If we do not learn to eliminate waste and to be more productive and more efficient in the ways we use energy, then we will fall short of this goal. But if we use our technological imagination, if we can work together to harness the light of the Sun, the power of the wind, and the strength of rushing streams, then we will succeed. 



Hydroelectricity is electricity produced from hydropower. In 2015, hydropower generated 16.6% of the world's total electricity and 70% of all renewable electricity and was expected to increase about 3.1% each year for the next 25 years.

Hydropower is produced in 150 countries, with the Asia-Pacific region generating 33 per cent of global hydropower in 2013. China is the largest hydroelectricity producer, with 920 TWh of production in 2013, representing 16.9 per cent of domestic electricity use.

Hydroelectric energy is made by moving water. Hydro comes from the Greek word for water. 

Watermills provide another source of hydroelectric energy. Watermills, which were common until the Industrial Revolution, are large wheels usually located on the banks of moderately flowing rivers. Watermills generate energy that powers such diverse activities as grinding grain, cutting lumber, or creating hot fires to create steel. 


2. Harnessing Hydroelectricity

To harness energy from flowing water, the water must be controlled. A large reservoir is created, usually by damming a river to create an artificial lake or reservoir. Water is channelled through tunnels in the dam. 

The process used to control this flow of water is called the intake system. During floods, the intake system is helped by a spillway. A spillway is a structure that allows water to flow directly into the river or other body of water below the dam, bypassing all tunnels, turbines, and generators. 


2.1 From Water Currents to Electrical Currents

Large, fast-flowing rivers produce the most hydroelectricity. The Columbia River, which forms part of the border between the U.S. states of Washington and Oregon, is a big river that produces massive amounts of hydroelectric energy. 

The Bonneville Dam, one of many dams on the Columbia River, has 20 turbines and generates more than a million watts of power every year. That's enough energy to power hundreds of thousands of homes and businesses.

Hydroelectric power plants near waterfalls can create huge amounts of energy, too. Water crashing over the fall line is full of energy. A famous example of this is the hydroelectric plant at Niagara Falls, which spans the border between the United States and Canada. 


2.2 Hydroelectric Energy and the Environment

Hydroelectricity relies on water, which is a clean, renewable energy source. A renewable source of energy is one that will not run out. Renewable energy comes from natural sources, like wind, sunlight, rain, tides, and geothermal energy (the heat produced inside the Earth). Non-renewable energy sources include coal, oil, and natural gas. 

Using water as a source of energy is generally a safe environmental choice. It's not perfect, though. Hydroelectric power plants require a dam and a reservoir. These man-made structures may be obstacles for fish trying to swim upstream. Some dams, including the Bonneville Dam, have installed fish ladders to help fish migrate. Fish ladders are a series of wide steps built on the side of the river and dam. The ladder allows fish to slowly swim upstream instead of being blocked by the dam. 

Dams flood river banks, destroying wetland habitat for thousands of organisms. Aquatic birds such as cranes and ducks are often at risk, as well as plants that depend on the marshy habitat of a riverbank. 


3. General Methods

3.1 Conventional (dams)

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. The power extracted from the water depends on the volume and 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.[14]


3.2 Pumped-storage

This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, the excess generation capacity is used to pump water into the higher reservoir. When the demand becomes greater, water is released back into the lower reservoir through a turbine. Pumped-storage schemes currently provide the most commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system. Pumped storage is not an energy source, and appears as a negative number in listings.


3.3 Run-of-the-river

Run-of-the-river will, can hurt not hydroelectric stations are those with small or no reservoir capacity so that only the water coming from upstream is available for generation at that moment, and any oversupply must pass unused. A constant supply of water from a lake or existing reservoir upstream is a significant advantage in choosing sites for run-of-the-river. In the United States, run of the river hydropower could potentially provide 60,000 megawatts (80,000,000 hp) (about 13.7% of total use in 2011 if continuously available).[16]


4. Hydroelectric Energy and People

Billions of people depend on hydroelectricity every day. It powers homes, offices, factories, hospitals, and schools. Hydroelectric energy is usually one of the first methods a developing country uses to bring affordable electricity to rural areas. 

Hydroelectricity helps improve the hygiene, education, and employment opportunities available to a community. China and India, for instance, have built dozens of dams over the past decade, as their development has quickly grown.

However, hydroelectricity often comes at a human cost. The huge dams required for hydroelectric energy projects create reservoirs that flood entire valleys. Homes, communities, and towns may be relocated as dam construction begins. 




5.1.1 Flexibility

Hydropower is a flexible source of electricity since stations can be ramped up and down very quickly to adapt to changing energy demands. Hydro turbines have a start-up time of the order of a few minutes. It takes around 60 to 90 seconds to bring a unit from cold start-up to full load; this is much shorter than for gas turbines or steam plants. Power generation can also be decreased quickly when there is a surplus power generation. Hence the limited capacity of hydropower units is not generally used to produce base power except for vacating the flood pool or meeting downstream needs. Instead, it can serve as a backup for non-hydro generators.


5.1.2 Low cost/high-value power

The major advantage of conventional hydroelectric dams with reservoirs is their ability to store water at low cost for dispatch later as high-value clean electricity. The average cost of electricity from a hydro station larger than 10 megawatts is 3 to 5 U.S. cents per kilowatt-hour.


5.1.3 Suitability for industrial applications

While many hydroelectric projects supply public electricity networks, some are created to serve specific industrial enterprises. Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed for aluminium electrolytic plants, for example. The Grand Coulee Dam switched to support Alcoa aluminium in Bellingham, Washington, United States for American World War II aeroplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In Suriname, the Brokopondo Reservoir was constructed to provide electricity for the Alcoa aluminium industry. New Zealand's Manapouri Power Station was constructed to supply electricity to the aluminium smelter at Tiwai Point.


5.1.4 Reduced CO2 emissions

Since hydroelectric dams do not use fuel, power generation does not produce carbon dioxide. While carbon dioxide is initially produced during the construction of the project, and some methane is given off annually by reservoirs, hydro generally has the lowest lifecycle greenhouse gas emissions for power generation. Compared to fossil fuels generating an equivalent amount of electricity, hydro displaced three billion tonnes of CO2 emissions in 2011.

5.1.5 Other uses of the reservoir

Reservoirs created by hydroelectric schemes often provide facilities for water sports and become tourist attractions themselves. In some countries, aquaculture in reservoirs is common. Multi-use dams installed for irrigation support agriculture with a relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project.



5.2 Disadvantages


5.2.1 Ecosystem damage and loss of land

Large reservoirs associated with traditional hydroelectric power stations result in the submersion of extensive areas upstream of the dams, sometimes destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. Damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife. The loss of land is often exacerbated by habitat fragmentation of surrounding areas caused by the reservoir.

Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of the plant site. The generation of hydroelectric power changes the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.


5.2.3 Water loss by evaporation

A 2011 study by the National Renewable Energy Laboratory concluded that hydroelectric plants in the U.S. consumed between 1,425 and 18,000 gallons of water per megawatt-hour (gal/MWh) of electricity generated, through evaporation losses in the reservoir. The median loss was 4,491 gals/MWh, which is higher than the loss for generation technologies that use cooling towers, including concentrating solar power (865 gals/MWh for CSP trough, 786 gals/MWh for CSP tower), coal (687 gal/MWh), nuclear (672 gals/MWh), and natural gas (198 gals/MWh). Where there are multiple uses of reservoirs such as water supply, recreation, and flood control, all reservoir evaporation is attributed to power production.


5.2.4 Siltation and flow shortage

When water flows it has the ability to transport particles heavier than itself downstream. This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation. 

One study from the Colorado River in the United States suggest that modest climate changes, such as an increase in temperature in 2 degree Celsius resulting in a 10% decline in precipitation, might reduce river run-off by up to 40%.


5.2.5 Methane emissions (from reservoirs)

Lower positive impacts are found in the tropical regions, as it has been noted that the reservoirs of power plants in tropical regions produce substantial amounts of methane. This is due to plant material in flooded areas decaying in an anaerobic environment and forming methane, a greenhouse gas. 


5.2.6 Relocation

Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In 2000, the World Commission on Dams estimated that dams had physically displaced 40-80 million people worldwide.

6. Application 

Hydropower is energy collected from flowing water that's converted into electricity or used to power machinery. Hydropower has been around for centuries, used to turn mill wheels or drive early industrial machinery, but in modern use, it typically refers to electrical generation. Today hydropower generates more electricity in the United States than any other renewable energy source, and the Department of Energy's Wind and Water Power Program promotes and accelerates its use throughout the country. For businesses, hydro offers recruiting benefits alongside a cost-effective and plentiful source of green energy.


6.1 Generating Clean Electricity

The primary use of hydropower energy is to produce electricity. The main ingredients of hydroelectric power plants are dams, rivers and turbines. Plants use dams to create reservoirs where the water is stored. This water is then released through turbines and spun to activate generators and create electricity. The first hydropower electrical systems were developed in the 19th century and used direct current technology to light Michigan theatres and shops. The first commercial installation of an alternating current hydro plant was in California in 1893.


6.2 Benefits For Business

Hydro sites can be good places to locate a major production facility because of the cheap and plentiful energy they produce — hydropower typically is a cost-competitive source of energy. Unlike fossil fuels, hydropower is a clean source of energy. Deriving power from hydro sources features prominently in the clean energy plans of many companies whose major selling points include their green credentials.


6.3 Offering Recreational Facilities

One of the major advantages of hydropower plants to the wider community is that by law the facilities must be open to the public, and many plants offer a wide range of recreations including swimming, fishing and boating. The largest American operator of hydroelectric power plants is the U.S. Army Corps of Engineers. The Corps's 75 bases have an installed capacity of about 21,000 megawatts — that's 24 per cent of the nation's hydroelectric output. The Corps is also the biggest federal operator of outdoor leisure activities in the country, providing 33 per cent of all freshwater fishing opportunities. There are thousands of boat launch ramps and 20 annual fishing tournaments at their largest parks and lakes. For businesses, the recreational use of hydro facilities makes their vicinity an agreeable place to live. This can help with staff recruiting and retention.


6.4 Flood Risk Management

Hydropower energy is also employed in flood risk management. There are 94 million acres of land in America that are vulnerable to floods, and the plants play a major part in preventing them and practising damage limitation. In 2010, working alongside teams at the University of Washington, the U.S. Army Corps updated the flood risk management program at the Columbia River basin, the country's largest hydropower system. A key factor in flood risk management is knowing exactly when to empty the basins in preparation for winter weather and when to refill them in the spring to store water for the year to come. The new system not only reduces any flood risks but also helps fish stocks by filling reservoirs more reliably.


6.5 Enabling Irrigation For Agriculture

Thousands of miles of irrigation canals in the United States are responsible for watering more than 60 million acres of crops, orchards and vineyards. Hydropower dams divert water for irrigation; in Colorado, three million acres of irrigated land use more than 12 trillion gallons of flowing water. The government awarded a $50,000 grant to Colorado State University to research new technologies that can use even these shallow depths of flowing water to generate power and tap into this underused resource.




Reclamation is helping to meet the needs of our country, and one of the most pressing needs is the growing demand for electric power. Reclamation power plants annually generate more than 42 billion kWh of hydroelectric energy, which is enough to meet the annual residential needs of 14 million people or the energy equivalent of more than 80 million barrels of crude oil. The deregulation of wholesale electricity sales and the imposition of requirements for open transmission access are resulting in dramatic changes in the business of electric power production in the United States. This restructuring increases the importance of clean, reliable energy sources such as hydropower. Hydropower is important from an operational standpoint as it needs no "ramp-up" time, as many combustion technologies do. Hydropower can increase or decrease the amount of power it is supplying to the system almost instantly to meet shifting demand. With this important load-following capability, peaking capacity and voltage stability attributes, hydropower plays a significant part in ensuring reliable electricity service and in meeting customer needs in a market-driven industry.