Image of Microgrid
Sandia engineers inspect a bank of switchgear, which are used to monitor, control, and protect different power assets that make up a microgrid.

The days and weeks following a natural disaster are a critical time for residents, emergency response teams, and government entities to recover and rebuild infrastructure. Recovery can be time consuming and rebuilding after disaster presents a critical juncture that requires methodical planning; however, few communities rebuild with resilience in mind.

A microgrid is electrical infrastructure that uses a system of power generation and automatic control to link buildings and other assets in a designated area, ensuring access to electricity for these buildings even if the power grid goes down. Sandia refers to these groups of microgrid buildings as resilience nodes because they assure access to essential services and allow for response and recovery after electric grid disruptions.

Island and rural communities present a unique opportunity for resilience research and development. Sandia, along with various partners, has developed a microgrid resilience modeling tool to help identify critical infrastructures in isolated and island communities.

The Microgrid Design Toolkit (MDT) developed by Sandia characterizes the trade-space and provides what-if analysis of design choices to provide quantitative insights to decision makers for hybrid energy solutions. Using the MDT tool, utilities or other community stakeholders, such as universities, can identify vulnerabilities in infrastructure particularly susceptible to natural disasters and related consequences. Cities and communities can then use the model to inform future building, policies, and emergency response plans.

The MDT couples an advanced design-level optimization search algorithm with a microgrid sizing capability that determines the cost versus load payment on all proposed microgrid placements. Using these algorithms and models, researchers can identify a net present value for day-to-day microgrid load to eventually reach a profitable outcome.

After Hurricane Maria in September 2017, Puerto Rican dependence on local electric supply prompted DOE-funded research on grid modernization and improvement. As part of this research, Sandia worked alongside the Puerto Rico Industrial Development Corporation to deploy six microgrid demo sites across the island.

These sites were intended to generate power to key infrastructure buildings, such as hospitals, during a time when the Puerto Rican Emergency Relief Administration could not address all critical power needs on the island. The demo sites were also used to develop replicable microgrids intended for use across the island and eventually in other rural, isolated communities.

In addition to the focus on rebuilding resilient infrastructure, the research team was faced with the additional burden of presenting a resilience plan that could be stood up in a condensed timeframe to assure residents have access to critical resources. The first phase of Puerto Rico resilience work focused on identifying opportunities to understand the community and critical infrastructure and ways to reduce societal burden.

Sandia researcher Bobby Jeffers said the societal burden is, “how hard people have to work to get critical infrastructure needs satisfied. It is determined by the level of effort required for people to satisfy their needs, divided by their overall ability.

“The higher the effort and lower the ability, the greater the societal burden,” he said. Societal burden metrics can include shelter, food, water, or other critical needs, and can be quantified by city zone, district, census block, or general geographic region.

The second phase of resilience work in Puerto Rico includes capacity building and workforce development. The phase two team is developing the Resilience Node Cluster Analysis Tool (ReNCAT), which optimizes locations for microgrids across a large planning region focused on decreasing societal burden at least cost.

Phase two also incorporates use of the quasi-static time series, which assesses the time-dependent aspects of power flow, frequency, and possible impacts of photovoltaic deployment on the grid.

The team continues to work on ReNCAT 2.0, which couples with MDT to provide a holistic cost benefit and societal burden analysis of any geographic region. Additional future work includes development of an explicit algorithm that no longer requires manual review of grid topology to automatically pinpoint opportunities for maximum community benefits and grid constraints.

“The rebuilding focuses on providing utility access and regulatory support as soon as possible after a disaster,” said former Sandia manager Abraham Ellis. “Whereas, without the tool, some areas of Puerto Rico could be without power for six to twelve months.”