Last November's IEEE's Spectrum Magazine edition had a very interesting article by Joel Schindall, associate director of the Laboratory for Electromagnetic and Electronic Systems at MIT, about ultracapacitors and their possible applications in the automotive industry. Schindall is involved actively in this field of research and is hopeful that they will provide a key role in automotive electricity.
An ultracapacitor is a "souped-up" version of a capacitor, an electric device which stores a great amount of energy in a remarkably small space.
Current Latest development in ultracapacitors can are expreted to store up to 50 times percent as much energy as a battery about the same size and are able to stand more than 300,000 charge/recharge cycles. But can they replace batteries? Schindall states that not really, but they can complement regular batteries to power current electric devices such as A/C, power brakes or window locks.
The truth is that ultracapacitors can't
hold discharge electricity for a long time [Edited], while regular batteries can. The moment electricity is released from ultracapacitors, it dissipates fast (about 2 minutes). Applications such as those mentioned above, where an important burst of energy is needed during a certain amount of time, are the most adequate.
The article continues with information about the methods of manufacturing ultracapacitors and very interesting notes about the use of nanotechnology for this purpose. Read it here.
[Source: IEEE (Thanks to Domenick for the tip)]
[Edited: Errors fixed]