Definition and classification of renewable energy


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Classification of renewable energy by C. Martz, ENSAIS engineer

The purpose of this file with multiple pages is to make a round-up of so-called renewable energy technologies with, for each, their advantages, disadvantages and limitations.

We will also try a delicate critique of current energy policies. But first a small definition.

Renewable energy is what?

as we consider renewable, sources of energy that renews itself quickly enough to be considered inexhaustible (hence its name) wide man but also in some cases of humanity (eg solar)!



Renewable energy is derived from constant or regular natural phenomena caused mainly by the Sun (solar but also hydro, wind and biomass ...), the moon (tidal, some currents: tidal energy ...) and Earth (deep geothermal ...).

Today, we often equate renewable energies with clean energies. This is not entirely true even if these energies are much less "dirty" than fossil fuels.

Indeed; renewable energy can also be put away from fossil fuelsWhich we now know, are not inexhaustible on a human scale. We will see in this folder as many links still unite fossil and renewable energy, at least from an economic point of view ...

Classification of renewable energy

Renewable energy can be divided into 3 basic categories: primary energy source:

  • A) direct solar: processes using direct solar radiation or light.
  • B) Indirect solar: the methods indirectly using the sun to provide another source of energy.
  • C) non-solar: not using sunlight (but can use the Sun's gravitational forces).

In all cases, the Sun is the basis of our energy source because without the sun, the Earth does not even exist in the group C). But Lackland no Serre either effect ... so do not quibble too ...

A) Details of direct solar energy:

B) Details of indirect solar energy:

  • Terrestrial biofuels : Plants use solar energy to grow and develop. There are several types of biofuels: those requiring "refining" and others. Exclusively from agriculture. More details.
  • Marine biofuels : Same remarks to terrestrial biofuels except that it is not algae and plants. They have a very strong development potential.More details.
  • Solid biomass : Primarily wood for heating but also some other fast growing plants (thistles in Spain for example).
  • Liquid biomass : Can be likened to biofuels in the final product but the process for obtaining is radically different. This is a liquefaction of a solid biomass fraction particular by the Fisher-Tropsch process. More details.
  • The gaseous biomass : Gasification of biomass: 2 known methods. Anaerobic digestion of waste ou wood gasification.The 1er process is more efficient than the latter.
  • Wind energy : without Sun, the wind does not exist. Probably the most "trendy" renewable energy but one of the least econo- mically efficient. This class includes the exploitation of wave energy.More details.
  • Hydraulic energy : Whatever its application (mechanical or electrical) hydropower would not exist without the water cycle from the sun. It's renewable energy the most exploited in the world.
  • Geothermal or aerothermal : Ie heat pumps. They capture their energy either in the ground or in the air. In 2 cases, it is the sun the primary source.
  • Muscle or animal power : That is to say the pull of muscles. This is obviously an indirect solar energy since energy comes from the food itself from the sun.

C) Details of non-solar energy:


  • The use of tides : Tidal power Rance.
  • Deep geothermal energy : Example of Soultz-sous-forests
  • The use of certain marine currents from tides (created by the action of the sun but also the Moon and the Earth rotation) by hyroliennes. More details.
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