Definition of Watt-Hour (Wh)
Watt-hour (Wh) is a unit of energy equal to 3,600 joules. It is equal to the rate of energy conversion of 1 watt operating for one hour.
Watt vs Watt-Hour
A watt is a unit of power, while a watt-hour is a unit of energy.
Watt refers to the amount of energy a device needs in order to function. It is equivalent to the electricity flowing at a rate of one joule per second.
Watt-hour, on the other hand, measures the amount of work generated by an appliance. It calculates the total energy consumed by an electrical device or appliance over a period of time. It indicates how many watts are used in one hour.
In short, watts measure power while watt-hours measure energy.
While watt is considered the SI unit of power, energy consumption is usually measured in kilowatt-hours for a typical household since most appliances consume more energy. Terawatt-hours may also be used for larger entities such as business establishments or in measuring consumption for the country as a whole.
For example, electricity consumption in the United States reached a total of 4,010 terawatt-hours in 2022. This is approximately equal to 4.01e+15 watt-hours (Wh).
Calculating Watt-Hour
In order to calculate the number of watt-hours consumed per device, determine the wattage rating and multiply it by the time used per day.
The energy (E) in watt-hour (Wh) is equal to the power (P) in watts multiplied by the time period (t) in hours (h).
Hence, watt-hour is simply watts times hours.
Example
If an air conditioner has a rating of 1,000 watts and is used for 4 hours in one day then it consumes 4,000 watt-hours in that period.
Watt-hour = watts x hours
= 1,000 x 4
= 4,000
Converting Watt-Hour to Watt
To convert watt-hours to watts, simply divide the energy (E) in watt-hours by the time period (t) in hours (h).
Hence, a watt is simply watt-hours divided by hours.
Example
Calculate the power consumption in watts if energy consumption is 20 watt-hour for a duration of 2 hours.
Watt = watt-hour / hours
Watt = 20/2
Watt = 10
FAQs
1. What is a kWh?
A kWh (kilowatt-hour) is equal to the consumption of 1 kW per hour. It can also be defined as 1000 watts for an illumination period of 1 hour. The symbol k stands for 'kilo' or thousand.
2. What are some examples of appliances that use kilowatt-hours?
Some examples of appliances that use kilowatt-hours are electric stoves, ovens, and dishwashers.
3. What does the SI unit mean?
SI unit means 'The International System of Units.' It is the most widely used system of units for measuring physical quantities. It is also called the 'Metric System'.
4. What is a joule?
Joule is the International System unit of energy and work. It is defined as the work done by a force of one newton to move an object through a distance of one meter.
5. What is the difference between power and energy?
Power is the rate at which energy is produced. It is measured in watts. Energy refers to the capacity to do work such as heating, lighting, and moving.
