Question

Where we use unit of energy in joules and where we use unit of energy in kilowatthour??

Answer 1

The kilowatt-hour (symbolized kW⋅h) is a unit of energy equivalent to onekilowatt (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.
So kWh is unit of power consumed in an hour, it is used for commercial proposes like measuring the amount of power that you have used in the month(check your electricity bill).
The unit of power is Watt and power is energy over time i.e. J/s. And J is the unit of energy.