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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 7 of 61 1 Introduction The topic of energy use continues to expand in importance as conventional energy sources diminish and as concerns over environmental affects related to energy use escalate as do concerns for the cost of energy. Public transportation agencies, and in particular electric rail transit systems, the subject of this report, are examining a diversity of approaches to improve operating efficiency, reduce energy use, and improve operational effectiveness. The driving forces affecting energy use are rooted in the fact that many U.S. rail transit systems are seeing rapidly increasing ridership placing heavy demands on propulsion systems and the consequential rise in energy use. Figure 1â1 shows the overall energy used by transit between the years 1950 and 2006. The sharp decline in transit energy use after 1955 is a result of a national shift away from transit to the automobile resulting in the removal of streetcar infrastructure. With increased ridership and continued expansion of transit systems beginning in the late 1970s, energy use is expected to continue its rapid growth. To meet energy and operational demands, agencies are examining energy storage technology as solutions to four principal problem areas; 1) braking energy recapture improvement, 2) peak power demand reduction, 3) voltage stabilization and 4) utilization of energy storage systems as replacements for traditional power substations. Traditional wisdom supported by some measurement data provides an argument for the need to better capture railcar braking energy, in which energy storage systems act to raise electrical power supply line receptivity and consequently the ability to utilize rather than waste excess energy from braking. Improving braking energy recapture and reducing peak power demand spikes saves energy and reduces energy cost based in proportion on local utility rate plans. Finally, energy storage is being considered as a lower cost alternative to traditional propulsion power electrical substations. Energy storage substations when electrically charged perform like traditional substations, providing distributed power along the track alignment, while also reducing peak power demand, serving as a recovery source for excess braking regeneration energy, and improving the power quality and voltage supply. With these potential benefits from four applications of energy storage 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 B ill io ns o f k W h 19 50 19 55 19 60 19 65 19 70 19 75 19 80 19 85 19 90 19 95 20 00 20 05 20 06 e Source: EIA Figure 1-1: Electricity consumed in public transit in the U.S.
