Regenerative Braking / Energy Recovery
In regenerative systems, energy is captured and re-used at a later time. The energy capture comes from the vehicle braking system and is subsequently used in acceleration or for the support of accessory loads in vehicle architectures. These events are typically short in duration (lasting just seconds to a few minutes) but very high in power.
Ultracapacitors provide an ideal solution as the energy storage device for these applications. With their high power capability, ultracapacitors are more efficient at recapturing and storing energy, especially when it comes in bursts.
Power density is the rate at which an energy storage device or system can be charged or discharged. How much electrical energy can a hybrid or electric application’s rechargeable battery be expected to absorb during a braking event that lasts only a few seconds? On the flip side, rapid, deep discharges to power acceleration apply stress to batteries and shorten their life. To overcome these charge-discharge rate limitations and make rechargeable hybrid and electric application batteries last longer, they typically are oversized, adding to the volume, weight and cost of the energy storage system. That’s where the ultracapacitor’s ability to re-charge virtually instantaneously is of great benefit in regenerative energy systems.
Batteries generate and store electrical energy in a fairly narrow temperature range. Batteries perform poorly at low temperatures and the high temperatures common in engine compartments also impair battery performance, shorten battery life and can create serious safety hazards. The ultracapacitor’s ability to retain and release a burst of power in extreme cold environments (all the way down to -40°C) is another reason it make sense for regenerative energy applications.
Every battery, irrespective of chemistry, has a finite operational life and wears out after hundreds to a few thousand charge/discharge cycles. To extend battery life and put off costly replacement, system designers build in power electronics that limit charge rate and depth of discharge. In compensating for those limitations and assuring acceptable performance, the battery must be built as oversized. Thus hybrid and electric applications must sacrifice efficiency by hauling around very large, heavy and, expensive battery systems. Ultracapacitors, on the other hand, perform reliably for one million or more charge/discharge cycles – effectively lasting the entire life of the application.
Scientists at the Argonne National Laboratory have demonstrated that an integrated system combining batteries with ultracapacitors dramatically improve braking energy recuperation efficiency and eliminate the need for battery over-sizing, reducing the weight and cost of the entire system.
|Examples of ultracapacitor applications in regenerative braking:
|Regenerative Energy for the support of accessory loads (Ultracapacitor only)
|Regenerative Energy for propulsion for Mild and Full Hybrid cars (Ultracapacitor only or in combination with battery)