(Bloomberg) — On a given sunny day in Puerto Rico, more than 37,100 rooftop solar installations–mounted atop homes, gas stations, malls and hospitals–churn out 255 megawatts of electricity. 

That’s only about 2.5% of the island’s overall power generation. But collectively, the rooftops might be considered Puerto Rico’s largest clean power plant, dwarfing the 101-megawatt Santa Isabel wind farm, the island’s largest renewable generator. 

As the US territory of 3.2 million people scrambles to shift to 100% renewables by 2050, much of the focus has been on utility-scale initiatives. In March, regulators conditionally approved 18 renewable power plants that should produce 884 megawatts by 2024. But even with that additional capacity, the island will still depend on fossil fuels for more than 84% of its electricity. 

Puerto Rico’s  green-power deficit is shedding new light on the oversized role of often tiny rooftop solar projects. 

Luma Energy, the consortium that began managing Puerto Rico’s notoriously aging and fragile electricity grid in June 2021, says it has connected more than 22,000 solar customers on its watch and is adding as many as 2,100 more per month. 

That has made rooftop solar “a player” in the power generation business, said Luma Energy Chief Executive Officer Wayne Stensby. “On a nice sunny day you can actually see the impact on net demand.” 

Despite being bathed in enough sunlight to draw tourists from around the world, Puerto Rico had done a poor job of harnessing it for power. Utility-scale renewables make up about 3.6% of Puerto Rico’s energy mix, and solar power is just a fraction of that. 

On an island where blackouts are depressingly common–and electricity rates are higher than in almost every other US jurisdiction–interest in solar is surging. The island now has more home solar installations per capita than all but eight US states, according to the Solar Energy Industries Association, a Washington, D.C.-based trade group. 

Before Hurricane Maria in 2017, there were about 9,000 solar rooftops connected to the grid, said Javier Rua-Jovet, the chief policy officer at the Solar and Energy Storage Association of Puerto Rico, an industry advocacy group.

Most of those projects were motivated by hopes of reducing electricity bills. But after the hurricane raked the island and plunged parts of it into darkness for more than 11 months, solar power became a means of survival. 

“Initially it was a savings proposition, now the rationale is simply having power,” Rua-Jovet said. “You have to remember that almost three thousand people died in Puerto Rico after Maria”–and many of those deaths were blamed on the grinding effects of prolonged power outages. 

That paradigm shift, from savings to survival, means that almost every solar installation is now sold with a battery backup. And that’s opening up entirely new possibilities for the island. 

In other markets, like Australia, rooftop solar batteries have been networked into virtual power plants, or VPPs, that can be pressed into service during peak demand or when generators fail. 

Rua-Jovet’s group estimates there are 60,000 batteries deployed on the island, representing some 300 megawatts of power. About 1,800 new batteries are being installed each month. A that rate, “I think you could argue that Puerto Rico has the largest untapped virtual power plant in Western civilization,” Rua-Jovet said. 

Luma says its priority is fixing 52,000 miles of precarious transmission and distribution lines and other critical infrastructure. (A fire at a five-decade old circuit-breaker in April, for example, knocked out power to the entire island and took almost five days to completely restore.) But the company is planning to build a new control center and energy management system that could support a virtual power plant, according to Stensby. 

“We’re looking at how you start to take advantage of rooftop solar and integrate it more directly into your system,” he said, “but we’re not there yet.” 

Puerto Rico isn’t alone in taking a second look at the collective power of small rooftop projects. Across the Caribbean, renewables account for about 12% of the energy mix, a number that has only budged four percentage points in the last decade, said Hyginus Leon, the president of the Caribbean Development Bank.

If CDB members want to hit their target of 55% renewables by 2030 they cannot rely on the “sluggish” growth of utility-scale renewable projects, he said in April at the Caribbean Renewable Energy Forum in Miami.

One of the bank’s proposals is mass producing prefabricated roofs embedded with solar panels and batteries and making them a regional building standard.

“This would tackle climate, housing, and energy distribution, if we could just get our mind around it,” Leon said. “We can’t rely on business as usual.”

Stensby says Luma is actively removing hurdles for individuals to connect their small solar installations to the grid. Before the company took over, it would often take years to get a project connected; now the company claims the average is 14 days. 

“There’s a determination here to get to renewable energy as quickly as possible,” Stensby said. “From the beginning we’ve known that this is very important to Puerto Rico.”

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