What Is a Microgrid? How They Work and Why They're Suddenly Everywhere

When Hurricane Maria flattened Puerto Rico's power grid in 2017, one building in the mountain town of Adjuntas never went dark.

Casa Pueblo, a local environmental group, had already wired its headquarters with solar panels and batteries.

That system kept the lights on while the rest of the island waited close to a year for power.

It also became the seed for one of the country's most closely watched community microgrids.

Nine years and several storms later, microgrids have moved well past the disaster-recovery story.

They're showing up on military…