A friend of mine sent me this, and when I suggested that he post it here, he asked if I would do it. So, any comments?

Saw this on a Slashdot thread. The thread itself is only marginally interesting, and the topic article:
http://money.cnn.com/2006/05/04/tech...2_wrightspeed/
is about a fast, cute, but non-essential racing-class EV.

What caught my eye was this computation in one of the comments, concerning a "fill-up". (The poster got the math wrong, so I've corrected it.)

1. Assume (correctly) that all-electric EVs will catch on with the public once they have approximately the same power, range, and fill-up convenience as typical modern passenger cars that run on chemical energy.

This is because it is demonstrably the case that people do not like to leave their cars on "charge" all night. They want to go out at night sometimes, or are traveling.

2. Assume (suspension of disbelief required here) that all-electric cars and battery technology have advanced to the point where they have approximately the same power and range characteristics as typical passenger cars. Which is to say:

- they can carry the energy required to sustain the ~30 HP required to maintain 55 miles per hour in an average-size passenger car, for a full-charge range of 300 miles.

(No such battery technology is even remotely available, at any cost, today; nor will it be in the near-term. But never mind that, we're suspending disbelief.)

3. What does this amount of energy translate to in terms of a "fill-up"?

=> 300 miles @ 55 miles per hour = ~5.5 hours

=> 30 HP for 5.5 hours = ~165 HP-hrs (A HP-hr = ~2.7 MegaJoules of energy.)

=> 165 x 2.7 MJ = ~450 MJ

4. How long does it take to conveniently pump a tank of gas? About a minute. Okay, charge the EV in a minute.

What's the power level required to deliver 450 MJ in 60 seconds? (A Watt is a Joule/sec.)

About 7 megawatts.

To grasp that figure, think of a 120 VAC line. That's 60,000 Amps. The power required to run 1000 homes with all the lights and appliances on. Consider the ridiculous power connector, and the cable, that would be required to accomplish the charge.

5. A filling station that can service just ONE car at a time will require a 7 Megawatt feed line -- basically, a small electric substation. Multiply by the number of cars in a typical gas station at one time during the day (let's say you might want to fill up to four cars at a time, and remember there's no local electrical storage) and you've got a medium substation.

6. Now unsuspend your disbelief only slightly for a moment, and consider the battery that's being charged. Let's say it's 99% efficient during charging. Only 1% of the incoming power is being wasted as heat. That's around 70KW of heat being generated for a minute. Where's it being generated? In the heart of the battery. That's called a massive explosion, or at best a meltdown, within a few seconds.

7. Remember that the above is predicated on the use of highly-advanced battery technology that isn't remotely available yet, at any price.

Moral #1: You can't ever charge an EV fast enough, and even if you could, you can't dissipate the heat of charging in the battery safely.

Moral #2: Pump and carry chemical energy, and convert to electricity on the fly. This is why hybrids eat all-electric vehicles' lunches, and always will.