Could you reasonably make a passenger car that charged itself using solar panels?
A few assumptions:
- The roof of a Honda Civic is ~56 ft^2 [assuming ~70% of the length is roof and ~95% of the width is usable]
- An area that big could hold solar panels that produce ~565 W [assuming 10 W/ft^2]
- An electric car holds a battery that gives it a range of 100 miles.
- A battery that big holds ~150 MJ of energy [assuming 1.3x10^8 J/gal of gas, 29 mpg and electric motors are 3x more efficient than gasoline motors]
- Some optimistic assumptions:
- you generate the same energy all day
- you work 8 hours/day
- battery charging is 100% efficient.
So you could recharge 11% of the battery a day, which would yield a range of ~10.8 miles.
If you assume the average commute is 33 miles each day (16.5 miles each way), that would mean:
- To allow for a full trip home would take ~12 hrs of recharge time or
- A panel that could generate ~0.9kW and be ~86 ft^2. That's more than 1.5x the area available on the car roof.
- To fully charge the battery would take ~73 hours or
- A panel that could generate 5.2 kW and be ~519 ft^2. That's more than 9x the area available on the car roof.
So self powered cars ALMOST make sense as long as you can recharge them from the grid after you get home. Fully self powered solar cars don't make sense.
It also strongly suggests that solar powered EV recharging stations (e.g. with the panels on a nearby roof or on the parking lot roof) actually make quite a bit sense.