When you think of green energy, are solar and wind power the first things that come to mind? Perhaps you think of hydropower, geothermal or biofuels instead. While regenerative braking has steadily gained traction in terms of adoption, the average person probably does not even rank it in the top 10 of green energy approaches, nor are most people likely to immediately think about green energy in mass transportation, a notoriously energy-intensive industry. However, regenerative braking in transportation is a renewable energy solution that helps make the world a bit greener and deserves greater attention for the benefits it can deliver.
Regenerative braking is the process of recapturing energy that would otherwise be lost during a vehicle’s braking event. That energy, rather than being wasted, can then be recycled and put to use — either to accelerate the vehicle again or to power some other electric load. By recuperating braking energy, hybrid cars and buses become up to 30 percent more fuel efficient than conventional combustion vehicles in urban settings. However, it’s not just cars and buses that are reaping benefits from green energy.
For example, the third largest consumer of electricity in Pennsylvania, the Southeastern Pennsylvania Transit Authority (SEPTA) has turned to regenerative braking to help the rail system address increasing costs for electricity and the system’s high demand for electricity. While 80 percent of SEPTA’s energy consumption goes toward train propulsion and operation, regenerative braking hadn’t been an option until recently because electrically powered trains could previously only take advantage of the benefits of regenerative braking if there was another vehicle in the vicinity accelerating at that moment. To solve its energy problem, SEPTA implemented a visionary project that combines regenerative braking with rail wayside energy storage and smart grid technologies to conserve energy and lower costs, while supporting the surrounding region as well.
In April 2012, SEPTA implemented an energy storage system that uses lithium-ion batteries to capture railcars’ braking energy, stores that energy in wayside battery banks or uses it for vehicle propulsion. SEPTA then sells any excess energy that is not used to the local utility grid. After piloting this sustainability program with lithium-ion batteries and seeing 5 to 20 percent energy recuperation rates over the course of two years, SEPTA is making plans to expand the program. The organization will next implement a hybrid system with an energy storage medium that has a high charge capacity to increase efficiency and lower costs and consumption of electricity even further.
Through systems integrator ABB, SEPTA will incorporate ultracapacitors, also known as supercapacitors, into the system alongside the batteries. Ultracapacitors are an energy storage and power delivery technology that have a high power density capability, meaning they can charge and discharge power in quick bursts without suffering the wear and tear that a battery would in such an application.
Because of these characteristics, ultracapacitors are better suited to reclaiming the braking energy more rapidly, meaning more of it is salvaged for reuse. Since braking energy is recaptured, SEPTA has greater opportunity to increase its revenue by selling off the excesses to the local electric grid that uses the power for frequency regulation. It has become a win-win situation for both SEPTA and the local utility, which receives the benefit of having an alternate source of energy to pull from when demand is high or a place to store power when it needs to reduce its load. ABB and SEPTA anticipate additional energy recoveries of 15 to 20 percent from using storage devices such as supercapacitors that have high charge acceptance rates compared to batteries. On top of this, by reducing the wear on batteries, the system expects non-monetary benefits such as the doubled lifetime of the system batteries that no longer have to bear the brunt of the energy recuperation process.
As energy prices rise and sustainability continues to gain attention, the SEPTA wayside energy storage project introduces another way an aging industry can reinvent itself and define the future while remaining financially stable. Innovative projects similar to this one will not only benefit their own ecosystems, but also the entire environments around them. The surprising revitalization of the transportation industry through smart grids, new energy generation techniques and energy storage technology signals the potential for other industries to also take advantage of renewable energies and help move the world toward a greener tomorrow.
Lead image: Train tracks via Shutterstock