What is Energy?
Energy is defined as the capacity of a system to do work. There are different types of energy (like thermal energy) but for simplicity, when this FAQ refers to energy we mean electrical energy.
You put electricity into a washing machine for a certain amount of time so that it can do work for you. To do a load of washing you will use a certain amount of energy. Energy is measured in watt hours (Wh) or kilowatt hours (kWh). Notice there is a time component with energy because energy is the product of time and power.
What is Power?
Power is the rate that the electricity is transferred. So when your washing machine is spinning it will use more power than when it is sitting in idle. It might use 1500W when it is spinning and 2W when it is sitting idle. Power is measured in watts (W) or kilowatts (kW). Notice there is no time component because power is instantaneous.
What is the Difference?
It is easiest to explain by thinking about a 10W light bulb. To power the light you need 10W. If you have that light on for 1 hour, the energy that the light uses is 10Wh. Or if you have it on for half an hour the energy that it uses is 5Wh.