Where does energy come from?

The sun is the main source of energy on earth.

Throughout human history the sun has risen every day and filled the earth with light and warmth. Scientists expect the sun to continue shining for billions of years.

As this is such a long time, we can describe the sun as a renewable form of energy.

The sun’s energy is needed for plants to make their own food using photosynthesis.

Plants are an important part of the food chain supplying food and energy to other living things. Plants also provide energy in the form of fuel. This may be firewood (biomass) or fossil fuel.

Fossil fuels are not in endless supply and nature does not replace them as fast as humans now use them. For instance, it takes 400 years to create the amount of coal the world now uses in just one year.

Because this energy takes such a long time to be replaced, we describe this type of energy as non-renewable.

How is energy measured?

The basic unit of measurement for energy used to the joule.

To measure large amounts of energy such as the output of a powerhouse we need larger units:

• 1 megajoule (MJ) = 1 million joules (1,000,000)
• 1 gigajoule (GL) = 1 thousand megajoules (1,000,000,000)
• 1 petajoule (PJ) = 1 million gigajoules (1,000,000,000,000,000)

Crazy facts

It takes approximately one megajoule to boil enough hot water for 14 cups of tea.

58 petajoules of hydroelectricity was produced in Australia in 2004. That’s enough energy to make 14,000,000,000 cups of tea!