How Are Kilowatt Hours Figured?
Kilowatt-hours (kWh) represent the units for energy consumption by electric appliances and other electronic devices. Calculating kWh is a straightforward matter if the power of the device (wattage) and the number of hours that it operates are known. Does this Spark an idea?
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Power (Wattage)
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Most manufacturers of household electronic items place tags on the devices that indicate their power consumption in watts (W). In some cases, however, the tags will indicate the device's operating voltage (in volts, V) and current (in amperes, A). In these cases, the power of the device can be determined by multiplying the voltage and amperage. Thus, for a device plugged into a standard wall outlet (which provides a voltage of about 120 V) that draws 2 A of current, then power = (120 V)(2 A) = 240 W.
Kilowatt-Hours
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Electric utility companies measure power consumption in kilowatt-hours (kWh). Determining kWh for a device is also straightforward. The power of a device can be converted to kilowatts by dividing the watts by 1000. From the previous example, 240 W/1000 = 0.240 kW. This means the device consumes 0.240 kW every hour it operates. Thus, if a 0.240-kW device operates for 3 hours (h), it will consume (0.240 kW)(3 h) = 0.720 kWh of electricity.
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Consumption by Appliance Type
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According to the Department of Energy, the power consumption of household appliances and electronic devices ranges from 20 W or less (clock radios and DVD players) to 5,000 W or more (clothes dryers, air conditioners and water heaters). In 2001, air-conditioning was responsible for 16 percent of household energy consumption, following by 10 percent for space heating and 9 percent for water heating.
Household Consumption
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According to the Department of Energy, in 2007 the average consumption of U.S. households was 937 kWh per month or just over 31 kWh per day.
Utility Bills
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Utility companies charge by the kilowatt-hour, usually measured at one-month intervals from meters located where the electrical service enters the structure. The exact rate per kWh should be stated on any electric bill. In 2009, the U.S. national average for residential customers was $0.113/kWh. Louisiana customers paid the lowest rates ($0.075/kWh) and Hawaii customers paid the highest ($0.262/kWh).
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References
- U.S. Department of Energy: Estimating Appliance and Home Electronic Energy Use
- U.S. Energy Information Administration: End-Use Consumption of Electricity 2001
- U.S. Energy Information Administration: Frequently Asked Questions--Electricity
- U.S. Energy Information Administration: Average Retail Price of Electricity, By State.
Resources
- Photo Credit electricity image by Mat Hayward from Fotolia.com
