Microgrids Put to the Test in Puerto Rico

The devastation caused by Hurricanes Irma and Maria in Puerto Rico prompted the installation of microgrids and other measures to improve the island’s electricity resiliency in the face of natural disasters.[1] Last week’s earthquake forced these newly installed technologies to prove that they can power critical facilities through long duration outages.

While it’s too early for a complete review of microgrid performance during this last disaster, initial feedback is positive. Energy experts at Rocky Mountain Institute and Tesla reported that solar-plus-storage microgrids installed at 10 schools on the island are up and running post-earthquake.[2] This news begs the question: Why are microgrids better at maintaining power during an outage than the larger utility-scale grid?

One answer to this question is simply about scale. By definition, microgrids are contained within a small area—which may or may not be in the region hit by a disaster. Also by definition, microgrids can be islanded—meaning operators can disconnect them from the larger grid to generate and distribute power independently. In contrast, a conventional grid comprises a vast network of connected components that can impact each other across great distances. So, in the event of an earthquake or other disaster, damage to a transmission line or electrical substation can cause power outages to large geographic areas—or even the whole island. Furthermore, to restore power, utilities need to shut off power to ensure the safety of their line workers during reconstruction. This process can impact large parts of the grid for long periods of time. The assortment of energy demands and storage or generation assets that need to be considered in a microgrid is far more manageable, allowing issues to be identified and repaired more quickly than in the larger grid setting.

Because microgrids can restore or maintain power more effectively than the larger grid, they can be a good solution for helping critical facilities function during and quickly after natural disasters. These critical facilities can include emergency service locations, hospitals, food markets, and others. Figure 1 illustrates a potential configuration for a microgrid serving two critical facilities and powering electric vehicles for mobility services. In this configuration, the microgrid has multiple sources of generation as well as multiple storage systems. The emergency facility has its own source of storage that can help prioritize its load during a natural disaster.

Figure 1: Illustration of Critical Facility Microgrid

While there are many solutions to create a more resilient grid in the face of increasingly large and reoccurring natural disasters, microgrids are a promising option.