The ultimate source of energy in hydroelectric power plants is solar energy. This may come as a surprise, but let me explain how this works.
Hydroelectric power plants generate electricity by harnessing the energy of flowing water, typically from rivers or dams. This flow of water is essentially the result of precipitation—such as rain or snow—that falls to the earth due to solar energy heating the atmosphere. When sunlight warms the surface of the earth, it causes water to evaporate, forming clouds that eventually lead to rainfall. This rainwater then accumulates and flows into rivers and streams.
In summary, as rainfall runs down into water reservoirs, it gets stored and is released through turbines in hydroelectric plants. The energy captured by these turbines is transformed into electricity. Hence, the entire process starts with solar energy, which drives the water cycle and ultimately leads to the generation of electricity in hydroelectric power plants.