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Solution to an Energy Riddle?

May 5, 2008
The Ultracapacitor Combines the Best Features of Batteries and Capacitors—Long-Term Storage and Instantly Available Power in Large Quantities
By Dan Hebert, Senior Technical Editor

Batteries can store energy for long periods of time, but can only discharge small amounts of power relatively slowly. On the other hand, capacitors can supply very large amounts of power virtually instantaneously, but can’t store energy for any length of time.  Wouldn’t it be great if one device could combine the best features of batteries and capacitors? It could store energy for a long time and supply large amounts of power quickly. Maybe, just maybe, such a device—an ultracapacitor—is in the works.

As we all learned in high-school science, capacitors store electricity as positive and negative static charges on two electrodes separated by an insulator. The amount of charge depends on the surface area of the electrodes, the strength and composition of the insulation between them, and the distance between electrodes.

On the other hand, batteries consist of an anode and a cathode, separated by an electrolyte. Chemical reactions in the battery cause a build-up of electrons at the anode, causing an imbalance. When the circuit between the anode and cathode is closed, (usually with a wire) the electrons can flow to the cathode, thereby generating power. 

The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge. Capacitors can’t store power for a long time, but can operate at high voltages and deliver large amounts of power.

Ultracapacitors may be able to bridge the gap between batteries and capacitors because, like batteries, they don’t rely on static charges. Instead, positively charged ions gather on the surface of the negatively charged electrode, and negative ions group on the surface of the positive electrode. Since the ions do not actually combine, no chemical reaction is involved.

The ionic layers are very close to the surfaces of the electrodes and run parallel with them. Careful design can increase the surface area and thus the storage capacity without increasing the volume. That means an ultracapacitor has the endurance of a battery and the speed of a capacitor.

A company called EEStor, located in Austin, Texas, is developing an ultracapacitor that it claims can store high levels of energy using a special insulator called barium titanate rather than an electrolyte. (EEStor is also extremely secretive. It has taken down its website and most information about it comes from bloggers. On the other hand, it has signed an agreement with Lockheed-Martin for exclusive rights to integrate and market the product in military and homeland security applications, giving it and its claims considerable street cred.)
Ultracapacitors would have numerous applications in process control plants.

In maintenance, improved electric vehicles powered by ultracapacitors, could be recharged in minutes rather than hours, reducing downtime and fleet size.

The military is investigating the use of ultracapacitors for rugged and portable power packs that could be used to power the myriad portable electronic devices used by maintenance techs, including PCs, PDAs, hand-held calibrators, multimeters, and other test instruments.

Electrical testing devices that need to deliver large amounts of power quickly could also be greatly improved with ultracapacitors.

Increasing energy storage time by replacing capacitors already in use in plant systems for for power-factor correction and voltage control with ultracapacitor should improve functionality, cut costs and reduce size.
Ultracapacitors could have a place in backup power systems as well. They could be used to provide much larger amounts of backup power at much higher voltages than batteries, and unlike generators, ultracapacitors could deliver power virtually instantaneously, filling the time gap between a power outage and generator start-up.
Ultracapacitors are a technology to watch. 

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