Hydropower is the energy captured from moving water. It is often used to make electricity, usually at dams. A renewable energy source, hydropower produced 6% of the United States’ total electricity and 67% of generation from renewables in 2008. Hydropower produces about 20% of the electricity used worldwide, according to the US Energy Information Administration.
How Hydropower is Formed
Nature’s water cycle is important to making hydropower work. The sun heats water on the Earth’s surface, causing it to evaporate. The water vapor condenses into clouds and then comes down as rain or snow. The precipitation collects and flows via rivers into the ocean, where it evaporates again and begins the cycle anew.
The amount of energy in water depends on its flow or fall. Swiftly flowing water and water that descends from a very high point (a waterfall) both have lots of energy.
The mechanical energy of the flowing water turns turbines to run generators that convert energy into electricity.
How a Dam Works
Most hydropower projects use a dam and a reservoir to retain water from a river. When the dam gates are opened, water flows through a pipe called a penstock and applies pressure to turbines, making them turn. Just like in other kinds of power plants, the spinning turbines power a generator to produce electricity.
Dams must have a powerful streamflow and enough vertical distance for the water to flow between the reservoir and the river below the power plant to effectively produce electricity.
Other hydropower plant projects do not require dams. Instead, the force of the river current that is diverted into canals or pipes applies pressure to the turbine blades to produce electricity.