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The title doesn't really tell you what they're actually doing. Toyota is basically running a program to put 34% efficient solar panels on a Prius to charge the

The title doesn't really tell you what they're actually doing. Toyota is basically running a program to put 34% efficient solar panels on a Prius to charge the battery during the day. Using typical panels on roof, hood, and trunk only nets you 4-6 miles / day of solar energy if you do the math. They're increasing surface area of panels here and using what are probably multi-junction (i.e. really expensive) cells for a fair boost in potential range / day. The claim of 18 miles per day of sun seems like a stretch and in actual production and real-world conditions you'd be more likely to get three quarters of that, but I could be wrong. Still impressive, though.

deleted 7y ago
[deleted]
dang 7y ago
Ok, we'll use your wording for the title above. Thanks!
dannyw 7y ago
I think any bit helps. If solar panels will ROI over the lifetime of vehicle ownership, then that’s awesome!
- msandford 7y ago
  How far is the average commute? There are a lot of places where this level of additional range for "free" could potentially halve your charging needs. Might also mean that people start looking for uncovered airport parking. Or that it's a lot harder to get really stranded with an electric car. Even at 100% efficiency (which we'll never get) I think electric cars will still have to charge off of something. But dragging the panels around with you so that you always have some kind of charging seem pretty reasonable.
  - wtallis 7y ago
    > But dragging the panels around with you so that you always have some kind of charging seem pretty reasonable. It might prevent the worst case scenario of being stranded in a desert without fuel. But for everyday driving, dragging around that extra weight has a real cost, which could quite plausibly outweigh the benefits to everyday driving. Remember, our auto industry has moved to the point where spare tires are starting to become uncommon and full-size spares are almost unheard of. The market isn't trying to optimize for the worst case scenario.
    - mattigames 7y ago
      You may be underestimating how much people dread chores like manually plugging their car to the electric outlet, and many people don't have those special garages with chargers on them, and if the house is a rented one modifying it is out of question (and renting is not only a poor people problem, a lot of people pay an insane amount of money renting, ask anyone in NYC).
      - wtallis 7y ago
        > You may be underestimating how much people dread chores like manually plugging their car to the electric outlet, I'm simply assuming that, for the foreseeable future, solar panels on your car won't put a noticeable dent in the frequency of those chores compared to with a current production Prius. If you can already go for two weeks of commuting and grocery runs without topping off the gas tank in your hybrid, stretching that by another day or two doesn't meaningfully change the ownership experience even if it does have a long-term impact on the economics of owning that vehicle.
    - luminiferous 7y ago
      When I first read your comment, I thought that there was no way that solar panels could be heavy enough to affect your mileage. So I did some quick calculations. Estimates of solar panel weight I found say that solar panels tend to weigh 2-4 lb per sqft.[1] Note that estimate is for roof-mounted solar panels, but if anything, car-based solar panels should be lighter. A Prius has dimensions of 180"x69".[2] The sqft of the solar panels will be less than that, since the panels don't cover the windshield, and they don't go all the way to the edge of the hood, etc. That's 86.25 sqft, so that puts an upper bound on the weight of the solar panels at 345 lb. If we assume the lighter end of the scale for solar panel weight, that becomes 172.5 lb. That's 6-11% of the curb weight of a Prius. That's pretty substantial! For reference, a 50 lb spare tire kit can reduce fuel economy (and presumably mileage, for EVs) by 1%.[3] Although that does imply that you're breaking even if the solar panels can increase your range by ~5%, not accounting for the weight. If you live somewhere like Arizona, that might work out. If you live in Seattle, maybe not. [1] https://sunmetrix.com/is-my-roof-suitable-for-solar-panels-and-what-is-the-weight-of-a-solar-panel/#targetText=On%20average%2C%20solar%20panels%20and,acceptable%20limits%20of%20your%20roof https://sunmetrix.com/is-my-roof-suitable-for-solar-panels-a.... [2] https://www.toyota.com/prius/features/dimensions/ https://www.toyota.com/prius/features/dimensions/ [3] https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=216 https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=...
  - WalterBright 7y ago
    I've often thought these cars should have a small gas generator you could use to charge the car if there's no outlet available.
    - blacksmith_tb 7y ago
      Most Prius-es are simple hybrids; the car they're testing with is a Prius Prime, a plug-in hybrid with ~25mi of all-electric range from an 8.8kWh battery, that's what they're trying to add range to. If that battery is exhausted you just drive on the gas engine as usual (I have a 2017 Prime). So this would just be a small boost, though to be fair I often can go a few days on a charge (but I don't drive a lot).
    - milkey_mouse 7y ago
      That's essentially what a plug-in hybrid is, modulo the "small."
      - outworlder 7y ago
        > That's essentially what a plug-in hybrid is, modulo the "small." Not exactly, Prius uses two drive trains and some fancy gearing to be able to use both engines. The gas engine actually propels the vehicle (either alone or together with the electric) Some 'hybrids' like the Volt only have EV drivetrains. The gas engine is just a generator and does not turn any wheels. Which also means that it can be much simpler – no transmission to worry about, you can run at whatever the ideal RPM is. And so on.
        greglindahl 7y ago
        You're incorrect about the Volt's drivetrain: https://en.wikipedia.org/wiki/Chevrolet_Volt#Drivetrain https://en.wikipedia.org/wiki/Chevrolet_Volt#Drivetrain Yes, the gas engine can turn the wheels.
    - outworlder 7y ago
      You are describing the Chevy Volt. Or the BMW i3.
- delfinom 7y ago
  That's the thing. Unless the option costs ~$1k extra, you will never ROI until after at least 10 years. In that time you'll be paying for replacing the glass on the solar panel when a rock inevitably cracks it.
angrygoat 7y ago
The claimed range would meet easily meet my mileage five days of the week – it's a big win! I'm in a fairly sunny city in Australia so I imagine I'd get a decent charge much of the time. I don't think this'd work so well in say, Vancouver, but then every place has to use the renewable energy sources locally available :-)
- sandworm101 7y ago
  If you don't park in the shade. If your parking space doesn't tilt slightly away from the the sun. For the same money you would be far better off installing some solar panels permanently somewhere along with a battery that can transfer that power into the car when you get home. Or, better yet, skip the batteries and plug the solar panels into the grid. The more solar panels attached to the grid the better. Anyone who cares about the environment would put panels on their house, lawn, driveway and pets long before their car. This is a fashion statement, a fancy paint job. (And most people would be shocked at how much solar power is available in Vancouver. Without dust in the air, droughts most summers, and the lack of mountains to the south, Vancouver does fairly well in terms of solar.)
  - mianos 7y ago
    +1 for the idea of putting solar panels on the pets. Pretty sure of the same marketing people who think putting solar cells on a car roof will be cost effective would love that idea.
  - sydd 7y ago
    Most people who live in big cities in the EU dont have a house (and they make up >50% of the population). They live in apartments. Isnt this the case for the USA too?
    - sandworm101 7y ago
      And those cars would be parked underground, or at least on city streets ... not the best places for solar.
- 7y ago
not_a_cop75 7y ago
5 * 365 > 1500 miles. I'd take that. And if I perchance ran out of fuel and battery, it'd be nice to know I could eat at a cafe for an hour in the afternoon and probably get it to hobble to a gas station. That's the kind of peace of mind that's worth maybe an extra grand.
- saagarjha 7y ago
  I'd expect full solar panels to cost significantly more than $1000.
  - not_a_cop75 7y ago
    Well retail, sure. You think the largest auto maker in the world is paying retail on everything?
    - ctack 7y ago
      But the public will be paying retail.
      - jacquesm 7y ago
        No, the public will pay much more than that because it is now a car part. Brand specific car parts are sold way above what an equivalent part would cost at retail. There was an interesting business model that consisted of buying brand new cars and breaking them up for parts.
        Ensorceled 7y ago
        Why did you say "No"? Clearly it will only be more expensive if you buy it as a part instead of as a car. Your own line explains it to yourself if you think about it: "There was an interesting business model that consisted of buying brand new cars and breaking them up for parts."
- killjoywashere 7y ago
crooked-v 7y ago
It seems like this could be useful for making electric cars more practical for apartment dwellers, in that a car in an open lot would stay indefinitely topped up when unattended and unplugged instead of the omnipresent worry of the battery running down.
- flukus 7y ago
  Yeah, a lot of people inner city won't drive everyday and often only have on street parking. Or they'll be renting somewhere that has garages without charging stations. Anything that can minimize the number necessary trips to a charging station or eliminate them completely for people that only drive once or twice would a week be a big win.
  - benj111 7y ago
    "renting somewhere that has garages" I still don't think solar panels will help in this situation.
    - crooked-v 7y ago
      A lot of city garages have an open roof level.
  - VBprogrammer 7y ago
    Getting those people to use a shared pool of electric cars would be a bigger win. That low utilisation means the initial environmental cost of producing the car is not amortised over nearly as many trips.
- de_watcher 7y ago
  Yea, if you've got a 15 minutes commute then you charge your Leaf2/Zoe/Ioniq not twice a month but once in three weeks.
elif 7y ago
4-6 miles? you only read the first paragraph, where the author summarized previous efforts. "If the car is driven four days a week for a maximum of 50 kilometers a day, there’s no need to plug into an outlet, NEDO’s Yamazaki said." This car maintains equilibrium at 124 miles per week, so basically anyone with a commute with a 1-way distance up to 12.4 miles, or 15.5 miles if you work from home one day a week, would not need to use a charger.
- mdorazio 7y ago
  I think you didn’t read my full comment.
thehappypm 7y ago
I just bought a new car. I was interested in a Tesla but don’t have a parking spot with an outlet, among other deterrents, that kept me from spending the initial $10k. My commute is about 8 miles per day. If a solar panel on a Prius could give me an almost free commute I would have bought it in a heartbeat.
masklinn 7y ago
> Using typical panels on roof, hood, and trunk only nets you 4-6 miles / day of solar energy if you do the math. FWIW there's a project to actually do that: https://lightyear.one https://lightyear.one This is an outgrowth from the WSC, the founders are alumni from TU/e. Now the car is really covered in panels (~5 sqm), it looks like they just replaced the rear window by panels (as well as panelling the hood, trunk and roof obviously). IIRC they were claiming up to 12km/h solar charging (as in you could crawl along on solar alone on sunny days). According to their calculator thingie, they're expecting about 5km/day in midwinter aberdeen (on average obviously).
agumonkey 7y ago
That has some value. How many people get stuck for a simple flat battery ? Having a way to avoid that is pretty nice to me. Depending on how costly is the option.

deleted 7y ago

[deleted]

dang 7y ago

Ok, we'll use your wording for the title above. Thanks!

dannyw 7y ago

I think any bit helps. If solar panels will ROI over the lifetime of vehicle ownership, then that’s awesome!

msandford 7y ago
How far is the average commute? There are a lot of places where this level of additional range for "free" could potentially halve your charging needs. Might also mean that people start looking for uncovered airport parking. Or that it's a lot harder to get really stranded with an electric car. Even at 100% efficiency (which we'll never get) I think electric cars will still have to charge off of something. But dragging the panels around with you so that you always have some kind of charging seem pretty reasonable.
- wtallis 7y ago
  > But dragging the panels around with you so that you always have some kind of charging seem pretty reasonable. It might prevent the worst case scenario of being stranded in a desert without fuel. But for everyday driving, dragging around that extra weight has a real cost, which could quite plausibly outweigh the benefits to everyday driving. Remember, our auto industry has moved to the point where spare tires are starting to become uncommon and full-size spares are almost unheard of. The market isn't trying to optimize for the worst case scenario.
  - mattigames 7y ago
    You may be underestimating how much people dread chores like manually plugging their car to the electric outlet, and many people don't have those special garages with chargers on them, and if the house is a rented one modifying it is out of question (and renting is not only a poor people problem, a lot of people pay an insane amount of money renting, ask anyone in NYC).
    - wtallis 7y ago
      > You may be underestimating how much people dread chores like manually plugging their car to the electric outlet, I'm simply assuming that, for the foreseeable future, solar panels on your car won't put a noticeable dent in the frequency of those chores compared to with a current production Prius. If you can already go for two weeks of commuting and grocery runs without topping off the gas tank in your hybrid, stretching that by another day or two doesn't meaningfully change the ownership experience even if it does have a long-term impact on the economics of owning that vehicle.
  - luminiferous 7y ago
    When I first read your comment, I thought that there was no way that solar panels could be heavy enough to affect your mileage. So I did some quick calculations. Estimates of solar panel weight I found say that solar panels tend to weigh 2-4 lb per sqft.[1] Note that estimate is for roof-mounted solar panels, but if anything, car-based solar panels should be lighter. A Prius has dimensions of 180"x69".[2] The sqft of the solar panels will be less than that, since the panels don't cover the windshield, and they don't go all the way to the edge of the hood, etc. That's 86.25 sqft, so that puts an upper bound on the weight of the solar panels at 345 lb. If we assume the lighter end of the scale for solar panel weight, that becomes 172.5 lb. That's 6-11% of the curb weight of a Prius. That's pretty substantial! For reference, a 50 lb spare tire kit can reduce fuel economy (and presumably mileage, for EVs) by 1%.[3] Although that does imply that you're breaking even if the solar panels can increase your range by ~5%, not accounting for the weight. If you live somewhere like Arizona, that might work out. If you live in Seattle, maybe not. [1] https://sunmetrix.com/is-my-roof-suitable-for-solar-panels-and-what-is-the-weight-of-a-solar-panel/#targetText=On%20average%2C%20solar%20panels%20and,acceptable%20limits%20of%20your%20roof https://sunmetrix.com/is-my-roof-suitable-for-solar-panels-a.... [2] https://www.toyota.com/prius/features/dimensions/ https://www.toyota.com/prius/features/dimensions/ [3] https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=216 https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=...
- WalterBright 7y ago
  I've often thought these cars should have a small gas generator you could use to charge the car if there's no outlet available.
  - blacksmith_tb 7y ago
    Most Prius-es are simple hybrids; the car they're testing with is a Prius Prime, a plug-in hybrid with ~25mi of all-electric range from an 8.8kWh battery, that's what they're trying to add range to. If that battery is exhausted you just drive on the gas engine as usual (I have a 2017 Prime). So this would just be a small boost, though to be fair I often can go a few days on a charge (but I don't drive a lot).
  - milkey_mouse 7y ago
    That's essentially what a plug-in hybrid is, modulo the "small."
    - outworlder 7y ago
      > That's essentially what a plug-in hybrid is, modulo the "small." Not exactly, Prius uses two drive trains and some fancy gearing to be able to use both engines. The gas engine actually propels the vehicle (either alone or together with the electric) Some 'hybrids' like the Volt only have EV drivetrains. The gas engine is just a generator and does not turn any wheels. Which also means that it can be much simpler – no transmission to worry about, you can run at whatever the ideal RPM is. And so on.
      - greglindahl 7y ago
        You're incorrect about the Volt's drivetrain: https://en.wikipedia.org/wiki/Chevrolet_Volt#Drivetrain https://en.wikipedia.org/wiki/Chevrolet_Volt#Drivetrain Yes, the gas engine can turn the wheels.
  - outworlder 7y ago
    You are describing the Chevy Volt. Or the BMW i3.
delfinom 7y ago
That's the thing. Unless the option costs ~$1k extra, you will never ROI until after at least 10 years. In that time you'll be paying for replacing the glass on the solar panel when a rock inevitably cracks it.

angrygoat 7y ago

The claimed range would meet easily meet my mileage five days of the week – it's a big win! I'm in a fairly sunny city in Australia so I imagine I'd get a decent charge much of the time. I don't think this'd work so well in say, Vancouver, but then every place has to use the renewable energy sources locally available :-)

sandworm101 7y ago
If you don't park in the shade. If your parking space doesn't tilt slightly away from the the sun. For the same money you would be far better off installing some solar panels permanently somewhere along with a battery that can transfer that power into the car when you get home. Or, better yet, skip the batteries and plug the solar panels into the grid. The more solar panels attached to the grid the better. Anyone who cares about the environment would put panels on their house, lawn, driveway and pets long before their car. This is a fashion statement, a fancy paint job. (And most people would be shocked at how much solar power is available in Vancouver. Without dust in the air, droughts most summers, and the lack of mountains to the south, Vancouver does fairly well in terms of solar.)
- mianos 7y ago
  +1 for the idea of putting solar panels on the pets. Pretty sure of the same marketing people who think putting solar cells on a car roof will be cost effective would love that idea.
- sydd 7y ago
  Most people who live in big cities in the EU dont have a house (and they make up >50% of the population). They live in apartments. Isnt this the case for the USA too?
  - sandworm101 7y ago
    And those cars would be parked underground, or at least on city streets ... not the best places for solar.
7y ago

not_a_cop75 7y ago

5 * 365 > 1500 miles. I'd take that. And if I perchance ran out of fuel and battery, it'd be nice to know I could eat at a cafe for an hour in the afternoon and probably get it to hobble to a gas station. That's the kind of peace of mind that's worth maybe an extra grand.

saagarjha 7y ago
I'd expect full solar panels to cost significantly more than $1000.
- not_a_cop75 7y ago
  Well retail, sure. You think the largest auto maker in the world is paying retail on everything?
  - ctack 7y ago
    But the public will be paying retail.
    - jacquesm 7y ago
      No, the public will pay much more than that because it is now a car part. Brand specific car parts are sold way above what an equivalent part would cost at retail. There was an interesting business model that consisted of buying brand new cars and breaking them up for parts.
      - Ensorceled 7y ago
        Why did you say "No"? Clearly it will only be more expensive if you buy it as a part instead of as a car. Your own line explains it to yourself if you think about it: "There was an interesting business model that consisted of buying brand new cars and breaking them up for parts."
killjoywashere 7y ago

crooked-v 7y ago

It seems like this could be useful for making electric cars more practical for apartment dwellers, in that a car in an open lot would stay indefinitely topped up when unattended and unplugged instead of the omnipresent worry of the battery running down.

flukus 7y ago
Yeah, a lot of people inner city won't drive everyday and often only have on street parking. Or they'll be renting somewhere that has garages without charging stations. Anything that can minimize the number necessary trips to a charging station or eliminate them completely for people that only drive once or twice would a week be a big win.
- benj111 7y ago
  "renting somewhere that has garages" I still don't think solar panels will help in this situation.
  - crooked-v 7y ago
    A lot of city garages have an open roof level.
- VBprogrammer 7y ago
  Getting those people to use a shared pool of electric cars would be a bigger win. That low utilisation means the initial environmental cost of producing the car is not amortised over nearly as many trips.
de_watcher 7y ago
Yea, if you've got a 15 minutes commute then you charge your Leaf2/Zoe/Ioniq not twice a month but once in three weeks.

elif 7y ago

4-6 miles? you only read the first paragraph, where the author summarized previous efforts. "If the car is driven four days a week for a maximum of 50 kilometers a day, there’s no need to plug into an outlet, NEDO’s Yamazaki said." This car maintains equilibrium at 124 miles per week, so basically anyone with a commute with a 1-way distance up to 12.4 miles, or 15.5 miles if you work from home one day a week, would not need to use a charger.

mdorazio 7y ago
I think you didn’t read my full comment.

thehappypm 7y ago

I just bought a new car. I was interested in a Tesla but don’t have a parking spot with an outlet, among other deterrents, that kept me from spending the initial $10k. My commute is about 8 miles per day. If a solar panel on a Prius could give me an almost free commute I would have bought it in a heartbeat.

masklinn 7y ago

> Using typical panels on roof, hood, and trunk only nets you 4-6 miles / day of solar energy if you do the math. FWIW there's a project to actually do that: https://lightyear.one https://lightyear.one This is an outgrowth from the WSC, the founders are alumni from TU/e. Now the car is really covered in panels (~5 sqm), it looks like they just replaced the rear window by panels (as well as panelling the hood, trunk and roof obviously). IIRC they were claiming up to 12km/h solar charging (as in you could crawl along on solar alone on sunny days). According to their calculator thingie, they're expecting about 5km/day in midwinter aberdeen (on average obviously).

agumonkey 7y ago

That has some value. How many people get stuck for a simple flat battery ? Having a way to avoid that is pretty nice to me. Depending on how costly is the option.