Impacts of adding PV solar system to internal combustion engine vehicles

https://www.jstor.org/stable/26169128

by red369 • 1 year ago

116 253 1 year ago

torginus4• 1 year 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.

nordsieck2• 1 year 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.

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1. https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_any...

torginus4• 1 year 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.

Veliladon4• 1 year 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• 1 year 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”.

pchew3• 1 year 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• 1 year ago

If he only drives Mo-fr the math works out though

torginus4• 1 year 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• 1 year 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.

torginus4• 1 year 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.

Veliladon4• 1 year 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• 1 year ago

Or above the parking lot. Shadow and energy for the car :)

Veliladon4• 1 year 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.

lm284692• 1 year ago

That's actually mandatory in France for large parking lots

willglynn• 1 year ago

Yes! Exactly this.

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.

BizarroLand2• 1 year ago

Honestly we should consider giving generous tax benefits so that every open air parking lot in any city in America that has more than 50,000 residents would be stupid to not have solar installed that covers the front of the cars in the parking lot and the walkways between the lot and the stores.

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.

parpfish2• 1 year ago

The panels themselves would be more efficient, but in terms of getting that power into the car you might be better off having inefficient panels that work everywhere you go rather than optimized panels that only work when you go to a charging station

IAmBroom4• 1 year ago

The study literally proves you wrong.

maccard2• 1 year ago

You’ve made an assumption - that the owner of the car has a roof, and can charge the car from there. People who don’t live in a place with off street parking to install a cable need a slightly different solution.

wojciii2• 1 year ago

So .. it would make sense to make a law that requires new parking spaces to have a solar roof which can charge the cars which park there for a few. This would spread rather quickly, I think.

I have solar panels at home and can charge a car .. but I'm mostly parked elsewhere when the sun is shining the most.

aqme282• 1 year ago

Exactly. Maybe just because I live in a city and almost everyone I know with a car will just find street parking somewhere within walking distance of their apartment.

janosch_1232• 1 year 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

walrus013• 1 year 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• 1 year 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.

bestouff2• 1 year ago

60kWh may be enough for occasional short trips.

gus_massa• 1 year ago

Using "270Wh/mile" from another comment,

(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.

agumonkey2• 1 year ago

I wonder if it would be OK-ish to build a very lightweight, very long, low powered solar "bus" (or a tram like chain). Just enough to roam around a city at 15-20mph for free.

You'd get enough surface to get ~4kW

bestouff2• 1 year ago

4kW on a bright sunny day, for a few hours around noon. Even my small EV outputs 100kW when floored, and 4kW doesn't get it very fast.

PunchyHamster3• 1 year ago

We have trams. We don't need to make worse trams

CerebralCerb• 1 year ago

It's an interesting idea. I did some napkin math based on the Solaris Urbino 18 bus. The buses have about 45 square meters of ceiling area (18m by 2.5m). Assuming efficient solar panels you could get 250w/sqm. That works out to 11.25 kwh/hour. The bus advertises with 600km of range with 800kwh of batteries so that is 1.33 kwh/km. Hence it could do ~8km/h on average when it is sunny.

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.

Zigurd• 1 year ago

I suspect the lightweight, and hence low power requirements, are the correct part of the hypothesis. But making the vehicle as big as a bus implicates a lot of weight. Maybe a solar charging cargo bike fairing would have some benefit, but that's an expensive bike and it will tend to get stored indoors.

jerf• 1 year ago

There have been solar car competitions that colleges have been doing for decades. Here's a YouTube compilation of one that ran last week: https://www.youtube.com/watch?v=ZBin-oXBJzM

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.

johannes1234321• 1 year ago

Well, if you have a fixed route you are not limited by space on the vehicle to put solar on, but can provide electricity via a rail or wire or something and then gather energy on some larger Solarstation or from wind turbines or what else comes to mind.

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)

BizarroLand2• 1 year ago

Maybe an electric assisted pedal bus with a solar roof would make sense.

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.

quickthrowman2• 1 year ago

One horsepower is roughly equivalent 754 watts. 4000/754 = 5.305 horsepower. Even tripling it only gets you to 15 HP.

I am not an automotive engineer but I doubt that is enough power for a bus that people can ride.

actionfromafar• 1 year ago

There was some car which used a small solar panel to pass fresh, cooler air into the cabin during sunny days. This both made the car more pleasant to enter and lowered the initial AC surge. I don't know if it also trickle charged the starter battery so it never could get completely depleted from just standing for longer periods. Both these things seemed worthwile.

pyk• 1 year ago

The 2010 Prius IV had this as an option - one of my favorite cars due to low maintenance (the lowest maintenance visits per year for its era). The solar panel air vent circulation is a nice feature (even if slightly gimmicky) and I suspect extends the hybrid battery life as well by preventing some marginal battery heat death while parked.

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).

eldaisfish2• 1 year ago

A more practical solution is to leave the windows slightly open so the hot air escapes.

pchew3• 1 year ago

I have a 100w solar panel on top of my car...to tend a 12v battery. It's got a Dewalt battery charger, mikrotik ltap, and raspberry pi hooked up to it. Little hotspot with multiple sims and resource server(mainly just for fun). Anyone that can do basic math should immediately realize there's just not enough area to make an appreciable difference in regards to mileage.

jollyllama3• 1 year ago

Very nice. How long does that tend to stay alive for? And what kind of cold weather conditions do you have to contend with?

barnas2• 1 year ago

The Prius Prime solar panel roof I think can net 3-6 miles a day under ideal conditions (which we're probably close to here in Arizona). I think that's a little more than people would expect, but still only applicable in niche conditions (tiny daily commute, or a longer non-daily commute). I think the math works out to ~4-6 years to break even for the cost of adding the solar roof assuming $0.15 per kwh, which isn't terrible.

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.

AdamJacobMuller• 1 year ago

I just started doing this with my car, mostly to add a camera/temp monitoring for when I leave my dog in the kennel in the car (she's well watched over, please don't fret over it).

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).

ben_w• 1 year ago

The maths says that the *mean* number of miles driven by a vehicle is surprisingly low, and that tiling the surface of a car can get to about 80% of that *mean* in places where the car is just left out on the street and not shaded parking.

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.

andoando• 1 year ago

If only we didnt start off with having 3000+ lbs of metal to move a 100-200lb person as a design limitation

HPsquared2• 1 year ago

Say the car gets 4 miles per kWh. So a 500 W charging rate (neglecting losses) can be expressed as 2 mph.

Compare to a fast charger which will be several hundred mph.

rfrey• 1 year ago

This is a good way to look at it, but perhaps a new unit, like range per hour? Since mph is alreday a unit of velocity.

VBprogrammer• 1 year ago

Not sure if I've slipped a 0 here but 500w taken over the year, at say a 10% capacity factor, is still over 3500 miles of range per year. A fair bit short of the average mileage (in the UK somewhere around 10k) but still more significant than I expected. Of course 500w is a lot of solar for a car and 4 miles / kWh is also quite efficient.

TrainedMonkey• 1 year ago

I think this is a flawed comparison. You only care about speed when driving, but charging we care about whenever the car gets sunlight. I would argue for most people car in sunlight time is a multiple of car driving time. Still pretty abysmal, but less bad than 2 mph.

jvanderbot• 1 year ago

This is a perfect nerd snipe. I can't imagine any car owning (esp ev owning) engineer hasn't or wouldn't eventually think about "why can't I charge my car from my car".

seltzered_• 1 year ago

You might like the series by youtuber 'Power of Light' where he packs solar panels in his car to charge his car to do a solar cannonball run from New York to California on those solar panels alone: https://m.youtube.com/playlist?list=PL9nfj0jfPXYBF8FO7sckzvV...

Can't remember how long it took, think a couple weeks at least?

PunchyHamster3• 1 year ago

Only advantage is if you use car rarely, park outdoors and don't want onboard battery to drain, tho way smaller panel needed to cover that

marcosdumay• 1 year ago

Yep. A solar car ceiling seems great to make EVs more reliable on the hands of people that only charge them rarely or may travel to the middle of nowhere and can get surprised by battery faults.

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.

sevensor2• 1 year ago

Can you comment more on the complexity? Like, is it running wire harnesses everywhere, is it the power electronics, cooling, mechanical mounting, something else, all of the above?

janosch_1232• 1 year ago

Of course. It is an intriguing idea, but a local maximum.

- 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.

msgodel• 1 year ago

People don't seem to talk about Watt hours per mile much but when you're generating the power yourself it really matters. Tesla's model 3 is AFAIK one of the more efficient EVs and gets ~260 Watt hours per mile. With solar a good rule of thumb is to take the nominal rating for the panels you can point south and multiply it by 4 to get the approximate daily energy you'll generate in watt hours. If you could optimally park a car and let's assume you could cover it in a couple 100 Watt panels that would give you about four extra miles of daily range.

Maybe it's interesting if you live in a city and drive once a week.

bee_rider• 1 year ago

Maybe an RV could be covered with solar? The top is much bigger, and if it isn’t charging fast enough you can always pull over and have lunch while the battery catches up.

ErikHuisman• 1 year ago

Who lunches for several days/weeks? logically you would charge high speed through a plug with energy generated by panels that are much more efficiëntly (money+yield) placed and not have to carry around.

mikepurvis3• 1 year ago

But an RV is also way bigger and heavier.

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.

masklinn2• 1 year ago

It’s always going to be anecdotal. I reckon a mid size RV (say upper class B) will have 1500-2000W of solar capacity, if it’s really boxy. It’s going to have the aerodynamics of a brick. Meaning you’ll be lucky to get 1mi/kwh at highway speed, maybe 2~2.5 if you keep under 30.

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.

SideburnsOfDoom• 1 year ago

Even better to get a fixed structure such as a garage or carport, that keeps the vehicle safe and out of the sun, and cover that in Solar.

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.

sixothree• 1 year ago

People are absolutely starting to populate their RVs with solar. What I've seen so far is just a few panels - around 600 watts. Usually connected to a battery separated from the RV wiring.

driverdan3• 1 year ago

It doesn't make sense to power any vehicle with onboard solar. There are no electric RVs yet because the batteries required to have any amount of range are cost prohibitive and heavy.

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.

chris_va• 1 year ago

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.

Aurornis3• 1 year ago

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.

secabeen2• 1 year ago

The simplicity of EVs is one of their big strengths! Compare all the cooling, transmission, lubrication and fuel systems of an ICE car to the simple Electric Motor of an EV. Vastly simpler. As an end user, I see it to, my EV has no scheduled maintenance, whereas the ICE wants me to take it to the dealer every 20k miles.

jillesvangurp• 1 year ago

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.

bongodongobob• 1 year ago

When I'm not using my vehicle, it's in my garage.

tempestn• 1 year ago

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).

infecto6• 1 year 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.

rbanffy3• 1 year 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.

infecto6• 1 year 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.

IAmBroom4• 1 year ago

It might shut up some of the people who think solar panels are magic.

PunchyHamster3• 1 year ago

Those people dont read papers or believe science

Jasp3r• 1 year ago

It's also not something that needs research IMO: Toyota has a Prius with solar panel option.

infecto6• 1 year ago

That option is a gimmick though.

danaris2• 1 year ago

But solar has been getting cheaper and more efficient by leaps and bounds.

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.

infecto6• 1 year ago

I don’t believe the primary cost is so much the physical panel but the cost to engineer and design it into a roof, also the additional systems needing to hook it into the wiring harness. It’s a fun toy for some but has no real benefit for the many.

ianbooker• 1 year 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• 1 year ago

Yes, the Priuses circa 2010 had them.

JamesCoyne• 1 year ago

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

throwaway3b03• 1 year 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• 1 year 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• 1 year 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

jollyllama3• 1 year 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.

potato37328422• 1 year 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• 1 year ago

Can you elaborate here?

teekert• 1 year 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.

gwbas1c• 1 year ago

I went the plugin hybrid route. The added complexity caused a lot of maintenance and reliability issues. I ended up having to dump the vehicle at a loss.

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.

jollyllama3• 1 year ago

I'm sure; it's certainly intuitive that a hybrid could do quite a lot with a PV setup. I just don't see PV doing much for a non-hybrid ICE vehicle outside of acting as a battery tender.

lenerdenator• 1 year 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• 1 year 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!

testing223212• 1 year 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

driverdan3• 1 year 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.

testing223212• 1 year 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• 1 year ago

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

jwr• 1 year 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• 1 year 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• 1 year 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• 1 year 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.

Aurornis3• 1 year 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.

meragrin_• 1 year ago

Or maybe you are just blind to the realities of normal people. Most people are not hell-bent on burning fossil fuels. There are numerous valid reasons for people to continue to choose ICE. I want an EV. I want to dump every piece of outdoor equipment with an ICE for something with an electric motor. I very much prefer the pieces I have switched to electric. I've been wanting to make the switch for years. It just does not make sense for me at this time.

condensedcrab• 1 year 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/)

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.

kibwen2• 1 year 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.

privatelypublic2• 1 year ago

You're forgetting america loves its covered parking

timerol• 1 year ago

10% of the battery per day, which would cover all of my driving other than the rare long road trip. I have plenty of weekends where I drive 200 miles, but then the battery would recharge over the week when I drive less than 40 miles a day

energ8• 1 year 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/ 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_explore4• 1 year 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• 1 year 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)

MostlyStable2• 1 year 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.

Aurornis3• 1 year 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.

imp0cat2• 1 year ago

It's not, but older cars tried to keep their batteries fully charged. Newer cars with the so-called "smart" alternators never keep the battery full, they always leave some empty capacity to recover energy while moving.

londons_explore4• 1 year ago

The big issue tends to be complex logic for going to sleep often getting stuck. Ie. "oh, I was trying to use the LTE connection to poll for updates, but the connection got reset so I kept the CPU awake forever whilst retrying every 5 minutes rather than going to sleep mode".

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.

pinkmuffinere2• 1 year ago

I had this same problem in my 2005-ish Lexus! I got a cheap switch[1] on Amazon and put it in-line with my battery. If I’m going to leave the car undriven for more than a week, I just disconnect the battery with the switch. It’s been great, no complaints so far.

[1] this is the switch I got https://a.co/d/90K0QiH

kevstev2• 1 year ago

Doesn't anti-theft precautions kick in when you do this? On my Honda, if the battery goes completely dead or when I replace it, I have to enter a code in after, and IIRC all my radio stations reset, so it would be really inconvenient to do this often.

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.

Qem• 1 year 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• 1 year 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• 1 year 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• 1 year 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

tootie• 1 year ago

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

westurner2• 1 year 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?

westurner2• 12 months 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_limi...

"How to cut U.S. residential solar costs in half" (2025) https://news.ycombinator.com/item?id=44551633

vondur• 1 year 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• 1 year 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• 1 year ago

even EVs still have the 12V battery

chris2225• 1 year 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• 1 year 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.

chris2225• 1 year 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/inli...

1dom2• 1 year 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.

chris2225• 1 year ago

You can do bidirectional with most GM vehicles now with the GM energy solution. I don’t have this but I did have a call with them.

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.

https://gmenergy.gm.com/

cryptoegorophy• 1 year ago

$0.05 is the rate we pay in BC at night. I was still debating whether to add solar or not, I guess your post answers the question. Until we can get to $0.01 there is no point in solar in BC at least.

slavik81• 1 year ago

From an efficiency standpoint, we should probably be building grid-scale solar in Alberta and pumped storage in BC. There's more sunshine on the east side of the Rockies.

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.

chupchap2• 1 year ago

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.

This is interesting. While it has the most storage capacity, the range is not good for that much battery.

chris2225• 1 year ago

Part of it is the weight of a battery this size but the bigger issue is the aerodynamics of the large frontal area.

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.

mbreese• 1 year ago

I don’t think the Silverado is optimized for driving range, but rather - can it do typical “truck” stuff. For example hauling and/or towing. For this workload, having more towing capacity in a slightly less aerodynamic package is probably a good trade off. You don’t get a truck for the efficiency, you get one so you can do stuff with it.

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.

killingtime74• 1 year ago

Just to be clear you're talking about variable costs not total costs. Total costing include time value of money, amortization etc. (I'm no hater I also drive an EV).

toddmorey• 1 year ago

Another less commonly discussed option is community solar (also called offsite solar). It's especially attractive if the roof line of your house isn't ideal for solar panels or if you expect to be replacing your roof within the lifespan of your panels. (Or if you have a historic association like I do that makes almost every home project impossible.)

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.

SlowTao• 1 year ago

I have always liked this idea, it is such a neat middle ground between massive grid scale systems and the hassle of individual system maintenance.

cman1444• 1 year ago

I don't understand the purpose of consumers owning individual solar panels in a large array. How is that better than a single entity owning the whole array, and what function does the consumer provide?

thegrim332• 1 year ago

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?

theoreticalmal2• 1 year ago

The relevance is readily apparent to people who aren’t grumpy yahoos.

amy214• 1 year ago

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.

mike-the-mikado• 1 year ago

(2016)

burnt-resistor• 1 year ago

Solar Freakin' Roadways:[0] Mobile Edition

0. https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtu...

Impacts of adding PV solar system to internal combustion engine vehicles

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