There are different energy resources in the world and the amount of energy stored by them varies greatly. For example, the energy within 1 kg of naturally occurring uranium contains the same amount of energy as 14,000 kg of coal.
Renewable resources are replenished either by:
A non-renewable energy resource is one with a finite amount. It will eventually run out when all reserves have been used up.
The table below shows the main features of the most common energy resources used today.
|Energy resource||Energy store||Renewable or non-renewable||Uses||Power output||Impact on environment|
|Fossil fuels (oil, coal and natural gases)||Chemical||Non-renewable||Transport, heating, electricity generation||High||Releases CO2 (causes global warming).|
|Nuclear fuels||Nuclear||Non-renewable||Electricity generation||Very high||Radioactive waste (needs to be disposed of safely).|
|Bio-fuel||Chemical||Renewable||Transport, heating, electricity generation||Medium||'Carbon neutral' so low impact. Although growing biofuels can take up land that could be used for farming.|
|Wind||Kinetic||Renewable||Electricity generation||Very low||Take up large areas that could be used for farming. Some people say wind turbines spoil the view and kill birds.|
|Hydroelectricity||Gravitational potential||Renewable||Electricity generation||Medium||Local habitats are affected by the large areas that need to be flooded to build dams.|
|Geothermal||Internal (thermal)||Renewable||Electricity generation and heating||Medium||Very low.|
|Tides||Kinetic||Renewable||Electricity generation||Potentially very high, but hard to harness||Tidal barrages can block sewage which needs to go out to sea.|
|Sun||Nuclear||Renewable||Electricity generation and heating||Dependent on the weather and only available during daylight||Very little.|
|Water waves||Kinetic||Renewable||Electricity generation||Low||Very low.|
Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy. These two types of stations provide most of the country's electricity. They operate almost continuously. When additional power is needed, gas power stations or hydroelectric power stations are usually used because they will come on very quickly and start generating electricity almost immediately.
The fuel for nuclear power stations is relatively cheap but the power stations themselves are expensive to build. It is also very expensive to dismantle, or decommission, old nuclear power stations at the end of their useful life and the highly radioactive waste needs to be stored for millions of years before the natural activity will reduce to a safe level.
Water power, eg tidal and hydroelectricity, are reliable and predictable because of the Moon causing the tides and rainfall filling reservoirs. These two can also be used to supply additional demand. But many of the renewable sources are unreliable, including wind and solar energy, and cannot respond to increased demand - sunny and windy weather cannot be guaranteed.
Renewable resources have no fuel costs, but the equipment used is expensive to build.
Generators in a power stations produce electricity when a coil of wire is in a changing magnetic field. This changing magnetic field is caused by spinning a magnet inside the coil.
Fossil fuel and nuclear power stations use the energy store to heat water and produce steam to turn a turbine which is connected to the magnet, causing it to spin.
Other energy sources are directly linked to the generator.