Where does energy come from?

There are different energy resources in the world and the amount of energy stored by them varies greatly. For example, the nuclear energy within 1 kg of uranium contains a very large amount of energy, but the gravitational potential energy stored by many thousands of tonnes of water held back by a dam contains less.

Renewable or non-renewable?

A renewable energy resource is one that is being (or can be) replenished as it is used.

Renewable resources are replenished either by:

  • human action, eg trees cut down for bio-fuel are replaced by planting new trees
  • natural processes, eg water let through a dam for hydroelectricity is replaced through the water cycle

A non-renewable energy resource is one with a finite amount. It will eventually run out when all reserves have been used up.

Different energy resources

Nine different energy resources, fossil fuels, nuclear, bio, wind, hydroelectric, geothermal, tides, sun, water waves; illustrated around a main label.

The table below shows the main features of the most common energy resources used today.

Energy resourceEnergy storeRenewable?UsesPower outputEnvironmental impact
Fossil fuels (oil, coal and natural gases)ChemicalNon-renewableTransport, heating, electricity generationHighReleases CO2 (causes global warming)
Nuclear fuelsNuclearNon-renewableElectricity generationVery highRadioactive waste (needs to be disposed of safely)
Bio-fuelChemicalRenewableTransport, heating, electricity generationMedium'Carbon neutral', so low impact
WindKineticRenewableElectricity generationVery lowTakes up large areas that could be used for farming, some people say windmills spoil the view
HydroelectricityGravitational potentialRenewableElectricity generationMediumLocal habitats are affected by the large areas that need to be flooded to build dams
GeothermalInternal (thermal)RenewableElectricity generation, heatingMediumVery low
TidesKineticRenewableElectricity generationPotentially very high, but hard to harnessTidal barrages can block sewage which needs to go out to sea
SunNuclearRenewableElectricity generation, heatingDependent on the weather and only available during daylightVery little
Water wavesKineticRenewableElectricity generationLowVery low

Comparing resources

Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy. These two types of station provide much of the country’s electricity. They operate almost continuously. When additional power is needed, gas 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, is reliable and predictable because of the Moon causing the tides and rainfall filling reservoirs. They 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.

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