• Energy cannot be created or destroyed; it can be transferred from one form into another.
• Electricity generation requires a source of energy.
• Almost all of our energy comes initially from the Sun. The exceptions are geothermal energy, energy from nuclear fission and tidal energy. The Sun’s energy comes from nuclear fusion.
• Fossil fuels (coal, oil and gas) are currently the main source of energy used worldwide. The chemical energy in fossil fuels can be used to produce electricity.
• Fossil fuels are formed from the very highly compressed remains of dead plants and animals that lived many millions of years ago. Fossil fuel reserves will eventually run out. They are a finite or non-renewable resource.
• Energy sources are renewable or non-renewable:
  

  Renewable

  waves

  solar

  tidal

  wind

  hydroelectric

  geothermal

  Non-renewable

  oil

  coal

  gas

  uranium (nuclear fission)

Nuclear fission and nuclear fusion

• Nuclear fission, which occurs in nuclear power stations, is the process in which large nuclei like uranium split into smaller ones, releasing an enormous quantity of energy.
• Nuclear fusion, which occurs in the Sun, is the process in which two small nuclei combine to form a larger one, again releasing a huge amount of energy. When hydrogen atoms within stars combine to form helium the process is called fusion (see page 235).