Saturday, August 14, 2010

Solar chargers for electric cars?

OK. This picture isn't what I'm actually talking about, but it does highlight part of the problem that would need to be solved:

Could you reasonably make a passenger car that charged itself using solar panels?

A few assumptions:
That would result in  ~16MJ of energy per day.
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 give a sense of the size of the problem of solar charging exclusively:
  • 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.
Most houses that get solar PV only go for 2 - 3 kW.

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.