When I lived in New York State in the mid 1990s, there was time-variable electricity pricing. Being a grad student, I exploited it to do my dishes and clothes after peak hours to save money. Eventually I put my water heater on a timer. I think the rate differential was significant (order of $.07/kWh vs. $.11/kWh).

This is still the case, see: http://www.nyseg.com/YourHome/pricingandrates/daynighrate.ht...

Perhaps you misinterpreted the scope of applicability of what the professor said.