Renewable energies (RE) harness the power of the elements: air, wind, water and fire. There are 5 main types of renewable energy: wind, solar, hydraulic, geothermal and biomass. They are all, in principle, low-carbon.
The forces of nature are immeasurable: the sea, the wind, the sun… The power they generate is enormous. If only we could capture some of it… That’s exactly what renewable energies propose to do. The main sources of renewable energy are sun, wind,water, biomass and geothermal. There are only a few mature, commercially viable technologies (photovoltaics, wind power, dams and biomass), but many new ones are being developed.
Wind power
Wind power is a fast-growing, mature renewable energy source that is inspiring a greener, more sustainable future. According to the International Energy Agency (IEA), global wind power capacity increased by almost 225% between 2010 and 2020, from 198 GW to 733 GW. Onshore and offshore wind farms have become a key part of the global energy landscape, with countries such as China, the USA and Germany leading the way in terms of installed capacity.
Nevertheless, they face a number of specific problems: the difficulty of dismantling them (which involves high provisions or the risk of structures disappearing at the end of operation), and the mechanical action of wind turbine blades, which endanger nearby birds. Their operation and maintenance is also a challenge, which more and more projects are helping to meet.
Onshore wind power
The main problems with onshore wind turbines lie in their spatial use. Firstly, the siting of wind farms can give rise to local concerns about landscape aesthetics and visual degradation. In addition, wind turbines can generate noise pollution for residents of neighboring areas. Secondly, the large expanses of land required can lead to land-use conflicts with other human activities, such as agriculture or housing.
Offshore wind power
Offshore wind farms are less concerned by problems of neighborliness and land use: no one uses the areas where they are installed. There remains an aesthetic problem for coastal populations, but it’s less acute than for onshore wind power, which can have a real impact on local life. The main difficulty with offshore wind power… is the sea. These huge structures have to be built, made operable and connected to the mainland, all in the middle of a gigantic mass of corrosive water in constant motion.
Solar energy
Solar power is a renewable form of energy that draws its energy from the sun’s rays. There are two main technologies for harnessing solar energy: photovoltaic and solar thermal.
Photovoltaic solar energy
Photovoltaic solar energy consists of converting sunlight directly into electricity using photovoltaic (PV) cells, generally made of silicon. Photons from the sun strike the PV cells and generate an electrical voltage, creating a direct current (DC). This current is then converted into alternating current (AC) using an inverter for use in the electrical grid or to power electrical devices.
Solar thermal
Solar thermal energy uses the sun’s energy to heat a fluid, usually water or a mixture of water and antifreeze, which circulates through tubes placed in solar thermal collectors. This heat can then be used to produce domestic hot water, heating or even to power Rankine cycle power plants, where the heat is used to produce steam, which drives a turbine and generates electricity.
Hybrid solar
Hybrid solar power combines both solar and photovoltaic technologies to optimize production. The photovoltaic cells are better cooled, and the heat captured is valorized. By exploiting both the thermal and electrical aspects of solar energy, hybrid systems can offer better performance and overall efficiency, reducing costs and environmental impact.
Biomass energy
It’s possible to produce energy from biomass: wood, crop residues, organic household waste and so on. Biomass can be converted into energy by burning, but not only by burning. They can be transformed into methane by anaerobic digestion, or into hydrogen-rich synthesis gas by pyrogasification (see the hydrogen site). The main sources of biomass are wood, biogas and biofuels.
To grow, these materials have absorbed CO2, which they release when burned. The carbon balance is therefore neutral overall, unless their production and transport generate too much carbon. It is also possible to capture the carbon released by transforming biomass into energy, for example with carbon capture or, in the case of pyrogasification, the solidification of carbon in the form of biochar. Biomass thus becomes a carbon sink.
The main challenge with biomass is the sheer size of the area involved: huge areas need to be exploited to generate enough biomass to produce energy. You also need to be financially viable to exploit it, which is not always a given.
Hydropower
Hydropower, or hydroelectricity, now accounts for the bulk of the world’s renewable energy. Almost all of this energy comes from hydraulic dams, which harness the gravitational energy of water and mobilize it as needed. Nevertheless, new avenues are being developed, notably to harness energy from the sea: swell, tide and osmotic energy.
Gravity power
Gravity-fed hydropower, generally harnessed through hydroelectric dams, is a renewable energy source that harnesses the power of moving water to generate electricity. The operating principle is based on converting the potential energy of water held in a reservoir into kinetic energy, as it is released and flows through turbines. These turbines are coupled to generators that convert mechanical energy into electricity. Hydraulic dams are a proven and reliable solution for large-scale power generation, offering flexible management of electricity production according to need. More minor, but still notable:run-of-river hydropower is a renewable form of energy that harnesses the kinetic energy of rivers to generate electricity. The river’s flow rate determines the potential for energy production, which can be calculated using the head of water and the flow rate.
Pumped-storage power stations (P.S.T.P.s ), on the other hand, are storage systems and, while they do indeed produce hydroelectricity using gravity power, it is power that has previously been stored by consuming electricity, with a pump. So it’s a storage system, not a production system.
Wave energy
Wave energy is a renewable form of energy that harnesses the power of waves to generate electricity. This technology harnesses the kinetic energy of ocean surface movements, generated by the interaction between wind and water. Various wave-generating devices have been developed to capture this energy, such as oscillating water columns, point absorbers or attenuators. These devices are generally installed offshore, near the coast or in deep waters, and are connected to the terrestrial power grid via submarine cables. Wave energy offers significant potential for clean, sustainable power generation, with low visual and environmental impact. However, it is still at a relatively early stage of development and faces technological, economic and regulatory challenges.
Tidal energy
Tidal power harnesses the energy of the tides to generate electricity. It uses the gravitational force between the Earth, Moon and Sun, creating predictable water movements. Tidal power plants, using tidal dams, harness these movements by holding the water in basins and then letting it flow through turbines, producing electricity. This energy source is predictable, stable and reliable, but presents environmental challenges and high initial costs. Indeed, the construction of tidal dams and other infrastructure can alter marine currents, sedimentation levels and, overall, disrupt existing ecological balances. It is also not commercially viable.
Osmotic energy
Osmotic energy, also known as salt pressure gradient energy, is a renewable form of energy that harnesses the energy potential between fresh and salt water. This process uses a semi-permeable membrane that allows the passage of water, but not salt ions. When fresh and salt water are separated by this membrane, the fresh water naturally migrates towards the salt water to balance the salt concentration on either side. This flow of water across the membrane generates osmotic pressure, which can be converted into mechanical energy and then into electricity using turbines.
Osmotic energy offers interesting potential in terms of clean, sustainable energy production, particularly in areas where rivers meet the oceans. However, this technology is still in its infancy and must overcome challenges in terms of cost, efficiency and membrane durability to become economically viable and competitive on the energy market.
Geothermal energy
Geothermal energy is a renewable energy source that harnesses heat from the Earth’s interior. It is based on the extraction of heat stored in geothermal reservoirs, generally located near areas of tectonic or volcanic activity. Hot fluids, such as water or steam, are extracted from drilled wells and used to generate electricity or for direct heating applications.
For electricity generation, geothermal steam powers turbines that drive generators. Geothermal systems can be dry-steam, wet-steam or binary, depending on the temperature and nature of the fluids extracted.
Geothermal energy offers advantages such as continuous availability, low greenhouse gas emissions and reduced dependence on fossil fuels. However, it is limited by its geographical distribution and can present environmental challenges, such as water consumption, non-condensable gas emissions and the induction of micro-earthquakes during hydraulic fracturing.
Intermittency: the great challenge for renewable energies
The intermittency of renewable energies, such as solar and wind power, is a major problem, as their electricity production depends on weather conditions and the time of day. This variability creates challenges for balancing electricity supply and demand on the grid, making it difficult to guarantee a stable, reliable power supply at all times.
To overcome this problem, various solutions are being studied, such as energy storage, demand management, grid interconnection and the integration of complementary energy sources. Energy storage, for example with batteries or pumped storage systems, enables surplus electricity to be stored for later use. Demand-side management aims to adapt energy consumption