Most of us don't think about how much electricity costs at different times of the day. But the state's two largest utilities are planning to change that. When it's really, really hot and humid out, what do lots of people do when they get home? They turn on, or turn up, the air conditioning. There are big spikes in electricity demand on the hottest summer days, between 2:00 in the afternoon to 7:00 in the evening. And that electricity is really expensive to produce. DTE Energy and Consumers