Ask the expert

Does the Time of Day I Use My Appliances Matter?

The short answer is “Yes, it does!” If you are concerned about protecting the environment and keeping electricity rates in check, the best time to use appliances is when overall electricity use is low. Avoiding energy use during times of peak demand can have a beneficial effect on electric rates over time because it can avoid the need for your utility to ramp up an additional power plant or to buy more expensive power or fuel from the market.

What is peak demand and how do appliances contribute?

Peak demand is when electricity use is high and electricity supply is constrained. Seasonal peak demand occurs when weather gets hotter or colder than normal and heating and cooling demand is at its highest. During hot spells, added heat from clothes drying, cooking, and dishwasher use can make your air conditioner run longer as it works to remove the excess heat and humidity.

In cold climates that rely heavily on natural gas both directly for heating and to run natural-gas fired electric generators, winter demand may be a bigger issue. In these areas, paying attention to gas consuming appliances such as furnaces and water heaters can be as important to keeping rates from rising as modifying electric appliance usage. That’s because when gas demand is high, fuel costs go up.

Peak demand conditions may also occur when there is a mismatch between the time electricity usage is highest and when low-cost, renewable generation is available. For example, in areas of the country that have a high penetration of solar energy, utilities may designate peak hours when the sun goes down and people return home work and start turning on appliances. That’s because solar-generated electricity is less available, yet it won’t be long until bedtime when electricity use plummets. In these situations, it’s potentially costly for utilities to ramp up another generator for a short period of time.

Do I save more money if I use less energy during peak times?

That depends. Some utilities add demand charges during peak times or offer mandatory or voluntary time-based rates. If you are on a time-based electric rate, you can save money on your utility bill by shifting to off-peak hours. While many utilities offer time-based rates, most are optional for residential customers and enrollment has been limited.[1] If your utility does not offer time-based rates or if they do and you don’t enroll, then you won’t experience direct energy savings based on the time of day that you use energy. You can however still do your part by reducing energy use when local peak conditions exist. 

How can I do my part?

If peak conditions exist, shift your appliance use to off peak hours as much as possible. Since peak demand differs by geography, season, hour and day of week, and generation mix, your local utility is the best source of information on when conditions peak. As a rule-of-thumb, after 9 pm and before 9 am are off-peak in most situations.

If peak conditions are due to weather extremes, consider pre-heating or pre-cooling your home during off-peak hours.

Perhaps the best defense is energy efficiency. By reducing energy use year-round, not only do you help avoid contributing to peak conditions, you can also save on utility bills and make a more meaningful contribution to helping the environment.

Here are a few tips:

  • Practice everyday conservation such as washing clothes in cold water, turning off lights and fans, and changing the filter on heating and cooling (HVAC) system.
  • Invest in ENERGY STAR-certified products, particularly HVAC systems. You’ll have a better experience and more options if you call a professional in the shoulder seasons (e.g., spring and fall), before your system breaks down!

For more tips, visit:  https://www.energystar.gov/campaign/waysToSave

Thanks for asking!

By: Maureen McNamara

[1] Source: Based on review of  EIA Form 861 Detailed Data (original data)