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The Grid: Tightly Coupled. My sister called via cell phone from Manhattan this evening. (She had nothing better to do in the dark.) She said, "You're so lucky. You have solar power, so a blackout like this wouldn't affect you."
Not true. Ours is an on-grid photovoltaic system. We're a cogenerator, just like any other, and when the signal from the grid goes away, our system drops off the grid and shuts down. We *could* rewire our system so that we could isolate from the grid and use our own power locally, but it would have to be on dedicated circuits only, whereas the on-grid system just adds our juice to the big pool out there. And why do we, like all other generators, have to leave the grid when it dies? One reason is phase lock. We can't put electricity onto the grid unless it's in phase with all the other generators on the grid. For our little 2.5kw system, it's just a matter of a solid-state inverter controlled by a phase-locked loop. But if you're running a huge mechanical turbine (i.e. with mass), it can take a long time to get it to the correct speed and phase, and when you suddenly put a load on it, it starts to slow, which means your frequency drops, you phase-lock goes to hell, and...well, you get the idea.
I wish I still had an article I read in IEEE Spectrum that described the step-by-step calamity that lead to the huge NY blackout in 1977. It was written like an action thriller with timestamps on each paragraph. I'll let you know if I find it online.
Posted Thursday, August 14, 2003 7:47:33 PM 
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