Kilowatt-hour (kWh)
The unit of energy on electricity bills and many gas bills: one kilowatt-hour is the energy used by something drawing one kilowatt of power for one hour.
Photo: Sebastian Scholz (Nuki) / Unsplash
Kilowatts (kW) measure power, how fast a device uses energy at a given moment; kilowatt-hours (kWh) measure energy, how much it used over time. A 2 kW electric heater left on for three hours uses 6 kWh; a 10-watt LED bulb needs 100 hours to use one kWh. Bills charge per kWh, while the power limit in a contract, where there is one, is in kW. One kWh equals 3.6 megajoules (1,000 watts for 3,600 seconds).
A smart meter records the kWh you use at intervals, which makes a time-of-use tariff possible. In Great Britain the gas unit rate is already per kWh, as in the Ofgem price cap tables. Italian bills count gas in standard cubic meters (Smc): with the conventional value ARERA uses in offers, 0.03852 GJ per Smc, one Smc is about 10.7 kWh.
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