"The more I find out, the less I know."

Thu - September 21, 2006 at 02:29 PM in

Doing the Math


Some years ago, I made the mistake of buying a multi-year subscription to Red Herring magazine just before it went bust. When Business 2.0 bought the assets and extended everyone's subscription, I wound up with a subscription to Business 2.0 which will probably survive my great-grandchildren.

The downside is that Business 2.0 epitomizes everything I can't stand about a lot of business reporting: its pages are full of "can't fail" business ideas, fluffy profiles of obscenely wealthy white men (not that there's anything obscene about wealth, only when it's not mine), and hype-filled coverage of improbable new technology.

I'd like to focus for a moment on the latter.

Take this profile of EEStor, which was part of an article on "disruptive technologies" in the current issue.

EEStor is proposing to power an electric car using a new generation of ultracapacitors. That's not a crazy idea, since today's electric cars have three significant technological challenges:

1) The batteries take up a lot of space and weight.

2) It takes a long time to charge the batteries.

3) Because of (1) and (2), the cars usually have a limited range in order to reduce charging time and size of the batteries.

Both batteries and capacitors store electricity, but traditionally, batteries can store more energy in a given volume, while capacitors have the advantage of charging and discharging much faster. Ultracapacitors are high-tech capacitors which boost the energy density over traditional capacitors, but still can charge and discharge quickly thus potentially solving problems #2 and #3.

So far so good. If the energy density is high enough, it makes a lot of sense to use an ultracapacitor to power an electric car. But where I fall down is this claim:

"If it works as its supposed to, it will charge up in five minutes and provide enough energy to drive 500 miles on about $9 worth of electricity."

Wow, it charges up in five minutes! (presumably at a special charging station not unlike a gas station)

But waitaminute, is that possible?

Let's see, $9 worth of electricity is about 100 kilowatt-hours, or the equivalent (more or less) of running a 1,000-watt hairdryer for about four days straight. It is really practical to get that much energy into a car in five minutes?

To make that work, while the car is charging our charging station will need to pump 1.2 megawatts of electricity into the ultracapacitor. That's enough to power about 1,200 average homes. For one car.

A single large charging station would have to be able to handle as much electricity as a small city, and worse, it would have to be able to turn the juice on and off constantly without dimming the lights in surrounding areas or causing massive power surges.

When you get to the megawatt levels, power transmission isn't as simple as connecting a couple wires together--it's more like a MIssissippi river of electricity, and if you stop it from going one way, it'll try to go somewhere else (sometimes with considerable force). Basic stuff like switching the power on and off becomes a significant engineering problem.

Don't forget the safety issues, either. The cables will have to handle tens of thousands of volts at very high currents (these would be essentially high-voltage transmission lines plugging directly into the car), so it probably isn't the sort of thing you want Joe Sixpack dealing with. In fact, you probably want Joe Sixpack standing safely behind a really big metal fence, since that much voltage can arc several feet if something goes wrong.

I don't mean to pick on this one technology--ultracapacitors really are a promising new technology if they can work out the cost and safety kinks--but a little more skepticism, or merely even balance, from this breed of business reportage would be greatly appreciated.

(As an aside--if you think the recent spate of exploding batteries in laptop computers is spectacular, imagine what would happen if a car-sized ultracapacitor developed an internal short-circuit such as might happen if it was damaged in a bad crash. Since capacitors can discharge almost instantaneously, all the energy content of the capacitor would be released at once. A quick calculation suggests that you'd get an explosion equivalent to a little under 200 lbs of TNT, giving new meaning to the phrase "car bomb." This doesn't happen with gasoline-powered cars because the fuel can't burn without first being mixed with an oxidizer.)

Posted at 02:29 PM | Permalink | | |


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