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Renewable energy

Renewable energy

Renewable energies (sometimes abbreviated EnR ) are sources of energy whose natural renewal is fast enough for them to be considered inexhaustible on a human time scale. They come from cyclical or constant natural phenomena induced by the stars  : the Sun mainly for the heat and light it produces, but also the attraction of the Moon ( tides ) and the heat generated by the Earth ( geothermal energy ).). Their renewable character depends on the one hand on the speed at which the source is consumed, and on the other hand on the speed at which it is renewed.

The expression “renewable energy” is the short and usual form of the expressions “renewable energy sources” or “energy of renewable origin”, which are more correct from a physical point of view .

The share of renewable energies in global final energy consumption was estimated in 2018 at 17.9%, including 6.9% of traditional biomass ( wood , agricultural waste ,  etc. ) and 11.0% of renewable energies " plants”: 4.3% of heat produced by thermal renewable energies (biomass, geothermal, solar ), 3.6% from hydroelectricity , 2.1% for other electric renewables ( wind , solar , geothermal, biomass, biogas ) and 1% for biofuels ; their share in electricity production was estimated in 2018 at 26.4%.

Intermittent renewable energies cannot modulate their production according to electricity demand . In the absence of large-scale energy storage , they must therefore be coupled with rapidly modulating electricity sources , such as those operating with a fossil fuel ( coal or gas- fired power stations ), hydroelectric energy or nuclear energy .

Definition elements 

The Sun is the main source of different forms of renewable energy: solar radiation is the energy vector for transporting usable energy (directly or indirectly) during photosynthesis , or in the water cycle (which allows ' hydroelectricity ) and the energy of the waves , the difference in temperature between the surface waters and the deep waters of the oceans ( thermal energy of the seas ) or even the ionic diffusion caused by the arrival of fresh water in the sea water ( osmotic energy). This solar energy, combined with the rotation of the Earth , is at the origin of the winds ( wind energy ) and marine currents ( tidal turbine ).

The Earth's internal heat ( geothermal ) is equated with a form of renewable energy, and the Earth-Moon system generates the tides of the oceans and seas allowing the development of tidal energy .

Solar energy like the internal heat of the Earth come from nuclear reactions ( nuclear fusion in the case of the Sun, nuclear fission in that of the internal heat of the Earth).

Fossil fuels and minerals ( fissile isotopes ) are not renewable energy sources, resources being consumed at a rate far greater than the rate at which they are naturally created or available.

The expression “renewable and recovered energies” (Renewable and R&R) is sometimes used when we add to renewable energies the recovery of the heat produced by various productive activities 1 .


For most of its history, humanity has had only renewable energies to cover its energy needs. In the Paleolithic , the only energies available were human muscle power and usable biomass energy through fire  ; but many advances have made it possible to use these energies with increasing efficiency (inventions of increasingly efficient tools).

The most significant advancement was the invention of animal traction , which came later than the domestication of animals. It is estimated that man began to hitch  cattle  to ploughs or wheeled vehicles during the 4th millennium BC. These techniques , invented in the former Fertile Crescent or in Ukraine , subsequently experienced worldwide development 2 .

The invention of the sailboat was an important step forward for the development of trade in the world.

That of water and windmills also brought considerable additional energy. Fernand Braudel describes as "the first mechanical revolution" the gradual introduction, from the 11th  century to the 13th century , of water and  windmills: "these 'primary engines' are undoubtedly of modest power, from 2  to 5  hp n 1for a water wheel, sometimes five, at most ten for the blades of a windmill. But, in a power-poor economy, they represent a considerable power boost. Older, the water mill is much more important than the wind turbine. It does not depend on the irregularities of the wind, but on the water, which is basically less capricious. It is more widely diffused, because of its age, the multiplicity of rivers and streams,...” 3 .

At the end of the 18th century  , on the eve of the industrial revolution , almost all of humanity's energy needs were still supplied by renewable energies. In an attempt to assess the distribution of consumption by energy source , Fernand Braudel estimates the share of animal traction at more than 50%, about 25% that of wood, 10 to 15% that of water mills, 5 % that of human power and a little more than 1% that of the wind for the merchant navy; he renounces quantifying the part of the windmills, for lack of data, while specifying:“Wind turbines, fewer in number than waterwheels, can only represent a quarter or a third of the power of controlled waters” 3 . We can therefore evaluate the total share of wind energy (sailing + windmills) between 3 and 5%. For the record, he mentions river shipping, the navy, charcoal and earth.

The appearance of the steam engine , then of the Diesel engine , led to the decline of water mills and wind energy in the 19th  century; water and windmills have disappeared, replaced by industrial mills . Hydraulic energy experienced a new golden age with hydroelectricity, which appeared in Switzerland, Italy, France and the United States at the end of the 19th century  .

In the 19th  century, François de Larderel developed techniques for using geothermal energy in Italy .

In the 1910s, the first individual solar water heaters appeared in California. In 1911, the first geothermal power station was built in Larderello .

In the middle of the 20th  century, wind energy was only used for pleasure boating and for pumping (agriculture, polders) .

Then, wind turbines reappeared, benefiting from more efficient techniques from aviation; their development gained momentum from the 1990s. Solar thermal and photovoltaic solar developed in the early 2000s. Under the effect of technological progress and economies of scale linked to the growing volumes installed, the sectors of renewable energy production, still emerging in the early 2000s, are seeing their costs evolve rapidly.

Since the end of the 20th century, in response to the onset of oil scarcity, to the negative climatic and health impacts of carbon energies 6 , as well as to the nuclear accidents at Chernobyl 7 and Fukushima 8 , 9 , 10 , 11 and controversies over the treatment of radioactive waste from the nuclear industry 7, 9 , 12 , a worldwide reorientation towards renewable energies has been observed 13.