Renewable energies (hydraulic, solar, wind, geothermal and biomass) are developing intensely all over the world, driven by the need to combat global warming by reducing greenhouse gas emissions.
What is renewable energy?
Energy is said to be renewable when it is produced by a source that nature constantly renews, unlike energy that depends on depleting sources. Renewable energies are very diverse, but they all come from two main natural sources:
the Sun: it emits radiation that can be converted into electricity or heat, it generates areas of unequal temperature and pressure at the origin of the winds, it generates the water cycle, it allows plant growth and the generation of biomass;
the Earth, whose internal heat can be recovered from the surface.
The renewable nature of these energies, their low emissions of waste, pollutants and greenhouse gases are advantages. But their energy power, which is relatively scattered, is much lower than that of highly concentrated non-renewable energies. They can be – in the case of solar and wind energy – “intermittent” and difficult to store because they are immediately transformed into electricity, requiring the occasional contribution of other energies. Their use also requires heavy investment, even if they become increasingly competitive with fossil fuels over time.
What are the different types of renewable energies?
Hydropower from large dams is today the leading renewable energy source. China, Brazil, Canada, the United States, and perhaps Africa tomorrow, are the leaders in the sector.
Solar energy is produced in two forms: photovoltaic solar energy, which transforms the sun’s light radiation into electricity using panels made up of semiconductor cells, and thermal solar energy, which captures the sun’s heat and uses it as such or transforms it into mechanical energy and then into electricity.
Wind power, the energy of the wind, has progressed, both offshore and onshore, with technology steadily improving. The highest wind turbines reach 170 metres in height, with rotors over 150 metres in diameter!
The different types of marine energy used come from the force of waves, currents and tides, differences in ocean temperature and certain characteristics of the saltwater/freshwater couple (osmotic energy). They are still at an early stage of development.
Biomass consists of all organic matter of plant (including micro-algae), animal, bacterial or fungal (fungi) origin. For centuries, wood was the main source of energy through its combustion, before being replaced by coal and then oil and gas. But there are other forms of biomass use. Methanisation produces biogas from our household or agricultural waste. The refining of plant biomass allows the production of biofuels.
Geothermal energy uses the heat from underground aquifers, or even dry rocks, captured at varying depths, to supply urban districts, buildings or factories, or to produce electricity via power plants. Some countries with favourable geological conditions use it on a massive scale, such as Iceland and the Philippines, two volcanic countries. Heat from other sources can also be captured and used in networks or industrial processes.
Nuclear power is not considered a renewable energy as it is based on a limited raw material, at least at acceptable operating costs, uranium. Nuclear fusion, on the other hand, if carried out at an industrial stage, would provide an inexhaustible source of energy.