State of Energy Storage in Electric Utility Systems and Its Effect on Renewable Energy Resources

This report describes the state of the art of electric energy storage technologies and discusses how adding intermittent renewable energy technologies (IRETs) to a utility network affects the benefits from storage dispatch. Load leveling was the mode of storage dispatch examined in the study. However, the report recommended that other modes be examined in the future for kilowatt and kilowatt-houroptimization of storage. The motivation to install storage with IRET generation can arise from two considerations: reliability and enhancement of the value of energy. Because adding storage increases cost, reliability-related storage is attractive only if the accruing benefits exceed the cost of storage installation. The study revealed that the operation of storage should not be guided by theoutput of the IRET but rather by system marginal costs. Consequently, in planning studies to quantify benefits, storage should be considered as an entity belonging to the system and not as a component of IRETs. The study also indicated that because the infusion of IRET energy tends to reduce system marginal cost, the benefits from load leveling (value of energy) would be reduced. However, if asystem has storage, particularly if the storage is underutilized, its dispatch can be reoriented to enhance the benefits of IRET integration.