Unlike nonrenewable energies, renewable energy resources are characterized by the fact that they are inexhaustible and available in large quantities subject to giving themselves the means to exploit them.
For example, wood energy is a renewable energy because the exploitation of a forest, if it is managed sustainably and regenerated after selective felling, provides a raw material (wood energy) while allowing the resource to reconstruct on the scale of a human generation.
Apart from the fact that they are inexhaustible, renewable energies also have another big advantage: they emit little or no greenhouse gases unlike fossil fuels.
Their development remains marginal, however, as they represent only 13.5% of world demand for primary energy.
Types of renewable energy
1- Hydroelectric Energy
It represents 2% of the world’s primary energy demand.
By means of turbines of variable power, placed on reservoirs or dams, the hydraulic power of rivers and streams is transformed into electricity injected into the networks.
2- Solar Energy
It represents less than 0.5% of world demand for primary energy. Solar energy can be transformed into thermal energy (heat): we speak of thermal solar or into electrical energy: we then speak of photovoltaic solar.
In the case of thermal solar, the solar radiation heats a heat-transfer fluid which itself will transfer its heat to a hot source (for example a domestic hot water tank or the water of the central heating of a dwelling).
In the case of photovoltaic solar, solar radiation is converted into electricity via sensors of the semiconductor type. The electricity produced is then used directly on site, stored in batteries or injected into an electricity network.
3- Geothermal energy
It represents less than 0.5% of world demand for primary energy. The principle of geothermal energy consists in capturing either the heat of the ground thanks to probes in which circulates a heat transfer fluid, or the heat of a layer of hot underground water.
By recovering the energy of the heat transfer fluid by means of a heat pump, or directly the heat contained in the underground water table, it is possible to supply an industrial process, to heat an installation, a dwelling or to produce electricity.
4- Wind power energy
It represents less than 0.5% of world demand for primary energy. This energy production requires the construction of wind turbines. The rotation of these converts the mechanical energy of the wind into electricity.
There are small wind turbines for reduced electricity requirements as well as large wind turbines which feed the current produced into an electricity network.
5- Biomass and waste energy
They represent 11% of the world’s primary energy demand. Biomass brings together different forms of organic matter (wood, straw, reeds, etc.) from which it is possible to produce energy. These organic materials can be burned (like wood chips in an industrial boiler room or firewood in an insert) to produce heat and / or electricity. They can be methanised (anaerobic degradation process of organic matter) to produce biogas which, itself burned, will produce heat and / or electricity. They can also be used for the preparation of biofuels for vehicles.
Regarding waste, it is burned in incinerators that produce energy and / or electricity. It is also possible to capture the biogas resulting from the degradation of household waste contained in a landfill to burn it in order to produce heat and / or electricity.