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'Powering the electric vehicle' - ultracapacitors: a burst of energy to electric vehicles

28 June 2011

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Ultracapacitors complement modern electric vehicle power sourcing - projects recently presented attempt to use the fast-charging technology as main power source for electric vehicles. presents the technology, current applications and how it contributes to the Electric Vehicle industry on the third and final instalment of the series ‘Powering the Electric Vehicle’.
Graphene structure used in University of Texas' developed ultracapacitor
Ultracapacitors have been used for years in electrical appliances. Electric Vehicles integrate ultracapacitors also but with different functionalities: from backup energy sources to load stabilisers, ultracapacitors’ contribute is small but essential to electric vehicle operation. In an ultracapacitor, the energy accumulates in the electrode, not on the electrolyte as in batteries. An ultracapacitor is charged by applying a different voltage on the positive and negative charge plates. Read more on the technical aspect in the ‘About Ultracapacitors’ section.

Current applications

The ultracapacitor is not a stand-alone energy storage device but rather a memory backup to bridge short power interruptions in electric systems. In plug-in hybrid vehicles, ultracapacitors act as peak-load enhancers and compensators. An ultracapacitor charges in about ten seconds and releases energy when the peak load requirement is attained during vehicle operation, thus reducing strain on the battery and prolonging battery life. In both the Nissan Leaf and the Chevrolet Volt, the ultracapacitor is used as backup energy to operate parking brake lights in case battery energy is no longer available. Recently, vehicle makers begun considering the ultracapacitor, with its virtually unlimited charge cycles, as main power source in electric vehicles.

The Industry

The ultracapacitor has already begun complementing batteries in electric vehicle applications. In June 2011, Maxwell Technologies was granted European Economic Community - Type Approval to it’s 125-volt Heavy Transportation Module. The ultracapacitor delivers power to hybrid buses and trucks. According to David Schramm, Maxwell Technologies CEO, heavy duty vehicle makers “ are designing the HTM125 (model launched) into brake-recuperation and torque-assist system for more energy-efficient products”. The ultracapacitor may, in this case, be used in conjunction with batteries, the combination of the two allowing instant accelerator response to be obtained and energy recovery from inverted AC motor operation to occur (in a process known as KERS).

Recently, startup Nanotune developed electrodes for ultracapacitors with five to seven fold the charging capacity of common ultracapacitors. The company has already tested a combination of ionic-liquid electrolyte and the proprietary electrodes to generate a 35 watt-hour per kg efficient device - Nanotube’s ultracapacitors competes with Nissan Leaf’s battery pack energy density of 80 watt-hour per kg. In cost terms, the technology largely exceeds reasonable costs during testing and should not become viable in commercial terms before production economies of scale and raw material price savings are achieved, according to the company.

To learn more on batteries and ultracapacitors, consult the paper “Batteries and Ultracapacitors for Electric , Hybrid, and Fuel Cell Vehicles’ quoted in this article’s 'More on this topic' linkbox.

About Ultracapacitors

Capacitors accumulate electricity by physically separating positive and negative charges, contrasting with batteries which separate charges electrochemically. Capacitors are used in several applications including radio frequency stabilisation (electrostatic stabilisator) and power filtering (electrolytic capacitor). In modern electric automotive applications, the capacitor is known as the ultracapacitor as it combines battery features to increase charge capacity and versatility - it includes special electrodes and electrolyte. An ultracapacitor is constituted of two non reactive porous charge plates, or collectors, suspended in an electrolyte - a voltage potential is applied on the collectors. The potential of each of the opposed charged electrodes attracts the other. As said previously, in an ultracapacitor, the energy accumulates in the electrode, not on the electrolyte as in batteries. An ultracapacitor is charged by applying a different voltage on the positive and negative charge plates.


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