atomic_fungus (atomic_fungus) wrote,
atomic_fungus
atomic_fungus

#580: Not so wrong as I thought (super-capacitor electric cars, again)

Here on Jerry Pournelle's blog there are folks who have done the "back of the envelope" calculations and come to much the same conclusions I did:
Morning Jerry

> A Austin-based startup called EEStor promised "technologies for replacement of electrochemical batteries," meaning a motorist could plug in a car for five minutes and drive 500 miles round trip between Dallas and Houston without gasoline."

The engineer in me just had to start scratching on the back of an envelope:-

My car does 33 miles to the gallon (imperial) on a long run. 500 mile trip = 15.2gal = 69.1l

Wikipedia tels me 91octane petrol has 34.8MJ/l (Mega Joules per litre).

Therefore I consume 2400MJ on my trip.

Assuming 25% efficiency for the car that gives me 600MJ of energy for the 500 miles.

Assume 90% efficiency for battery/capacitor/electric motor transport = 666MJ for the trip.

Charging time = 5min = 300sec.

1 Watt = 1 Joule/sec

666MJ in 5 min = 2.2MW

Assuming 200V for the operating voltage gives an average charging current of 11,000A!!!! (and remember this is a capacitor based system so the initial current will be much higher.....).

A big filling station in the UK can refuel 10,000+ cars a day. Can you say on site multiple nuclear reactors :-)

I can only assume that the 5min is the time taken to swap out the capacitor pack but even so charging and handling thousands of packs a day is going to change the face of filling stations.

All the best

Ian Crowe
In other words, maybe I wasn't wrong.
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