I don't see how you can ration electricity. Take water, you have a dam full of the stuff and you try and stretch that out until it rains. We don't have a big dam of electricity, only that which is being made - unless I've missed a whole bunch of capacitors lying around the country.
So, by telling me to use 20% less you are saying I should work a day less per week - fine. I get that. But what happens if every single one of us decides that we will all flip on the lights at exactly 7am on a Monday. Eishkom cannot meet the demand.