# The Science Guys

### July 2004

How much electricity does a typical family use?

This question is similar to asking how much food one of us science guys can eat. It really depends on the person; however, we can certainly talk of averages. First, we need to investigate exactly what the homeowner is buying when they pay their electricity bill.

What is electricity? Electricity is a flow of electrical charges; in our homes, it consists of electrons flowing through copper wires and all the devices in our house. The electrons arrive at your home from the electric company with considerable energy, or as some would say, with a lot of potential. After working their way through all the electrical devices in your home; the lights, the motors, the heaters, the microwave, etc. they have used up their energy, they are spent (have little potential), and must go back to the power plant to be reenergized.

The homeowner is billed for the energy these electrons have expended in the home. The official energy unit in the metric system is joules; however, several other energy units are used depending upon the particular source of the energy. Mechanical energy is described in units of joules, heat energy in units of calories, atomic energy levels in units of electron volts, etc. Electricity is calculated in terms of kilowatt-hours (kWh).

To calculate how much electricity (electrical energy) a device uses, simply multiply the power rating of the device in kilowatts times the number of hours of use. For example, a 500 watt (0.5 kW) security light used for 8 hours consumes 0.5 kW x 8 hr = 4 kWh of energy.

Thus, the amount of electricity (energy) you buy is measured in kWh and that is what your electric bill reports. In Tennessee in 2002, the average residential cost of electricity was 6.4 cents per kWh and the average home used 1303 kWh of electricity per month. Compare this to the national average for the United States, which was 8.46 cents per kWh, and an average home used 907 kWh per month Tennesseans use a lot more electricity than the average person in the U.S. In fact, Tennessee homeowners use more electricity than any other state, 44% more than the average. (Maybe we should ask ourselves why?)

For comparison, homes in New York use only 535 kWh, in Michigan 683 kWh, California 549 kWh, and Arkansas 1077 kWh. We are fortunate that the cost of electricity is rather low in Tennessee and that keeps our electric bills reasonable. The most expensive electricity is in Hawaii where a kWh cost 15.6 cents and our neighbor Kentucky has the least expensive at 5.65 cents per kWh.

So, how much electricity does a family use? It depends on how many switches you turn on and how long you leave it on. In Tennessee, the electric bill averages 1303 kWh at a monthly cost of \$83.50. Now, how does your bill compare? Are you average?