to the discussion at hand as 87% efficient solar panels.
Let me be clear: the most efficient cells that have ever been experimentally demonstrated under any conditions are less efficient than the number you originally stated. In real world conditions the number is half of what you originally.
> Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the
I guess I’m just feeding the trolls here.
I believe having a carport and house roof covered with solar panels + (PH)EV is the best option.
But looking at some proper pictures, it covers most of the midroof with 7x8 tiles of solar. But you could fit a good percentage, even sticking with a design where a huge amount of the roof into the trunk is all glass. And there are no panels on the hood. So that's an easy doubling right there, more with an average car roof shape.
>13.6 kWh battery. 39mile EPA range... 915 Wh... 2.86 miles, not 3-6
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?
i think there was an interview later where he said, "yeah never doing that again" or something to that effect.
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.
Why doesn't the Leaf have it: afaik the leaf is a normal car, not like the Aptera that I'd be looking to buy. Even the Lightyear One was claiming to be more efficient than normal but pretty disappointing in how much range you get from the solar roof. Still more than zero though, so yeah ask them why they don't sell that variant ¯\_:|_/¯ While we're at it, let's find out why there isn't a smartphone that fits my niche (modern chipset with dual frequency GNSS for less than twice the price that competitors charge for it, operable with one average-sized hand, sdcard slot, and ideally a headphone jack but at this point I'd settle just for a bit of storage and really don't feel like it should be a hard-to-find device) or a laptop that makes sense (arrow keys and no annoying tapered edges that don't fit a network port, for example, already limits your options to a tiny percentage of the available systems)
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.
It's probably more 10~20, possibly as much as 30, if it's a long and sunny summer day FWIW.
For references:
- the F150 lightning gets close to 2 miles / kWh on average, ~1.5 at highway speeds but as much as 3~4 at consistent low speeds
- on the other side of an RV, Volvo markets their FH Electric (cabover semi) for 1.1kWh/km — 0.7 mi/kWh — at 80km/h (50mph), DAF/Innovate UK's Battery Electric Truck Trial yielded similar results (1.08kWh/km over 287000 km), it's also close to the numbers of the electric trucker in their very recent MAN eGTX video (0.83 kWh/km = 0.75 mi/kWh)
But that's assuming you use no power. When I was living in it I was using 50% to 100% of the solar output a day.
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.
That's the problem. I don't need or want any of that extra nonsense. You can't replace the radio in these contraptions. The only thing a car needs is: drive-line control, braking/ABS/ESP, steering, HVAC. Electronics wise dump the lame glued on tablet look and just give me a single up front dash display and a double DIN cutout in the dash. HVAC only needs knobs. I hope a Chinese auto maker comes out with an EV that dumps all of this stupidity and just gives us cars again.
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.
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.
>it would make sense to make a law that requires new parking spaces to have a solar roof... This would spread rather quickly, I think.
Sure, probably true!
If solar parking lots are such a great idea, why do you need the threat? It seems like businesses or environmental groups would already be clamoring to install them.
PV parking is a highly visible status symbol and good PR signal for your community or company (hence the few installations), but actually it isn't a great RoI either financially or for the environment.
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
My way around this, which is also somewhat inconvenient- is that I pop the hood and connect a trickle charger if I have a feeling I won't be driving for a few weeks. I have a garage so this is the lesser evil.
A current gen 2.5L petrol Camry has a 12v 80A alternator. That 80amps likely covers driving at night in the rain (ie headlights on, window wipers going, HVAC fan blowing, etc). Normal daytime driving would be much less demanding, say 50A load, thus 600W power. Then you have to factor in the alternators inefficiencies, which could raise that demand to 1kW.
Next consider what the engine is having to generate whilst cruising, which could be 20kW for the Camry. In this scenario, that 1kW of alternator load is responsible for 5% of the engines load. So ditching the alternator would give 5% fuel efficiency increase on this Camry. A smaller car that only needs 12kW to cruise would see an 8% improvement (8% of a low consumption value though), whilst a much bigger car that needs 50kW to cruise would only see a 2% gain (but that's 2% of a high consumption value).
So if "solar body panels" could generate 500W like people have already guessed in this thread, then that would be close to offsetting the normal day-time electrical load. In this scenario it's probably a good idea to power the vehicles electrical system from a lithium battery, which wouldn't mind the gradual draw-down, because that could then be offset by parking the car in the sun (and possibly even by regenerative braking). Then there could still be an isolated lead-acid battery that is purely for starting the engine (because that needs high cranking amps), and that could be DC to DC charged from the vehicle circuit.
That 12v 80A alternator can generate almost 1kW at max effort. So even if you drive all night in the rain, that's still less than 1/5th of the energy in a Tesla or BYD vehicle battery. So this alternator-less car could get away with a much smaller battery, and it might even be smaller in area than the cars boot!
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.
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...
Besides, I just checked out panels, and there's a lot of 500w ones that are appx 1mx2m, these station wagons are huge, easily 2m wide and 5m long, half of it a flat roof, so its not outrageous.
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.
Edit: Never mind, “hybrid station wagon”.
Even then, he said hybrid.
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.
(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.
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.
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.
I am happy to go that slow when I’m such a fascinating part of the world.
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.
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.
0. https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtu...
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?
There is.
The albedo of solar panel products varies with the coating and level of dirt.
There are waterless methods of cleaning solar panels.
TPV Thermo-Photovoltaic (TPV) cells generate some energy from infrared (heat). Regular PV cells waste the heat difference.
The Shockley-Quiesser limit is only conjectured to be applicable to single-junction cells.
Shockley-Quiesser limit > Exceeding the limit: https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...
"How to cut U.S. residential solar costs in half" (2025) https://news.ycombinator.com/item?id=44551633
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.