Introduction
Operational changes to the grid, caused by restructuring of the electric utility industry and electricity storage technology advancements, have created an opportunity for storage systems to provide unique services to the evolving grid. Regulatory changes in T&D grid operations, for instance, impact the implementation of electricity storage into the grid as well as other services that storage provides. Although electricity storage systems provide services similar to those of other generation devices, their benefits vary and are thoroughly discussed in this chapter.
Until the mid-1980s, energy storage was used only to time-shift from coal off-peak to replace natural gas on-peak so that the coal units remained at their optimal output as system load varied. These large energy storage facilities stored excess electricity production during periods of low energy demand and price and discharged it during peak load times to reduce the cycling or curtailment of the coal load units. This practice not only allowed the time-shifting of energy but also reduced the need for peaking capacity that would otherwise be provided by combustion turbines. The operational and monetary benefits of this strategy justified the construction of many pumped hydro storage facilities. From the 1920s to the mid-1980s, more than 22 gigawatts (GW) of pumped hydro plants were built in the United States. After this period, the growth in pumped hydro capacity stalled due to environmental opposition and the changing operational needs of the electric grid, triggered by the deregulation and restructuring of the electric utility industry.
By the mid-1980s, the push was stronger to develop battery and other storage technologies to provide services to the electric grid. However, these technologies could not match the ability of pumped hydro to provide large storage capacities. In the late 1980s, researchers at DOE/SNL and at EPRI were identifying other operational needs of the electric grid that could be met in shorter storage durations of 1 to 6 hours rather than the 8 to 10+ hours that pumped hydro provided.
Two SNL reports in the early 1990s identified and described 13 services that these emerging storage technologies could provide. A more recent report, Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide expanded the range of the grid services and provided significantly more detail on 17 services as well as guidance on estimating the benefits accrued by these services. Other works have also documented use cases and services
that storage provides to the grid. Most notably, EPRI’s Smart Grid Resource Center Use Case Repository contains over 130 documents that discuss various aspects of storage. Similarly, California Independent System Operator (CAISO) also describes eight scenarios supplemented by activity diagrams to demonstrate the use of storage for grid operations and control.
This course combines that knowledge base and includes the description and service-specific technical detail of 18 services and applications in five umbrella groups, as listed in Table 1.
