NOAA is just up the road from us and outputs sophisticated Solar data to Users.
The simplified story is that Solar current induced into terrestrial Power Lines trips protective circuitry, which typically then trips other protective Power Grid circuitry as subsequent/interconnected Breakers trip.
NOAA data Users include Satellite 'Managers'. They turn various Satellites 'away' from predicted/observed Solar currents to minimize damage. There's a need to limit Astronaut exposure, too. Solar Flare currents also affect Satellite-based Ship positions as they try to remain stationary while drilling for Gas/Oil. On and on...
I happened to wander in their 'Control Central' area [visible through Glass] RIGHT when a monster Flare hit a few years back. It looks like any major Newsroom facility with lots of high def Video Monitors. Impressive!
I've been in SoCal for some of the Quakes 'Hiker Chick' mentions. The 'interconnectedness' of the Power Grid was driven home during one Quake while we were here in CO. I heard the loudest Steam Whistle sound from 'somewhere' distant I'd ever heard. The Boulder CO Power Plant was shedding Steam as fast as possible to prevent damage. Power Generation is like a giant 'See Saw'. When the CA Quake caused huge power loads in SoCal to shed, there was excess generating capacity here locally 'with nowhere to go' that had to be shedded to prevent Boiler damage from excess pressure. Having been there in all Seasons, Japan's ability to 'just' power innumerable A/Cs means they don't have a lot of excess capacity 'sitting around'. Neither does CA and the Western Region [including power imported from Canada] in recent Summer heat waves. When Summertime power cutbacks affected giant pre-shipment Veggie Chillers in CA, availability of items like Lettuce dropped and prices rose.
Japanese Reactors ruined by Salt Water inundation represents lost capacity that, as we shall soon see, affects Semiconductor and Vehicle Production capacity; Japanese Citizen discomfort being the larger concern, of course. Japanese imports and future orders of U.S. Beef have changed already. The idea that we can 'let japan worry about japan' doesn't reflect Reality as I know it, as WY Cattlemen might discover 1st person.
'The Thigh Bone connected to the Leg Bone', as the old Song goes...
Japanese Parts Shortage Idles GM Plant
Hiker Chick, and others, make some great points about how the 'familiar' can be the 'gotcha' event that tests Emergency Preparedness. Gas Line ruptures, as happened just this week in TX, and Train derailments can get cha.
NOAA Solar Site