If I had to give renewable energy a definition, I would say that it is based on inexhaustible resources, continuously renewed by nature. In other words, exploiting this energy does not lead to the extinction of its source.
Unlike non-renewable energy sources, such as fossil or nuclear power, renewable energies are distinguished by their capacity to renew themselves on a human scale, like crops or forests.
The use of energy from renewable sources is based on more or less developed sectors. It constitutes a significant challenge in the energy transition.
1. Solar as a renewable energy source
Solar energy comes from the Sun’s radiation. The use of solar energy makes it possible to produce electricity or heat.
How does solar energy work?
There are two ways to make the Sun a renewable energy source :
Photovoltaic solar energy
Solar thermal energy
1. This is electricity produced from solar panel installations. These photovoltaic panels are made up of cells that transform solar radiation into electric current. If electricity can be consumed at the place of production, it can also be reinjected into the electricity distribution network.
2. This corresponds to the heat produced by thermal collectors. Concretely, these sensors absorb solar radiation and heat a gas or a liquid, generally water. This energy is used to power, for example, domestic heating and domestic hot water.
2. Water as a renewable energy source
Hydraulic energy comes from exploiting water movements caused by the water cycle, itself caused by solar energy.
How does hydraulic power work?
Even before producing electricity, hydraulic energy is, above all mechanical. This is how water mills have been used to grind grain since Antiquity. They even found other applications later, notably with the swifts of the forges or the paper mills of the paper mills.
In hydroelectric power plants, this mechanical energy can be transformed into electrical energy. As it moves, the water activates turbines which produce electricity.
Water, as a renewable energy source, can be exploited in different ways:
Thanks to waterways;
Thanks to the waterfalls;
Thanks to sea currents;
Thanks to the waves;
Thanks to the difference in ocean temperatures,
And thanks to many other experimental techniques.
Hydroelectric energy from rivers
Like water mills, certain hydroelectric power stations exploit the power of rivers. Their power can, therefore, vary depending on weather conditions, for example, in case of heavy rain or drought. The current drives a turbine which sets in motion an alternator, a device which transforms this mechanical energy into electricity.
Hydroelectric energy from falling water
Other hydroelectric power stations exploit the energy from the height of the water’s fall. A dam forms what is called a reservoir lake. The water is then transported through pipes to turbines which activate an alternator capable of transforming this mechanical energy into electricity.
Hydroelectric energy from marine currents
Placed at the bottom of seas or rivers, a tidal turbine uses the power of currents to produce electricity a bit like wind turbines with the wind. The tidal turbines have a turbine, rotated by the current, which sets in motion an alternator and thus generates electricity.
Hydroelectric wave energy
Also called wave energy, wave energy generates electricity from waves. That is to say, the undulating movement that agitates the surface of the seas.
Do you know the articulated floating chain?
The articulated floating chain is the most advanced technique today for using waves to hydroelectric energy. The principle? A series of floats are placed perpendicular to the waves. We recover the energy at the joints using a pump that activates a turbine.
Hydroelectric energy from the difference in temperature of the oceans
The thermal energy of the seas also called tidal energy, is generated from the temperature difference between the heat of surface waters and the cold of deep waters oceans.
On one side, hot surface water is pumped to transform a fluid (generally ammonia) into steam. Under pressure, a turbine activates and allows the generator to produce electricity.
On the other side, deep cold water is pumped to cool the ammonia and return it to its liquid state before starting a new cycle.
Finally, note that many other techniques exist at the experimental stage. Note for example, the exploitation of hydroelectric energy resulting from the difference in salinity of the oceans.
3. Tides as a renewable energy source
This involves using the movement of the tides as a source of renewable energy. That is to say, the difference in the height of sea and ocean levels is caused by the gravitational forces of the Moon and the Sun.
How does tidal energy work?
While the first tidal mills date back to antiquity, current tidal power plants continue operating. They are located in estuaries, that is to say, where the tide enters the river.
Tidal power plants have a dam, which lets water through when the tide rises. This water is retained until the tide falls again. The movement of the water then activates turbines which produce electricity using a generator.
4. Wind as a renewable energy source
Wind energy involves harnessing winds as a source of renewable energy. Note that these winds are themselves caused by the Sun’s uneven heating of the air.
How does wind energy work?
Remember that wind energy is above all the kinetic energy of the wind. That is to say, the energy results from exploiting its movements’ force. And it is because it depends on the wind that it is considered an intermittent energy. It has been used since man used sailboats to travel.
Since ancient times, windmills have transformed this kinetic energy to benefit various agricultural mechanisms: pressing, grinding, irrigation, etc.
The wind generator device most used today to exploit this renewable energy source is the wind turbine: the wind activates blades, which set in motion an electricity generator.
We can distinguish different types of wind turbines:
Onshore and offshore wind turbines;
Horizontal axis and vertical axis wind turbines.
Onshore and offshore wind turbines
We can distinguish wind turbines installed on land, called onshore or onshore, from wind turbines installed at sea, called offshore.
Offshore wind turbines are installed more than 10 kilometers from the coast. They are more expensive and complex to install and maintain than onshore wind turbines. On the other hand, they benefit from more substantial and regular winds and therefore, better performance.
There are also floating offshore wind turbines. Installed further from the coast, they make it possible to exploit stronger winds despite deeper waters.
Horizontal-axis and vertical-axis wind turbines
The horizontal axis wind turbine is the most common model. It has an axis parallel to the direction of the wind and profiled blades placed perpendicular to it.
Other wind turbines have a vertical axis perpendicular to the direction of the wind. We distinguish:
The Darrieus wind turbines, with their spiral or parabolic blades;
THE Savonius wind turbines are composed of half-cylinders into which the wind rushes.
Rotating blade wind turbines, each edge of which is dynamically oriented about the direction of the wind.
5. Organic materials as a renewable energy source
Bioenergies come from the exploitation of biomass, that is, all organic matter of plant, animal, bacterial, or fungal origin (mushrooms). By extension, we speak of biomass to qualify these renewable energy sources.
How does biomass energy work?
To produce renewable biomass energy, the quantity of material exploited must be less than or equal to the amount of material generated. Depending on the organic materials and processes used, biomass can generate heat, electricity, biogas or even biofuels. There are 3 ways to use biomass as a renewable energy source:
Biomass energy from combustion;
Biogas from fermentation;
Biofuels from fermentation.
Biomass energy from combustion
With the discovery of fire, biomass energy from combustion constitutes the first energy source in History. Even today, wood is the most common fuel for generating heat, electricity or both in cogeneration. I am talking about energy wood and energy forestry. Solid biomass can also consist of agricultural residues (straw, bark, sawdust, etc.).
Biogas from fermentation
More complex, this process transforms plant matter or household waste into biogas.
These organic materials are placed in an environment deprived of oxygen. Under the action of micro-organisms, they are transformed into gas, mainly methane. We are also talking about mechanization. Once burned, this methane can generate heat, electricity or both, in cogeneration.
Biofuels from fermentation
Biofuels are liquid or gaseous fuels made from non-fossil organic materials. There is a biofuel sector and a biodiesel sector.
The biofuel sector transforms sugar beet, cereals or certain wine residues into alcohol by fermentation. We then obtain bioethanol.
The biodiesel consists of extracting oil from certain plants, such as rapeseed or sunflower. Once treated or even mixed with another product, this oil can be used as fuel. We then speak of biodiesel or diester.
6. Earth’s heat as a renewable energy source
Geothermal energy is harnessing the natural heat contained in the Earth’s soil as a renewable energy source. This heat comes from the disintegration of natural radioactive elements in the terrestrial globe.
How does geothermal energy work?
Man has always made use of hot water springs. Used directly for baths, they were then used for thermal baths and later the first heating networks.
Geothermal energy is based on a simple principle. The deeper you dig into the ground, the higher the released heat.
The idea then consists of recovering the water at depth or injecting water under pressure. This will be retrieved via a heat pump to produce electricity or heat before being reinjected in-depth and starting a new cycle.
To exploit this renewable energy source, geothermal power plants rely on different techniques depending on the drilling depth and temperature.
Very low-energy geothermal power plants
I also speak of superficial or very low-temperature geothermal energy. By drilling less than 200 m deep, very low-energy geothermal power plants can recover heat of less than 30°. Amplified by a heat pump, this energy can heat an individual house or a tertiary building.
Low-energy geothermal power plants
I also talk about low-temperature geothermal energy. The principle is the same, with the difference that drilling is carried out up to 2,500 m deep. The heat released is higher, up to 90°. It is particularly used for heating farms or district heating via heating networks.
High-energy geothermal power plants
I also talk about high-temperature geothermal energy. By exceeding 2,500 m of drilling, it can benefit from thermal energy at more than 150°. In addition to generating heat, the recovered water can be injected as steam into a turbine to generate electricity. Note that high-energy thermal power plants are mainly found in volcanic regions.