[Coda]

I'm talking about single little warning flashers, not crossing lights. I would imagine those things draw so little power that they could run for a week without a recharge. I've also seen roadside speed indicators ("YOUR SPEED: ___ MPH") with a solar panel that I would guess to be about... oh, half a square meter? Big compared to the rest of the sign but not enormous. If one of those were to run dead, it wouldn't cause any trouble, so it's not a problem if it's cloudy for a few days.

It doesn't actually have to make it all the way back. Like I said, it's not all that hard to combine sources of electricity, so just pushing more current into the line instead of pulling it out is enough to share that energy for other nearby buildings. The power meter keeps track of how many kilowatt-hours you draw in compared to how many you push out and you get billed for the difference or get credit to your account.