Watt Is It? – Explaining How We Measure Energy

Within ZERO EMISSION WORLD, we do our best to keep the technical terms to a minimum. Unfortunately, when it comes to energy, some technical terms are just unavoidable. As such, to ensure you always know what we are talking about, here are some simple definitions for the various energy-related terms that we use.

Q1 // What is a Watt?

A watt, symbolised by W, measures the rate at which energy flows.1 An excellent way to picture this is by imagining a tap. The larger the tap, the faster the energy can flow out of it. An example of a device that has a low flow rate is an incandescent light bulb. This generally has a rating of around 100 watts. At a larger scale, a typical coal power plant has a high flow rate of around 500 million watts.2

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03 // The watt is named after James Watt (1736 -1819).3

Q2 // What is a Watt-hour?

A Watt-hour measures energy quantities and is symbolised by ‘Wh’. To calculate energy quantities, the flow rate is multiplied by the number of hours the device was used for.4 For example, a 100 Watt light bulb running for one hour uses 100 Watt-hours, whereas a 100 Watt light bulb running for ten hours uses 1,000 Watt-hours.

Q3 // How Much is a Kilowatt-hour?

One kilowatt-hour, symbolised by ‘kWh’, is equal to 1000 Watt-hours.5 For example, one standard 100 Watt light bulb running for ten hours consumes 1000 Watt-hours, or 1 kWh. This unit is typically used for larger amounts of energy such as domestic energy bills. For example, the average UK home will consume around 50 kWh per day.6

Q4 // How Much is a Megawatt Hour?

One megawatt-hour is 1,000 kilowatt-hours and is symbolised by MWh.7 For example, one 100 watt light bulb running for ten thousand hours consumes 1 MWh of energy. This unit is used for very large quantities of energy, such as a factory. For example, around 19 MWh of energy is required to make a car.8

One light bulb consumes around 100 Watt-hours of energy for each hour it is used.

Q5 // How Much is a Gigawatt Hour?

One gigawatt hour equals 1000 megawatts hours, and is symbolised by ‘GWh’.9 For example, one standard light bulb running for ten million hours consumes 1 GWh. This unit is used for even larger quantities of energy, such as the wind farm which can generate some 280 GWh per year.10

How Fossil Fuels Took Over the World

Now we know how to measure energy, we need to understand what made fossil fuels so popular and why we are still so reliant on them even today. To do this, simply select the link below. Alternatively, find out how we can stop using fossil fuels by returning to the main menu.

Image Credits

Title image created by Ase and reproduced under license from Shutterstock.

Image of James Watt painted by Carl Frederik von Breda and released into the public domain.

Image of light bulbs created by Tottem Torro and reproduced under license from Adobe Stock.

General Notes

For the total landmass of the UK, a figure of 248,532 square kilometres has been used. The figure has been sourced from UK Office for National Statistics – 'The UK and Its Countries: Facts and Figures' – www.ons.gov.uk.

Barrels of oil equivalent based on 1628.2 kWh of energy being contained within each barrel. Data sourced from Unit Juggler – 'Converter: Barrel of Oil Equivalent to Kilowatt-Hour' – unitjuggler.com.

Article Endnotes

  1. Union of Concerned Scientists – ‘How is Electricity Measured?’ – ucsusa.org.
  2. Union of Concerned Scientists – ‘Coal Generates 44% of Our Electricity and is the Single Biggest Polluter in the US’ – www.ucsusa.org.
  3. Lira, Carl – ‘Biography of James Watt’ – www.egr.msu.edu.
  4. Union of Concerned Scientists – ‘How is Electricity Measured?’ – ucsusa.org.
  5. Union of Concerned Scientists – ‘How is Electricity Measured?’ – ucsusa.org.
  6. Based on a UK home using an average 18,738 kWh of energy in 2014. Sourced from UK Department of Energy and Climate Change – ‘Energy Consumption in the UK’ – Page 7. 
  7. Union of Concerned Scientists – ‘How is Electricity Measured?’ – ucsusa.org.
  8. Ashby, Michael – ‘Materials and the Environment: Eco-Informed Material Choice’ – Page 214.
  9. Union of Concerned Scientists – ‘How is Electricity Measured?’ – ucsusa.org.
  10. Svenska Cellulosa Aktiebolaget – ‘New Wind Farm Inaugurated’ – www.sca.com.

The damage caused by climate change does not stop here. Find out what disasters our greenhouse gas emissions will likely cause in the next decade by clicking the link below. Alternatively, find out how we can stop climate change by returning to the main menu.

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