Microgrid technology has emerged as a promising solution to address the challenges posed by public safety power shutoffs (PSPS) in California. In the past, Pacific Gas and Electric (PG&E) has led the development of temporary distribution microgrids for PSPS mitigation with diesel-backed generation. This pioneering pilot in Calistoga, California, focuses on replacing existing temporary diesel generation with a permanent, clean energy solution that will enable Calistoga to have clean, long-duration power during future PSPS events.

The City of Calistoga in California has experienced multiple transmission-level PSPS events in the past. The substation, located at the edge of a high-fire threat district (HFTD), is the sole source of power in the city, and during a transmission-level PSPS event when the substation loses power, so does the city and its surroundings. This project will focus on delivering power to safe-to-energize non-HFTD areas of Calistoga during a PSPS event. The pilot consists of a hybrid system that will include hydrogen fuel cells combined with a battery energy storage system; it will deliver a peak power of 8.5MVA and generate at least 293MWh of energy to meet the city’s energy demands during a PSPS event. This is PG&E’s largest and first-of-its-kind microgrid project utilizing third-party-owned hydrogen fuel cell generation. The project has involved complex protection and microgrid control system design to enable the use of multiple boundary points, blackstart operation, and inverter-based resources. 

A notable aspect of this pilot project is PG&E’s first implementation of a standardized Microgrid Islanding Study (MIS). The study scenarios and assumptions were determined based on the proposed microgrid design and historical load profile of the Calistoga feeder. This information was used to simulate both worst-case and realistic transient scenarios for the microgrid, which looked at various cases of load and generation fluctuations as well as microgrid assets switching sequences. This approach offers a comprehensive understanding of the system’s behavior during islanded mode of operation and investigates the microgrid system performance during steady-state and transient conditions while in islanded mode.

In this session, the following will be shared: accomplishments and challenges PG&E has experienced through the initial development of this microgrid, including communications system considerations, Microgrid Islanding Study scenarios, and operational logistics across the multiple stakeholders involved in its development and operation.