1. Environmental Science Mr. Hartley

2. What the heck is a kilowatt hour? Before we see how much electricity costs, we have to understand how it's measured. When you buy gas they charge you by the gallon. When you buy electricity they charge you by the kilowatt-hour (kWh). When you use 1000 watts for 1 hour, that's a kilowatt-hour. For example: DeviceWattageHours used kWh medium window-unit AC1000 wattsone hour1 kWh large window-unit AC1500 wattsone hour1.5 kWh

3. Cost Formula To get kilowatt-hours, take the wattage of the device, multiply by the number of hours you use it, and divide by 1000. (Dividing by 1000 changes it from watt-hours to kilowatt- hours.) Here's the formula to figure the cost of running a device: wattage x hours used ÷ 1000 x price per kWh = cost of electricity

4. Cost Formula Example For example, let's say you leave a 100-watt bulb running continuously (730 hours/month), and you're paying 15¢/kWh. Your cost to run the bulb all month is 100 x 730 ÷ 1000 x 15¢ = $10.95. Question: Assume that the lights in your kitchen and living room together use 400 watts. How much does it cost if the lights are on 24 hours a day, for a whole month? How much per year? Assume 15¢/kWh.

5. Cost Formula Example Answered Step 1. 400 watts x 24 hours/day x 30.5 days/month = 292,800 Total Watt-hours Step 2. 292,800 Wh / 1000 Wh = 293 kwh Step 3. 293 kWh x 15¢/kWh = $44/mo. or, Step 4. 44/mo. X 12 mo. = $528/yr.

6. Cost Formula Example 2 Question 2: Assume your window AC uses 1440 watts. How much does it cost to run it continuously for a month? How much per year? Assume 15¢/kWh.

7. Cost Formula Example 2 Answered Step 1. 1440 watts x 24 hours/day x 30.5 days/month = 1,054,080 Total Watt-hours Step 2. 1,054,080 Wh / 1000 Wh = 1,054 kWh Step 3. 1,054 kWh x 15¢/kWh = $158/mo. Step 4. $158/mo. X 12 mos. = $1897/yr.

8. How much does electricity cost? The cost of electricity depends on: where you live how much you use the time of year (summer rates are usually higher than winter) possibly when you use it (some utilities have lower rates in the evenings) who your provider is (every utility has different rates).

9. kWh The electric company measures how much electricity you use in kilowatt-hours, abbreviated kWh. Your bill might have multiple charges per kWh 14.0 ¢/kWh Highest Price (On-peak) 11.4 ¢/kWh Mid Price (Mid-peak) 7.7 ¢/kWh Lowest Price (Off-peak)