An EMP: what it would do, and will your solar survive?

What an EMP is

A nuclear weapon set off high above the atmosphere sends out an electromagnetic pulse in three parts. The first, very fast part hits electronics. The slow, last part acts like a severe solar storm on long power lines (EMP Commission). It's an act of war, not weather. There's no forecast and no honest way to put odds on it. What can be said is what it would and wouldn't do.

The grid

Experts disagree about how bad it would be:

EPRI, the utilities' research institute, studied it for three years. A burst could cause a regional blackout, not a national one. Damage to the big transformers was found to be minimal, and recovery should look like other large outages if protective relays are hardened (APPA on EPRI, T&D World).
The EMP Commission took the darker view: a widespread, long outage, because damaged grid parts take months to replace, or years if many fail at once (Baker testimony, EMP Commission).

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

Your solar

The panels are tough. Sandia National Laboratories hit eight solar panels with simulated EMP pulses up to 100 kV/m. Afterward, testing showed no loss of function (Sandia).

The weak points are long wires. The pulse couples into anything long and conductive. "Smaller, self-contained systems that are not connected to long-lines tend not to be affected," vehicles and hand-held radios included, and when they are, it's "more often temporary upset rather than component burnout." Systems tied to long lines are the vulnerable ones (Baker testimony). For a home system, that points at the inverter and charge controller, the parts with electronics and cables running to them, and at any connection to the grid. CISA advises keeping backup power generation off the grid connection unless it has very good surge protection (CISA).

An off-grid system is the self-contained kind, which is the better place to be.

What actually helps

A spare inverter or charge controller, wrapped. CISA's simple method: put it in a plastic or paper bag, then wrap it in two or more layers of heavy-duty aluminum foil, seams overlapped, cables inside too. Or use a real Faraday bag, not a Mylar food bag (CISA). The guides can add a boxed spare to your parts list.
Not a trash can, as is. CISA notes metal trash cans usually don't protect what's inside unless they've been modified to close the gaps at the lid and handles.
Small electronics matter less. Handhelds are "relatively immune" unless long antennas or cords are attached (CISA). A wrapped spare radio is still cheap insurance.
Power that doesn't need the grid, sized for your darkest month. That's what the guides do. The run above shows how long yours lasts.

Solar storms are a different thing: slow, with warning, and a threat to the grid's transformers rather than your electronics. More on that.

Common questions

Will solar panels survive an EMP?

In Sandia National Laboratories' 2019 tests, eight solar panels hit with simulated EMP pulses up to 100 kV/m showed no loss of function. The more vulnerable parts are the electronics connected by long cables: the inverter and charge controller.

Do I need a Faraday cage?

For spares, yes, and it's cheap. CISA's guidance is to put the item in a plastic or paper bag, then wrap it in two or more layers of heavy-duty aluminum foil with the seams overlapped, or use a real Faraday bag. A plain metal trash can usually doesn't work unless it's modified.

Would my car still run after an EMP?

Probably. The EMP Commission's former staff director testified that small self-contained systems not connected to long lines, vehicles included, tend not to be affected, and that effects are more often a temporary upset than burnout.

How long would the grid be down?

Estimates disagree. EPRI's 2019 study found a regional blackout, not a national one, with recovery like other large outages. The EMP Commission warned that damaged grid parts take months to replace, or years if many fail.