Energy is usually measured in joules (J). One joule of energy is transferred to a one watt device used for one second.
\(Energy~transferred = power \times time\)
\(E = P \times t\)
\(1~J = 1~W \times 1~s\)
However energy companies use a different unit called kilowatt hours (kWh).
Appliances are usually used for long periods of time so very large amounts of energy are transferred.
1 kWh is the amount of energy transferred to a 1kW appliance in 1 hour.
\(Energy~transferred = power \times time\)
\(1~kWh = 1~kW \times 1~h\)
