There is a design and configuration practice called “graceful degradation” in telecom circles. It diverts all communications functionality to a limited group of subscribers that have the most critical needs. Microgrids present interesting possibilities to similarly support graceful degradation of the distribution grid through deployment at locations that are deemed most important for grid or community resiliency.
Borrego Springs was one of nine microgrid demonstration projects partially funded by the Department of Energy (DOE). For this San Diego Gas & Electric (SDG&E) project, additional funding was provided by the California Energy Commission (CEC) and the utility. Vic Romero, Director- Technology Solutions & Reliability, provided an update to the project and discussed four important lessons as the utility gains new observations and experience on a daily basis.
The remote Borrego Springs community is served by a single transmission line that is subject to disruptions at times from weather and wildfire. The relative fragility of this connection to the primary distribution system, coupled with a local substation and a proliferation of customer-side-of-the-meter rooftop solar made this location an excellent microgrid test bed for this possibility across a contained distribution grid.
As noted in my 2012 article, SDG&E put a real investigative focus on energy storage. The microgrid was configured to include substation energy storage of 500 Kw for 1500 Kwh plus 3 strategically-placed community energy storage units. The utility anticipated that energy storage would firm the intermittency exhibited by significant numbers of rooftop solar photovoltaic (PV) systems on specific Borrego Springs circuits. Energy storage has performed well, and sometimes exceeded expectations while providing a surprise or two. “We found energy storage to be very effective in dealing with rapid fluctuations,” stated Romero. They are now planning to boost their energy storage capacity to 1.5 megawatts of power for a total of 4.5 mWh of runtime.
The microgrid testing also included islanding, using stored energy and two on-site 1.8 Mw generators to deliver electricity to address unplanned or planned outages. The SDG&E engineers learned that operating storage in parallel with the local distribution grid wasn't as easy as it sounds. They had some challenges to resynchronize frequencies after islanding events. However, the energy storage and generators became vital last fall when intense thunderstorms cut power to Borrego Springs’ 2,780 customers. As SDG&E crews repaired power poles damaged in the storm, they were able to call on the Borrego Springs Microgrid for assistance, which used its local power generation to restore electricity to 1,060 customers, including the essential downtown business area and the local library, which is the designated cool zone for the community. This is one of the first times in the nation’s history that a microgrid has been used to power a large portion of a community during an emergency situation. This deliberate re-routing demonstrated that microgrids can mitigate grid disruptions and support community resiliency. Microgrids should become part of any Smart Grid or Smart Infrastructure plan.
The project also tested a price-driven load management (PDLM) program that enlisted residential volunteers in Borrego Springs. They were asked to be part of an experiment that sent simulated electricity price signals to Home Area Networks (HANs) and devices such as pool pumps, electric vehicles (EVs), and thermostats. There were challenges in the technology integrations as well as enrolling volunteers. The takeaway for SDG&E is that this “prices to devices” has to overcome some challenges to become successful on a wide-scale basis. There’s no doubt that if a program is too difficult to implement and/or lacks benefits that are considered worthwhile to customers, then most people would sensibly conclude that participation is not worth the effort. That’s a problem for product vendors, policy makers, and consumer engagement program specialists to tackle.
The most exciting lesson from this microgrid project to date is that the Borrego Springs microgrid could be used to energize the primary distribution system. Traditional uses (such as they are for microgrids) dictate that a microgrid keeps all the power it produces or stores within the confines of its footprint. This innovative use as an energy source to return power to the grid hints at new opportunities to engineer more resiliency into electric grids. “Microgrids provide an excellent opportunity to maximize the benefits of integrating renewable energy while improving reliability,” stated Romero. That possibility should interest utilities, regulators, and vendors and spark a fresh round of innovation to build upon this and the other knowledge gained from this microgrid demonstration. For its part, SDG&E will continue to explore and experiment with the Borrego Springs microgrid. Look for continued discoveries that will infuse utility planning and operations over the next few years.
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