With the drought, will we still be able to make electricity with dams?

Alice, age 12, future headmistress of Hogwarts.

Not all the dams you see are designed to generate electricity; some are used to feed agriculture or regulate the flow of rivers. In France, dams thatgenerate electricity account for between 11 and 12% of the electricity produced, less than nuclear power but more than wind and solar power. On a global scale, hydropower is the world's leading source of carbon-free energy. It's called that because it doesn't emit CO2, even though carbon is produced during dam construction. Above all, these structures are a means of storing electricity: we store water because we don't know how to store electricity on a large scale under economic conditions.

There are three main types of dam: run-of-river dams, which provide continuous turbines on a river; lake dams, which have a large reservoir and can therefore be used for inter-seasonal storage; and pumped storage stations, which consist of two dams, one upstream and one downstream of a penstock. Water is pumped upstream at off-peak times, and electricity is generated at peak times by turbining water from the upstream dam. This optimizes the timing of electricity generation.

There is still considerable potential for hydroelectric production worldwide, but this potential remains limited in France. Global warming is likely to jeopardize the use of hydropower, not only because of the lack of water in rivers, but also because of reduced snowfall in mountain areas, as snowmelt is a major contributor to river flow. What's more, 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 power plants will tend to be built by the sea. Dams sometimes have to release water for irrigation purposes, particularly in summer. But the water released is no longer available in winter, which reduces electricity production.

Jacques Percebois - Professor Emeritus at the University of Montpellier.

An article in partnership with The Conversation website.