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Why Solar Microgrids May Fall Short in Replacing the Caribbean’s Devastated Power Systems

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After the destruction inflicted across the Caribbean by hurricanes Harvey, Irma, and Maria, renewable energy advocates are calling for a rethink of the region’s devastated power systems. Rather than simply rebuilding grids that delivered mostly diesel generation via damage-prone overhead power lines, renewables advocates argue that the island grids should leapfrog into the future by interconnecting hundreds or thousands of self-sufficient solar microgrids.

“Puerto Rico will lead the way for the new generation of clean energy infrastructure. The world will follow,” asserted John Berger, CEO for Houston-based solar developer Sunnova Energy in a tweet before meeting in San Juan with Puerto Rico Governor Ricardo Rosselló this week. Rosselló appears to be on board, inviting Elon Musk via tweet to use Puerto Rico as a “flagship project” to “show the world the power and scalability” of Tesla’s technologies, which include photovoltaic (PV) rooftops and Powerwall battery systems.

Some power system experts, however, say the solar-plus-batteries vision may be oversold. They say that the pressing need to restore power, plus equipment costs and other practical considerations, call for sustained reliance on centralized grids and fossil fuels in the Caribbean. “They need to recover from the storm. Unfortunately I think the quickest way to do that is to go back to how things were before,” says Brad Rockwell, power supply manager for the Kauaʻi Island Utility Cooperative that operates one of the most renewable-heavy grids in the U.S.

Now is a tough time for a debate, given the ongoing power and communications blackouts afflicting many Caribbean islands, including Puerto Rico, the U.S. and British Virgin Islands, Dominica, and St. Martin. As of Thursday 12 October—more than three weeks after Maria’s cyclonic wrecking ball crossed the region—over four-fifths of customers in Puerto Rico and the U.S. Virgin Islands remained without power, according to U.S. Department of Energy status reports.

Puerto Rico lost major transmission lines that dispatched electricity generated at oil, coal, and natural gas-fired power plants on its lightly populated South shore to all corners of the territory. Its outage level actually slipped from 88.3 to 89.4 percent earlier this week after a tie line went down near San Juan. But it bounced back slightly, to an estimated 83 percent outage level, by yesterday.

What is clear is that several firms are trying to move fast while they talk, equipping rooftop solar systems with battery storage that enables consumers to operate independently of stricken grids. For example:

  • German storage system manufacturer sonnen launched a PV-plus-battery collaboration with local Aguadilla-based solar developer Pura Energía early this month;
  • Sunnova is crafting storage options for roughly 10,000 customers in Puerto Rico that it has already equipped with PV systems;
  • Tesla says it is sending “hundreds” of its Powerwall battery systems to Puerto Rico and, after reports of price gouging by independent installers, plans to dispatch installers from the mainland to expand its local teams.

Peter Asmus, a microgrids analyst with Navigant Research, says that such solar microgrids will deliver power to solar system owners far faster than grid restoration, which is still months away for many customers. He says microgrids will also make the island systems more resilient in the long run.

Asmus sees the situation as reminiscent of post-war Europe, when devastated European grids left a vacuum that enabled something better. “They built a more advanced grid than we have in the U.S.,” says Asmus. He says the Caribbean has a similar opportunity today: “The infrastructure was devastated so severely. They can start over with a cleaner slate.”

Some suppliers see microgrids actually supplanting some of the region’s largest transmission lines. “The grid in Puerto Rico will never be built back the way it used to be,” wrote John Merritt, applications engineering director for Austin, Texas-based Ideal Power in an email to IEEE Spectrum. Ideal Power’s multi-port power converters enable microgrids to efficiently swap power between their alternating current and direct current components, including PV systems, generators, and storage batteries.

Giving up big transmission lines sounds optimistic to Rockwell at the Kauaʻi Island Utility Cooperative (KIUC). It would, he says, represent a major system overhaul and thus lost time that Puerto Rico’s residents and economy can ill afford. “The people of Puerto Rico are not going to want to withstand any more delays than they have to while people figure out how to rebuild in a different way,” he says.

Rockwell adds that batteries are still a rather costly way to balance variable renewable generation. He speaks from experience. KIUC’s grid is over four-fifths solar-powered during some midday hours. Several utility-scale storage systems help integrate such a high degree of  variable power by quickly covering for lost PV generation when clouds pass overhead or by absorbing surplus midday generation and discharging it after the sun sets. But Rockwell says high battery costs mean KIUC still relies heavily on its diesel power plants.

Merritt at Ideal Power acknowledges that the same is true for microgrids. Integrating solar can cut an island microgrid’s fuel consumption by 60 to 70 percent, slashing operating costs and pollution, but he says diesel generators remain “important” assets. “Moving a site from 24/7 diesel-powered microgrid to a 24/7 solar + storage microgrid would be cost prohibitive in most cases,” says Merritt.

There are also questions about PVs’ hardiness. Harvey, Irma, and Maria left many PV systems in shambles. Merritt says that a microgrid for a commercial facility on Saint Croix that Ideal Power participated in assembling before the storms is operating without its six 33-kilowatt solar arrays. While they are out of commission for the next few months, the microgrid is relying solely on its diesel generators, battery, and converters.

Some utility-scale solar plants also took a beating, especially Puerto Rico’s solar array at Humacao. PV panels shattered and flew out of their frames when Maria’s Category-4 winds ripped over the Humacao solar plant, where its French owner Reden Energie was in the process of doubling capacity from 26 to 52 megawatts.

Houston-based microgrid developer Enchanted Rock advocates rugged microgrids supported by natural gas, which is cheaper and cleaner than diesel and may be more reliable than both diesel and solar during heavy weather. “You can build community-type microgrids that have some combination of natural gas generation, solar and storage,” says Enchanted Rock CEO Thomas McAndrew.

Enchanted Rock made a name for itself during Hurricane Harvey when its natural gas-powered microgrids at Houston-area grocery stores and a truck stop turned into hubs for first responders and weary residents. Diesel deliveries were hard to come by for 4-5 days, says McAndrew, but natural gas kept flowing underground throughout the storm.

At present few Caribbean islands have access to natural gas, and even Puerto Rico’s gas infrastructure is limited to one liquefied natural gas (LNG) import terminal that pipes the fuel to two power plants. Before Irma and Maria struck Rosselló had been working to expand LNG imports so more of its oil-fired power plants could burn gas.

Enchanted Rock’s McAndrew favors a network to distribute the gas more widely, which he says would be much cheaper than putting power lines underground to protect them from weather. He acknowledges that his proposal is ambitious, but says the outside investors that Puerto Rico will need to attract to support its revival can insist on infrastructure that will survive future storms. As McAndrew puts it: “Whether it’s private or government money, there’s got to be some sense that we might want to do this differently so we don’t just end up rebuilding it every couple of years.”



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