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Mass Transit Goes Green With Enhanced Energy Storage

To avoid ever-rising gas prices, more people are making the switch to public transportation. Instead of traveling by car, they are more apt to ride the bus or train which increases the need for mass transportation. Manufacturers and design engineers are feeling pressure to produce hybridized transportation, making it cleaner and more efficient, while simultaneously increasing the number of public transportation options available to meet the growing consumer demand. This shift to clean transportation has been addressed in Asia, South America and Europe where energy efficient transits have been the recipient of noteworthy investments. Now, this initiative is also coming to the top of the US agenda, with the US Department of Transportation looking to decrease the negative environmental impacts of mass transit by funding energy efficient transit projects. The agency is allocating $112 million in funds to 46 energy-efficient mass transit projects across seven states.

The funding comes at an opportune time, as local governments are readily prepared to support green transit options and technology has been developed to assist in improved efficiency. There’s more focus on hybridized asymmetric concepts, which combine an ultracapacitor and battery, in commercial transportation markets because of the greatly reduced carbon footprint enabled by hybridized transportation. Ultracapacitors are used in this hybrid combination to enhance batteries in transportation applications like hybrid buses and light rail.

Because ultracapacitors store a high amount of energy in a small container, and have a large capacitance with a longer amount of time between replacement requirements, they are an ideal solution to increase fleet efficiency. Engineers more frequently look to ultracapacitors as an energy storage solution because the high power density and long life cycle makes hybridizing public transportation a cost effective solution with immediate environmental impact.

Enhanced efficiency in hybrid buses

Ultracapacitors are the choice technology of hybrid bus manufacturers because they allow for better performance while reducing negative environmental impact. Compared to batteries, ultracapacitors have a longer lifespan and more power. When paired with a battery in a hybrid system, ultracapacitors increase the power density of the hybrid supply, allowing the battery to operate more efficiently since it is not exposed to large current spikes. This provides more usable energy per charge from the battery.

Hybrid bus applications typically have high cooling requirements which negatively impact the cell’s lifespan. Ultracapacitors with a low equivalent series resistance (ESR) are beneficial as they increase efficiency and power capabilities of the cell by parallel amounts.  The resulting higher performance and reduced cooling requirements lengthen the operating lifespan of the cell.

This technology is also advantageous during regenerative braking, a process in which otherwise wasted energy is captured during braking and released rapidly for re-acceleration. Ultracapacitors are charged during the braking process and provide power capable of a fast discharge, accelerating the vehicle without delay.

Electrifying light rail applications

Light rail applications make use of ultracapacitor technology in a number of ways. Like hybrid buses, high cooling requirements can diminish the life of a cell in a light rail application, so a low ESR is especially important. Ultracapacitors can provide the power needed to propel the train up to speed and across distances as long as 500 meters, but a large number are required. This means the number of necessary cycles is significantly increased – they can reach 350,000 cycles per year – which produces more heat from the system and creates higher cooling requirements. Using an ultracapacitor with a low ESR decreases the heat of the system, thereby lowering the cooling requirements and boosting overall efficiency.

Light rail applications also capitalize on reusing energy during regenerative braking. Ultracapacitors provide the fast charge necessary to accelerate the train away from the station, which means costly overhead wires can be removed. Ultracapacitors are the only energy storage product with enough volumetric power and longevity to handle the high cycle life requirements of this application.

Finally, ultracapacitors help to eliminate brown-outs and dim lighting by maintaining voltage during power-station switches. This wipes out any issues with power breaks in digital electronics.

What’s the future of ultracapacitor technology?

Designers and manufacturers seek improved energy storage solutions to enhance fleet efficiency and many have found a solution in ultracapacitor technology, either alone or in conjunction with a battery. Ultracapacitor manufacturers constantly research new technology to lower the ESR and increase energy density in order to meet customer demands. When this is achieved, which is likely in the near future, ultracapacitor use will increase even more.

Over the next decade, ultracapacitor volumes are predicted to see a 25 to 45 percent compounded annual growth, showing that this technology will become common. The immediate environmental benefits of implementing ultracapacitors in hybridized transportation will contribute to the mass adoption of hybrid transportation options and enable the US to put greener vehicles on the roads and rails.

Jeff Colton is vice president of sales, North America at Ioxus.  He is responsible for managing and growing the company’s North American sales operations in multiple alternative energy sectors. Previously, Jeff held executive roles at companies including General Electric Corporation, Sanyo Electric Corporation and Saft Battery Corporation. Jeff can be contacted at jcolton@ioxus.com or (858) 663-1609.

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