Automotive DesignLine reports on a hybrid bus design by ISE Corporation which incorporates ultra capacitors. What are these ultra capacitors, and why are they needed in a hybrid vehicle? Regenerative braking, the key to the increase in fuel economy of hybrids, allows a vehicle to recapture and store part of the kinetic energy that would otherwise be lost to heat when braking. We’ve all been stuck on or behind the city bus while it is making frequent stops, and you can imagine the tremendous potential to capture all this braking energy with a hybrid electric drivetrain. This scenario sounds great in theory, but current battery technology doesn’t necessarily allow us to implement it in the most optimal way. One major drawback of current batteries is their limited ability to capture and regenerate energy during braking and to provide bursts of high power during short duration events. You can only push electrical energy in to a battery at a specific rate, and you can only draw it out at a specific rate.  These rates are often too slow to capture all the braking energy from the constant brake-acceleration cycles of a heavy city bus.

One possible solution to this problem is the use of ultra capacitors to complement the battery performance. An ultra capacitor is an electrochemical capacitor that has an unusually large amount of energy storage capability relative to its size when compared to regular capacitors. These ultra capacitors perform well in cold weather, have a long life-cycle, have a higher efficiency than batteries, have a high power output, and can effectively capture energy from braking. They probably won’t be seen on smaller vehicles any time soon, since the problem is more critical with heavier vehicles. I really have no idea how expensive these are, but I assume their are cost issues as well.

[Source: Automotive DesignLine]