With droughts, will we still be able to generate electricity using dams?
Not all dams are built to generateelectricity; some are used to irrigate farmland or regulate river flow. In France, hydroelectric dams account for between 11% and 12% of the country’s electricity generation, far behind nuclear power but ahead of wind and solar power.
Jacques Percebois, University of Montpellier
Hydropower also supplies one-sixth of the world’s electricity, making it the world’s leading source of carbon-free energy. It is a form of energy that, in fact, emits noCO2 (even though carbon is produced during the construction of the facility) and, above all, it is a way to store electricity (water is stored because we do not yet know how to store electricity on a large scale in an economically viable manner). In this case, we refer to a dispatchable power plant because we can choose when to generate electricity.
There are three main types of dams: run-of-river dams, which generate electricity continuously from a river; reservoir dams, which have a large water storage capacity and thus allow for inter-seasonal storage; and pumped-storage plants, which consist of two dams, one upstream and the other 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 for the optimization of when electricity is generated. It is important to note that a dam’s electrical output is proportional to the head and the flow rate.
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.
In any case, global warming threatens to undermine the use of hydropower due to water shortages in rivers, as well as reduced snowfall in the mountains, since snowmelt is a major contributor to river flow.
It is estimated that this warming could reduce the flow of major rivers by about 20% in the coming decades; however, the impacts will vary from region to region. Taking the Rhône as an example, its flow (and likely that of other rivers) is estimated to have decreased by 6% to 7% over the past 50 years, and the closer the river gets to its mouth, the more its flow decreases.
According to the French Electricity Transmission Network (RTE), hydroelectric generation 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 is why new plants are typically built near the coast. Dams sometimes have to release water to allow for irrigation, especially in the summer. But the water released is then no longer available in the 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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