Electrical energy is the amount of electricity generated, delivered or consumed over a period of time, and is measured in watt hours.

The amount of electrical energy is calculated by multiplying the amount of electrical power by the hours over which the electricity was generated, delivered or consumed.

As an example, BC Hydro’s Site C dam is expected to generate 5,100 GWh of electrical energy over the course of a year.

At the household level, BC Hydro reports its average household customer consumes approximately 10,000 kWh per year.

This illustration explains the key concepts of electricity.

Watt hours

The common multiples are:

Multiple	Name	Symbol
1	watt hour	Wh
1,000	kilowatt hour	kWh
1,000,000	megawatt hour	MWh
1,000,000,000	gigawatt hour	GWh
1,000,000,000,000	terawatt hour	TWh
1,000,000,000,000,000	petawatt hour	PWh
1,000,0000,000,000,000,000	exawatt hour	EWa

Conversion to joules

Watt hours can be converted to joules (an alternative unit of energy) as follows:

1 watt hour = 3,600 joules

And conversely:

1 joule = 0.000278 watt hours (to six decimal places)