With droughts, will we still be able to generate electricity with dams?
Not all dams are designed to generateelectricity; some are used to supply agriculture or regulate river flow. Dams that generate electricity account for between 11 and 12% of the electricity produced in France, far behind nuclear power but ahead of wind and solar power.
Jacques Percebois, University of Montpellier
Hydropower also provides one-sixth of the world's electricity, making it the world's leading source of carbon-free energy. It is an energy source that does not emitCO2 (even though carbon is produced during the construction of the building) and, above all, it is a means of storing electricity (water is stored because it is not possible to store electricity on a large scale in an economical way). In this case, we refer to it as a controllable power plant because we can choose when to generate electricity.
There are three main types of dams: run-of-river dams, which continuously generate electricity on a river; lake dams, which have a large water reservoir and therefore allow for inter-seasonal storage; and pumped storage plants, which consist of two dams, one upstream and one downstream of a penstock. Water is pumped from downstream to upstream during off-peak hours and electricity is generated during peak hours by turbining the water from the upstream dam. This allows the timing of electricity generation to be optimized. It should be noted that the electrical power of a dam is proportional to the head and the turbined flow.
There is still significant potential for hydroelectric power generation worldwide, but this potential remains limited in France. It is difficult to build new dams for environmental reasons (preservation of biodiversity), but we can hope to increase the potential of existing dams through new investments.
Global warming is likely to compromise the use of hydroelectricity due to the lack of water in rivers, but also because of reduced snowfall in the mountains, as melting snow greatly increases river flow.
It is estimated that this warming could reduce the flow of major rivers by around 20% in the coming decades; however, the impacts will vary from region to region. Taking the Rhône as an example, its flow (and therefore probably that of other rivers) is estimated to have decreased by 6% to 7% in 50 years, with the flow decreasing the closer the river gets to its mouth.
According to Réseau de transport d’électricité (RTE), hydroelectric production was down 35% in July 2022 compared to July 2021.
Furthermore, competition between energy and agricultural uses is likely to intensify if water becomes scarcer. River water is also used to cool nuclear power plants, which explains why new plants are more likely to be built on the coast. Dams sometimes have to release water for irrigation, especially in summer. But the water released is then no longer available in winter, which reduces electricity production.
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Jacques Percebois, Professor Emeritus at the University of Montpellier, researcher at the CNRS Art-Dev joint research unit, University of Montpellier
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