“Peak” energy hours are the time of day during which the most electricity is used typically the daytime. The high usage of energy can strain the electrical grid, can cause brown / black outs and even the use of older (dirtier) backup plants. It is best to have the energy usage spread out more evenly throughout the day to prevent these things from happening. As an incentive, most utility companies offer a two-tiered rate plans, charging less for energy used during off-peak hours.
If you run your dishwasher, washing machine and other energy intensive appliances during off-peak electric times, you’ll save on energy and in turn money. Off-peak hours are different for every area, but are usually after 9pm and before 7am during the week.