SAE-2000
HYBRID ELECTRIC VEHICLES TOPTEC: THE NORTHERN PERSPECTIVE
Metro Toronto Convention Center

Tavrima Supercapacitors Prove Their Worth in Hybrid Electric Vehicle Storage Systems.
Frank Lev Tavrima Canada Ltd

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The first phase of the NASA Hybrid Electric Transit Bus (HETB), project has proven the viability of super-capacitors. In the concluding remarks, in their technical memorandum, the NASA project team indicates that test results clearly demonstrate the capacitors superiority to batteries in this application, necessitating further development efforts with the capacitors due to their distinct advantages. [4]

The HETB used a bank of 30 super-capacitors, with the rated storage capacity of 1.6 MJ at 400 volts. Each capacitor had the rated capacity of 50 kJ at 200 volts and a weight of 32 kg (70 lb). The capacitors were used as an energy storage system for the fuel economy tests over a four-mile route (28 CBD driving cycles). NASA reported an improvement of 21.2% with the use of regenerative braking [4].

To simulate passenger load and provide a capacitor to battery performance comparison, NASA had two banks of 28 starved electrolyte lead/acid batteries, weighing a total of 1145 kg (2520 lb), temporarily installed upon the main isle of the coach.

From the initial speed of 25 km/h (15.5 mph) the regenerative distance with capacitors was 103 feet, whereas the regenerative braking distance with the batteries was 157 feet. This translates into a 34% improvement explained by the capacitors higher efficiency. NASA reports that using the capacitors for the regenerative braking is sufficient to stop the vehicle in a Central Business District, greatly increasing brake life, while reducing maintenance costs. A combination of regenerative and mechanical braking is required when batteries are used.

The data from the first phase HETB testing demonstrates that the capacitors were superior to the batteries in delivering load currents to the traction motor when accelerating as well as decelerating in the regenerative mode. [9] Based on the NASA hybrid electric bus experience, Tavrima has unveiled new improved super-capacitors, developed specifically for the hybrid electric market. The new units are powerful, efficient, robust and inexpensive. Their voltage is high and internal resistance is low. These units have the following characteristics:

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