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That's interesting. Cheap 15% efficient solar panel produces 0.75 kWh per square meter per day in "average US location" [1], whatever that is. Let's assume ave

by ajuc 9y ago

That's interesting. Cheap 15% efficient solar panel produces 0.75 kWh per square meter per day in "average US location" [1], whatever that is. Let's assume average parking space area is 10 square meters (it depends, but it's close [2]) - so that's 7.5 kWh per day. Average energy consumption of electric cars is 11-16 kWh/100 km [3], let's assume 10 kWh/100 km - that's 75 km range for a day of standing in sun. That's actually not bad, and should be enough for driving back home from work. Actually, why not just put the solar cells on the car and do away with the batteries (car already has them). It would be less area, but even 20 km of driving for free would be enough for many people. Hell, I use a car maybe twice a week, usually to drive for less than 10 km. Such a car would basically drive for free for my use case :) [1] https://dothemath.ucsd.edu/2011/09/dont-be-a-pv-efficiency-snob/ https://dothemath.ucsd.edu/2011/09/dont-be-a-pv-efficiency-s... [2] https://www.quora.com/What-is-the-size-of-a-standard-parking-spot https://www.quora.com/What-is-the-size-of-a-standard-parking... [3] http://pushevs.com/2017/05/23/electric-car-range-efficiency-table-nedc/ http://pushevs.com/2017/05/23/electric-car-range-efficiency-...

mercutio2 9y ago
You’re ignoring conversion/storage losses when charging, which are on the order of 20%. And I think actual EVs are much closer to the less efficient end of your range (with the heat on, I barely get 3 miles / kWh on my Bolt, with no environmental controls, it’s about 4 miles / kWh, which is already the least efficient end of your range).
mikestew 9y ago
Actually, why not just put the solar cells on the car and do away with the batteries Because you might squeeze 200W worth of panels up there at best. On a sunny day you’ll get about 4 extra miles at the end of your workday. And now you can’t drive home with the sunroof open on that sunny day.
- ajuc 9y ago
  Sorry, I meant do away with the batteries at the charging station, not the batteries in the car.
  - mikestew 9y ago
    I was more pointing out that with current panels, putting panels on the car isn’t a good idea.
    - Retric 9y ago
      From a weight perspective they still add range so it's not a bad idea. Further, being able to run some fans or even AC while in full sun is a significant benefit. Car companies are not adding panels because the benefit is not huge, they add complexity and cost, and panels negatively impact styling. Still, you see a lot of campers with solar panels on the roof because a few kwh/day of extra power really does add up over time.
      - mikestew 9y ago
        Further, being able to run some fans or even AC while in full sun is a significant benefit. You’re going to need those fans with giant, black heat sinks on your roof. To the point that I wonder if the panels heat the car faster than fans can remove it. Still, you see a lot of campers with solar panels on the roof because a few kwh/day of extra power really does add up over time. You see a solar panel on our VW camper because a 100W panel can easily recharge the battery that runs the 20W of LED lighting, and charge the occasional laptop, not run a 80,000W traction motor. My parents have a 35 foot fifth wheel with A/C, microwave, and other goodies. It has an option for solar panels. They didn’t buy that option because solar panels ain’t gonna do squat for that load. They figured it might buy an extra half day of boondocking before the house batteries run out. No, you see a lot of campers with solar because they either have a small load like us, or the salesman convinced them it would be a good idea on their 40 foot Class A tour bus.
        Retric 9y ago
        Solar panels convert sunlight to energy, this means they don't heat up as much as you might think. Further, painting the outside of a car black does not heat up the inside of a car as much as you might think. Most heat gain is from sunlight hitting the inside of the car converting to IR, and then being blocked by glass. Thus, painting the inside black is a larger issue. A 120mm computer at full speed is ~6w and can move 75 cubic feet of air per minute. So, 20w worth of fans can quickly exchange a lot of air. Anyway, 100W of panels is minimal if your using 20+% panels. You can get that from a 1.5 foot x 3 foot section, a camper can have 20 of those on the roof assuming your starting with mostly clear space.
- Retric 9y ago
  For reasonable cost you can get 22.5% panels. A Camry is 193 inch x 72 inch or ~9 square meters. However, you don't get to tilt the panels and need to deal with shade, but can add cells to the sides which helps though at lower efficiency. Still ~6 hours of full sun equivalent x 9 * 0.225 ~= 12 kwh for a fairly normal shape. Tesla Model 3 gets 310 miles on 75kwh so call it 4 miles per kwh that's 40-50 ish miles per day if you can stay in the sun. Current records for solar panels well over 40%, so a fully solar powered car may actually be possible even if stupid expensive. PS: Those solar challange cars are getting impressive. http://solarteameindhoven.itility.nl/ http://solarteameindhoven.itility.nl/ is a 4 seater doing 60+mph though far from street legal.

by ajuc 9y ago

mercutio2 9y ago

You’re ignoring conversion/storage losses when charging, which are on the order of 20%. And I think actual EVs are much closer to the less efficient end of your range (with the heat on, I barely get 3 miles / kWh on my Bolt, with no environmental controls, it’s about 4 miles / kWh, which is already the least efficient end of your range).

mikestew 9y ago

Actually, why not just put the solar cells on the car and do away with the batteries Because you might squeeze 200W worth of panels up there at best. On a sunny day you’ll get about 4 extra miles at the end of your workday. And now you can’t drive home with the sunroof open on that sunny day.

ajuc 9y ago
Sorry, I meant do away with the batteries at the charging station, not the batteries in the car.
- mikestew 9y ago
  I was more pointing out that with current panels, putting panels on the car isn’t a good idea.
  - Retric 9y ago
    From a weight perspective they still add range so it's not a bad idea. Further, being able to run some fans or even AC while in full sun is a significant benefit. Car companies are not adding panels because the benefit is not huge, they add complexity and cost, and panels negatively impact styling. Still, you see a lot of campers with solar panels on the roof because a few kwh/day of extra power really does add up over time.
    - mikestew 9y ago
      Further, being able to run some fans or even AC while in full sun is a significant benefit. You’re going to need those fans with giant, black heat sinks on your roof. To the point that I wonder if the panels heat the car faster than fans can remove it. Still, you see a lot of campers with solar panels on the roof because a few kwh/day of extra power really does add up over time. You see a solar panel on our VW camper because a 100W panel can easily recharge the battery that runs the 20W of LED lighting, and charge the occasional laptop, not run a 80,000W traction motor. My parents have a 35 foot fifth wheel with A/C, microwave, and other goodies. It has an option for solar panels. They didn’t buy that option because solar panels ain’t gonna do squat for that load. They figured it might buy an extra half day of boondocking before the house batteries run out. No, you see a lot of campers with solar because they either have a small load like us, or the salesman convinced them it would be a good idea on their 40 foot Class A tour bus.
      - Retric 9y ago
        Solar panels convert sunlight to energy, this means they don't heat up as much as you might think. Further, painting the outside of a car black does not heat up the inside of a car as much as you might think. Most heat gain is from sunlight hitting the inside of the car converting to IR, and then being blocked by glass. Thus, painting the inside black is a larger issue. A 120mm computer at full speed is ~6w and can move 75 cubic feet of air per minute. So, 20w worth of fans can quickly exchange a lot of air. Anyway, 100W of panels is minimal if your using 20+% panels. You can get that from a 1.5 foot x 3 foot section, a camper can have 20 of those on the roof assuming your starting with mostly clear space.
Retric 9y ago
For reasonable cost you can get 22.5% panels. A Camry is 193 inch x 72 inch or ~9 square meters. However, you don't get to tilt the panels and need to deal with shade, but can add cells to the sides which helps though at lower efficiency. Still ~6 hours of full sun equivalent x 9 * 0.225 ~= 12 kwh for a fairly normal shape. Tesla Model 3 gets 310 miles on 75kwh so call it 4 miles per kwh that's 40-50 ish miles per day if you can stay in the sun. Current records for solar panels well over 40%, so a fully solar powered car may actually be possible even if stupid expensive. PS: Those solar challange cars are getting impressive. http://solarteameindhoven.itility.nl/ http://solarteameindhoven.itility.nl/ is a 4 seater doing 60+mph though far from street legal.