# Why don't EV's have solar panels too? **URL:** \ **Category:** Factual Questions\ **Created:** [November 18, 2019, 5:53pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621 "2019-11-18T17:53:29Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![RioRico](https://avatars.discourse-cdn.com/v4/letter/r/f04885/32.png) [@RioRico](https://boards.straightdope.com/u/RioRico)\ **Post date:** [November 19, 2019, 9:08pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/21 "2019-11-19T21:08:29Z")
> [@Chronos](#): > > With an RV that you’re parking for a while, you might also not be restricted to the roof area. While you’re parked, you **might** be able to set up more panels in the area around the vehicle (possibly doubling as awnings). Not _might_. Wander around some campgrounds and you’ll see some RVs surrounded by panels. Those are the folks who didn’t want to pay the hookup fee. 😉 > [@](#): > > I suspect, though, that most RV customers would want significantly more than 100 miles range. For vacationers, sure, so they can reach the destination expediently. For full-timers ambling from park to park, not so much, but eventually, yes. We classify as extended vacationers. We’ll take our little RV out for a few months, only staying anywhere a few days between hookups. But 350-mile days can occur. > [@](#): > > What might make more sense would be to have a conventional gasoline-powered RV, that can carry some smaller electric vehicle (somewhere in the scooter to golf cart range), that charges from panels carried on or deployed from the RV, and which you can use to travel around the vacation spot where you have the large vehicle parked. I’m too lazy to search now but I’ve read of Greyhound-sized RVs with a small “garage” in back. Drop the tailgate and drive out your SmartCar, no towing. I hate towing. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [November 19, 2019, 11:22pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/22 "2019-11-19T23:22:35Z")
I’ve been considering making a road transportable solar charging system for my Model 3. You can get thin, flexible solar panels these days for fairly cheap. About 1x0.5 meters, and 100 watts. They’re \<1 cm thick. In principle, I can stack 20-30 of them in my trunk. So, I show up to a big campsite, spread out the panels and stake them down. Since I wouldn’t have space for a frame to hold them at an angle, they wouldn’t be as efficient as typical roof-mounted panels. I could achieve maybe 2 kW peak power, and in an ideal spot maybe 20 kWh/day. That’s 80 miles, or a full recharge after 4 days. It’s still not that practical, not least because I have to fill most of the trunk with panels, and because just setting them up would likely take an hour or so. It’s only worthwhile for the amusement value. And also makes clear why body-mounted panels are going to be almost worthless. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 20, 2019, 12:04am UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/23 "2019-11-20T00:04:40Z")
> [@muldoonthief](#): > > Isn’t that how Matt Damon did it in “The Martian” ? More or less. In the book, he drove for about half a day, stopped and set up the panels. And then every 4th or 5th day (I forget which) he’d have to stop for a full day to completely recharge. He missed a couple points, though. His panels were mostly stacked on top of his rover in two stacks, IIRC, so he could have connected the top ones while driving. And connected the RTG he had for heat while driving too. These wouldn’t have added much to his daily drive, though, maybe 10-15 minutes or so. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 20, 2019, 5:59am UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/24 "2019-11-20T05:59:06Z")
I wonder if the next step is the forthcoming Tesla Pickup modified into an RV - or hauling a fifth-wheel. Stick a Powerwall in the RV, have fold-out or awning solar cells when parked; I even imagine one wing on the roof would be flip-flop, so the top layer of the fold-out would either allow some small bit of charging while under way, or flip over the other way as a protective cover for the solar array. when you just can’t wait for a full charge, there will be electric car chargers along the road, far cheaper than gasoline. ---
**Author:** ![RioRico](https://avatars.discourse-cdn.com/v4/letter/r/f04885/32.png) [@RioRico](https://boards.straightdope.com/u/RioRico)\ **Post date:** [November 20, 2019, 8:05pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/25 "2019-11-20T20:05:19Z")
> [@md2000](#): > > I wonder if the next step is the forthcoming Tesla Pickup modified into an RV - or hauling a fifth-wheel. Stick a Powerwall in the RV, have fold-out or awning solar cells when parked; I even imagine one wing on the roof would be flip-flop, so the top layer of the fold-out would either allow some small bit of charging while under way, or flip over the other way as a protective cover for the solar array. when you just can’t wait for a full charge, there will be electric car chargers along the road, far cheaper than gasoline. For those interested, here are [current US RV industry statistics](https://www.thewanderingrv.com/rv-industry-statistics-trends-facts/). I expect that within a generation, by law, motor vehicles will be electric and probably autonomous. Trucks and bus-size RVs will need more and bigger batteries. (Tip: invest in battery manufacturers.) But many solar panels will be needed. I must go now so I’ll let someone else calculate how much battery is needed to propel a Greyhound-size RV and how much roof space covered with panels will recharge, and over what duration. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [November 20, 2019, 8:59pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/26 "2019-11-20T20:59:06Z")
> [@Little\_Nemo](#): > > The added weight would be an issue. And so would the aerodynamics. A car with a solar panel might end up consuming more extra energy while traveling than the panel would produce. Yeah, the aerodynamics of [this](https://en.wikipedia.org/wiki/Lightyear_One) look terrible … (Link goes to wikipedia article on Lightyear One solar car prototype, which for some reason hasn’t got panels mounted at the optimal angle like a PV field installation.) ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [November 20, 2019, 9:07pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/27 "2019-11-20T21:07:59Z")
Googling, it appears that most solar cells are about 20% efficient. What happens if that’s doubled or even tripled? Do permanently mounted solar cells make sense then? ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 20, 2019, 9:13pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/28 "2019-11-20T21:13:27Z")
> [@Dewey\_Finn](#): > > Googling, it appears that most solar cells are about 20% efficient. What happens if that’s doubled or even tripled? Do permanently mounted solar cells make sense then? FWIW there is a thermodynamic limit to how efficient the solar panels can be so it’s not like 100% is in the cards. I don’t know if tripling is possible. ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [November 20, 2019, 10:13pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/29 "2019-11-20T22:13:22Z")
While it makes intuitive sense to put solar cells on EVs, that’s kind of a backwards approach. Rather than asking “can I put solar cells on a car?,” consider this: “I have $X,000 to spend on solar cells to power my car. Where should I put them?” Very quickly, it becomes clear that almost anywhere is better than the car itself. You’ll generate much more power per dollar by building a static array than you will by diverting some of the budget to put solar cells on your car. This goes for EV manufacturers too. The cost to integrate solar cells into the body is high, and the benefit is low. The money spent integrating solar cells would be put to better use increasing battery energy density. Per Chronos’ comment, I agree that manufacturers whose concept cars include PV panels are primarily trying to appeal to the expectations of customers who haven’t walked through the math. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 21, 2019, 12:07am UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/30 "2019-11-21T00:07:33Z")
The absolute, fundamental, cannot-be-avoided limit for efficiency is that a solar panel is a heat engine, operating between reservoirs at approximately 6000 K (the Sun) and 300 K (the Earth). Since that’s a temperature ratio of around 20, the absolute upper limit of efficiency is 95%. For any given technology for making solar panels, there are lower limits, based on things like the electrical properties of silicon. But I’m not sure what those limits are, off the top of my head. But if you could make a solar panel twice as efficient as what we have now, then you’d get twice the range. It’s as simple as that. Though most research nowadays isn’t aiming for more efficient solar cells, but cheaper ones: You don’t care if the efficiency is low if you can afford to cover a large enough area. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [November 22, 2019, 6:01pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/31 "2019-11-22T18:01:16Z")
Elon Musk has tweeted that the Cybertruck will have a solar roof and bed cover option that will allow charging 15 miles per day. The truck also has a 110 volt and 220 volt power outlets, so it is likely the real usefulness of the solar roof will be in providing accessory power while in the backcountry. He also tweeted that the “pressurized version” will be the official truck of Mars. So, the solar panel (and Mars) thing could be anything from a joke, to wishful thinking, to actual engineering projects that are being worked on. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [November 22, 2019, 6:02pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/32 "2019-11-22T18:02:30Z")
There’s another rather stern absolute limit on solar cell effectiveness: Total insolation (the absolute amount of energy reaching the surface of the Earth from sunlight) is [198 W/m²](http://www.renewable-energy-concepts.com/solarenergy/solar-basics/insolation-weather.html). So for a perfect conversion of all solar spectra reaching a solar panel, the solar panel will generate at most less than 200 watts per square meter of panel. The power needs of an EV are orders of magnitude higher. ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [November 22, 2019, 6:35pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/33 "2019-11-22T18:35:54Z")
No solar car claims to cover the instantaneous driving power with their solar cells. This is about energy collected during a day and stored in the batteries. Several kWh seems easily achievable. [Here](https://www.youtube.com/watch?v=OxgzOP8XGvo) (Youtube video) is a guy who claims to be able to charge significant extra range into his old Nissan Leaf over the course of a day even with just a tiny solar panel on his hood. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 22, 2019, 8:26pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/34 "2019-11-22T20:26:14Z")
I’m sure he does claim that. He’s wrong. ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [November 22, 2019, 9:54pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/35 "2019-11-22T21:54:25Z")
It does look pretty unlikely. My guess would be that he had those extra batteries already charged when he left home. If it’s not a flat out scam. Real solar cars have a much larger solar panel area. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 22, 2019, 10:21pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/36 "2019-11-22T22:21:08Z")
> [@gnoitall](#): > > There’s another rather stern absolute limit on solar cell effectiveness: > > Total insolation (the absolute amount of energy reaching the surface of the Earth from sunlight) is [198 W/m²](http://www.renewable-energy-concepts.com/solarenergy/solar-basics/insolation-weather.html). So for a perfect conversion of all solar spectra reaching a solar panel, the solar panel will generate at most less than 200 watts per square meter of panel. > > The power needs of an EV are orders of magnitude higher. This panel seems to be producing more then 200W/m^2 or at least claims to do so, at 206W/m^2 Size = 1.6 M^2, power 330 W, efficiency 19.7% [https://tandem-solar-systems.com/buy-solar-products/panasonic-330w-module-blkwht/?gclid=Cj0KCQiAq97uBRCwARIsADTziyYUNeMTjPa8v3JYYE3a3NUMpVO-3tFuNdqqHcGnrhHMWXGybessGEkaAkS3EALw\_wcB](https://tandem-solar-systems.com/buy-solar-products/panasonic-330w-module-blkwht/?gclid=Cj0KCQiAq97uBRCwARIsADTziyYUNeMTjPa8v3JYYE3a3NUMpVO-3tFuNdqqHcGnrhHMWXGybessGEkaAkS3EALw_wcB) Edit your link shows a max of 1000 W/m2 which makes sense that this can do 200 ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [November 22, 2019, 10:24pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/37 "2019-11-22T22:24:07Z")
The newly announced [Tesla Cybertruck](https://www.tesla.com/cybertruck) will have a [solar option](https://twitter.com/elonmusk/status/1197889310550216704): > [@Elon Musk](#): > > Will be an option to add solar power that generates 15 miles per day, possibly more. Would love this to be self-powered. Adding fold out solar wings would generate 30 to 40 miles per day. Avg miles per day in US is 30. Given the large flat surface available, 15 miles is plausible under good conditions. But that’s a few square meters, not the fraction of a square meter that you would get on a conventional car. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [November 22, 2019, 11:06pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/38 "2019-11-22T23:06:08Z")
> [@echoreply](#): > > Elon Musk has tweeted that the Cybertruck will have a solar roof and bed cover option that will allow charging 15 miles per day… The problem with a solar powered Cybertruck is that if you want that sweet solar power, the truck has to be parked outside where someone might see it. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [November 22, 2019, 11:35pm UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/39 "2019-11-22T23:35:17Z")
> [@kanicbird](#): > > This panel seems to be producing more then 200W/m^2 or at least claims to do so, at 206W/m^2 > > Size = 1.6 M^2, power 330 W, efficiency 19.7% > > [https://tandem-solar-systems.com/buy-solar-products/panasonic-330w-module-blkwht/?gclid=Cj0KCQiAq97uBRCwARIsADTziyYUNeMTjPa8v3JYYE3a3NUMpVO-3tFuNdqqHcGnrhHMWXGybessGEkaAkS3EALw\_wcB](https://tandem-solar-systems.com/buy-solar-products/panasonic-330w-module-blkwht/?gclid=Cj0KCQiAq97uBRCwARIsADTziyYUNeMTjPa8v3JYYE3a3NUMpVO-3tFuNdqqHcGnrhHMWXGybessGEkaAkS3EALw_wcB) > > Edit your link shows a max of 1000 W/m2 which makes sense that this can do 200 A 300W panel does not produce 300W in anything other than perfect conditions (direct sunlight, clean, angled properly to the sun, etc). Solar insolation i California is between 5 and 6 kWh/m^2. That is the maximum theoretical power you can get at 100% efficiency. So a 1m^2 solar panel at 20% efficiency can get at most around 1 kWh per day. This is probably the number manufacturers are using for their range claims. In the real world, that panel will lose 15-25% in efficiency for not being angled into the sun. Call it 20%. Now we are down to about 800Wh per day. Now add in shade from buildings and trees since you aren’t on a roof, dirt on the panel, and conversion losses, and you’re probably not putting more than 500Wh per day i to the battery. A Nissan leaf has a 24 kWh battery, which gives it a range of 135 km, so it needs about 177 Wh per mile. So… under real world conditions in California, assuming the vehicle is always parked in an area where it gets lots of sun, a 1 square meter solar panel woild be doing well to add 3 miles per day in range. I do not believe the guy who says he’s getting 15 miles per day of charge from a solar panel on the hood of his car. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 23, 2019, 1:45am UTC](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621/40 "2019-11-23T01:45:41Z")
> [@Sam\_Stone](#): > > The problem with a solar powered Cybertruck is that if you want that sweet solar power, the truck has to be parked outside where someone might see it. Unless you’re worried about theft, I don’t see this as a negative. People are going to see it when you drive it, after all. And if you believe all the negative tweets about it, no one is going to _want_ to steal it. [Previous page](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621.md?page=1) [Next page](https://boards.straightdope.com/t/why-dont-evs-have-solar-panels-too/843621.md?page=3)