How to Harden Puerto Rico’s Grid Against Hurricanes

Photo: Dennis M. Rivera Pichardo/AP Resilience: The yearlong blackout following Hurricane Maria underscored the fragility of Puerto Rico's power grid. Since then, installations of rooftop solar combined with battery storage have soared.

Another devastating hurricane season winds down in the Caribbean. As in previous years, we are left with haunting images of entire neighborhoods flattened, flooded streets, and ruined communities. This time it was the Bahamas, where damage was estimated at US $7 billion and at least 50 people were confirmed dead, with the possibility of many more fatalities yet to be discovered.

A little over two years ago, even greater devastation was wreaked upon Puerto Rico. The back-to-back calamity of Hurricanes Irma and Maria killed nearly 3,000 people and triggered the longest blackout in U.S. history. All 1.5 million customers of the Puerto Rico Electric Power Authority lost power. Thanks to heroic efforts by emergency utility crews, about 95 percent of customers had their service restored after about 6 months. But the remaining 5 percent-representing some 250,000 people-had to wait nearly a year.

After the hurricanes, many observers were stunned by the ravages to Puerto Rico's centralized power grid: Twenty-five percent of the island's electric transmission towers were severely damaged, as were 40 percent of the 334 substations. Power lines all over the island were downed, including the critical north-south transmission lines that cross the island's mountainous interior and move electricity generated by large power plants on Puerto Rico's south shore to the more populated north.

In the weeks and months following the hurricane, many of the 3.3 million inhabitants of Puerto Rico, who are all U.S. citizens, were forced to rely on noisy, noxious diesel- or gasoline-fired generators. The generators were expensive to operate, and people had to wait in long lines just to get enough fuel to last a few hours. Government emergency services were slow to reach people, and many residents found assistance instead from within their own communities, from family and friends.

The two of us weren't surprised that the hurricane caused such intense and long-lasting havoc. For more than 20 years, our group at the University of Puerto Rico Mayagi1/4ez has studied Puerto Rico's vulnerable electricity network and considered alternatives that would better serve the island's communities.

Hurricane Maria turned our academic questions into a huge experiment that included millions of unwilling subjects-ourselves included.

Hurricanes are a fact of life in the Caribbean. Preparing for natural disaster is what any responsible government should do. And yet, even before the storm, we had become increasingly concerned at how the Puerto Rico Electric Power Authority, or PREPA, had bowed to partisan politics and allowed the island's electrical infrastructure to fall into disrepair. Worse, PREPA, a once well-regarded public power company, chose not to invest in new technology and organizational innovations that would have made the grid more durable, efficient, and sustainable.

In our research, we've tried to answer such questions as these: What would it take to make the island's electricity network more resilient in the face of a natural disaster? Would a more decentralized system provide better service than the single central grid and large fossil-fuel power plants that Puerto Rico now relies on? Hurricane Maria turned our academic questions into a huge, open-air experiment that included millions of unwilling subjects-ourselves included. [For more on our experiences during the storm, see "For Two Power Grid Experts, Hurricane Maria Became a Huge Experiment."]

Dennis M. Rivera Pichardo/AP Smart Solar: A homeowner uses his smartphone to monitor how much power his solar system is generating and how much electricity his household is consuming.

As Puerto Rico rebuilds, there is an extraordinary opportunity to rethink the island's power grid and move toward a flexible, robust system capable of withstanding punishing storms. Based on our years of study and analysis, we have devised a comprehensive plan for such a grid, one that would be much better suited to the conditions and risks faced by island populations. This grid would rely heavily on microgrids, distributed solar photovoltaics, and battery storage to give utilities and residents much greater resilience than could ever be achieved with a conventional grid. We are confident our ideas could benefit island communities in any part of the world marked by powerful storms and other unpredictable threats.

As is typical throughout the world, Puerto Rico designed its electricity infrastructure around large power plants that feed into an interconnected network of high-voltage transmission lines and lower-voltage distribution lines. When this system was built, large-scale energy storage was very limited. So then, as now, the grid's control systems had to constantly match generation with demand at all times while maintaining a desired voltage and frequency across the network. About 70 percent of Puerto Rico's fossil-fuel generation is located along the island's south coast, while 70 percent of the demand is concentrated in the north, which necessitated building transmission lines across the tropical mountainous interior.

The hurricane vividly exposed the system's vulnerability. Officials finally acknowledged that it made no sense for a heavily populated island sitting squarely in the Caribbean's hurricane zone to rely on a centralized infrastructure that was developed for continent-wide systems, and based on technology, assumptions, and economics from the last century. After Maria, many electricity experts called for Puerto Rico to move toward a more decentralized grid.

It was a bittersweet moment for us, because we'd been saying the same thing for more than a decade. Back in 2008, for instance, our group at the university assessed the potential for renewable energy [PDF] on the island. We looked at biomass, microhydropower, ocean, photovoltaics (PV), solar thermal, wind, and fuel cells. Of these, rooftop PV stood out. We estimated that equipping about two-thirds of residential roofs with photovoltaics would be enough to meet the total daytime peak demand-about 3 gigawatts-for the entire island.

To be sure, interconnecting so much distributed energy generation to the power grid would be an enormous challenge, as we stated in the report. However, in the 11 years since that study, PV technology-as well as energy storage, PV inverters, and control software-has gotten much better and less costly. Now, more than ever, distributed-solar PV is the way to go for Puerto Rico.

Photo: GDA/AP Economic Boost: A move to solar-powered microgrids benefits small and medium-size companies, which tend to invest in the local community.

Sadly, though, renewable energy did not take off in Puerto Rico. Right before Maria, renewable sources were supplying just 2.4 percent of the island's electricity, from a combination of rooftop PV, several onshore wind and solar-power farms, and a few small outdated hydropower plants.

Progress has been hamstrung by PREPA. The utility was founded as a government corporation in 1941 to interconnect the existing isolated electric systems and achieve islandwide electrification at a reasonable cost. By the early 1970s, it had succeeded.

Meanwhile, generous tax incentives had induced many large companies to locate their factories and other facilities in Puerto Rico. The utility relied heavily on those large customers, which paid on time and helped finance PREPA's infrastructure improvements. But in the late 1990s, a change in U.S. tax code led to the departure of nearly 60 percent of PREPA's industrial clients. To close the gap between its revenues and operating costs, PREPA periodically issued new municipal bonds. It wasn't enough. The utility's operating and management practices failed to adapt to the new reality of more environmental controls, the rise of renewable energy, and demands for better customer service. Having accumulated $9 billion in debt, PREPA filed for bankruptcy in July 2017.

Then the hurricane struck. After the debris was cleared came the recognition-finally-that the technological options for supplying electricity have multiplied. For starters, distributed energy resources like rooftop PV and battery storage are now economically competitive with grid power in Puerto Rico. Over the last 10 years, the residential retail price of electricity has fluctuated between 20 and 27 U.S. cents per kilowatt-hour; for comparison, the average price in the rest of the United States is about 13 cents per kWh. When you factor in the additional rate increases that will be needed to service PREPA's debt, the price will eventually exceed 30 cents per kWh. That's more than the levelized cost of electricity (LCOE) from a rooftop PV system plus battery storage, at 24 to 29 cents per kWh, depending on financing and battery type. And if these solar-plus-storage systems were purchased in bulk, the LCOE would be even less.

Photo: Sara Irizarry Read about the authors' experiences after Hurricane Maria.

Also, the technology now exists to match supply and demand locally, by using energy storage and by selectively lowering demand through improved efficiency, conservation, and demand-response actions. We have new control and communications systems that allow these distributed energy resources to be interconnected into a community network capable of meeting the electricity needs of a village or neighborhood.

Such a system is called a community microgrid. It is basically a small electrical network that connects electricity consumers-for example, dozens or hundreds of homes-with one or more sources of electricity, such as solar panels, along with inverters, control electronics, and some energy storage. In the event of an outage, disconnect switches enable this small grid to be quickly isolated from the larger grid that surrounds it or from neighboring microgrids, as the case may be.

Here's how Puerto Rico's grid could be refashioned from the bottom up. In each community microgrid, users would collectively install enough solar panels to satisfy local demand. These distributed resources and the related loads would be connected to one another and also tied to the main grid.

Over time, community microgrids could interconnect to form a regional grid. Eventually, Puerto Rico's single centralized power grid could even be replaced by interconnecting regional grids and community microgrids. If a storm or some other calamity threatens one or more microgrids, neighboring ones could disconnect and operate independently. Studies of how grids are affected by storms have repeatedly shown that a large percentage of power outages are caused by relatively tiny areas of grid damage. So the ability to quickly isolate the areas of damage, as a system of microgrids is able to do, can be enormously beneficial in coping with storms. The upshot is that an interconnection of microgrids would be far more resilient and reliable than Puerto Rico's current grid and also more sustainable and economical.

Could such a model actually work in Puerto Rico? It certainly could. Starting in 2009, our research group developed a model for a microgrid that would serve a typical community in Puerto Rico. In the latest version, the overall microgrid serves 700 houses, divided into 70 groups of 10 houses. Each of these groups is connected to its own distribution transformer, which serves as the connection point to the rest of the community microgrid. All of the transformers are connected by 4.16-kilovolt lines in a radial network. [See diagram, "A Grid of Microgrids."]

A Grid of Microgrids Hurricanes are a fact of life in the Caribbean. Installing community microgrids throughout Puerto Rico would greatly improve the island's ability to recover from severe storms and other natural disasters. In this model, groups of homes and small businesses would share rooftop solar power and battery storage. In the event of an outage on the central grid, the entire microgrid would operate in "islanded" mode. Each household would have enough power to operate essential loads, such as a small refrigerator, personal electronics, lights, and fans. Community members would be trained to operate and maintain the microgrid.

Each group within the community microgrid would be equipped with solar panels, inverters, batteries, control and communications systems, and protective devices. For the 10 homes in each group, there would be an aggregate PV supply of 10 to 20 kW, or 1 to 2 kW per house. The aggregate battery storage per group is 128 kWh, which is enough to get the homes through most nights without requiring power from the larger grid. (The amounts of storage and supply in our model are based on measurements of energy demand and variations in solar irradiance in an actual Puerto Rican town; obviously, they could be scaled up or down, according to local needs.)

In our tests, we assume that each community microgrid remains connected to the central grid (or rather, a new and improved version of Puerto Rico's central grid) under normal conditions but also manages its own energy resources. We also assume that individual households and businesses have taken significant steps to improve their energy conservation and efficiency-through the use of higher-efficiency appliances, for instance. Electricity demand must still be balanced with generation, but that balancing is made easier due to the presence of battery storage.

That capability means the microgrids in our model can make use of demand response, a technique that enables customers to cut their electricity consumption by a predefined amount during times of peak usage or crisis. In exchange for cutting demand, the customer receives preferential rates, and the central grid benefits by limiting its peak demand. Many utilities around the world now use some form of demand response to reduce their reliance on fast-starting generating facilities, typically fired by natural gas, that provide additional capacity at times of peak demand. PREPA's antiquated grid, however, isn't yet set up for demand response.

During any disruption that knocks out all or part of the central grid, our model's community microgrids would disconnect from the main grid. In this "islanded" mode, the local community would continue to receive electricity from the batteries and solar panels for essential loads, such as refrigeration. Like demand response, this capability would be built into and managed by the communications and control systems. Such technology exists, but not yet in Puerto Rico.

Besides the modeling and simulation, our research group has been working with several communities in Puerto Rico that are interested in developing local microgrids and distributed-energy resources. We have helped one community secure funding to install ten 2-kW rooftop PV systems, which they eventually hope to connect into a community microgrid based on our design.

Photos, top: Efrain O'Neill-Carrillo; bottom: Borintek-Jayuya Keeping the Lights On: Staff, students, and faculty from the University of Puerto Rico Mayagi1/4ez, with support from IEEE-EPICS, built five PV kiosks in rural communities that were among the last to be reconnected to the grid after Hurricane Maria. Each kiosk provided lights, a small refrigerator for storing medicine and other perishables, and charging ports for cellphones and other electronics.

Other communities in central Puerto Rico have installed similar systems since the hurricane. The largest of these consists of 28 small PV systems in Toro Negro, a town in the municipality of Ciales. Most are rooftop PV systems serving a single household, but a few serve two or three houses, which share the resources.

Another project at the University of Puerto Rico Mayagi1/4ez built five stand-alone PV kiosks, which were deployed in rural locations that had no electricity for months after Maria. University staff, students, and faculty all contributed to this effort. The kiosks address the simple fact that rural and otherwise isolated communities are usually the last to be reconnected to the power grid after blackouts caused by natural disasters.

Taking this idea one step further, a member of our group, Marcel J. Castro-Sitiriche, recently proposed that the 200,000 households that were the last to be reconnected to the grid following the hurricane should receive rooftop PV and battery storage systems, to be paid for out of grid-reconstruction funds. If those households had had such systems and thus been able to weather the storm with no interruption in service, the blackout would have lasted for 6 months instead of a year. The cost of materials and installation for a 2-kW PV system with 10 kWh of batteries comes to about $7,000, assuming $3 per watt for the PV systems and $100/kWh for lead-acid batteries. Many households and small businesses spent nearly that much on diesel fuel to power generators during the months they had no grid connection.

To outfit all 200,000 of those households would come to $1.4 billion, a sizable sum. But it's just a fraction of what the Puerto Rico government has proposed spending on an enhanced central grid. Rather than merely rebuilding PREPA's grid, Castro-Sitiriche argues, the government should focus its attention on protecting those most vulnerable to any future natural disaster.

As engineers, we're of course interested in the details of distributed-energy resources and microgrid technology. But our fieldwork has taught us the importance of considering the social implications and the end users.

One big advantage of the distributed-microgrid approach is that it's centered on Puerto Rico's most reliable social structures: families, friends, and local community. When all else failed after Hurricane Maria, those were the networks that rose to the many challenges Puerto Ricans faced. We think it makes sense to build a resilient electricity grid around this key resource. With proper training, local residents and businesspeople could learn to operate and maintain their community microgrid.

A move toward community microgrids would be more than a technical solution-it would be a socioeconomic development strategy. That's because a greater reliance on distributed energy would favor small and medium-size businesses, which tend to invest in their communities, pay taxes locally, and generate jobs.

Rooftop PV and battery storage are now economically competitive with grid power in Puerto Rico.

There is a precedent for this model: Over 200 communities in Puerto Rico extract and treat their own potable water, through arrangements known as acueductos comunitarios, or community aqueducts. A key component to this arrangement is having a solid governance agreement among community members. Our social-science colleagues at the university have studied how community aqueducts are managed, and from them we have learned some best practices that have influenced the design of our community microgrid concept. Perhaps most important is that the community agrees to manage electricity demand in a flexible way. This can help minimize the amount of battery storage needed and therefore the overall cost of the microgrid.

During outages and emergencies, for instance, when the microgrid is running in islanded mode, users would be expected to be conservative and flexible about their electricity usage. They might have to agree to run their washing machines only on sunny days. For less conscientious users, sensors monitoring their energy usage could trigger a signal to their cellphones, reminding them to curtail their consumption. That strategy has already been successfully implemented as part of demand-response programs elsewhere in the world.

Readers living in the mainland United States or Western Europe, accustomed to reliable, round-the-clock electricity, might consider such measures highly inconvenient. But the residents of Puerto Rico, we believe, would be more accepting. Overnight, we went from being a fully electrified, modern society to having no electricity at all. The memory is still raw. A community microgrid that compels people to occasionally cut their electricity consumption and to take greater responsibility over the local electricity infrastructure would be far more preferable.

This model is applicable beyond Puerto Rico-it could benefit other islands in the tropics and subtropics, as well as polar regions and other areas that have weak or no grid connections. For those locales, it no longer makes sense to invest millions or billions of dollars to extend and maintain a centralized electric system. Thanks to the advance of solar, power electronics, control, and energy-storage technologies, community-based, distributed-energy initiatives are already challenging the dominant centralized energy model in many parts of the world. More than two years after Hurricane Maria, it's finally time for Puerto Rico to see the light.

About the Authors

Efrain O'Neill-Carrillo and Agustin Irizarry-Rivera are professors of electrical engineering at the University of Puerto Rico Mayagi1/4ez.