Hydroelectricity

Hydroelectricity is the generation of electricity using hydropower. It is a vital part of the global energy supply. In 2023, hydropower supplied about 15% of the world's electricity. This equals almost 4,210 TWh of energy. This amount is larger than all other renewable sources combined. It is also greater than the electricity produced by nuclear power.

Because it can provide electricity on demand, it helps create secure and clean energy systems.

Most hydroelectricity comes from conventional dams. These systems use the potential energy of water held in a reservoir. A dam creates a height difference between the source and the outflow. This height difference is known as the head. Water travels from the reservoir through a large pipe called a penstock. The flowing water then drives a water turbine. This spinning turbine is connected to a generator. The generator then produces electricity. The amount of power depends on the water volume and the head.

There are several other ways to generate power from water. Run-of-the-river stations have little to no reservoir capacity. They rely on the natural flow of water from upstream. Pumped-storage is a different method used for energy storage. It moves water between two reservoirs at different elevations. During low demand, excess energy pumps water to the higher reservoir. When demand rises, the water is released through a turbine. In 2021, pumped-storage provided almost 85% of the world's 190 GW of grid energy storage.

Other methods include tidal power, which uses the predictable rise and fall of ocean tides. Conduit hydroelectricity uses existing water pipelines or canals to capture mechanical energy.

Hydroelectric facilities vary greatly in size and capacity. They are divided into large hydropower plants (LHP) and small hydropower plants (SHP). A plant is usually considered an LHP if it has a capacity of 50 MW or more. In some places, the limit is lower. For example, in Europe, SHP is below 10 MW. Small hydro can serve small communities or industrial plants. Micro hydro produces up to 100 kW. This can power isolated homes or small villages. Pico hydro is the smallest type, producing under 5 kW.

These tiny systems can be very useful in remote areas.

Humans have used water power since ancient times. It was once used to grind flour. In the mid-1700s, Bernard Forest de Bélidor published work on hydraulic machines. By 1771, Richard Arkwright used water power to help develop the factory system. The late 19th century brought the electrical generator. This allowed hydraulics to be coupled with electricity. In 1878, William Armstrong created the first hydroelectric scheme. It was located at Cragside in England. It powered only one arc lamp.

Later, the first Edison plant began operating in 1882 in Wisconsin.

As technology grew, hydroelectric projects became much larger. In the United States, the Federal Power Act was enacted in 1920. This helped regulate stations on federal lands. Large dams began serving many purposes. They provided flood control, irrigation, and navigation. The Hoover Dam was a major project completed in 1928. In 1936, the Hoover Dam's 1,345 MW station was the largest in the world. Later, the Grand Coulee Dam surpassed it in 1942. The Three Gorges Dam in China became the largest in 2008. It has a capacity of 22.5 GW.

While hydroelectricity is clean, it has environmental impacts. Building large complexes can cause the loss of arable land. It can also lead to population displacement. Dams can disrupt river ecology and affect animal habitats. They also change siltation and erosion patterns. In some lowland rainforest areas, flooding can release greenhouse gases. However, most plants emit much less greenhouse gas than fossil fuel plants. In 2021, global installed hydropower capacity reached almost 1,400 GW. This remains the highest capacity among all renewable technologies.