Stacked Services―Use Case Combinations
Electricity storage can be used for any of the services listed above, but it is rare for a single service to generate sufficient revenue to justify its investment. However, the flexibility of storage can be leveraged to provide multiple or stacked services, or use cases, with a single storage system that captures several revenue streams and becomes economically viable. How these services are stacked depends on the location of the system within the grid and the storage technology used. However, due to regulatory and operating constraints, stacking services is a process that requires careful planning and should be considered on a case-by-case basis.
In the California Public Utility Commission’s (CPUC’s) energy storage proceeding R1012007, a series of electricity storage use cases was considered and studied by multiple stakeholders. CPUC divided the use cases into three general categories based on the location of the storage as shown in Table 2. When connected to the grid at the transmission level, energy storage can provide grid-related service to ancillary markets under the control of ISOs while bidding into the energy market. Energy storage can also act as a peaker to provide system capacity. When placed on the distribution circuits, energy storage can help solve local substation-specific problems (mitigating voltage problems, deferring investment upgrades, etc.) while providing ancillary services to the grid. On the customer side of the meter, energy storage system can shave the customer’s peak load and reduce the electricity bill while improving power quality and reliability. Detailed documents about the CPUC-defined electricity storage use cases can be found on the CPUC website. As part of the CPUC proceeding’s effort to understand better the cost-effectiveness of different electricity storage use cases, EPRI conducted cost-benefit analyses using the Energy Storage Valuation Tool (ESVT), discussed in Chapter 3, for a subset of the CPUC use cases, including the bulk storage peaker substitution use case, the ancillary services only use case, and the distributed peaker use case. The results of the EPRI analyses were presented in a public workshop in March 2013.
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