Maxwell Technologies

Maxwell Ultracapacitor Regenerative Power Solutions

In regenerative systems, energy is captured and re-used at a later time. The energy capture can be from a vehicle braking system to the controlled drop of a shipping container to shaving the peak from a wind turbine, the grid or a solar panel. This energy is subsequently used in acceleration, a lifting operation or to prevent an electrical dropout. These events are typically short duration (seconds to a few minutes) but very high power.

Ultracapacitors provide the best 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.

In an electric or hybrid application, regenerative braking is the conversion of kinetic energy into energy stored in a battery or an ultracapacitor, where it can be used later to power a vehicle, forklift, crane or any application where a burst of power is required. It is braking because it also serves to slow the application process. It is regenerative because the energy is recaptured in the battery or ultracapacitor where it can be used again.

In a regenerative braking system, the electric motor that is responsible for all or part of an electric or hybrid’s propulsion also does most of the braking. When the operator steps on the brake pedal, instead of activating a conventional friction-based braking process, it sends an electronic signal to the electric motor, directing it to run in reverse mode, which creates resistance to slow the application through a process that is analogous to down-shifting a standard transmission vehicle. An electric motor running backwards also acts as an electric energy generator or dynamo that can convert the kinetic energy of motion into electrical energy that can be stored for future use. As an added bonus, regenerative braking with an electric motor takes most of the load off mechanical brakes, reducing brake maintenance and replacement expense.

Everyone is driven to reduce fossil fuel consumption and want to stimulate the development of cleaner, greener technology to reduce greenhouse gas emissions as well as increase productivity. Most applications have electrochemical rechargeable batteries based on nickel or lithium chemistries that have some inherent characteristics that limit batteries’ efficiency and their suitability for the hybrid or electric application energy storage role. These include low power density, impaired performance at low temperatures and finite operational life:

Maxwell Ultracapacitor Regenerative Power Applications:

  • Power
    Power density is the rate at which an energy storage device or system can be charged or discharged. It takes hours to recharge the batteries of a mobile phone, laptop computer or other consumer electronic device. 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 stress 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.
  • Low Temperature Performance
    Batteries generate and store electrical energy in a fairly narrow temperature range. The 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 down to -40°C is another reason it make sense for regenerative energy applications.
  • Battery Life
    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 provide acceptable performance, the battery must be oversized, so hybrid and electric applications must sacrifice efficiency by hauling around very large, heavy, expensive battery systems. Ultracapacitors, on the other hand, perform reliably for one million or more charge/discharge cycles – effectively the life of the application.

Given those efficiency limitations, an ultracapacitor is used as standalone energy storage or the perfect complement to rechargeable batteries for greener, more efficient and affordable hybrid and electric applications. In a regenerative energy system, ultracapacitors can absorb virtually all of the recycled energy each braking event produces. The stored energy is then fed back to the electric motor just as quickly for acceleration or to recharge the battery at whatever rate is most conducive to battery health and longevity. 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.

Maxwell Ultracapacitors

With a cycle life of 1,000,000 cycles, Maxwell Technologies ultracapacitors can be rapidly charged and discharged over, and over again, making them one of the most energy efficient, environmentally friendly, and cost effective ways to store energy.