This technology seems to be moving along pretty well, and it’s one of the revolutions that will constitute a major solution to our energy problems.

This approach allowed the engineers at Standard Oil to build a multifarad device. At the time, even large capacitors had nowhere near a farad of capacitance. Today, ultracapacitors can store 5 percent as much energy as a modern lithium-ion battery. Ultracapacitors with a capacitance of up to 5000 farads measure about 5 centimeters by 5 cm by 15 cm, which is an amazingly high capacitance relative to its volume. The D-cell battery is also significantly heavier than the equivalently sized capacitor, which weighs about 60 grams.

I’ve probably told this story before about innumeracy, even of physics students, and the inability of some to think through a problem. When I was teaching an E&M lab in college, we were doing experiments with capacitors, and someone came up and said, “The lab instructions say to use a microfarad capacitor, but this one says MFARAD instead of (greek letter mu–the symbol for micro)FARAD. I assume it means megafarad. Don’t we have smaller ones?

I explained to him that the largest capacitor I’d ever seen (this was in the late seventies) was a quarter farad, and it took a truck to deliver it. Did he really think that he was holding something in his hand with four million times that capacity?

The article is also a good tutorial on capacitors in general, for those unfamiliar with how they work. The way that I like to think about this is that the positive charge accumulates on one plate, and the negative on the opposite one. They are held in place by their mutual attraction (being opposite charges), but cannot combine because of the insulation gap represented by the dielectric. The more accumulated charge, the higher the attraction (and field force) and accompanying voltage and potential energy. When the plates are allowed to connect to each other through an external circuit, the charges flow toward each other and create current (and power). The breakdown voltage is the voltage at which the gap can no longer restrain the attraction between the two groups of charge, and they jump across it to meet their destiny. This is to be avoided.

[Update a few minutes later]

Sorry, link was slightly mangled (though usable) before. Fixed now.