SPONSORED CONTENT: Continuing urban growth is driving increased demands on metro rail systems. To meet this demand, rail authorities are increasing the number of vehicles per train, number of trains per hour and operating hours per day. These changes result in higher electric energy consumption and higher operating energy costs. Rail authorities are increasingly investigating how to increase energy efficiency and decrease operating energy costs with existing infrastructure. Modern metro trains have regenerative braking which helps reduce their electric energy consumption. The reduction in electric energy consumption depends on the instantaneous ability of the rail section near the braking train to use or store regenerative braking energy. This paper introduces rail wayside energy storage systems, presents specifications for a wayside energy storage system, and investigates metro rail wayside energy storage technologies best applied to projects seeking low replacement costs and high return on investment, while satisfying high-power density requirements and improving energy efficiency. This paper introduces the 3 leading energy storage options: flywheels, supercapacitors and batteries. It compares lifetime, cyclability, cost, energy characteristics, ease of installation and environment effects, such as temperature. It describes flywheel and supercapacitor energy storage system sizing for a high-power density energy storage application and compares the lifetimes, costs and return on investment. For a high power, high cyclable environment, such as a metro passenger station, the paper shows the flywheel wayside energy storage system has the lower cost of ownership and quickest return on investment.

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