Renewable energy defined, with examples of sources

Some energy sources exist infinitely in nature; they can never be depleted, for example sunlight and wind.

They are regarded as renewable energy (“green energy”). Other sources have finite amounts: they were formed over millions of years and will run out eventually, for example coal and crude oil. These sources are regarded as non-renewable energy.

Energy is renewable if it meets the following requirements:

  • Its sources cannot run out (e.g. the sun) or can be easily replaced (e.g. new vegetation being planted).
  • Its sources are carbon neutral, thus do not produce carbon compounds (e.g. greenhouse gases) when consumed.
  • Its sources do not pollute the environment (air, land or water).

Renewable energy, which can be converted into electricity, comes from the following sources:


Biomass is any organic matter of recently living plant or animal origin, such as wood products, dried vegetation, crop residues, aquatic plants and even garbage. Biomass decomposition creates energy.

Wind energy

Wind turns the blades of wind turbines, spinning a shaft connected to a generator, thus creating electricity.


Falling water is channelled through water turbines, and the pressure of the water on the blades drives an electrical generator.

Ocean energy

This can be classified as:

  • Wave energy – generated by converting the energy of waves into electricity
  • Tidal energy – generated from tidal movements, which include the vertical fluctuations in sea level and the horizontal movements of the water
  • Ocean thermal energy – generated by converting the temperature difference between surface and deep water into energy

Geothermal energy

Heat flows upwards from the molten rock deep below the surface of the earth. Hot water circulating among subsurface rocks can be extracted, or cold water can be pumped into the hot rocks and the heated water can then be used to drive steam turbines to generate electricity.

Solar energy

The heat of the sun is harnessed through:

  • Solar thermal systems, which convert sunlight into thermal energy (heat)
  • Solar photovoltaic systems, which convert sunlight directly into electricity

Unless the sun dies, winds stop, plants die and rivers stop running, there will always be green energy to be had. Some of these energy sources are completely free and we have them no matter what. Why not take advantage of them?

– Edgar Cervantes

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