Editing Kilowatt-hour (section)

==Electricity sales==
Electrical energy is typically sold to consumers in kilowatt-hours. The cost of running an electrical device is calculated by multiplying the device's power consumption in kilowatts by the operating time in hours, and by the price per kilowatt-hour. The [[unit price]] of electricity charged by utility companies may depend on the customer's consumption profile over time. Prices vary considerably by locality. In the United States prices in different states can vary by a factor of three.<ref>[https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a Average Price of Electricity to Ultimate Customers by End-Use Sector], U.S. Energy Information Administration, April 2018</ref>

While smaller customer loads are usually billed only for energy, transmission services, and the rated capacity, larger consumers also pay for peak power consumption, the greatest power recorded in a fairly short time, such as 15 minutes. This compensates the power company for maintaining the infrastructure needed to provide peak power. These charges are billed as demand changes.<ref>[https://www.nationalgridus.com/niagaramohawk/non_html/eff_elec-demand.pdf "Understanding Electric Demand"] {{webarchive |url=https://web.archive.org/web/20160606043318/https://www.nationalgridus.com/niagaramohawk/non_html/eff_elec-demand.pdf |date=6 June 2016 }}, National Grid</ref> Industrial users may also have extra charges according to the [[power factor]] of their load.

Major energy production or consumption is often expressed as terawatt-hours (TWh) for a given period, often a [[calendar year]] or [[financial year]]. A 365-day year equals 8,760 hours, so one gigawatt sustained over a year corresponds to 8.76 terawatt-hours of energy. Conversely, one terawatt-hour is equal to the sustained power of about 114 megawatts for a period of one year.