6.7 Hydroelectric power

Water power is another energy source that has been harnessed for many centuries for pumping, milling corn and driving machinery. The original source of this water flow is solar energy, warming the world’s oceans and causing evaporation. In the atmosphere, this forms clouds of moisture which eventually fall back to Earth in the form of rain or snow. The water then flows down through streams and rivers, where its energy can be harnessed using water wheels or turbines to generate power. Since the beginning of the 20th century, its main use has been in the generation of hydroelectric power. Its use has grown, in 2023 globally supplying about 14% of the world’s electricity (Energy Institute, 2024).

When harnessed on a small scale, hydroelectric plants create few adverse environmental impacts. However, many installations have been built on an enormous scale, for example the world’s largest scheme, the 22.5 gigawatt Three Gorges Dam in China. Such schemes have involved the building of massive dams and the flooding of extremely large areas of land. This particular scheme has required the relocation of 2 million people and considerable disturbance to the fish population in the river. The flooding can also result in methane emissions from rotting vegetation, meaning that hydro power is not a totally ‘climate friendly’ technology.

What of the future? The world’s hydro resource is estimated to be about four times current hydroelectricity production. However, developing this potential may not be easy. For example, the construction of large dams on rivers where they flow from one country to another can give rise to international disputes over rights to water.

The International Energy Agency’s ‘Net Zero by 2050’ scenario projects an increase in the global amount of hydroelectricity but only to about 70% above its 2022 value.