When the grid goes down for months

It has happened

On September 20, 2017, Hurricane Maria knocked down about 80% of Puerto Rico's utility poles and all of its transmission lines. Every one of the island's 1.57 million power customers lost service (EIA, Columbia Climate School).

One month later, 89% still had no power, 44% had no running water and 58% had no phone service. A quarter of the hospitals (25 of 69) were still off the grid (Columbia).
At the end of the year, about 45% were still without power (Columbia).
The last homes, two families in the mountains above Ponce, got power back in August 2018, about 11 months later (NPR). Mountain towns like Adjuntas went about six months without grid power (Renewable Energy World).

A survey of 3,299 households found the average home went 84 days without electricity, 68 without water and 41 without cell coverage through the end of 2017. About a third of the deaths families reported were blamed on delayed or interrupted medical care (New England Journal of Medicine). The official estimate is 2,975 more deaths than normal in the six months after the storm, with the risk highest in the poorest towns (George Washington University).

That's why the run above uses 84 days as the usual case and 328 days as the worst.

What fails over months, not days

Fuel. Generators help for days. Over months, the problem is keeping them fed. Even FEMA was short of generators in the first weeks (FEMA after-action report, NPR).
Water, wherever pumps or treatment depend on grid power. A month in, 44% had no running water; the average household went 68 days without it.
Phones and internet. A month in, 58% had no phone service. It was mostly back by the end of the year, long before the power was.
Medicine and medical devices. Insulin needs a fridge. Oxygen concentrators, CPAPs and dialysis need power every day.

The thing that kept working

Local solar with batteries. In the Adjuntas mountains, the Casa Pueblo community center's solar and battery system kept running for nine days when Hurricane Fiona knocked out the island again in 2022 (Renewable Energy World). One Adjuntas mother told TIME her daughter kept up her dialysis because of their solar system (TIME).

Solar and batteries don't need fuel deliveries. A system sized for your darkest month refills itself every sunny day, for as long as the gear lasts.

The catch: ordinary rooftop solar shuts off

Most rooftop solar is grid-tied, and it switches off within seconds when the grid fails. That's deliberate: it stops your panels from powering lines that crews are repairing (Enphase). To keep your lights on, you need batteries and an inverter that can disconnect from the grid and run your house on its own. The home guides size exactly that kind of system.

What you'd need for months

Power sized for your darkest month, with enough batteries for a few cloudy days. That's what the guides calculate. The run above shows how long your own setup lasts, and what to add if it falls short.
Water you can get without the grid: stored water, a filter, and on a well, power for the pump.
Medicine: a fridge on your batteries for anything that needs cold, and power for any medical device, every day.
A way to hear news: a battery or hand-crank radio. Phones may be out for weeks.
Know your neighbors: who has a well, who has a generator, who needs power for medical care.

Common questions

Has the US grid ever been down for months?

Yes. After Hurricane Maria in September 2017, all of Puerto Rico lost power. A month later 89% still had none, about 45% were still without power at the end of the year, and the last neighborhood was reconnected 328 days after the storm.

Will my grid-tied solar panels work if the grid goes down?

Not on their own. Grid-tied inverters must shut off within seconds when the grid fails (anti-islanding), so they don't energize lines crews are repairing. You need a battery system that can disconnect from the grid and form its own small grid for your house.

What runs out first in a long grid-down?

In Puerto Rico, generators and fuel were scarce in the first weeks; a month in, 44% had no running water and 58% had no phone service, and a quarter of hospitals were still off the grid. On average, households went 84 days without power, 68 without water and 41 without cell coverage.

How much solar do I need to live through months without the grid?

Enough to cover your darkest month with batteries for the cloudy stretches. That's exactly how the guides size a system; the run above shows how long your own setup lasts.