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Guiding the Selection & Application of Wayside Energy Storage Technologies for Rail Transit and Electric Utilities Transit Cooperative Research Program Transportation Research Board Page 48 of 61 8 Conclusions This project has taken a detailed look at the potential benefit of wayside energy storage as a solution to several problems transit agencies may face particularly in light of increasing demands on the operation of their systems resulting from increased ridership and infrastructure expansions, and as transit agencies examine ways to reduce energy use. To address these needs an energy storage research consortium was formed at the American Public Transportation Association to gain more detailed knowledge of the potential effectiveness of wayside energy storage concepts. Representatives from transit agencies, energy storage providers, state energy programs, U.S. national laboratories and other associations such as the Electric Power Research Institute began discussions on the science of wayside systems. From this initial dialog, the Transportation Research Boardâs Transit Cooperative Research Program enlisted its financial and programmatic support to carry the study further and accelerate findings on the potential of wayside energy storage and to produce a guide for the potential application and operation of such systems. Results from computer simulations of candidate systems representing the rail transit modes of light rail, subway and commuter rail demonstrate the potential of energy storage to solve many energy related problems seen by transit agencies. Wayside energy storage devices can be designed to resolve problems of propulsion power voltage sag, energy inefficiency resulting from ineffectual capture of regenerated braking energy, high electric utility costs associated with large propulsion peak demand loads, and the high cost of conventional electrical utility substations installed along the rail line right-of-way. Based on dynamic modeling of system behavior with and without energy storage systems, the study concluded that energy storage is most practical when simultaneously solving more than one of these problems rather than focusing the application primarily on any one problem alone, such as energy savings. It was determined that using wayside energy storage to mitigate problems associated with propulsion voltage sag is a good starting point in sizing and optimizing the initial system design. Using voltage sag design as a basis, it was then more practical to consider variations in design parameters to optimize other simultaneous benefits including peak power reduction and energy use reduction. However, it is also possible to develop a system that is built around the need to reduce peak power demands or to utilize less costly wayside energy storage substations as replacements for conventional substations. However, determining the effectiveness of such a system requires careful economic analyses to estimate payback periods and allowable capital cost expenditures for system installation. It was also shown from further analyses that system performance is measurably sensitive to energy storage power rating and voltage set point, train headway, degree of multiple train schedule synchronization, and effect of power system voltage limit (electrical line receptivity). 9 Recommendations Agencies wishing to use wayside energy storage systems to address problems discussed here would benefit from a more detailed simulation modeling exercise to allow optimal energy
