3 Responses

1. There is a forum here that might give you more info than can be posted here easily:

   http://www.ultracapacitors.org/

2. How do they work?

   In an electrolytic capacitor, the electrolyte is effectively one of the electrodes, and an oxide film is formed between the electrolyte and the other plate. That gives you the capacitance and the dielectric function, too.

   In an ultracapacitor, there is a (thin) film formed between each of the electrodes and the electrolyte. The thing that allows the ultracapitor to reach such great numbers is that each of the electrodes has a greatly increased surface area, with which to react with the electrolyte. Think of of the electrode as a sponge, and the electrolyte as water. The surface area of the sponge that is in contact with the water is many times greater than if the water contacted a flat plate of that same overall dimension. Such as it is, comparing a capacitor and an ultracapacitor.

   How do they compare with fuel cells? Well, fuel cells actually generate electricity from chemical reactions, whereas ultracapacitors only store energy that is provided to them.

   The applications of ultracapacitors in the transportation industry will be in combination with batteries.

   You see, batteries can store great amounts of energy for delivery to a load, but they can only supply it at a limited rate. Ultracapacitors cannot rival the pure storage capacity of batteries, but their strength comes in being able to accept and deliver their energy very fast. So, the two (batteries and ultracapacitors) in combination will make a very effective energy storage and delivery system for transportation applications (cars and busses and the like).

3. Ultra capacitors use a material called aerogel for their dielectric. Electrolytics use an electrolyte as the dielectric. Electrolytics are cheaper, and can have higher voltages before they break down then ultracaps. Ultracaps are generally capable of having much higher capacitance (scale of Farads) compared to electrolytic, especially for the size.

   Ultracaps can be charged and discharged much more quickly then a battery. If I were to use them in an automobile application, it would be because you can charge them rapidly, batteries take much longer. For example though, a lot of the hybrid cars use a voltage much too high to work with ultracaps currently available.

   Comparing ultracaps to fuel cells doesn’t make much sense because the caps only store energy, where as a fuel cell would convert energy.

   As a side note aerogel is a pretty cool material, see wikipedia for more info…