The Sun periodically ejects large quantities of charged particles. When one intersects Earth, it induces currents in long conductors – power lines, pipelines, undersea cables – and disturbs the upper atmosphere where satellites operate.
The historical reference
The largest recorded event, in 1859, induced currents strong enough to operate telegraph equipment with the batteries disconnected and to set paper alight in some offices.
The telegraph network was the only significant electrical infrastructure then. An equivalent event now would encounter a great deal more.
What would be affected
High-voltage transformers are the main concern. Induced direct current can saturate their cores and overheat them. Large transformers are custom-built with lead times measured in months to years, and there is no inventory of spares.
Satellites face increased drag as the atmosphere expands, along with charging effects that damage electronics. Navigation and communication would degrade for days.
What the fixes are
Blocking devices installed on transformer neutrals, which prevent the induced current from entering. Known technology, modest cost per unit, enormous cost across a whole grid.
Operational procedures – reducing load and reconfiguring the network when a warning arrives. Cheap and dependent on warning time.
Warning comes from spacecraft positioned between Earth and the Sun, which provide somewhere between fifteen and sixty minutes of notice.
Why it is underfunded
Because the return period is long and uncertain, so the expected annual cost looks small, and the budget cycle is short. The classic profile of a low-probability, high-consequence risk that gets deferred indefinitely.
Several grid operators have installed protection. Most have not.