11 ms·

Impacts of adding PV solar system to internal combustion engine vehicles

116 points by red369 1y ago

lenerdenator 1y ago
If someone just put a battery-powered and solar-charged AC system in a car, I think it'd do a lot to reduce idling, if nothing else.
- ralphhughes 1y ago
  Good idea! The AC in my Nissan Leaf uses about 3kw so I assume it'd be about the same in my Corsa. However the Corsa disables auto-start stop and keeps the engine idling whenever the AC is on, negating any fuel savings!
torginus 1y ago
I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon. Even though the sun doesn't really shine all that much there, he still got enough power out of it, to never have to charge his car for his 20kmish daily commute.
- nordsieck 1y ago
  > I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon. 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. --- 1. https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_anyone_was_ever_curious_you_can_fit_1000_watts/ https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_any...
  - torginus 1y ago
    My exact numbers might be off (which is kind of a problem it seems on HN), but the point still stands - you can add practical amounts of range by having the car just sitting there, even in places where there's not that much sunlight. 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.
- Veliladon 1y ago
  No he didn't. Sweden gets ~2.6kWh/day per kW of solar panels. Malmö is at 55N latitude. If he put the panels on the car I hope he had a decent anti reflection coating because at that latitude he could be looking at 25% reduction in performance from the incident angle. 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 1y ago
    Are we sure his car wasn’t a Twike or something? There’s ultralight EVs for which this could work. Edit: Never mind, “hybrid station wagon”.
    - IAmBroom 1y ago
      Regardless, it's not going to generate the claimed 1kW.
  - pchew 1y ago
    Let's not forget to do the math on how much less efficient the vehicle is over all with panels strapped to the top messing with the aerodynamics. Even then, he said hybrid.
  - nielsole 1y ago
    If he only drives Mo-fr the math works out though
  - torginus 1y ago
    I don't remember the exact details, it's possible that he charged it over the weeked (or just didn't use it, thus getting 2 extra day of charge). 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 1y ago
  Won't work for most cars in cities, as they will be parked in indoor/underground garages, so no solar to speak of for their parking time, and the bit of solar you get while driving will maybe power the lights/electronics/audio system at most. (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.
  - torginus 1y ago
    A lot of car parks have chargers. Wiring up low wattage chargers is no big deal, considering AC chargers are just wiring+breakers. Considering cars will spend a long time here, large wattages are not needed, you could wire up a multi-story parking lot for chump change, and the entire wattage would be still less than a DC fast charger serving half a dozen cars.
Veliladon 1y ago
They're not wrong but if you stick a solar panel on a car that's almost constantly going to be in less than perfect conditions to gather power the EROEI for the panel is going to struggle to be above 1. 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.
- Mashimo 1y ago
  Or above the parking lot. Shadow and energy for the car :)
  - Veliladon 1y ago
    Exactly. 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.
    - sillystu04 1y ago
      My understanding is that V2G (vehicle to grid) requires transfer switches etc to be installed to your home electrical setup so you don't accidentally backfeed electricity into the grid. So it's never going to be a simply a matter of getting a better EV. 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.
      - Veliladon 1y ago
        Transfer switches are trivial to have installed. I already have a manual, interlocked one for a portable generator. 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.
janosch_123 1y ago
I built my own electric cars and calculated if this would be worth it. Roof of car is curved and you get the conversion losses (needs to be bumped to 400V to charge batteries). 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 https://www.youtube.com/@foxev-content
- walrus01 1y ago
  I agree on this. Using the pvwatts calculator for a very rough estimate of cumulative kWh produced per *month*, a theoretical 380W panel on top of a car that is in perfect sunshine from sunrise to sunset, never shaded or obstructed, on a car in the sunny climate of San Diego CA will produce the following: 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.
  - chiph 1y ago
    I believe that solar panels were an option on the Maybach 62S, and they would run the ventilation fan while you were parked so you wouldn't return to a hot car after going to the store. Like everyone else has said - there just isn't enough area on the top surfaces of a car to do any noticeable charging.
    - walrus01 1y ago
      If you were to theoretically have a perfect 400W PV panel on top of a car, and left in direct sunlight, it might be enough to run a medium sized peltier/TEC cooling unit to somewhat cool down the car while you leave it parked. Or a very small heat pump. Would definitely add a lot of extra cost in manufacturing and complexity.
      - gabrielhidasy 1y ago
        Or just keep the car fan running and use the existing AC system (in ventilation mode, no compressor) to keep the car just as hot as outside (instead of much hotter). If you have some spare power maybe even run the AC when the key gets back in range.
infecto 1y ago
Maybe I am missing something but this feels like a study for the sake of a study? Has this not been solved for a long time. The complexity cost and the potential losses from drag make this fairly pointless. You would be better off with a fixed solar installation.
- Jasp3r 1y ago
  It's also not something that needs research IMO: Toyota has a Prius with solar panel option.
  - infecto 1y ago
    That option is a gimmick though.
- rbanffy 1y ago
  Drag can be resolved by installing a flush panel conformal to the roof. If the vehicle is a van or truck, the flatness of the top makes it far easier.
  - infecto 1y ago
    Needless manufacturing complexity. Far better having static panels with current tech. They are nice gimmicks like that newer model of Prius but far from being economic reality.
    - rbanffy 1y ago
      For larger utility vehicles you can cover 80% or more of the top, almost doubling the numbers of the study. Depending on the region, this seems to be an obvious way to extend range without adding larger batteries. 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.
ianbooker 1y ago
Solar sun roofs for ICEs were a thing 20 years ago. Solar was able to ventilate your car on sunny days.
- fred_is_fred 1y ago
  Yes, the Priuses circa 2010 had them.
JamesCoyne 1y ago
mirror https://sci-hub.se/https://www.jstor.org/stable/26169128 https://sci-hub.se/https://www.jstor.org/stable/26169128
throwaway3b03 1y ago
Alternator delete is a very common hack in the ecomodder community (usually coupled with LiFePo or Lithium battery instead of the regular lead-acid). It reduces the complexity and load on the engine, and does give a few percentage better fuel efficiency. But if you mostly ride at night, yeah ...
- neRok 1y ago
  Everyone except you has approached this discussion with the intent of using the solar power to drive the car, but they should actually be thinking of using it to power the cars electrical system, and thus negating the need for the alternator. 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!
frzen 1y ago
For a moment I thought this was somehow about putting solar PV panels inside an engine and getting energy from the light from the detonation.... I need a cup of coffee
- kylebenzle 1y ago
  [flagged]
  - fortran77 1y ago
    Since the title said "internal combustion" my first thought, too, was could they make an engine a bit more efficient with some electrical process that increases the efficiency. The actual article was much more nonsensical than this take.
jollyllama 1y ago
ICE Vehicle is hiding a major category division here, hybrid vs. traditional ICE. I think in the case of the latter this would only make sense as a bandaid to deal with parasitic battery drainage on a vehicle that is usually parked outside.
- potato3732842 1y ago
  The cyclic nature of the sun actually makes for way better maintenance of lead acid batteries in practice than float chargers. Basically everyone with a boat, RV or rarely used heavy equipment has switched over at this point.
  - htrp 1y ago
    Can you elaborate here?
    - potato3732842 1y ago
      Float chargers do fairly frequently kill batteries by evaporating the fluid over time. It's like the difference between a battery being dead in a month or two of non-use vs 3-6 on a conventional float. It's hard to get the charge current just right. By contrast a charger that's voltage naturally decreases in proportion with what the battery is willing to suck up and tapers its charging and turns off overnight has the effect of more or less just "topping off" the battery without boiling much/any of the fluid. If you don't have a parasitic draw in excess of what the solar charger can make up for a battery is likely to be good for 6+mo without being touched. I can go 6mo on cars and other stuff that has digital electronics that draw a little bit and I can go 12+ for heavy equipment that has a hard cutoff switch.
- teekert 1y ago
  And yet I know quite some people who report to be very happy with their plugin hybrid, doing max 40 km they hardly have to use fuel anymore and some can charge off their own PV setups (in summer). I guess it’s a testament to the Netherlands being very compact.
testing22321 1y ago
This couple drove their EV the length of West Africa (and more) powered by solar panels they brought with them. Very cool. https://www.instagram.com/4x4electric https://www.instagram.com/4x4electric
- driverdan 1y ago
  It was a cool trip but everyone needs to understand how much downtime they had waiting for their batteries to charge. They had to deploy their solar while stopped, not while driving.
  - testing22321 1y ago
    They drove the route faster than I did in my gas powered 4x4. I am happy to go that slow when I’m such a fascinating part of the world.
phkahler 1y ago
I'd like to see PV added to a Ford Maverick hybrid.
condensedcrab 1y ago
Even the Aptera, which is designed to be super lightweight, can only regen about 10% of the battery (40 mi vs. 400 mi total capacity) with rooftop solar (https://aptera.us/ https://aptera.us/) 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.
- kibwen 1y ago
  But the average American drives less than 40 miles per day (33 is the current estimate). The relative charge doesn't matter, because what this suggests is that most Americans would be able to go most days without spending any effort or money at all on charging.
  - privatelypublic 1y ago
    You're forgetting america loves its covered parking
    - kibwen 1y ago
      America also loves reserving vast swathes of the road for on-street parking, as well as endless fields of parking lots, not to mention that an enormous number of homeowners would rather park in their driveway and use their garage for storage. 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.
      - WorldMaker 1y ago
        It's interesting how much people expect an EV battery to be at 100% charged at all times but have you met the sort of person that tries to keep an ICE vehicle 100% fueled at all times? (It's costly and wasteful and a logistics nightmare, before also getting into questions of how dangerous it can be.)
jwr 1y ago
When I looked at the title, I immediately thought that even if this makes sense from an engineering standpoint, psychology is going to be the bigger problem. For some reason many people are hell-bent on burning fossil fuels, almost in a sect-like belief kind of way. I do not understand it, but the backlash against anything electric for example is real.
- droopyEyelids 1y ago
  People make noise about a lot of subjects, but money is what really talks. Whatever is cheaper will end up gaining market share until it wins.
- ArtemZ 1y ago
  Burning fossil fuels is relatively simple and well understood by general public. Modern business strategies to squeeze every cent out of a customer that involves subscriptions, planned obsolescence, adding bizarre complexity for marginal gains are not helping. Buying a very expensive black box with questionable reliability, possible dependency on a manufacturer provided internet services (APIs for updating etc), questionable availability of parts and probably not really fixable by yourself or your local shop with rednecks with wrenches is not very appealing when you are living paycheck to paycheck.
  - seabrookmx 1y ago
    This is the real answer. 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.
- Aurornis 1y ago
  Top Gear, one of the most popular car shows of all time, was responsible for a lot of this. They spent years spreading myths about electric cars being worse for the environment and doing things like filming fake segments where they were pushing an EV claiming the battery had died. They did come around in later years, changing their tune to be more pro-EV. A lot of the damage was done, though.
energ8 1y ago
"significant increase in the range of 10.7-42.2% for lightweight and aerodynamic efficient vehicles" shout out to aptera motors https://aptera.us/vehicle/ https://aptera.us/vehicle/ that's currently vapor ware "Designed with ~700 watts of integrated solar cells, drive up to 40 miles per day completely off the grid and enjoy 400 miles of range per full charge"
londons_explore 1y ago
One big benefit: 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.
- conductr 1y ago
  I use a PV trickle charger, the panel is barely 1 square foot or so. Would be nice if it was integrated instead of having to connect/disconnect it constantly. Although, and I'm just guessing, many vehicles that are so seldomly driven are being kept indoors/garaged? (Mine is)
  - MostlyStable 1y ago
    I haven't found any appreciable drain on my EV's primary battery over the longest period I've left it sitting so far (a little over a week, so not that long, admittedly), but the car _does_ do a very bad job of keeping the 12V battery charged and I've already had to replace it once in <2 years of ownership, plus I bought one of those small jump start packs in case it ever dies not at home (luckily, for an EV, it barely requires any power at all to turn everything on and get it started, so the very smallest, cheapest, jump packs are way more than sufficient). A built in trickle charger to combat that would indeed be nice, if the car companies are incapable of figuring out the logic necessary to do it off of the massive primary battery.
    - londons_explore 1y ago
      EV's are the worst at keeping their 12V batteries charged. Many EV's don't even charge the battery if they're plugged into an AC charger!!! You can literally leave it plugged in charging for a month and come home to find it dead.
- Aurornis 1y ago
  > Electrical engineers in 2025 have so many little power drains that any car left undriven for a few months has a dead battery. 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.
Qem 1y ago
It appears they didn't cover cargo transportation in the analysis. Curious if it may be worth for large trucks, over 20m long, as there is a large area available to install panels, and cargo transport is a hard to decarbonize sector. In long routes that extend east-west, I also imagine one coud try to adjust timing so the truck travels along the sun while it's day, and against it while it's night, so days in the local frame are slightly lenghtened, and nights are slightly shorter, improving light availability.
- amoshebb 1y ago
  20m by 3m is 60m^2, with 300W/m^2 solar panels, it's less than 20kW. 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.
lutusp 1y ago
> [ ... ] by adding on-board PVs to cover less than 50% of the projected horizontal surface area of a typical mid-size vehicle (e.g., Toyota Camry or Nissan Leaf), up to 50% of total daily miles traveled by an average U.S. person could be driven by solar energy. 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.
somid3 1y ago
And that’s exactly why we added 1000 watts of solar to any vehicles’ roof rack here at DartSolar. We created and aftermarket roof rack so any car can add solar. More details at https://dartsolar.com https://dartsolar.com
tootie 1y ago
Moot point since Trump just killed CAFE. No more mileage standards will be enforced in the US.
westurner 1y ago
A similar question: 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?
- westurner 1y ago
  > 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_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 https://news.ycombinator.com/item?id=44551633
vondur 1y ago
If you have a small battery and use it to add ventilation in the vehicle on hot days when parked would be cool.
Glyptodon 1y ago
I've wondered if there could be a way to make it so that internal combustion cars don't need lead acid batteries w/ a few solar panels and a setup like a scaled version of a solar watch. But that wouldn't be about big efficiency gains, just dropping a little space and the annoyance of them going dead every three years.
- blibble 1y ago
  even EVs still have the 12V battery
chris222 1y ago
I’ve just done a legtimate 425 mile solar powered round trip which is the culmination of many things I will explain below. I can now effectively drive anywhere in a 225 mile radius and back for about $10 total cost and on 100% solar power. 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.
- hex4def6 1y ago
  I assume you're on a pretty attractive net metering agreement? That's a huge 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.
  - chris222 1y ago
    I consume about 17MWh a year between two EVs and a large heat pump for winter heating. 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/inline-documents/sonh/net-metering-tariff-2023-overview.pdf https://www.energy.nh.gov/sites/g/files/ehbemt551/files/inli...
- 1dom 1y ago
  I'm looking at doing similar stuff right now. I already have a house battery. 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.
mike-the-mikado 1y ago
(2016)
burnt-resistor 1y ago
Solar Freakin' Roadways:[0] Mobile Edition 0. https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtuHtlndPUSOPgsujUdq1c5Mr9 https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtu...

116 points by red369 1y ago

If someone just put a battery-powered and solar-charged AC system in a car, I think it'd do a lot to reduce idling, if nothing else.

ralphhughes 1y ago
Good idea! The AC in my Nissan Leaf uses about 3kw so I assume it'd be about the same in my Corsa. However the Corsa disables auto-start stop and keeps the engine idling whenever the AC is on, negating any fuel savings!

torginus 1y ago

I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon. Even though the sun doesn't really shine all that much there, he still got enough power out of it, to never have to charge his car for his 20kmish daily commute.

nordsieck 1y ago
> I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon. 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. --- 1. https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_anyone_was_ever_curious_you_can_fit_1000_watts/ https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_any...
- torginus 1y ago
  My exact numbers might be off (which is kind of a problem it seems on HN), but the point still stands - you can add practical amounts of range by having the car just sitting there, even in places where there's not that much sunlight. 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.
Veliladon 1y ago
No he didn't. Sweden gets ~2.6kWh/day per kW of solar panels. Malmö is at 55N latitude. If he put the panels on the car I hope he had a decent anti reflection coating because at that latitude he could be looking at 25% reduction in performance from the incident angle. 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 1y ago
  Are we sure his car wasn’t a Twike or something? There’s ultralight EVs for which this could work. Edit: Never mind, “hybrid station wagon”.
  - IAmBroom 1y ago
    Regardless, it's not going to generate the claimed 1kW.
- pchew 1y ago
  Let's not forget to do the math on how much less efficient the vehicle is over all with panels strapped to the top messing with the aerodynamics. Even then, he said hybrid.
- nielsole 1y ago
  If he only drives Mo-fr the math works out though
- torginus 1y ago
  I don't remember the exact details, it's possible that he charged it over the weeked (or just didn't use it, thus getting 2 extra day of charge). 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 1y ago
Won't work for most cars in cities, as they will be parked in indoor/underground garages, so no solar to speak of for their parking time, and the bit of solar you get while driving will maybe power the lights/electronics/audio system at most. (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.
- torginus 1y ago
  A lot of car parks have chargers. Wiring up low wattage chargers is no big deal, considering AC chargers are just wiring+breakers. Considering cars will spend a long time here, large wattages are not needed, you could wire up a multi-story parking lot for chump change, and the entire wattage would be still less than a DC fast charger serving half a dozen cars.

Veliladon 1y ago

They're not wrong but if you stick a solar panel on a car that's almost constantly going to be in less than perfect conditions to gather power the EROEI for the panel is going to struggle to be above 1. 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.

Mashimo 1y ago
Or above the parking lot. Shadow and energy for the car :)
- Veliladon 1y ago
  Exactly. 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.
  - sillystu04 1y ago
    My understanding is that V2G (vehicle to grid) requires transfer switches etc to be installed to your home electrical setup so you don't accidentally backfeed electricity into the grid. So it's never going to be a simply a matter of getting a better EV. 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.
    - Veliladon 1y ago
      Transfer switches are trivial to have installed. I already have a manual, interlocked one for a portable generator. 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.

janosch_123 1y ago

I built my own electric cars and calculated if this would be worth it. Roof of car is curved and you get the conversion losses (needs to be bumped to 400V to charge batteries). 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 https://www.youtube.com/@foxev-content

walrus01 1y ago
I agree on this. Using the pvwatts calculator for a very rough estimate of cumulative kWh produced per *month*, a theoretical 380W panel on top of a car that is in perfect sunshine from sunrise to sunset, never shaded or obstructed, on a car in the sunny climate of San Diego CA will produce the following: 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.
- chiph 1y ago
  I believe that solar panels were an option on the Maybach 62S, and they would run the ventilation fan while you were parked so you wouldn't return to a hot car after going to the store. Like everyone else has said - there just isn't enough area on the top surfaces of a car to do any noticeable charging.
  - walrus01 1y ago
    If you were to theoretically have a perfect 400W PV panel on top of a car, and left in direct sunlight, it might be enough to run a medium sized peltier/TEC cooling unit to somewhat cool down the car while you leave it parked. Or a very small heat pump. Would definitely add a lot of extra cost in manufacturing and complexity.
    - gabrielhidasy 1y ago
      Or just keep the car fan running and use the existing AC system (in ventilation mode, no compressor) to keep the car just as hot as outside (instead of much hotter). If you have some spare power maybe even run the AC when the key gets back in range.

infecto 1y ago

Maybe I am missing something but this feels like a study for the sake of a study? Has this not been solved for a long time. The complexity cost and the potential losses from drag make this fairly pointless. You would be better off with a fixed solar installation.

Jasp3r 1y ago
It's also not something that needs research IMO: Toyota has a Prius with solar panel option.
- infecto 1y ago
  That option is a gimmick though.
rbanffy 1y ago
Drag can be resolved by installing a flush panel conformal to the roof. If the vehicle is a van or truck, the flatness of the top makes it far easier.
- infecto 1y ago
  Needless manufacturing complexity. Far better having static panels with current tech. They are nice gimmicks like that newer model of Prius but far from being economic reality.
  - rbanffy 1y ago
    For larger utility vehicles you can cover 80% or more of the top, almost doubling the numbers of the study. Depending on the region, this seems to be an obvious way to extend range without adding larger batteries. 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.

ianbooker 1y ago

Solar sun roofs for ICEs were a thing 20 years ago. Solar was able to ventilate your car on sunny days.

fred_is_fred 1y ago
Yes, the Priuses circa 2010 had them.

JamesCoyne 1y ago

mirror https://sci-hub.se/https://www.jstor.org/stable/26169128 https://sci-hub.se/https://www.jstor.org/stable/26169128

throwaway3b03 1y ago

Alternator delete is a very common hack in the ecomodder community (usually coupled with LiFePo or Lithium battery instead of the regular lead-acid). It reduces the complexity and load on the engine, and does give a few percentage better fuel efficiency. But if you mostly ride at night, yeah ...

neRok 1y ago
Everyone except you has approached this discussion with the intent of using the solar power to drive the car, but they should actually be thinking of using it to power the cars electrical system, and thus negating the need for the alternator. 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!

frzen 1y ago

For a moment I thought this was somehow about putting solar PV panels inside an engine and getting energy from the light from the detonation.... I need a cup of coffee

kylebenzle 1y ago
[flagged]
- fortran77 1y ago
  Since the title said "internal combustion" my first thought, too, was could they make an engine a bit more efficient with some electrical process that increases the efficiency. The actual article was much more nonsensical than this take.

jollyllama 1y ago

ICE Vehicle is hiding a major category division here, hybrid vs. traditional ICE. I think in the case of the latter this would only make sense as a bandaid to deal with parasitic battery drainage on a vehicle that is usually parked outside.

potato3732842 1y ago
The cyclic nature of the sun actually makes for way better maintenance of lead acid batteries in practice than float chargers. Basically everyone with a boat, RV or rarely used heavy equipment has switched over at this point.
- htrp 1y ago
  Can you elaborate here?
  - potato3732842 1y ago
    Float chargers do fairly frequently kill batteries by evaporating the fluid over time. It's like the difference between a battery being dead in a month or two of non-use vs 3-6 on a conventional float. It's hard to get the charge current just right. By contrast a charger that's voltage naturally decreases in proportion with what the battery is willing to suck up and tapers its charging and turns off overnight has the effect of more or less just "topping off" the battery without boiling much/any of the fluid. If you don't have a parasitic draw in excess of what the solar charger can make up for a battery is likely to be good for 6+mo without being touched. I can go 6mo on cars and other stuff that has digital electronics that draw a little bit and I can go 12+ for heavy equipment that has a hard cutoff switch.
teekert 1y ago
And yet I know quite some people who report to be very happy with their plugin hybrid, doing max 40 km they hardly have to use fuel anymore and some can charge off their own PV setups (in summer). I guess it’s a testament to the Netherlands being very compact.

testing22321 1y ago

This couple drove their EV the length of West Africa (and more) powered by solar panels they brought with them. Very cool. https://www.instagram.com/4x4electric https://www.instagram.com/4x4electric

driverdan 1y ago
It was a cool trip but everyone needs to understand how much downtime they had waiting for their batteries to charge. They had to deploy their solar while stopped, not while driving.
- testing22321 1y ago
  They drove the route faster than I did in my gas powered 4x4. I am happy to go that slow when I’m such a fascinating part of the world.

phkahler 1y ago

I'd like to see PV added to a Ford Maverick hybrid.

condensedcrab 1y ago

Even the Aptera, which is designed to be super lightweight, can only regen about 10% of the battery (40 mi vs. 400 mi total capacity) with rooftop solar (https://aptera.us/ https://aptera.us/) 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.

kibwen 1y ago
But the average American drives less than 40 miles per day (33 is the current estimate). The relative charge doesn't matter, because what this suggests is that most Americans would be able to go most days without spending any effort or money at all on charging.
- privatelypublic 1y ago
  You're forgetting america loves its covered parking
  - kibwen 1y ago
    America also loves reserving vast swathes of the road for on-street parking, as well as endless fields of parking lots, not to mention that an enormous number of homeowners would rather park in their driveway and use their garage for storage. 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.
    - WorldMaker 1y ago
      It's interesting how much people expect an EV battery to be at 100% charged at all times but have you met the sort of person that tries to keep an ICE vehicle 100% fueled at all times? (It's costly and wasteful and a logistics nightmare, before also getting into questions of how dangerous it can be.)

jwr 1y ago

When I looked at the title, I immediately thought that even if this makes sense from an engineering standpoint, psychology is going to be the bigger problem. For some reason many people are hell-bent on burning fossil fuels, almost in a sect-like belief kind of way. I do not understand it, but the backlash against anything electric for example is real.

droopyEyelids 1y ago
People make noise about a lot of subjects, but money is what really talks. Whatever is cheaper will end up gaining market share until it wins.
ArtemZ 1y ago
Burning fossil fuels is relatively simple and well understood by general public. Modern business strategies to squeeze every cent out of a customer that involves subscriptions, planned obsolescence, adding bizarre complexity for marginal gains are not helping. Buying a very expensive black box with questionable reliability, possible dependency on a manufacturer provided internet services (APIs for updating etc), questionable availability of parts and probably not really fixable by yourself or your local shop with rednecks with wrenches is not very appealing when you are living paycheck to paycheck.
- seabrookmx 1y ago
  This is the real answer. 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.
Aurornis 1y ago
Top Gear, one of the most popular car shows of all time, was responsible for a lot of this. They spent years spreading myths about electric cars being worse for the environment and doing things like filming fake segments where they were pushing an EV claiming the battery had died. They did come around in later years, changing their tune to be more pro-EV. A lot of the damage was done, though.

energ8 1y ago

"significant increase in the range of 10.7-42.2% for lightweight and aerodynamic efficient vehicles" shout out to aptera motors https://aptera.us/vehicle/ https://aptera.us/vehicle/ that's currently vapor ware "Designed with ~700 watts of integrated solar cells, drive up to 40 miles per day completely off the grid and enjoy 400 miles of range per full charge"

londons_explore 1y ago

One big benefit: 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.

conductr 1y ago
I use a PV trickle charger, the panel is barely 1 square foot or so. Would be nice if it was integrated instead of having to connect/disconnect it constantly. Although, and I'm just guessing, many vehicles that are so seldomly driven are being kept indoors/garaged? (Mine is)
- MostlyStable 1y ago
  I haven't found any appreciable drain on my EV's primary battery over the longest period I've left it sitting so far (a little over a week, so not that long, admittedly), but the car _does_ do a very bad job of keeping the 12V battery charged and I've already had to replace it once in <2 years of ownership, plus I bought one of those small jump start packs in case it ever dies not at home (luckily, for an EV, it barely requires any power at all to turn everything on and get it started, so the very smallest, cheapest, jump packs are way more than sufficient). A built in trickle charger to combat that would indeed be nice, if the car companies are incapable of figuring out the logic necessary to do it off of the massive primary battery.
  - londons_explore 1y ago
    EV's are the worst at keeping their 12V batteries charged. Many EV's don't even charge the battery if they're plugged into an AC charger!!! You can literally leave it plugged in charging for a month and come home to find it dead.
Aurornis 1y ago
> Electrical engineers in 2025 have so many little power drains that any car left undriven for a few months has a dead battery. 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.

Qem 1y ago

It appears they didn't cover cargo transportation in the analysis. Curious if it may be worth for large trucks, over 20m long, as there is a large area available to install panels, and cargo transport is a hard to decarbonize sector. In long routes that extend east-west, I also imagine one coud try to adjust timing so the truck travels along the sun while it's day, and against it while it's night, so days in the local frame are slightly lenghtened, and nights are slightly shorter, improving light availability.

amoshebb 1y ago
20m by 3m is 60m^2, with 300W/m^2 solar panels, it's less than 20kW. 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.

lutusp 1y ago

> [ ... ] by adding on-board PVs to cover less than 50% of the projected horizontal surface area of a typical mid-size vehicle (e.g., Toyota Camry or Nissan Leaf), up to 50% of total daily miles traveled by an average U.S. person could be driven by solar energy. 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.

somid3 1y ago

And that’s exactly why we added 1000 watts of solar to any vehicles’ roof rack here at DartSolar. We created and aftermarket roof rack so any car can add solar. More details at https://dartsolar.com https://dartsolar.com

tootie 1y ago

Moot point since Trump just killed CAFE. No more mileage standards will be enforced in the US.

westurner 1y ago

A similar question: 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?

westurner 1y ago
> 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_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 https://news.ycombinator.com/item?id=44551633

vondur 1y ago

If you have a small battery and use it to add ventilation in the vehicle on hot days when parked would be cool.

Glyptodon 1y ago

I've wondered if there could be a way to make it so that internal combustion cars don't need lead acid batteries w/ a few solar panels and a setup like a scaled version of a solar watch. But that wouldn't be about big efficiency gains, just dropping a little space and the annoyance of them going dead every three years.

blibble 1y ago
even EVs still have the 12V battery

chris222 1y ago

I’ve just done a legtimate 425 mile solar powered round trip which is the culmination of many things I will explain below. I can now effectively drive anywhere in a 225 mile radius and back for about $10 total cost and on 100% solar power. 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.

hex4def6 1y ago
I assume you're on a pretty attractive net metering agreement? That's a huge 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.
- chris222 1y ago
  I consume about 17MWh a year between two EVs and a large heat pump for winter heating. 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/inline-documents/sonh/net-metering-tariff-2023-overview.pdf https://www.energy.nh.gov/sites/g/files/ehbemt551/files/inli...
1dom 1y ago
I'm looking at doing similar stuff right now. I already have a house battery. 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.

mike-the-mikado 1y ago

(2016)

burnt-resistor 1y ago

Solar Freakin' Roadways:[0] Mobile Edition 0. https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtuHtlndPUSOPgsujUdq1c5Mr9 https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtu...