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>Justify why you think you can only stick a single 400W panel on a car. Because a 400W solar panel is basically the size of a car (~1mX2m). And under IDEAL CON

>Justify why you think you can only stick a single 400W panel on a car. Because a 400W solar panel is basically the size of a car (~1mX2m). And under IDEAL CONDITIONS, you're looking at a 150 to 250 hour charge [1] ... and you're not going to get ideal conditions most of the time. Maybe you can stick 5 of those panels on a trailer and have the EV haul that around, and now you've improved your charging time from 250 hours to 50 hours (still, under ideal conditions) ... congrats, you still made negligible difference in extending EV range or making it practical. >Cars are large 3D objects, you aren’t going to get nearly as much power from side panels or the dashboard as the roof ... You're guaranteed to get 0 power from the sides that aren't facing the sun. So now you're horribly complicating the manufacturing process and increasing the EV price, all for an approach that would provide, at best, miniscule improvement to range. >How effective this would be in Alaska is irrelevant if nobody buys it in Alaska. It won't work in California either. But let's try something else ... with EV manufacturers being obsessed with squeezing out every km of range, why do you think approximately 0 of them are actually building an EV with built-in solar panels? What do you know, that they don't? [1] Assuming a 60kWh-100kWh battery and dividing by 400W = 150h to 250h

mattmaroon 4y ago
Ha, nobody's camper has 2kw solar on the roof. You've got a huge installation if you've got half that. Your roof has ACs, skylights, vents, ect to work around. I've got a 35' travel trailer I live in 4 months a year (and that's close to as bit as they get) and I think I could get 1,200w up there if I really squeezed. I took some measurements because I'm planning to. RVs are often parked in full sun at least, but even then. I think I'd be lucky to get more than 5kwhh a day. Which is great for me as long as I'm not running the ACs. But that would not even remotely account for the extra drag it put on an EV to trailer it ten miles. There've been attempts to make "solar paint" for cars, which would be lovely if possible, but even then I think the economic argument will essentially never work out when you factor in time value of money. As the original article said, the economics will likely always be much better for putting the solar panels on your house and charging at home.
- Retric 4y ago
  It’s true many RV’s have a lot of random junk on their roofs but this discussion is about what happens if you optimize the vehicle for solar at the design phase rather than trying to slap whatever you can after market. Here’s a random 2.6 kW example which still has a great deal of wasted space. https://youtu.be/Ekoh_QhiJJI https://youtu.be/Ekoh_QhiJJI 5th wheel with 3kW and still a significant amount of wasted space. https://youtu.be/BPTfkocNEu4 https://youtu.be/BPTfkocNEu4
  - macspoofing 4y ago
    >Here’s a random 2.6 kW example which still has a great deal of wasted space. https://youtu.be/Ekoh_QhiJJI https://youtu.be/Ekoh_QhiJJI Did you watch that video? The solar panels are not even able to fully handle their appliances and AC, and they still use a generator to supplement. They aren't used for charging a car battery at all. >but this discussion is about what happens if you optimize the vehicle for solar at the design phase It still doesn't change the equation because you're not looking at a order of magnitude difference. In the case of RVs and the YouTube videos you posted, you don't need to worry about what happens if you 'optimize' a vehicle for solar during a design phase - just do a back-of-the-napkin calculation by doubling the output and ... nothing changes. The challenges are the same. The use-cases are still the same (namely, hope for sunny days to generate power to run some appliances). You're still not making any meaningful progress towards extending EV range - and that's assuming double output (and you're not going to get double in the real world).
    - Retric 4y ago
      That’s moving the goalposts you just said, “nobody's camper has 2kw solar on the roof” and yet here’s several people who do. Clearly a camper that people live in has different demands for things like AC and a microwave than a car that’s just sitting around empty most of the day. A 15.5 foot long car is half the length and nearly the same with so downscaling a 3kW system to ~1kW seems perfectly reasonable. Toyota built a demo by sticking solar panels on a stock Prius and says it added roughly 25 miles per day of range. That would cover the majority of what the average American drives per year. Yes most people would still need to charge their cars, but suddenly using a normal outlet at home rather than paying for a level 2 charger looks reasonable. So not only are you saving on electricity but also instillation costs.
Retric 4y ago
Actual cars much larger than 1x2m. The Tesla Model 3 a fairly small car and even that’s 4.7 m X 2.09m. Of course cars have a smaller roof if you ignore the hood, trunk, and the ability to have panels on the dashboard, rear deck, and side panels. Also, you can approximate aerodynamic curves with multiple flat segments, current cars with a solar roof have then installed in a survey body segment.
- macspoofing 4y ago
  >The Tesla Model 3 a fairly small car and even that’s 4.7 m X 2.09m. Uh huh. Do you want to put some numbers behind your assumptions. How much do you actually think you can generate that would make a difference to a Tesla 60kWh-100kWh battery? How much extra range do you think solar panels would provide? And finally, what aren't EV manufacturers seeing that you are seeing? It's not like solar panels on an EV are such a novel idea. In fact, it's the very first (naive) idea that everyone has as a potential solution to EV range and charging.
  - Retric 4y ago
    Currently there are 200W systems on real world cars that don’t cover that much of the car, but Toyota just made a Prius demo without changing the underlying design or using panels on the sides or dashboard which they say adds 25miles of range per day. https://global.toyota/en/newsroom/corporate/28787347.html https://global.toyota/en/newsroom/corporate/28787347.html So, assuming 4miles per kWh that Prius was expected to hit over 6kWh per day. That might not look like much vs a 100kWh battery pack but it’s 9,000 miles per year when the majority of Americans are only driving 13,000 or less. Their design doesn’t look practical, but 5kW/day in sunny areas seem to be a reasonable real world goal.
    - mikem170 4y ago
      > So, assuming 4miles per kWh that Prius was expected to hit over 6kWh per day. That might not look like much vs a 100kWh battery pack but it’s 9,000 miles per year when the majority of Americans are only driving 13,000 or less. I checked your link after reading your math, above. Coming from the RV solar world I found these numbers surprising. I think your comment about the 100 kWh battery pack is what threw me off. The normal battery in a Prius is 8.8 kWh with a 25 mile all-electric range [0]. Toyota is saying that the panels they used generate approximately 860 watts of power. The normal rule of thumb in the RV world (which I am familiar with) is to multiply panel wattage by 5 for watt-hours per day in good sun, so I would assume 5 kWh total per day for 860 watts of panels, in real life. So their numbers look optimistic to me, but aren't crazy - I would have said 15 miles under ideal conditions (5 kWh of their 8.8 kWh 25 mile battery), they said 44.5 km. They used 34% efficient panels to get that many watts from the limited space available on a car, something normally only available to the likes of NASA at this time (normal panels are around 20%). Only people in places like Arizona and Texas would get most of that power output, others not so much. I don't think people realize how much impact clouds, shade and optimal panel angle towards the sun have on solar power output. Even partial shade, like form a sign post, greatly diminishes power generation, unless you want to wire the panels differently and loose early/late/cloudy power capacity. For example, in 2021 Germany had 58728 MW of solar panels generating 49011 GW of power per year [1], which is 134.2 GW per day, which is only 2.3 times their panel capacity, and this is due to clouds. Based on this math that solar prius car in Germany may only get 5.6 miles per day of extra solar powered range with 860 watts of panels (860 watts times 2.3 is 2 kWh, or 22.5% of a 8.8 kWh 25 mile battery), or about 2050 miles per year, and perhaps a good bit less because the car panels are not oriented towards the sun like fixed panel installations usually are, and people park in shade under trees, or partial shade near telephone poles, or next to buildings sometimes, or winter when it's below freezing and cloudy the battery needs to warm itself to safely be charged, etc. The only other thing I would add to this discussion is that panels fixed to the surface of a car may have problems with heat. Normal rigid solar panels are in frames and elevated, allowing air to flow under the panels and cool them. Panels loose efficiency with heat. Flexible solar panels, which don't need a frame and can be attached to curved surfaces, typically fail in a year or three, they are nowhere near as reliable as rigid panels. There's a lot of discussion about this in the RV and boating communities. If the numbers work out on this idea, then that's great. Reliability would be my biggest concern, these panels need to last to pay for themselves. [0] https://getjerry.com/car-repair/toyota-prius-plug-in-hybrid-battery-size https://getjerry.com/car-repair/toyota-prius-plug-in-hybrid-... [1] https://en.wikipedia.org/wiki/Solar_power_in_Germany#Generation https://en.wikipedia.org/wiki/Solar_power_in_Germany#Generat...

mattmaroon 4y ago

Ha, nobody's camper has 2kw solar on the roof. You've got a huge installation if you've got half that. Your roof has ACs, skylights, vents, ect to work around. I've got a 35' travel trailer I live in 4 months a year (and that's close to as bit as they get) and I think I could get 1,200w up there if I really squeezed. I took some measurements because I'm planning to. RVs are often parked in full sun at least, but even then. I think I'd be lucky to get more than 5kwhh a day. Which is great for me as long as I'm not running the ACs. But that would not even remotely account for the extra drag it put on an EV to trailer it ten miles. There've been attempts to make "solar paint" for cars, which would be lovely if possible, but even then I think the economic argument will essentially never work out when you factor in time value of money. As the original article said, the economics will likely always be much better for putting the solar panels on your house and charging at home.

Retric 4y ago
It’s true many RV’s have a lot of random junk on their roofs but this discussion is about what happens if you optimize the vehicle for solar at the design phase rather than trying to slap whatever you can after market. Here’s a random 2.6 kW example which still has a great deal of wasted space. https://youtu.be/Ekoh_QhiJJI https://youtu.be/Ekoh_QhiJJI 5th wheel with 3kW and still a significant amount of wasted space. https://youtu.be/BPTfkocNEu4 https://youtu.be/BPTfkocNEu4
- macspoofing 4y ago
  >Here’s a random 2.6 kW example which still has a great deal of wasted space. https://youtu.be/Ekoh_QhiJJI https://youtu.be/Ekoh_QhiJJI Did you watch that video? The solar panels are not even able to fully handle their appliances and AC, and they still use a generator to supplement. They aren't used for charging a car battery at all. >but this discussion is about what happens if you optimize the vehicle for solar at the design phase It still doesn't change the equation because you're not looking at a order of magnitude difference. In the case of RVs and the YouTube videos you posted, you don't need to worry about what happens if you 'optimize' a vehicle for solar during a design phase - just do a back-of-the-napkin calculation by doubling the output and ... nothing changes. The challenges are the same. The use-cases are still the same (namely, hope for sunny days to generate power to run some appliances). You're still not making any meaningful progress towards extending EV range - and that's assuming double output (and you're not going to get double in the real world).
  - Retric 4y ago
    That’s moving the goalposts you just said, “nobody's camper has 2kw solar on the roof” and yet here’s several people who do. Clearly a camper that people live in has different demands for things like AC and a microwave than a car that’s just sitting around empty most of the day. A 15.5 foot long car is half the length and nearly the same with so downscaling a 3kW system to ~1kW seems perfectly reasonable. Toyota built a demo by sticking solar panels on a stock Prius and says it added roughly 25 miles per day of range. That would cover the majority of what the average American drives per year. Yes most people would still need to charge their cars, but suddenly using a normal outlet at home rather than paying for a level 2 charger looks reasonable. So not only are you saving on electricity but also instillation costs.

Retric 4y ago

Actual cars much larger than 1x2m. The Tesla Model 3 a fairly small car and even that’s 4.7 m X 2.09m. Of course cars have a smaller roof if you ignore the hood, trunk, and the ability to have panels on the dashboard, rear deck, and side panels. Also, you can approximate aerodynamic curves with multiple flat segments, current cars with a solar roof have then installed in a survey body segment.

macspoofing 4y ago
>The Tesla Model 3 a fairly small car and even that’s 4.7 m X 2.09m. Uh huh. Do you want to put some numbers behind your assumptions. How much do you actually think you can generate that would make a difference to a Tesla 60kWh-100kWh battery? How much extra range do you think solar panels would provide? And finally, what aren't EV manufacturers seeing that you are seeing? It's not like solar panels on an EV are such a novel idea. In fact, it's the very first (naive) idea that everyone has as a potential solution to EV range and charging.
- Retric 4y ago
  Currently there are 200W systems on real world cars that don’t cover that much of the car, but Toyota just made a Prius demo without changing the underlying design or using panels on the sides or dashboard which they say adds 25miles of range per day. https://global.toyota/en/newsroom/corporate/28787347.html https://global.toyota/en/newsroom/corporate/28787347.html So, assuming 4miles per kWh that Prius was expected to hit over 6kWh per day. That might not look like much vs a 100kWh battery pack but it’s 9,000 miles per year when the majority of Americans are only driving 13,000 or less. Their design doesn’t look practical, but 5kW/day in sunny areas seem to be a reasonable real world goal.
  - mikem170 4y ago
    > So, assuming 4miles per kWh that Prius was expected to hit over 6kWh per day. That might not look like much vs a 100kWh battery pack but it’s 9,000 miles per year when the majority of Americans are only driving 13,000 or less. I checked your link after reading your math, above. Coming from the RV solar world I found these numbers surprising. I think your comment about the 100 kWh battery pack is what threw me off. The normal battery in a Prius is 8.8 kWh with a 25 mile all-electric range [0]. Toyota is saying that the panels they used generate approximately 860 watts of power. The normal rule of thumb in the RV world (which I am familiar with) is to multiply panel wattage by 5 for watt-hours per day in good sun, so I would assume 5 kWh total per day for 860 watts of panels, in real life. So their numbers look optimistic to me, but aren't crazy - I would have said 15 miles under ideal conditions (5 kWh of their 8.8 kWh 25 mile battery), they said 44.5 km. They used 34% efficient panels to get that many watts from the limited space available on a car, something normally only available to the likes of NASA at this time (normal panels are around 20%). Only people in places like Arizona and Texas would get most of that power output, others not so much. I don't think people realize how much impact clouds, shade and optimal panel angle towards the sun have on solar power output. Even partial shade, like form a sign post, greatly diminishes power generation, unless you want to wire the panels differently and loose early/late/cloudy power capacity. For example, in 2021 Germany had 58728 MW of solar panels generating 49011 GW of power per year [1], which is 134.2 GW per day, which is only 2.3 times their panel capacity, and this is due to clouds. Based on this math that solar prius car in Germany may only get 5.6 miles per day of extra solar powered range with 860 watts of panels (860 watts times 2.3 is 2 kWh, or 22.5% of a 8.8 kWh 25 mile battery), or about 2050 miles per year, and perhaps a good bit less because the car panels are not oriented towards the sun like fixed panel installations usually are, and people park in shade under trees, or partial shade near telephone poles, or next to buildings sometimes, or winter when it's below freezing and cloudy the battery needs to warm itself to safely be charged, etc. The only other thing I would add to this discussion is that panels fixed to the surface of a car may have problems with heat. Normal rigid solar panels are in frames and elevated, allowing air to flow under the panels and cool them. Panels loose efficiency with heat. Flexible solar panels, which don't need a frame and can be attached to curved surfaces, typically fail in a year or three, they are nowhere near as reliable as rigid panels. There's a lot of discussion about this in the RV and boating communities. If the numbers work out on this idea, then that's great. Reliability would be my biggest concern, these panels need to last to pay for themselves. [0] https://getjerry.com/car-repair/toyota-prius-plug-in-hybrid-battery-size https://getjerry.com/car-repair/toyota-prius-plug-in-hybrid-... [1] https://en.wikipedia.org/wiki/Solar_power_in_Germany#Generation https://en.wikipedia.org/wiki/Solar_power_in_Germany#Generat...