Puerto Rico is slowly rebuilding its electrical grid and the generating stations damaged by hurricane Maria, but for some residents the sun holds the best promise of restoring light.
And a hospital parking lot in San Juan covered in hundreds of solar panels has become a test area.
"There are a little bit under 800 solar panels," says Juliana Canino, who runs the Hospital del Niño.
The nonprofit hospital is the only rehabilitation facility for children in Puerto Rico. It's involved in one of the first alternative-energy experiments of its kind on the island, an agreement between the government and Tesla, the company best-known for electric cars.
The hospital's microgrid is an alternative to the regular public grid. Microgrids are self-contained power systems with enough capacity to run a small neighbourhood or a large facility.
Canino expertly steps between the rows of panels as she gives a tour. "They were assembled and tested in eight days, and on a sunny day we can produce up to 250 kilowatts of energy."
That's enough electricity to power the hospital for about 20 hours a day. It relies on its generators for the rest.
"It gives us the opportunity to continue our services," says Canino. "We have 35 patients with chronic and physical and mental conditions, and they need skilled nursing services 24 hours a day seven days a week."
The power is precious in a place that still has so little.
The island's systems for generating and distributing electricity, already crippled due to years of neglect, were decimated when hurricane Maria plunged all of Puerto Rico into darkness two months ago.
The storm destroyed the public grid, and most of the island remains without electricity. Service — where it exists at all — is spotty.
Puerto Rico Governor Ricardo Rossello has pledged to restore power to 95 per cent of the island's residents by mid-December.
Meanwhile, the U.S. Army Corps of Engineers is less optimistic, saying it expects to reach just 75 per cent by the end of January.
Until late last month when Tesla came forward, the Hospital del Niño was forced to run its generators non-stop to keep critical medical equipment going. The generators are expensive to run, and there's the constant risk of mechanical failure.
"Generators are not built to run 24 hours a day, seven days a week, for 50 days," says Canino.
"We only had one generator working at the time of the hurricane, and it was after two weeks we were able to put the second generator to work. So definitely we were scared that the first generator was going to break."
Then the call offering help came, and Canino says it was like winning the jackpot.
Tesla said it would lend the hospital a solar microgrid as part of a humanitarian aid initiative in Puerto Rico. The hospital can use it until the local electrical system is fixed.
"I actually felt a little bit skeptical at the beginning, but then when I saw them working I was very relieved," Canino says. "Definitely, it's less of a burden for us not to use diesel [generators] all the time."
Tesla is one of several companies intent on transforming Puerto Rico's power grid by offering things like panels and batteries to the devastated island. Only 3 per cent of the island's power is solar-generated now, but that could change as Puerto Rico rebuilds its infrastructure.
Government officials are evaluating options that focus on microgrids for individual facilities, as well as larger regional grids that use solar and other renewable sources.
The Hospital del Niño was chosen as a microgrid test case because of its importance to the community and its need for reliable power. More than 3,000 children from around the island come for services like speech and occupational therapy, as well as psychological services. It's also basically a medical orphanage — the kids here are under children's aid and many will likely grow up in the facility.
"We have patients with many critical, chronic, severe conditions," says Dr. Elizabeth Pagan, the medical director.
"We have patients that have respiratory conditions that need frequent respiratory therapies. We have patients that need ventilatory support for sleep during the night. We have patients with cardiac conditions ... we have patients, they need equipment for them to be fed during the day. [Electricity] was critical."
The CBC News team experienced the hospital's need for a reliable source of energy first-hand when, on a visit, the elevator suddenly stopped and the lights went off. During the hours when the hospital wasn't operating on the solar system there was an island-wide blackout and the breaker for the hospital's generator tripped as well, underlining how fragile both systems are.
The system of panels and batteries in the hospital's microgrid cost about $1 million US. With the local power situation so precarious, the hospital is launching a fundraising campaign aimed at keeping the solar setup permanently.
"I don't want to go back to the grid," says Canino, gesturing to the batteries that store the hospital's solar-generated power. "This is my future now."