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This sounds interesting. It got me thinking about some other ideas. What about solar panels on the roof? I found this article [1], and Elon Musk has said they'

This sounds interesting. It got me thinking about some other ideas. What about solar panels on the roof? I found this article [1], and Elon Musk has said they'll "probably offer it as an option" [2]. I wonder how many extra miles you could get with that. If nothing else, it would be nice to know that you could slowly recharge your battery if you get stuck in the middle of nowhere. Another idea - highways where you could drive while recharging. Maybe something similar to train tracks, or an overhead wire. Or wireless power transfer through the wheels, if that would be possible? (I don't think it is.) [1] https://thinkprogress.org/prius-solar-roof-breakthrough-2b929f467061/ https://thinkprogress.org/prius-solar-roof-breakthrough-2b92... [2] https://twitter.com/elonmusk/status/794575003446480896 https://twitter.com/elonmusk/status/794575003446480896

Xeoncross 9y ago
Solar panels charge really slowly compared to how much energy is needed to move a car. I'm probably totally wrong here, but if the whole car was solar panels I would expect 600 watt to be generated. An electric car would need that for 0.8hrs or so to move one mile (0.44 kWh/mile?) plus acceleration.
- dangero 9y ago
  Still seems worth it for a slight efficiency gain plus the ability to gain charge just by waiting if you run out of juice in the middle of nowhere.
  - tempestn 9y ago
    Another issue is that most people prefer to have a sunroof on their car. (Ideally a large, panoramic one, as Teslas have.) Can't really do that with solar panels.
- mikestew 9y ago
  Our Nissan Leaf does (give or take) 4 miles/kWh, or 0.25 kWh/mile, FWIW. I did the math one time, or someone else did, I forget. Anyway, cover the roof of the Leaf with panels and it would make a negligible difference in range. In a fit of dreaming of life off the grid in an RV, I can fit eight 100W panels on the top of our VW camper, and the usable roof on that thing is probably twice what the leaf has.
maxerickson 9y ago
The sun is ~1 kw/square meter and solar panels are 15-20% efficient. So for every square meter of roof space covered in panels you can get a max of about 200 watts of power. This is a lazy, handwavy characterization of the situation, but it paints the picture, it isn't much of a contribution as batteries head north of 50 kw-h.
- jacquesm 9y ago
  > The sun is ~1 kw/square meter At 90 degree incidence, after that it falls off as the co-sine of the angle. So if you don't track the sun it will drop considerably, you daily average compared to the ideal is more likely going to be between 7 and 12%.
perilunar 9y ago
I was thinking about this the other day actually. You can’t get enough power from panels on a regular car roof to do anything useful. A 100W solar panel typically generates about 400 Wh per day, and has an area of 0.7 m², weighs about 8 kg, and costs about $100. Using the range and battery data for the Tesla S: A 200 km daily commute (i.e. an hour each way) you would require ~35 kWh, and require 90 100W panels, or 60 m², weigh 700 kg, and cost $9000. Possible, but only as a fixed install, not on the car’s roof! For touring, you could do 500 km per night (about maximum range for the 100 kWh Tesla S) and charge during the day, but would require 250 panels / 175 m² / 2000 kg / $25,000. You would require a trailer to carry them, and the set up & tear down each day would be laborious, but it would be possible and you could then travel indefinitely. A bit like what Mark Watney does in The Martian. If you were willing to spend multiple days charging for each 500 km leg, or only travel a couple of hours per day it would be even easier. Edit: I just looked up The Martian and Watney had 18 kWh of batteries for his rover, 28 m² of panels (with longer days but less power), travelling a max of 90 km per day for over a month. So yeah.

Xeoncross 9y ago

Solar panels charge really slowly compared to how much energy is needed to move a car. I'm probably totally wrong here, but if the whole car was solar panels I would expect 600 watt to be generated. An electric car would need that for 0.8hrs or so to move one mile (0.44 kWh/mile?) plus acceleration.

dangero 9y ago
Still seems worth it for a slight efficiency gain plus the ability to gain charge just by waiting if you run out of juice in the middle of nowhere.
- tempestn 9y ago
  Another issue is that most people prefer to have a sunroof on their car. (Ideally a large, panoramic one, as Teslas have.) Can't really do that with solar panels.
mikestew 9y ago
Our Nissan Leaf does (give or take) 4 miles/kWh, or 0.25 kWh/mile, FWIW. I did the math one time, or someone else did, I forget. Anyway, cover the roof of the Leaf with panels and it would make a negligible difference in range. In a fit of dreaming of life off the grid in an RV, I can fit eight 100W panels on the top of our VW camper, and the usable roof on that thing is probably twice what the leaf has.

maxerickson 9y ago

The sun is ~1 kw/square meter and solar panels are 15-20% efficient. So for every square meter of roof space covered in panels you can get a max of about 200 watts of power. This is a lazy, handwavy characterization of the situation, but it paints the picture, it isn't much of a contribution as batteries head north of 50 kw-h.

jacquesm 9y ago
> The sun is ~1 kw/square meter At 90 degree incidence, after that it falls off as the co-sine of the angle. So if you don't track the sun it will drop considerably, you daily average compared to the ideal is more likely going to be between 7 and 12%.

perilunar 9y ago

I was thinking about this the other day actually. You can’t get enough power from panels on a regular car roof to do anything useful. A 100W solar panel typically generates about 400 Wh per day, and has an area of 0.7 m², weighs about 8 kg, and costs about $100. Using the range and battery data for the Tesla S: A 200 km daily commute (i.e. an hour each way) you would require ~35 kWh, and require 90 100W panels, or 60 m², weigh 700 kg, and cost $9000. Possible, but only as a fixed install, not on the car’s roof! For touring, you could do 500 km per night (about maximum range for the 100 kWh Tesla S) and charge during the day, but would require 250 panels / 175 m² / 2000 kg / $25,000. You would require a trailer to carry them, and the set up & tear down each day would be laborious, but it would be possible and you could then travel indefinitely. A bit like what Mark Watney does in The Martian. If you were willing to spend multiple days charging for each 500 km leg, or only travel a couple of hours per day it would be even easier. Edit: I just looked up The Martian and Watney had 18 kWh of batteries for his rover, 28 m² of panels (with longer days but less power), travelling a max of 90 km per day for over a month. So yeah.