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This paper briefly describes the results of the second phase of the systems analysis portion of a research project to assess energy storage systems suitable for use by electric utilities. Estimates of the maximum on-peak energy and power requirements capable of being supported by so-called base-load supplied off-peak energy are provided for the U.S. electric utility industry. A generalized relationship observed among available off-peak energy, on-peak energy requirements, annual system load-factor and assumed base-load capacity levels for charging energy storage systems is described. The distribution of both the on-peak and the off-peak energy is also described on a seasonal, weekly and daily basis. A complete spectrum of duty cycle parameters including charge and discharge times, charge to discharge power ratios, operating time and frequency, and required storage capability are defined for energy storage systems for the peaking and intermediate generation applications on electric utilities based on daily and weekly operating cycles. In addition, the effect of overall energy storage system efficiency on the amount of supportable on-peak energy storage capacity is analyzed.