Gravity power: the weight of water
Mainstream hydropower: dams
Hydroelectric dams are a major source of renewable energy (the main one, to be precise), harnessing the potential energy of water to generate electricity. They are found all over the world, with countries such as China, Brazil, the USA, Canada and Russia home to some of the largest dams. The most notable include the Three Gorges Dam in China, the Itaipu Dam between Brazil and Paraguay, the Hoover Dam in the USA, the James Bay Complex in Canada and the Saiano-Shushensk Dam in Russia.
The potential energy contained in a dam is calculated using the formula E = mghη, where E is the potential energy, m the mass of water, g the acceleration due to gravity, h the average head of water and η the efficiency of the system. Hydroelectric dams can have power generation capacities ranging from a few megawatts to gigawatts, depending on their size and head of water. Dams offer benefits such as the production of renewable energy, the regulation of water flows and the creation of reservoirs for irrigation and water supply. However, they can also have significant environmental and social impacts, such as altering ecosystems and displacing local populations.
Run-of-river power plants
Run-of-river hydropower is a renewable form of energy that harnesses the kinetic energy of rivers to generate electricity. The flow of the river determines the potential for energy production, which can be calculated using the head of water and the flow rate.
The advantages of this form of hydropower include reduced environmental impact compared with large dams, installation flexibility and decentralized power generation potential. However, disadvantages include less constant energy production, dependence on weather conditions and potential limited by the availability of suitable sites.
Run-of-river hydropower is present in many countries, including the USA, Canada, Germany, France, Norway, Brazil and China. Installations vary in size and capacity, from a few megawatts to several thousand megawatts. Run-of-river power generation fluctuates according to weather conditions and seasonal variations in river flow.
What about STEPs?
Pumped-storage power stations (P.S.T.P.s ) are facilities for storing electricity: water is pumped into a reservoir high up to store energy, then allowed to flow back down and release its gravitational energy, like a dam. This is a form of electricity storage, not generation (although it’s often lumped together in statistics), so I’ll talk about it in the section on electricity storage.
New hydropower sources
New hydraulic energies are being mobilized to extend the possibilities of generating electricity from the movement of water. In particular, we’re mobilizing three forces that may seem similar, but are fundamentally different: the tide, the current and the swell.
Tidal energy: the power of the tide
The tide is the periodic rise and fall of the oceans caused by the gravitational forces of the Moon and Sun on the Earth.Tidal power harnesses these variations in sea level to drive turbines and generate electricity.
Tidal power plants operate by building a dam at the mouth of estuaries to hold back water from the rising tide and create a reservoir. When the tide goes out, the water is released through turbines, producing electricity by converting the water’s kinetic energy into mechanical energy.
The International Energy Agency estimates that the global potential of tidal power is around 1,200 TWh per year, or 4% of global electricity consumption. However, this potential is largely untapped due to technical, environmental and economic challenges. Initial investment and installation costs are high, and the potential environmental impact of installations on marine ecosystems must be taken into account and minimized.
Despite these challenges, tidal power offers considerable potential for diversifying the energy mix and contributing to the transition to cleaner, more sustainable power generation. Successful examples of tidal power plants, such as La Rance in France and Sihwa in South Korea, are promising.
A tidal turbine will be installed off the UK coast in 2021.
Wave energy: the power of the swell
Wave power is a renewable energy source that harnesses the movement of waves to generate electricity. This technology offers a number of advantages, including its constant availability and predictability, as well as its ability to reduce dependence on fossil fuels and cut greenhouse gas emissions. However, it must overcome certain challenges, such as environmental impacts, high development and installation costs, and grid integration constraints.
Several types of wave technology are currently under development, including articulated floats, submerged devices, buoys and oscillating water columns. Possible applications of wave energy range from electricity generation to water desalination.
Notable wave power projects include Scotland’s Pelamis Wave Power, which uses articulated floats to convert wave energy into electricity; Finland’s WaveRoller, which harnesses the rocking motion of waves to drive a submerged turbine; the Australian CETO project, which uses submerged buoys to pump high-pressure seawater to onshore turbines; the Scottish Oyster project, which captures wave energy at the surface using a flexible membrane; and the Mutriku wave power plant in Spain, which uses oscillating water column technology. In 2021, a 2MW wave power plant was announced for Brittany.
Tidal turbines: marine currents
[I need to check whether the marine current is really an autonomous form of energy, and not simply the result of tides, swells and the like]
Marine currents are movements of water in the oceans and seas, influenced by various factors such as winds, temperature and salinity. The energy of ocean currents is harnessed by submerged turbines that use the force of the current to generate electricity.
Osmotic energy or salt pressure gradient energy
Osmotic energy is a renewable energy source that exploits the chemical potential created by the difference in salt concentration between two solutions. These are often freshwater and seawater, which meet at river mouths. This energy can be used to generate electricity, desalinate seawater, store energy, irrigate farmland and treat wastewater.
Electricity is generated by passing water through a semi-permeable membrane, creating osmotic pressure which drives the rotation of a turbine. Desalination can be combined with other technologies, such as reverse osmosis or electrodialysis. Osmotic energy can also be used to store energy in the form of freshwater and concentrated saltwater.
In agriculture, osmotic energy can be used for irrigation, by mixing salt water with fresh water to create a solution with a lower salt concentration. Finally, osmotic energy can facilitate wastewater treatment by separating contaminants through direct osmosis.
Further research and technological improvements are needed to optimize the efficiency and cost-effectiveness of osmotic energy, but its potential in various fields is promising.
Marine thermal energy (MTE)
Marine thermal energy(MTE) is a renewable energy source that exploits the temperature difference between warm surface waters and cold deep waters in the oceans. This technology mainly uses closed and open cycles to generate electricity. Tidal energy has significant energy potential and can provide continuous energy production, unlike intermittent sources such as solar and wind power.
However, the exploitation of tidal energy is limited to regions where the temperature difference is sufficiently large, generally in tropical and equatorial zones. Existing projects and facilities include Georges Claude in France, Jules Verne in Martinique, and Makai Ocean Engineering in Hawaii. The construction and maintenance costs of tidal-thermal power plants can be high, but could fall as technologies improve and the scale of production increases.
The advantages of tidal energy include its low environmental impact and the possibility of using it for ecological air conditioning. However, technological, economic and environmental challenges need to be overcome to fully exploit this energy source on a large scale.
- On the immaturity of wave energy: https://twitter.com/TristanKamin/status/1483135827546972160