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.
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.
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.
One can now get (flexible-ish) multi-junction PV (say 29% efficiency) from the factory for under $1/W. Still a higher price than the $0.2/W, lower efficiency panels, but when I messed with panels I felt like we were living in the future.
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.
> You add a lot of complexity for marginal gains. Peak time you get maybe 500W which doesn't go very far.
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.
The math is biased towards when you are using the vehicle. The solar panels also work when you aren't using the vehicle. They work from when the sun comes up until it goes down. And actually most people don't actually use their cars most of the time. It's just sitting there parked doing nothing well over 90 percent of the time. And especially hybrids have tiny batteries to begin with. Instead of charging those burning petrol, you could be partially charging those with solar.
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.
Agreed. Using solar to power vehicles is great, but there's little benefit in the panels being on the vehicle. Put panels on your house, charge your EV, and you've got a solar powered vehicle (and house).
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.
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 ...
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!
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
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.
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!
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.
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.
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/)
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.
"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/ 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"
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.
> [ ... ] 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.
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
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.
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.
The article is about installing solar panels on vehicles. Your truck has no solar panels installed on it. What is the relevance of your anecdote to this discussion?
>This has a mode where it communicates with the solar system,
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.
37 comments
[ 4.0 ms ] story [ 58.0 ms ] threadStick 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.
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
Anyway, one could also set up the panel to output a much higher voltage by having the factory wire cells in series (though how well that trades off with partial shading for a car roof I have no idea, and I have no idea the minimum quantity required to get that).
... but I agree, even with all that, it seems like a stretch to make it work.
The complexity should not be overlooked. The PV panels add a lot of things that can fail: An additional layer that must be adhered or fastened the roof. Transparent panel covers that can become damaged in ways that aren’t as easy to repair as a rock chip in paint. Extra wiring that runs into the vehicle. A charging regulator. Systems to monitor that it’s all working and give the appropriate diagnostic codes if it fails.
Having worked on a lot of older and newer cars when I was younger, I’ve come to appreciate a degree of simplicity in vehicles. Modern electronics and vehicle systems are more reliable, but when the number of motors, sensors, and functions in a car goes up by 10X with all of the new features, a lot of little things start to fail in annoying ways as cars age out.
With solar I imagine old car owners would just ignore the system when it stopped working, but you’re still hauling all of that extra weight around for the lifetime of the car. That extra weight subtracts from your efficiency.
If you get 400W watt performance for a few hours per day, that's maybe a couple of kwh per day. 2 would be alright. 4 would be amazing. 6 probably not that likely unless you live in a very sunny place. Most decent EVs do at least 3 miles per kwh. So, you get maybe 6-12 "free" miles per day. Maybe more with an efficient one. Up to 20 miles even.
Most commute round trips aren't that long. You are might need more power than that. But not a lot. You could be cutting how often you charge by some meaningful percentage. It's not going to be that useful on a long journey. But most people don't do those all the time but they drive small distances on a daily basis. Imagine you drive to work, and back maybe covering 20 miles. You go to sleep, and the car is back at 100% charge. Because you only used a few kwh driving there and back and the car had plenty of time parked to collect those back because the weather is nice. Or maybe it got to 95%. The difference is meaningless because you only use a few percent on a given day. Basically you'd be charging a bit less often and stretch existing charges a bit longer.
If you have a 60kwh battery and you get 2kwh per day from the sun, that's 1 full charge per month. Most people would charge maybe 2-4 times per month. So that's a meaningful amount. Cutting them amount of power that you have to pay for by 25 or more percent can be interesting. I think for most the savings aren't going to be dramatic. But it's nice that the car just sits there slowly topping its battery up without you having to worry about it. That's convenient.
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!
https://www.instagram.com/4x4electric
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.
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.
This is nonsense and would easily be proven false except that the article's technical content is paywalled. But common sense says that, if the claim were true, simple economics would make it a reality.
The publishing journal, the "SAE International Journal of Alternative Powertrains", appears to be one of thousands of online-only journals meant to provide a fee-based publication opportunity for authors who have no chance to publish in a reputable journal. In short, the authors pay, then the readers pay -- quite a system.
How large does a solar panel array have to be on a solar laser crop weeder, and how much acreage can it cover on a sunny day?
Is there potential to optimize solar beyond the perceived limits?
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
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.
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.