Hydroelectric Power

    Hydropower is considered a renewable form of energy because it is based on solar energy that drives the hydrologic cycle. The hydrologic cycle refers to the following process: the sun heats water (about 97 percent from oceans); water evaporates; rising air currents transport water vapor to the upper atmosphere where lower temperatures condense vapour into clouds. Air currents move the clouds around the globe and eventually, water falls as precipitation. Through this process, water can reach altitudes higher than sea level.

    Gravity causes water to descend from higher elevations creating opportunities to harness water energy—gravitational energy from falling water and kinetic energy from flowing water. The amount of kinetic energy available from water flow depends on the height from which the water drops, the angle of the slope, and the volume of water per unit of time, i.e., the discharge.

    The energy of flowing water is harnessed by turbines, which are placed in the path of the water flow. The force exerted by water moving over turbine blades rotates the turbine runner; the turbine runner rotates the generator, which produces electricity.

    The power extracted from the water depends on the volume and on the difference in height between the source and the water’s outflow. This height difference is called the head. A large pipe (the “penstock”) delivers water from the reservoir to the turbine.


    Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. The dam was named after President Herbert Hoover.

    Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power. In 1928, Congress authorized the project. The winning bid to build the dam was submitted by a consortium called Six Companies, Inc., which began construction on the dam in early 1931. Such a large concrete structure had never been built before, and some of the techniques were unproven. The torrid summer weather and lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned over the dam to the federal government on March 1, 1936, more than two years ahead of schedule.

    Hoover Dam impounds Lake Mead, the largest reservoir in the United States by volume (when it is full). The dam is located near Boulder City, Nevada, a municipality originally constructed for workers on the construction project, about 30 miles southeast of Las Vegas, Nevada. The dam’s generators provide power for public and private utilities in Nevada, Arizona, and California.

    Following an uprating project from 1986 to 1993, the total gross power rating for the plant, including two 2.4 megawatt Pelton turbine-generators that power Hoover Dam’s own operations is a maximum capacity of 2.08 gigawatts. The annual generation of Hoover Dam varies. The maximum net generation was 10.348 TWh in 1984, and the minimum since 1940 was 2.648 TWh in 1956. The average power generated was 4.2 TWh/year for 1947-2008. In 2015, the dam generated 3.6 TWh.

    The images below are photographs of the Hoover Dam.

    The image below is a photograph of the generating room of the Hoover Dam generation facility.


    The Three Gorges Dam is a hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in Yiling District, Yichang, Hubei province, China. The Three Gorges Dam is the world’s largest power station in terms of installed capacity (22,500 MW). In 2014 the dam generated 98.8 TWh of electricity, setting a new world record by 0.17 TWh previously held by the Itaipú Dam on the Brazil/Paraguay border in 2013 of 98.63. But in 2015, the Itaipu power plant resumed the lead in annual worldwide production, producing 89.5 TWh, while production of Three Gorges was 87 TWh.

    Except for a ship lift, the dam project was completed and fully functional as of July 4, 2012, when the last of the main water turbines in the underground plant began production. The ship lift was complete in December 2015. Each main water turbine has a capacity of 700 MW. The dam body was completed in 2006. Coupling the dam’s 32 main turbines with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of the dam is 22,500 MW.

    As well as producing electricity, the dam is intended to increase the Yangtze River’s shipping capacity and reduce the potential for floods downstream by providing flood storage space. The Chinese government regards the project as a historic engineering, social and economic success, with the design of state-of-the-art large turbines, and a move toward limiting greenhouse gas emissions. However, the dam flooded archaeological and cultural sites and displaced some 1.3 million people, and is causing significant ecological changes.


    The Itaipu Dam is a hydroelectric dam on the Paraná River located on the border between Brazil and Paraguay. The name “Itaipu” was taken from an isle that existed near the construction site. In the Guarani language, Itaipu means “the sounding stone”. Completed in 1984, it is a binational undertaking run by Brazil and Paraguay at the border between the two countries, 15 km (9.3 mi) north of the Friendship Bridge. The project ranges from Foz do Iguaçu, in Brazil, and Ciudad del Este in Paraguay, in the south to Guaíra and Salto del Guairá in the north. The installed generation capacity of the plant is 14 GW, with 20 generating units providing 700 MW each with a hydraulic design head of 118 metres (387 ft). In 2016 the plant generated a record 103.1 TWh, supplying approximately 75% of the electricity consumed by Paraguay and 17% of that consumed by Brazil.

    Of the twenty generator units currently installed, ten generate at 50 Hz for Paraguay and ten generate at 60 Hz for Brazil. Since the output capacity of the Paraguayan generators far exceeds the load in Paraguay, most of their production is exported directly to the Brazilian side, from where two 600 kV HVDC lines, each approximately 800 kilometres (500 mi) long, carry the majority of the energy to the São Paulo/Rio de Janeiro region where the terminal equipment converts the power to 60 Hz.