  Because energy storage systems have better ramping characteristics than
traditional generators, their participation in frequency regulation should
facilitate the balancing of load and generation. However, they cannot sustain
their output indefinitely. System operators have therefore implemented new
frequency regulation policies to take advantage of the fast ramps that energy
storage systems can deliver while alleviating the problems associated with
their limited energy capacity. This paper contrasts several U.S. policies that
directly affect the participation of energy storage systems in frequency
regulation and compares the revenues that the owners of such systems might
achieve under each policy.
