A New Style Of Grid Design: Puerto Rico Is a Prime Candidate

While restoration of Puerto Rico’s electrical transmission and distribution systems following Hurricane Maria was still in its early stages, Gov. Ricardo Rossello pledged to have power restored to 95 percent of the commonwealth’s citizens within two months. The U.S. Army Corps of Engineers (USACE) took charge of the reconstruction effort, working to replace the previous system, like-for-like. However, some are wondering if this might be a good time to imagine a break from the island’s centralized, spoke-and-wheel approach to transmission and distribution and move toward a more distributed—and, possibly, resilient—design, incorporating solar, energy storage and microgrids.

Few electrical systems could have survived the hit Puerto Rico took from Hurricane Maria without significant damage. However, years of neglect made Puerto Rico Electric Power Authority (PREPA)’s infrastructure especially vulnerable. The system sustained losses that included at least 50,000 poles supporting power lines and more than 6,000 miles of transmission and distribution lines. 

“There are many distribution assets that have been effectively wiped out, and the Army Corps is focused on how do we repower and get diesel generators shipped. That has to be the top priority,” said Roy Torbert, principal of Rocky Mountain Institute’s Islands Energy team. 

Population centers will be the focus of immediate efforts. In the medium term, opportunities exist to bring distributed resources to less-populated communities that could otherwise face months without power.

For Cathy Kunkel, energy analyst with the Institute for Energy Economics and Financial Analysis, the geography of the transmission and distribution system the USACE is reconstructing lies at the heart of its vulnerability. Transmission lines must pass through rugged terrain to connect customers to kilowatts. 

“The important thing to know is that the majority of the generation is on the southern shore, and the majority of the load is on the northern shore,” Kunkel said. “There is an opportunity to build more generation closer to the load.”

Regardless of location, the nature of replacement generation resources remains a concern. Diesel, fuel oil and coal have dominated Puerto Rico’s fuel mix for decades, accounting for 64 percent of generation in 2016, according to the U.S. Energy Information Administration. Diesel, especially, likely will remain a player in the commonwealth’s energy market for some time to come, Torbert and Kunkel said. But, given abundant solar resources and the falling cost of energy storage, it’s possible the fossil fuel could take more of a backup role in electricity generation.

“Our team has done a number of analyses on island grids, and we’ve generally found that diesel or a fuel like it has a real important role to play,” Torbert said. 

Having a reliable backup resource is especially critical for island-grid operators in case extended cloud cover depletes stored solar energy or other problems arise. However, that doesn’t mean fossil fuels would need to remain a primary source for generation.

There is also a question of how much generation capacity needs to be rebuilt, because Puerto Rico has experienced falling demand due to declining population as people move to the U.S. mainland. Population dropped 11 percent between 2004 and 2015, according to the World Bank with PREPA, which reported electricity consumption falling 19 percent and peak demand reducing by 14 percent over that period. In 2016, according to the National Renewable Energy Laboratories, the island had an installed generation capacity of 5,800 megawatts (MW), while peak demand that year only reached 3,685 MW. 

PREPA had plans to replace aged, oil-fired generators with equivalent-sized natural gas units, but a distributed, microgrid-based approach could provide a more flexible solution in the face of current demographic trends.

“If your load is reducing dramatically, you face the risk of stranded assets, if that load keeps going away,” she said.

A number of solar and storage suppliers have offered to help Puerto Rico rebuild with a distributed, microgrid-based approach in mind. German battery maker Sonnen has shipped batteries from its Atlanta manufacturing center, working with local solar leader Pura Energia in a subsidized effort to get medical clinics and shelters powered up. Tesla CEO Elon Musk discussed similar efforts using Tesla battery systems with Rossello. The governor has stated an interest in rebuilding the island’s grid in a more distributed design, but he will still have to get PREPA officials to agree to such plans.

PREPA CEO Ricardo Ramos Rodriguez quit on Nov. 17. His departure may improve Puerto Rico’s prospect of getting federal aid.

“One of the core problems is that the utility and the government need the opportunity to see eye to eye,” Torbert said. “Our approach is to bring the two parties together. That seems like one of the key leverage points that can make a difference.”

About the Author

Chuck Ross

Freelance Writer

Chuck Ross has covered building and energy technologies and electric-utility business issues for a range of industry publications and websites for more than 25 years. Contact him at chuck@chuck-ross.com.

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