[HN Gopher] Impacts of adding PV solar system to internal combus...
___________________________________________________________________
Impacts of adding PV solar system to internal combustion engine
vehicles
Author : red369
Score : 97 points
Date : 2025-07-14 11:00 UTC (12 hours ago)
(HTM) web link (www.jstor.org)
(TXT) w3m dump (www.jstor.org)
| torginus wrote:
| 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 wrote:
| > 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_any...
| Veliladon wrote:
| No he didn't. Sweden gets ~2.6kWh/day per kW of solar panels.
| Malmo 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 wrote:
| 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 wrote:
| Regardless, it's not going to generate the claimed 1kW.
| pchew wrote:
| 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 wrote:
| If he only drives Mo-fr the math works out though
| torginus wrote:
| 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 wrote:
| 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.
| Veliladon wrote:
| 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 wrote:
| Or above the parking lot. Shadow and energy for the car :)
| Veliladon wrote:
| 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 wrote:
| 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 wrote:
| 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.
| MostlyStable wrote:
| My understanding is that the only vehicle for which both
| the vehicle and the necessary house-side equipment are
| _currently_ available on the market is the Ford Lightning.
| Several other manufacturers have promised that their
| vehicles will support it, but there isn't yet any available
| source of the house side yet.
|
| I assume this means that no one is using open standards or
| else you could conceivably just use the Ford Lightning
| equipment with any other vehicle.
|
| The Quasar 2 bi-directional charger has been on the verge
| of coming out for years now but still isn't ready to just
| go out and buy it.
|
| I agree with you though. I work from home and so my EV sits
| in front of my house for the vast majority of the time, and
| the battery is more than 2x my total usage during high cost
| hours. I don't have solar, but I do have time of use
| rating, so if I could use the giant battery to demand
| shift, that would save me a ton of money every year.
| londons_explore wrote:
| I suspect the main issue is the north american 2 split
| phases+neutral design.
|
| Specifically, without the neutral, the car can already
| generate that with the onboard charger. A bidirectional
| charger costs no more than a unidirectional one if you
| are designing it.
|
| But generating that neutral is expensive. You either need
| a hundred lbs of transformer, or some expensive power
| electronics.
| cptskippy wrote:
| > Only thing holding off my EV purchase is that I want
| proper V2G support.
|
| I always find this argument strange and it just feels like
| an excuse people use to sound informed while also dumping
| on EVs.
|
| Do you have frequent enough power outages that you need a
| backup power solution? Why don't you have that solution
| already? Did the lack of ability to use an ICE vehicle as a
| generator for your home stop you from purchasing ICE
| vehicles? What's your definition of "proper V2G support"
| and why don't current EVs with V2G suffice?
|
| V2G has a number of downsides. The most glaring is that
| you're stranded at home during a power outage or your house
| is without power while you go out. It requires to your EV
| to be plugged in, and won't automatically kick in when the
| power fails.
|
| The power needs of a home are minimal compared to an EV, if
| having power during power outages is important then you're
| far better off investing in a whole home battery backup
| system. They're significantly cheaper than an EV because
| they aren't optimized for density and portability.
| lm28469 wrote:
| That's actually mandatory in France for large parking lots
| willglynn wrote:
| 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.
| BizarroLand wrote:
| 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.
| parpfish wrote:
| 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
| IAmBroom wrote:
| The study literally proves you wrong.
| parpfish wrote:
| Having only read the abstract, no?
|
| In high sun areas there's a positive ROI
| maccard wrote:
| 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.
| wojciii wrote:
| 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.
| immibis wrote:
| There's no reason to assume the charger and the panel have
| to be colocated if the panel isn't on the car. We have an
| electricity grid.
| wojciii wrote:
| So do we, but you can't produce the electricity at one
| location and consume it in another. In the non-practical
| sense where our government decided that this is not
| possible.
| aqme28 wrote:
| Still doesn't solve the problem for people who use street
| parking.
| maccard wrote:
| Sorry - I wasn't explicit enough. The vast majority of
| existing and new developments where I live have on street
| parking - it's not allocated, there's no bays.
| aqme28 wrote:
| 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_123 wrote:
| 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
| walrus01 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| bestouff wrote:
| 60kWh may be enough for occasional short trips.
| gus_massa wrote:
| 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.
| walrus01 wrote:
| The rough estimate calculation for the theoretical 39 to 61
| kWh per month are for a perfectly mounted, south facing, 15
| degree tilted PV panel such as might be on the roof of a
| warehouse, or in a field somewhere. With no buildings or
| trees or shade obstructions around it. And perfectly
| exposed to sunlight from the moment of sunrise all the way
| to sunset. That's the 'default' assumptions built into
| pvwatts for calculating a fixed installation PV site.
|
| On an actual car that parks under trees, in parking
| garages, beside buildings in the shade, etc, the actual
| production would be much less. Not to mention the panel
| would be 'flat' on the roof and rarely if ever angled
| facing south, unless you happened to park on a hill with
| the roof of the car angled south...
|
| It's also not possible to say that a theoretical 39kWh can
| be turned into so many miles at 270Wh/mile because it's not
| a perfectly efficient system, I'd guess at least 15-20%
| would be lost to heat in charging the battery and DC-DC
| conversion.
| agumonkey wrote:
| 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
| bestouff wrote:
| 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.
| lazide wrote:
| In direct, unshaded sunlight. Which is the opposite of any
| significant sized city I'm aware of.
| PunchyHamster wrote:
| We have trams. We don't need to make worse trams
| CerebralCerb wrote:
| 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.
| sdeframond wrote:
| Would that be more interesting with tram because of the
| low-friction wheels?
|
| I imagine that could be viable in, say, Dubai or some other
| extremely sunny place ?
| lm28469 wrote:
| Why bother ? Have the solar panels on top of the tram
| warehouse, use the tram batteries for storage, swap empty
| ones for full ones when needed. If the solar array is
| down use the grid. That way you divid points of failure
| instead of multiplying them
| immibis wrote:
| Or... power the tram lines from the grid and feed solar
| power into the grid somewhere else.
|
| Trams use fixed infrastructure, including overhead power
| lines. I'm sure they must exist somewhere, but battery-
| powered trams are not popular.
| cesarb wrote:
| > I'm sure they must exist somewhere, but battery-powered
| trams are not popular.
|
| Yes, they do exist. The Alstom Citadis at Rio de Janeiro,
| which I take often, uses a supercapacitor for small
| pieces of its route (mostly crossings where the third
| rail would be damaged too often by vehicle traffic, or be
| impractical); according to the Wikipedia article
| (https://en.wikipedia.org/wiki/Alstom_Citadis), the
| Alstom Citadis at Nice uses batteries for parts of its
| route (https://www.railway-technology.com/projects/nice-
| trams/). I'm sure there are others.
| AstralStorm wrote:
| Why bother? Put the charge station in the bus stop instead.
| They have a longer runtime to charge and the bus does not
| have to be slow. Potentially easier to maintain too.
| BobaFloutist wrote:
| Or even do light rail and electrify the tracks with a
| solar network wherever you want.
| agumonkey wrote:
| Yeah I wasn't clear enough but I was really thinking about
| the most limited form of "transportation", low speed, low
| weight, so minimal frame and no protections really.
| Basically a string of bus stops on wheels. Maybe an average
| speed of 13mph would be enough. That's 3 three times the
| average walking speed.
| Zigurd wrote:
| 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 wrote:
| 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.
| willvarfar wrote:
| Thx that was a really awesome video!
|
| Commenting here to encourage other HNers to go watch it.
| Right now it has under 400 views and no comments.
| mikepurvis wrote:
| Yup, was just going to link something like that-- here's
| the University of Waterloo's solar car team's vehicles:
| https://www.uwmidsun.com/our-cars
|
| And even _those_ IIRC don 't drive continuously. They drive
| for part of the day, then park them angled into the sun for
| the other part of the day to top up the batteries.
|
| It's pretty hard to beat fixed panels + fast charging +
| parking your vehicle in a garage where it doesn't see the
| sun anyway (or get super hot).
| johannes1234321 wrote:
| 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)
| BizarroLand wrote:
| 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.
| actionfromafar wrote:
| 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 wrote:
| 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).
| eldaisfish wrote:
| A more practical solution is to leave the windows slightly
| open so the hot air escapes.
| SoftTalker wrote:
| Not practical if rain is forecast.
| imp0cat wrote:
| The car already has a rain sensor so it can close the
| windows automatically. I do believe some VWs already
| do/did that.
| SoftTalker wrote:
| My car has that to activate the wipers. To say it works
| reliably is to lie.
| gabrielhidasy wrote:
| There are places where a marginally open window will invite
| vandalism, or rain, or bugs, or smoke and bad smells.
| pchew wrote:
| 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.
| jollyllama wrote:
| 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 wrote:
| 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.
| jeffbee wrote:
| The Prius Prime solar roof is a $610 option available only
| on the top XSE trim level, so a hypothetical buyer is
| paying ~$7500 to access this effectively negligible amount
| of energy.
|
| ETA: and the fact that this option is tied to the
| significantly less efficient 19" wheel package, instead of
| the standard 17" wheels, means that this will never, ever
| be a net benefit.
| mattmaroon wrote:
| Not if they were getting that trim level anyway.
| beAbU wrote:
| Does the extra 3-6 miles factor in the need to now run the
| AC much more aggressively because the car will be hot from
| sitting in the sun all day?
|
| If this quoted number comes from the manufacturer itself,
| then I think the answer is "no".
| kgermino wrote:
| I don't think you'd have to run the AC any more
| aggressively with the solar panels than with a
| traditional steel roof?
|
| If you're suggesting it wouldn't work in a garage, that's
| obviously true (and another factor in whether car solar
| makes sense) but many (most?) people park their cars
| outside during the day anyway. I for one can't remember
| the last time I parked under cover
| danans wrote:
| > Does the extra 3-6 miles factor in the need to now run
| the AC much more aggressively because the car will be hot
| from sitting in the sun all day?
|
| Most cars are already sitting in the sun all day.
| aziaziazi wrote:
| Not here in European cities where they're either within a
| multi story park or in the side of a half day shaded tiny
| street.
| parsimo2010 wrote:
| You are not getting the 3-6 mile per day boost if your
| car is parked in the shade.
| tstenner wrote:
| That's his point. You won't get any reasonable charge
| because you (mostly avoid parking your car in direct
| sunlight
| sdenton4 wrote:
| Yah, it's a great point that the whole scheme is
| predicated on very questionable land use policy...
| gambiting wrote:
| What kind of European cities are you talking about lol,
| no offence but I hate this generalisation of "European"
| anything as if Southern Spain has the same culture and
| architecture as Poland or Lithuania.
| gunalx wrote:
| It is a somewhat fair generalisation of urban europe to
| have more innside parking or tall ish buildings that give
| shade.
| thinkalone wrote:
| The initial use of solar on the Prius was to power a
| ventilation fan while the car was parked, and the current
| version seems to specifically be designed to provide
| power to the air conditioner while driving. But, I also
| can't imagine the difference between cooling down the
| cabin is much different from parking in the sun or in the
| shade - you'd be running it continually to achieve "room
| temperature" during the entire drive either way.
| saltcured wrote:
| You can't imagine that air conditioning power draw varies
| with the heat load that it is working against? As a heat-
| pump, it takes more energy to move more energy.
|
| In the old days, they used duty cycle to adapt to the
| changing load. Modern ones do things like varying
| compressor displacement or compressor speed to adapt to
| the load. Variable frequency inverters are used to
| efficiently drive electric compressors.
|
| The variable displacement trick is used in ones
| mechanically linked to internal combustion engines. It
| can vary the compression stroke to account for different
| load as well as different engine speed.
| geerlingguy wrote:
| Watching power draw on my Leaf with LeafSpy, the AC seems
| to use between 500-1000W (maybe more sometimes, but
| that's just off the top of my head from a few times
| running it while driving).
|
| At the low end maybe achievable with a full rooftop
| covered in solar panels, but probably not adequate at
| 1kW+.
| lupusreal wrote:
| To my thinking, the best use of a solar panel on a car is
| running a low power AC unit all the time whenever the car
| is in the sun. Parking in the shade often isn't possible.
| singpolyma3 wrote:
| That's still 3-6 fewer miles worth of charging to do from
| more expensive sources. Even if it can't come close to
| covering your full use it's still covering something
| IAmBroom wrote:
| Not if it won't recover it's own costs.
| cma wrote:
| It may still lose on this, but you would also want to
| include the externality costs that the consumer doesn't
| themselves bear for whether it is worth it overall.
| dzhiurgis wrote:
| Cost is convenience.
|
| Manufacturing cost is like $40 cells, $20 electronics and
| $200 in glass fusion, mounting, etc.
|
| My car eats 200W just being online so it would be useless
| to charge from solar.
| thegrim33 wrote:
| 13.6 kWh battery. 39mile EPA range. Equals 2.87 miles of
| range per kWh. Leaving it out for 8 hours straight, on a
| sunny day, in LA, netted 915 Wh. Or, 2.86 miles. [0] Not
| 3-6, 2.86.
|
| 2.86 miles of charge, but only if left outside, uncovered,
| in full sun, on a fully sunny day, for a full 8 hours, in a
| place that gets effectively the maximum amount of solar
| radiation per day out of anywhere in the entire country.
|
| Now, do the same experiment anywhere else in the country,
| that doesn't get max solar radiation, or that can't get
| full sunlight for full 8 hours, or where it's cloudy at
| all, or rainy at all.
|
| 2.86 miles per day is the practical MAXIMUM, given perfect
| conditions. For the average scenario it'd be some fraction
| of that.
|
| The 6 miles figure is what they said you'd get if, in
| addition to perfect conditions, "if the sun shifted its
| orbit" (?) and gave perfect sunlight for 12 hours straight.
| Which is a number which should obviously not be thrown
| around as if it's obtainable.
|
| The fact that they're quoting numbers about what range
| you'd get if the solar system was constructed differently
| also makes me doubt the impartiality of their experiment
| and the numbers they provided.
|
| [0] https://www.motortrend.com/features/the-2023-toyota-
| prius-pr...
| conjecTech wrote:
| EPA range tends to be pessimistic for EVs as it assumes
| you are always traveling at highway speeds. Even small
| reductions in speeds can make EVs much more efficient
| since drag is quadratic. A quick google search shows
| Prius prime owners reporting 4-5.5 miles/kwh, so the 3-6
| mile range is entirely plausible.
| slaw wrote:
| EPA's city cycle speed is an average 19.6 mph, highway
| speed is an average of 48.3 mph. City range weighted at
| 55% and the highway range at 45%.
| bangaladore wrote:
| I don't think it's that simple. IIRC you don't have to do
| the city testing.
|
| https://www.epa.gov/greenvehicles/fuel-economy-and-ev-
| range-...
| bangaladore wrote:
| > EPA range tends to be pessimistic for EVs as it assumes
| you are always traveling at highway speeds.
|
| EV EPA range historically has been overstated. However,
| the water is muddied because the EPA doesn't really force
| the manufacturers to give an accurate number. A
| manufacturer can choose a highway only test, but then
| also arbitrarily decide to derate the value (EPA example
| is 70%). A manufacturer can choose to include city
| driving in the rating and weigh it accordingly and also
| derate the value (if they want).
|
| Tesla traditionally (still the vast majority of new and
| used EV market share) has been the only manufacturer that
| uses the highway + city driving tests. People then get
| surprised when the car cannot do the full range at 85
| MPH.
|
| All in all, this is the EPAs fault. For EVs they really
| need two numbers, city driving range and highway driving
| range. EVs are so much more efficient than ICE that speed
| makes a huge difference given there substantially smaller
| energy density.
|
| https://www.epa.gov/greenvehicles/fuel-economy-and-ev-
| range-...
| pchew wrote:
| Everyone is also glossing over the distinction that
| regardless of the actual amount, it's not at an actual
| voltage that can charge the battery to add mileage. You
| can hypothetically say that because it's offsetting the
| power usage from the AC that it could theoretically be
| saving that battery usage...but there's so many gross
| assumptions being made that it's a pointless statement to
| make, and it's all out the window the second the car
| starts the ICE side of the hybrid drive system for even
| an instant.
| cornholio wrote:
| > 2.86 miles per day is the practical MAXIMUM, given
| perfect conditions
|
| In your particular setup.
|
| A typical car can expose about 3 square meters of lateral
| area for those same 8 hours, and receive 3 kW of
| irradiance. multijunction cells can exceed 50%
| efficiency, so we're talking about a theoretical upper
| limit of 12 kWh electric per day.
|
| That would require a vehicle totally covered in cells,
| including the windows, so not very practical, but adding
| up to 30 miles/50 km per day is nothing to sneeze at.
|
| We could also imagine all sorts of solar receivers that
| engage during parking and inflate the apparent surface
| within the limits available, track the sun etc. to
| maximize energy.
| bgnn wrote:
| I wonder how much extra range you would get if one leaves
| the car in the shade so that it doesn't get super hot and
| there is no need to turn on the AC hard? I bet it's more
| than 2.86 miles.
|
| I believe having a carport and house roof covered with
| solar panels + (PH)EV is the best option.
| roamerz wrote:
| There is going to be a parasitic drag loss to figure into
| it as well. I think the only way to accurately calculate
| that would be in a wind tunnel or maybe an amp meter with a
| before and after installation under identical conditions.
| AdamJacobMuller wrote:
| 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 wrote:
| 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 wrote:
| If only we didnt start off with having 3000+ lbs of metal to
| move a 100-200lb person as a design limitation
| HPsquared wrote:
| 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 wrote:
| 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.
| HPsquared wrote:
| Same dimensions, same units. Sure it can be expressed more
| specifically e.g. "miles of nominal range per hour". But
| it's still miles per hour to facilitate mental calculation.
| jameshart wrote:
| It expresses how many miles you can get in a given number
| of hours. It _is_ a velocity.
| jermaustin1 wrote:
| Range isn't a unit though, so it isn't actually telling you
| anything technical. Since range is a distance unit, it
| would still be "miles per hour" or "kilometers per hour" or
| "meters per second" or anything to let you know how long it
| will take to top up to full range.
|
| Could be "%/minute" maybe, but that is less useful if you
| know you need to go 45 miles, you would want to know how
| many hours (or fraction there of) that would take.
| kgermino wrote:
| Miles (of range) per hour (of charge) is somewhat widely
| (and accurately) used as a metric for charging speed
| VBprogrammer wrote:
| 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 wrote:
| 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 wrote:
| 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_ wrote:
| 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=PL9nf
| j0jfPXYBF8FO7sckzvV...
|
| Can't remember how long it took, think a couple weeks at
| least?
| PunchyHamster wrote:
| 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 wrote:
| 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.
| sevensor wrote:
| 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_123 wrote:
| 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.
| Aachen wrote:
| > not totally impossible, but not worth adding it
|
| I don't drive 24km per day, and don't have a good way to
| get to the train station other than by car. The bus is too
| tight, they miss each other often. Cycling isn't safe
| between towns, you have to basically go on a highway
| without any separation (yes that's legal in Germany to
| cycle on, as there is no other way than perhaps a farmer's
| grass path to go between towns, so they don't call them
| highways but cars drive highway speeds - or more, if they
| don't stick to the limit). I also don't have charging
| infrastructure or a driveway. A vehicle that does those
| couple km a few times per week without needing to drive
| elsewhere to charge gets me a long way. Charge me up,
| Scotty
|
| I've looked into this and the moment the Aptera ships
| (probably never but here's for hoping) I'm buying my first
| car. I've looked critically at the range they assume you
| get at my latitude and it would keep topped up for enough
| months of the year that it's totally worth it (maybe it was
| even year-round because they're so efficient, I don't
| remember now, but I'm also okay charging it thrice a year)
| labcomputer wrote:
| But 24 km per day is under ideal conditions (perfectly
| sunny day, mid-latitude, panels angled southward) and
| 500W requires 2 square meters of panels[1].
|
| Unless you own a big American pickup truck, it's hard to
| see where those panels fit on the car. And if you _do_
| own a big American pickup truck, you will not achieve the
| 150 Wh /km assumed by the GP (it will be more like double
| that). GP also used quite optimistic loss figures for
| conversion.
|
| It begs the question: Why not a Nissan Leaf and solar
| panels on your (home) roof?
|
| [1] Only 1000 W of solar energy falls on each square
| meter of the earth's surface at noon. The best
| commercially available solar panels have about 25%
| efficiency converting light to low voltage DC. This means
| you need a flat surface of about 2 square meters
| _directly facing the sun_ to collect 2000 W of light,
| which will achieve 500 W of electrical power.
| sevensor wrote:
| Thanks! That helps clarify the engineering challenges.
| There's never a free lunch!
| msgodel wrote:
| 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 wrote:
| 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 wrote:
| Who lunches for several days/weeks? logically you would
| charge high speed through a plug with energy generated by
| panels that are much more efficiently (money+yield) placed
| and not have to carry around.
| mikepurvis wrote:
| 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.
| kgermino wrote:
| Agreed. There's an EV camper van with rooftop solar. IIRC
| it gets about 1000W peak, which isn't bad for the home
| batteries but is basically nothing for the high voltage
| drive system
| amluto wrote:
| How about charging your house batteries, which power fans
| and lights and perhaps cooking and A/C? This kind of solar
| setup can be rather cheap and quite effective.
| wing-_-nuts wrote:
| This and you could also charge an ebike
| mikepurvis wrote:
| Yes, that's what I'm meaning. AIUI off-grid camping tends
| to be more limited by the drinking water supply more than
| electricity, but if collecting solar power lets you avoid
| running the generator quite as often, that sounds like a
| win.
| thijson wrote:
| Boats have been doing this for ages.
|
| https://www.youtube.com/watch?v=BmbH-
| TAM2Wk&list=PLQp8FoQ4t-...
| masklinn wrote:
| 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 wrote:
| 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 wrote:
| 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.
| driverdan wrote:
| 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.
| masklinn wrote:
| > I'd guess it'd be enough for something like 1-2 miles a
| day on an electric drive train
|
| It's probably more 10~20, possibly as much as 30, if it's a
| long and sunny summer day FWIW.
|
| For references:
|
| - the F150 lightning gets close to 2 miles / kWh on
| average, ~1.5 at highway speeds but as much as 3~4 at
| consistent low speeds
|
| - on the other side of an RV, Volvo markets their FH
| Electric (cabover semi) for 1.1kWh/km -- 0.7 mi/kWh -- at
| 80km/h (50mph), DAF/Innovate UK's Battery Electric Truck
| Trial yielded similar results (1.08kWh/km over 287000 km),
| it's also close to the numbers of the electric trucker in
| their very recent MAN eGTX video (0.83 kWh/km = 0.75
| mi/kWh)
| chris_va wrote:
| 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.
| Aurornis wrote:
| > 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.
| secabeen wrote:
| 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.
| MisterTea wrote:
| Mechanically simple, yes. Electronically simple, no.
| WorldMaker wrote:
| To be fair, modern PV cells are purely solid state (no
| moving parts, no lubricants or coolants), so a solar system
| shouldn't add a scheduled maintenance burden, just add to
| potential unscheduled maintenance costs in worst case
| scenarios.
| jillesvangurp wrote:
| 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 wrote:
| When I'm not using my vehicle, it's in my garage.
| tempestn wrote:
| 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).
| infecto wrote:
| 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.
| rbanffy wrote:
| 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 wrote:
| 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 wrote:
| 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.
| infecto wrote:
| Again, needless manufacturing complexity. You would be
| paying for a gimmick and not a real economic benefit.
| immibis wrote:
| Almost everything humans do is a gimmick. Eating anything
| other than nutrient slop is a gimmick. Gimmicks make life
| interesting.
| infecto wrote:
| Huh? This paper is about the economics or gain from
| adding solar powers to vehicles hence my statement that
| it's a gimmick and it adds complexity (cost) for a gain
| that is not beneficial. Now if we were talking about
| marketing the vehicle, sure it perhaps drives a fun idea
| for buyers.
|
| From an economic standpoint solar panels on vehicles are
| a gimmick.
| rbanffy wrote:
| One thing the paper does is introduce a mathematical
| model that allows us to decide when it's a gimmick and
| when it actually becomes useful. As PV panels get more
| efficient and lighter, there is a point it'll start to
| make sense despite conversion losses. It's very unlikely
| to make much sense in Sweden (or even in Ireland, where I
| live), but different locations, with different
| infrastructure and, most important, solar exposure, will
| drive different economics.
| IAmBroom wrote:
| It might shut up some of the people who think solar panels are
| magic.
| PunchyHamster wrote:
| Those people dont read papers or believe science
| Jasp3r wrote:
| It's also not something that needs research IMO: Toyota has a
| Prius with solar panel option.
| infecto wrote:
| That option is a gimmick though.
| danaris wrote:
| 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.
| infecto wrote:
| 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.
| danaris wrote:
| But even stipulating this, with the way solar is improving,
| it may very well not be the case for much longer.
|
| If you can guarantee that, in moderately sunny weather, the
| solar panel on your car's roof can provide enough power to
| keep the car going at, say, 30mph indefinitely, that's no
| longer just a fun toy.
|
| Now, that level of utility may still be a long way off--or
| may even never be possible!--but I'm not willing to write
| it off for good, given solar's curve.
|
| ETA: sorry, realized I should unpack a bit why I think this
| is worth mentioning: Your GP post was expressing confusion
| over why people would study this; I think it's very
| valuable to continue studying it as solar continues to
| improve, so that we can understand just where we are in
| relation to that utility curve.
| ianbooker wrote:
| Solar sun roofs for ICEs were a thing 20 years ago. Solar was
| able to ventilate your car on sunny days.
| fred_is_fred wrote:
| Yes, the Priuses circa 2010 had them.
| JamesCoyne wrote:
| mirror https://sci-hub.se/https://www.jstor.org/stable/26169128
| throwaway3b03 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| Thank you for posting your nonsensical take.
| fortran77 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| Can you elaborate here?
| potato3732842 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| jollyllama wrote:
| 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 wrote:
| 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.
| testing22321 wrote:
| 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
| driverdan wrote:
| 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 wrote:
| 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 wrote:
| I'd like to see PV added to a Ford Maverick hybrid.
| jwr wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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_ wrote:
| 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 wrote:
| 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.
| kibwen wrote:
| 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 wrote:
| You're forgetting america loves its covered parking
| kibwen wrote:
| 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 wrote:
| 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.)
| timerol wrote:
| 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 wrote:
| "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_explore wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| > 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.
| imp0cat wrote:
| 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_explore wrote:
| 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.
| pinkmuffinere wrote:
| 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
| Qem wrote:
| 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 wrote:
| 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 wrote:
| > [ ... ] 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 wrote:
| 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 wrote:
| Moot point since Trump just killed CAFE. No more mileage
| standards will be enforced in the US.
| westurner wrote:
| 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?
| vondur wrote:
| If you have a small battery and use it to add ventilation in the
| vehicle on hot days when parked would be cool.
| Glyptodon wrote:
| 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 wrote:
| even EVs still have the 12V battery
| chris222 wrote:
| 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 wrote:
| 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.
| 1dom wrote:
| 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.
| cryptoegorophy wrote:
| $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.
| chupchap wrote:
| > 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.
| killingtime74 wrote:
| 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).
| mike-the-mikado wrote:
| (2016)
___________________________________________________________________
(page generated 2025-07-14 23:00 UTC)