Quick explanation. A large electricity plant, of whatever kind, cannot be shut down for so short a period as overnight. So electricity companies have for years been selling cities "street lights" in an attempt to get a few bucks out of this otherwise wasted energy.
I live in a city that has basically banned street lights. It's one of the safest cities in the area (so much for the "security" part of lights). And its wonderful because you can see the stars at night.
So, shut off the street lights. Generate the hydrogen. And at whatever ineficiency that might be, its still better than totally wasting the energy.