Tech Report: Increasing energy efficiency in transportation with ultracapacitors

Posted on October 23, 2014 by Kimberly McGrath

Energy storage solutions, for applications, such as for onboard regenerative braking or wayside energy recuperation for railcar propulsion, are gaining traction in the energy-intensive transportation industry. As systems integrators look for new ways to be more energy and cost-efficient, they are increasingly turning to ultracapacitors as the energy storage and power delivery solution for transportation applications.

At first glance, an ultracapacitor, also known as a supercapacitor, may appear similar to a lithium-ion battery in terms of size and shape. However, what makes ultracapacitors different from batteries is the way they charge and store energy. In batteries, a chemical reaction converts stored chemical energy into electrical energy, which then flows out of terminals to power an application. Ultracapacitors, on the other hand, put an electric charge on plates that are separated by an insulator to store energy in an electric field. This allows them to quickly charge and discharge energy to power a variety of applications more reliably than a standard battery.

Bursts of power
Even though batteries and ultracapacitors are different, ultracapacitors can support batteries and other primary energy sources, like fuel cells and combustion engines, in a variety of ways. When paired with a battery, ultracapacitors deliver bursts of energy during times of peak power demands to take the electrical load off the battery and can extend battery life by 20% to 25% in certain transportation applications. Because ultracapacitors can discharge and recharge quickly, they have incredible durability and can perform more than hundreds of thousands charge-and-discharge cycles, leading to less maintenance, lower costs and less waste from dead batteries. They can reliably perform at temperatures ranging from -40 degrees Celsius to 65 degrees Celsius, and efficiently absorb and reuse energy that would have otherwise been lost by inefficient storage systems.

Integration in transportation
Ultracapacitors are used in a variety of industries ranging from automotive, rail, truck and bus, amongst others. One of the main applications of ultracapacitors is in hybrid and electric vehicles to support alternative means of transportation.

In hybrid-electric bus systems, ultracapacitors can provide an alternative energy solution to reduce carbon emissions for cleaner air and increased energy efficiency. Ultracapacitors provide power for the initial acceleration of the bus, so the vehicle can operate on a hybrid engine that is half the size of a traditional diesel engine. They can also improve acceleration performance, increase energy-recapture capability and increase driving range on a single charge. This allows the vehicle to cut down on fuel costs by 25% to 30%, which will pay for the additional cost of the hybrid system.

In Cerro Negro, Spain, ultracapacitors are being used in an electric rail system to improve energy efficiency in the country’s public transportation. Win Inertia, an engineering firm specializing in power electronics, energy storage and control, and communication systems, was contracted by the Spanish government’s Administrator of Railway Infrastructures (ADIF) to design and install the hybrid system in an effort to reduce energy waste and increase transportation reliability. Through rapid charge-and-discharge cycles, ultracapacitors in this application are able to recuperate energy as the rail vehicle brakes to power the vehicle’s propulsion, as well as support an electric vehicle charging station at the rail terminal. Ultracapacitors are able to significantly reduce energy waste by converting the kinetic energy from the rail into stored electric energy. In this station, ultracapacitors recover 8% to 10% of the total energy used by the railway system for reuse, creating a more sustainable operation. If the energy recuperated is not enough to completely power the EV charging station, the rail system also integrates a solar photovoltaic system to supply additional energy.

Across the various applications, ultracapacitors offer a green, maintenance-free way to increase reliability of systems to increase energy efficiency. Through their increased adoption, they can help support wider renewable energy efforts and reduce carbon emissions in the transportation industry.

Dr. Kimberly McGrath is director, business development for Maxwell Technologies. Follow Maxwell on Twitter:

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