The global demand for energy is continually increasing. Our population is growing even though we already have more people on the planet than ever before.
As well as this, modern lifestyles demand transport and communications technology, which also require more energy.
This raises issues about the availability of energy sources and the environmental effects of using them.
Primary and secondary sources
A primary source of energy is one that occurs naturally.
Fossil fuels (coal, oil and gas), biofuels, wind, waves, solar radiation and nuclear fuels are all primary sources of energy.
A secondary energy source is one that is made using a primary resource. Electricity is secondary resource, and can be generated by a number of different primary sources.