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Ultracapacitors
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Ultracapacitors, also known as electric double capacitors or supercapacitors, are energy storage devices that have a much higher energy capacity than conventional batteries. Unlike a traditional battery, which uses a chemical reaction process to produce energy, an ultracapacitor has a reversible reaction process that allows allows it to be charged and discharged hundreds of thousands of times. Ultracapacitors were at first used as motor startup capacitors for large engines in tanks and submarines. Scientists have been researching on applications of ultracapacitors for regenerative braking systems in hybrid cars, taking advantage of their fast rate of charge and discharge. However, the high cost to produce ultracapacitors and their requirement for different charging stations hinder ultracapacitors' commercial use.
Technology basics
Ultracapacitors store electricity by physically separating positive and negative charges, whereas conventional batteries use a slower chemical reaction process.
As explained by the ultracapacitor program of the National Renewable Energy Laboratory, “an ultracapacitor can be viewed as two nonreactive porous plates, or collectors, suspended within an electrolyte, with a voltage potential applied across the collectors. In an individual ultracapacitor cell, the applied potential on the positive electrode attracts the negative ions in the electrolyte, while the potential on the negative electrode attracts the positive ions. A dielectric separator between the two electrodes prevents the charge from moving between the two electrodes. Diagram 2 depicts an ultracapacitor, its modules, and an ultracapacitor cell.” 1
The ultracapacitor stores a much larger amount of energy compared to a standard capacitor, but stores a smaller amount of energy than a battery. However, it is superior to a normal battery in terms of the fast rate of charging as well as long life span. Ultracapacitors can be used as power assistants for acceleration and hill climbing, as well as for recovery of braking energy.
Ulracapacitors vs. Batteries
Ultracapacitors differ from batteries in many ways:
- Charge Cycle:While batteries last for a limited number of charges and discharges, ultracapacitors can be charged and discharged for hundreds of thousands of cycles without performance loss. 2
- Charging Time: Ultracapacitors have a very fast charging rate compared to batteries, which take more time to charge because of the chemical reaction involved.
- Size and Weight: Ultracapacitors will be smaller and lighter than regular batteries.
- Energy Density: Typically ultracapacitors hold one fifth to one tenth the energy of an electrochemical battery. This will likely to change with the development of ultracapacitor technology.
- Energy Release: Ultracapacitors release stored energy very quickly, whereas batteries release energy slowly and take a a longer time. This makes ultracapacitors good candidates candidates for powering regenerative braking systems, which can greatly improve fuel efficiency under stop-and-go, urban driving conditions.
Footnotes
1: Ultracapacitors, National Renewable Energy Laboratory. Retrieved Feb 24, 2009.
2: Differences between Ultracapacitors and Batteries, UltraCapacitors.org. Retrieved Feb 24, 2009.
Resources
- UltraCapacitors.org: a specialized organization introducing ultracapacitor technology and products.
- NREL Ultracapacitors webpage: National Renewable Energy Laboratory's ultracapacitor's webpage.
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