A kilowatt-hour is the amount of energy equivalent to a steady power of 1 kilowatt running for 1 hour, or 3.6 megajoules. Energy cost can be illustrated in a similar example: a 100-watt (i.e. 0.1 kilowatt) light bulb turned on for 8 hours uses 800 Wâh or 0.8 kWâh.If the energy cost is 25 cents per kilowatt-hour, it would cost 0.1 kW Ã 8 h Ã $0.25/kWâh = $0.20.Whereas individual homes only pay for the kilowatt-hours consumed, commercial buildings and institutions also pay for peak power consumption (the greatest power recorded in a fairly short time, such as 15 minutes).he kilowatt-hour (symbolized kWâh) is a unit of energy equivalent to one kilowatt (1 kW) of power sustained for one hour. One watt is equal to 1 J/s. One kilowatt-hour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.