Carbon emissions, the depletion of natural resources, traffic congestion and the rising cost of fossil fuels are all issues pushing the world to search for alternative means of transportation. Mass transit buses are now able to reduce emissions by as much as 75% through the use of hybrid-electric propulsion systems. Hybrid-electric (HEV) buses and plug-in hybrid-electric (PHEV) buses are powered by an electric motor and a smaller-than-normal, conventional internal combustion engine that operates at periods of maximum efficiency. In general, there are two different types of hybrid systems—parallel and series hybrids. The type of hybrid system employed depends upon the expected duty cycle of the bus; however, in both systems a regenerative braking system is employed. That system is comprised of ultracapacitors that absorb and store virtually all kinetic energy from the braking system so that it can be used later in the propulsion system.
Over the next decade and beyond, automotive companies have to achieve dramatic improvements in CO2 emissions to satisfy stricter emission standards. At the same time, consumer demand for more fuel-efficient vehicles continues to drive automotive research and development to reduce weight and fuel consumption, manage continuously increasing internal power loads, and capture and recapture energy. As a result, there are several emerging applications for ultracapacitors in the automotive ecosystem, including regenerative braking systems, start-stop systems, active suspension systems, voltage stabilization systems and other higher power functions within the automotive boardnet. Maxwell is at the forefront of these new developments.
Heavy transportation vehicles, such as trains and trams, place particular demands on energy storage devices. Such devices must be robust and reliable, providing long operational lifetimes and low maintenance requirements. Further, the storage devices must operate efficiently under harsh conditions, including:
- Peak currents
- High duty cycles
- Frequent deep discharge/charge cycles
Ultracapacitor systems/modules can withstand these harsh conditions and support the energy demands of heavy transportation vehicles. Braking energy recuperation provides assisted propulsion, bridged power, and grid/voltage stabilization in many rail applications today. Additionally, ultracapacitors provide locomotive engine starting and assisted starting (battery and ultracapacitor combined system) as a mechanism to eliminate large batteries, or in some cases, to extend the life of the large batteries historically used in locomotive engine starting applications.