Massive hurricanes in 2017 turned out the lights in Puerto Rico and several other Caribbean islands—in some cases, for months—and sparked a conversation about energy security and resilience that continues today, in the hurricane belt and beyond. Increasingly, decision-makers are looking at developing microgrids to power the most critical infrastructure and services in the event the electrical grid goes down. But what makes something critical? Most people would probably put a hospital first in line for backup electricity, but what about after that?

A recent workshop in Puerto Rico—Advancing Caribbean Energy Resilience—took participants through the basics of designing a microgrid with critical infrastructure in mind. Convened by the U.S. Department of Energy (DOE), in partnership with the Organization of American States (OAS), the workshop included more than 50 participants from 15 countries, including energy officials, regulators, electric utility executives, and others.

In small breakout sessions, they worked through different aspects of the decision-making process that goes into establishing a microgrid, guided by a team of experts from DOE and Sandia National Laboratories—part of the DOE’s network of federally funded research and development centers. Participants in the workshop were asked to play the roles of different stakeholders, to think through the various viewpoints and priorities that drive energy decisions.

First, a little context. Microgrids come in many shapes and sizes; at the most basic level, a set of solar panels on the roof of a house can be considered a microgrid. The workshop in Puerto Rico explored the ins and outs of establishing distributed energy systems on a somewhat larger scale—say a microgrid to cover a city district or a university campus or a cluster of government buildings.

The idea is to develop a grid within a grid—a system that is tied to the main electric grid in normal times but can be “islanded” and operate independently, on its own source of power, if the main grid fails. In the wake of Hurricanes Irma and Maria, in 2017, microgrids powered by solar energy and battery storage began to crop up on a “boutique” scale in many places (see earlier story: For a Resilient Power Grid, Think “Micro”); now, many energy planners and electric utilities are looking at more advanced systems.

Sandia National Laboratories, which began working on this issue for military bases more than a decade ago, has developed a methodology that aims to achieve “energy surety”—safety, security, reliability, sustainability, cost-effectiveness, and resilience—by integrating a whole range of distributed energy resources into a local service area or microgrid. It has created publicly available materials, including a software program called the Microgrid Design Toolkit, to provide process recommendations and technical guidance.

Tough Decisions

During the workshop in Puerto Rico, participants covered some of the key decisions that come up in the earliest planning stages—such as determining what facilities or services are most critical for the microgrid to serve. These decisions can be harder than they may seem, according to two of the Sandia engineers who helped lead the workout sessions, Brooke Marshall Garcia and Matthew Lave.

While everyone may agree that a hospital gets priority, “almost nobody agrees on the second thing,” Lave said. For a utility, he explained, the focus might be the ports; after all, that’s where the fuel for the local power plant needs to arrive. For an emergency management agency, it might be the communications network that’s top of mind.

“Everything’s critical to somebody,” Garcia added. Law enforcement is another aspect to consider, she said; think of the potential for violence if people have been waiting in line for gasoline for hours and someone tries to cut to the front.

Microgrids, by definition, are small and therefore cannot deliver the same amount of electricity as a system that includes central power plants and high-voltage transmission lines. “In most cases, you’re not going to be able to do everything you want to do,” Lave said.

At the core of the challenge, he said, is matching generation and load—in other words, making sure the supply of locally generated electricity matches the demand within the area being served. Advanced microgrids can shed less critical parts of their service area when necessary.

Unlike a simple backup generator, which typically covers one building or facility, microgrids can be designed to serve a larger area and can incorporate renewable energy sources. And because they are usually tied to the main grid, they can feed renewable energy into the system during normal times.

The design of each microgrid system depends on a host of factors, including the nature and probability of the threats an area faces. It’s not only hurricanes that can disrupt the power supply, after all—it’s also floods, ice storms, earthquakes, forest fires, and cyberattacks, to name just a few.

Other variables in developing a microgrid include budget, performance targets, regulatory considerations, and policy goals: Is the primary focus on renewable energy? Low cost? Very high reliability? The process developed by Sandia is not a specific microgrid design but a map of decision points that will help local stakeholders customize their own solutions based on the technology available.

“If you don’t have a technical appreciation for what’s involved, it’s difficult to develop policy,” Garcia said.