All calculations in and motivation for this post are credited to Prof. Robert Laughlin and his course on the physics of energy. One thing I’ve learned from good old Laughlin is how to be a pessimist — but, presumably, how to be a pessimist with good reason. His course this quarter has been largely a propaganda-debunking-slash-sanity-reinforcing look at alternative energy technology, and (in a nutshell) why nothing is as good at storing energy as fossil fuels. Which, you know, is a problem. Anyway, I wanted to share my favorite example he’s used so far (and highlight the point that no one who talks about this stuff knows what they’re saying, or at least doesn’t care enough to check). One of the big next-generation storage methods that’s been touted by several companies is the “ultra-capacitor.” Capacitors work by storing charge between two metal plates, and ultra-capacitors do this on — surprise! — a much larger scale. Supposedly, these things will replace batteries because they’re green (provided the electricity comes from a renewable source), efficient, and charge super quickly — basically everything the automotive industry needs to create awesome electric cars.
Aside. We’re ignoring the problem of shorting one of these huge capacitors here. Unlike gasoline, capacitors discharge energy really quickly. Laughlin posed a question to our class: what happens if your kid touches the capacitor plates in your car? One student’s answer: what kid? The contents of a car’s gas tank is roughly 2-3 sticks of dynamite worth of energy. The reason dynamite is dynamite and not gasoline is because it releases energy really, really quickly — hence the problem here.
Anyway, supposing we figure that problem out, let’s take a look at these capacitors. Some of the biggest capacitors in the world today live at CERN, buried underneath Geneva. There are 4000 of these babies, so the energy stored is:
E = 4000*½*C*V² = 3.4 × 108 Joules
That’s a big number, ten to the eighth power. That’s one hundred million. Nine goddamn digits. If you had $100 million, you’d be set. If that was in miles, it’d be the distance from the sun to the earth. Big.
So wow, you say, that sounds like a lot of energy! And CERN agrees. That’s enough to accelerate protons to 50 mega electron-volts!, they say. (Whatever that is!) That’s enough to collide particles at over 400 giga electron-volts! (Giga is big!) And when a company makes a new capacitor, they’ll give you an energy storage number of comparable magnitude.
What they don’t publish is the fact that a Joule is a tiny unit, and so 3.4 × 108 Joules is exactly the same energy content as (wait for it) 2.77 gallons of gasoline. So congratulations. Four thousand of the world’s most advanced capacitors — each much larger than a man, mind you — holds about eight bucks worth of gas.