Microgrids

When Hurricane Maria knocked out Puerto Rico's grid for months, a small hospital in Castaner stayed lit. It was running on a microgrid, disconnected from the rest of the island and powering itself.

A microgrid is a localized cluster of generation, storage, and loads that operates as a controllable unit and can either work with the main grid or detach and run independently. That independent mode is called islanding. The critical feature is a disconnect switch at the point of common coupling that severs the microgrid from the main grid. Most distribution infrastructure cannot do this: the radial design assumes one-way power flow with no local generation or control logic.

A military base during a wildfire shutoff. A California base has solar panels, a battery bank, and a diesel backup. Normally it draws power from the utility. During a public safety power shutoff, the utility cuts the feeder.

Before islanding, who decides whether the base stays powered?

The utility does, and the answer is no. After islanding, the base's own control system balances solar, battery, and generator to keep critical loads running indefinitely. The hospital in Castaner operated the same way: local generation plus storage plus a disconnect switch equals resilience that the main grid cannot provide.

For remote communities without grid access and critical facilities that cannot afford outages, microgrids are a structural alternative to waiting for centralized infrastructure. Federal resilience grants increasingly fund them as defense against both extreme weather and deliberate attacks on grid chokepoints.

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