atomic_fungus (atomic_fungus) wrote,

#537: Randy Milholland is a MENACE! (And a lot about electric cars)

Because of this comic he has just about assured that I will never have another girlfriend. At least, not for long. Why?

Because the relationship will eventually move into the bedroom, and things will get going, and as soon as I see a certain female body part I'll start laughing.

Her: What's so funny?
Me: Ha ha ha ha ha ha!
Her: What? What?
Me: Ha ha ha ha ha!
Her: Why are you laughing so much?
Me: Va--!
Her: Huh? "Va"?
Her: This relationship is over.

* * *

PS the linked comic is NSFW or children.

* * *

Capacitors instead of batteries in electric cars. But what about leakage current?

Capacitors have several propeties which make them better than batteries for some things. Still, I'm not sure this is the do-all-be-all of electric cars. Supposedly the company responsible has a new dielectric which somehow improves the performace of their capacitors but I'm going to remain skeptical for a while.

Plug the car in for five minutes, and drive 500 miles? I'll have to see that before I believe it.

Even assuming a typical power requirement of around 15 horsepower to go 55 miles per hour (which would equal about 11 kilowatt-hours per hour of driving) that's on the order of 1,100 kilowatt-hours just for cruising a 500-mile distance at 55 MPH; it doesn't include power needed to accelerate to that speed.

Let me see, a megawatt-hour in five minutes means 200 kilowatt-hours per minute. Assume 240 volts; that'd require a current on the order of about a thousand amps, I think, unless I've made a mistake somewhere.

I don't doubt that a super-capacitor may be better than a bunch of batteries in an electric car. What I do doubt is that they can dump 1.1 megawatt-hours of electricity into one in five minutes without blacking out an entire neighborhood or starting a really nasty fire. (Or both.)

One thing is certain: the major sticking point we have with electric cars is how we store the energy.

The reason we use gasoline is that it is a very dense energy storage medium. (Diesel is even denser, in fact.) A gallon of gasoline occupies very little space, yet it can move a 3,500 pound vehicle; my Escort would go 36 miles on that single gallon in average driving, including a mix of city and highway miles.

A similar electric car with a battery the size of a gallon of gasoline--even using the most expensive battery with the highest energy density we can manage--would not go nearly as far, nor could it be driven "normally".

And even modern batteries take time to charge, because the process is a chemical one. And the process is subject to the laws of thermodynamics and conversion losses: about sixty percent of the energy expended on charging a nickel metal hydride (NiMH) battery is actually stored in the battery; the rest is wasted. And you can't prevent that..

People have tried to tell me there are battery chargers which are "90% efficient". I don't believe them. (Unless they are magical battery chargers.) The chemistry of the battery is the sticking point; while the chargers themselves may not use too much more power than they actually pump through the batteries, they cannot avoid wasting some power (laws of thermodynamics again) and the entire process ends up being wasteful to one degree or another. Certainly there are no batteries which will return 90% of the power required to charge them. (As far as I know, anyway.)

Think about this: it takes 12 hours to charge a NiMH battery; if you put it into a device which then consumes all the power in one hour--my old digital camera was a power hog; it used up a set of four NiMH AA's in about an hour if I wasn't careful--that's 12:1. And charging NiMH batteries any faster would damage the batteries.

So: your electric car can go 50 miles on a charge. For that 50 miles you need to charge it for 12 hours, and you spend--oh, let's just pick a WAG number from an unlikely orifice and say you spend $10 charging it every day. It may be more or less, depending on where you get your electricity (but if you use solar panels and a windmill that involves a rather high dollar investment in hardware...and several other conversion inefficiencies to boot).

My Escort goes 72 miles on $6 worth of gasoline. And can go farther than that, without waiting for a recharge, because the gas tank stores 10 gallons, the car averages 36 MPG, and gas is about $3 per gallon right now.

Until the problems with energy storage are solved, electric cars will be an expensive novelty or the purview of the few who are willing to reorder their lives around them. I don't think this "super capacitor" stuff is going to make all that much of a difference.

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