What a solar storm actually does

The Sun sometimes throws a huge cloud of charged particles at Earth. When it hits, Earth's magnetic field shakes, and that pushes currents through anything long and conductive lying across the ground. NOAA lists power grids and pipelines (NOAA). In the strongest storms, rated G5, NOAA warns that "some grid systems may experience complete collapse or blackouts," HF radio can go quiet for a day or two, and GPS can be off for days (NOAA scales).

The weak point is the grid's high-voltage transformers. Extreme storms can damage them, and repairs could take "days, weeks, or even longer" (NOAA). New large transformers now take about three years to build, and up to five (DOE).

What has happened

  • 1859, the Carrington event. The biggest storm on record. It hit when the only wires were telegraph lines.
  • March 1989, Quebec. Hydro-Québec's grid collapsed in under 90 seconds, and six million people lost power for up to nine hours (Hydro-Québec, Boteler 2019). In the US, transformers were damaged at one power plant, with no loss of service. Since 1932 only four storms have significantly affected grids anywhere (GAO).
  • May 2024. The strongest storm in over 20 years, a G5. No major blackouts were reported (Royal Society Open Science).

How bad, and how likely

The worst case people plan for is a storm like 1859's hitting today's grid. In 2013, Lloyd's estimated it would put 20 to 40 million Americans at risk of long outages, lasting 16 days to one or two years depending on how fast transformers could be replaced, with losses of $0.6 to $2.6 trillion (Lloyd's).

How likely is it? One widely quoted estimate gave about 12% per decade (Riley 2012). Later work stressed how uncertain these numbers are (Riley and Love 2017), and a 2019 study put it at 0.5% to 1.9% per decade (Moriña et al. 2019). The honest answer: rare, but not rare enough to ignore. G5 storms in general come about four times every 11-year solar cycle (NOAA scales).

That's why the run above uses 16 days as the usual case and a full year as the worst.

What it means for you

  • Your phone, appliances and panels aren't the target. The currents build up over long lines, which is why NOAA's list is power grids and pipelines. A home system's short wiring isn't on it.
  • The sun keeps shining. Unlike a winter storm, there's no cloud. A solar and battery system that can run your house without the grid keeps refilling itself every day.
  • Ordinary grid-tied solar still shuts off when the grid does, by design. You need batteries and an inverter that can run on their own. More on that.
  • Weeks without the grid means the same needs as any long outage: heat, water, food and medicine.

Solar storm or EMP?

They often get lumped together. They're different. A solar storm builds up slowly over long lines and threatens the grid's transformers. A high-altitude nuclear EMP starts with a sudden, fast pulse that's a concern for electronics too, which is where Faraday-cage advice comes from (EMP Commission). For a solar storm, the thing to have is power that doesn't depend on the grid. More on EMPs.