Ultracapacitor, also known as supercapacitor, supercondenser, electric double layer capacitor (EDLC) or pseudocapacitor, is an electric capacitor that has an unusually high energy density when compared to common capacitors, typically on the order of thousands of times greater than a high capacity electrolytic capacitor. 

Compared to batteries, ultracapacitors are capable of more than ten times the power and more than thousand times the cycle life. These are two main reasons why engineers choose ultracapacitors over batteries in different applications. Ultracapacitors are proven energy storage devices that can replace conventional capacitors or batteries in many applications that require much more energy than what conventional capacitors are able to provide and that also require higher power outputs that batteries cannot provide.

While many applications can benefit from ultracapacitors, the applications that would benefit the most are the ones that require quick charging and discharging with a large amount of energy. For example, only ultracapacitors can capture and store large amounts of re-generated electrical energy during braking and release it quickly for reacceleration in hybrid vehicles. Even with a minor role in today's micro- to mild-hybrid cars, the energy savings can add up to 15% in fuel savings. Used in even bigger roles, such as energy storage systems in electrical trains, trams, and subways, those savings can easily add up to 25% savings in the amount of electricity used. 

Ultracapacitors are also great in supporting roles as they can be used in conjunction with batteries and fuel-cell devices to enhance the performance and the lifetime. Using ultracapacitors in conjunction with batteries combines the power performance of the ultracapacitors with the greater energy storage capability of the batteries. This can extend the life of the batteries and enable the battery systems to be downsized, all the while enhancing the overall performance by increasing the available energy for high peak power.

The ultracapacitor enjoys boundless growth potential because it responds to key markets that also address societal needs of our time: it is environmentally-friendly, helps conserve energy, and enhances the energy-saving performance of other devices when used in conjunction.

Comparison between ultracapacitor and battery