What is Hydroelectric Power and How it Works? 0

First, here are a few hydroelectric power facts:

Hydropower is one of the earliest forms of power sources on the planet. 

Nearly 20% of all electricity in the world is generated by hydropower.

A good example is the Hoover Dam in the US, which is an imposing concrete arch-gravity facility that stores the power of the entire Colorado River.

Niagara Falls, which is located in Ontario, Canada, and connected to the US by the Rainbow Bridge, was the first hydroelectric facility for the country.

If we talk about hydroelectric power worldwide, the leading countries in producing this power are China, Brazil, Canada, the US, Russia, Norway, India, Japan, Venezuela, and France.

Figure 1: Hydropower Generation by Countries in 2018 (Source: statista.com)

Coming back to the US, hydropower produces enough electricity to meet the demands of 28 million residential customers. It can cover all the households in Indiana, Iowa, Kansas, Kentucky, Ohio, Michigan, Minnesota, Missouri, Nebraska, North and South Dakota, Tennessee, and Wisconsin. 

Hydropower is clean. It prevents the burning of 22 billion gallons of oil or 120 million tons of coal each year.

What Exactly is Hydroelectric Power?

Hydroelectric is a form of energy, which is a renewable resource. 

As we know, other renewable resources are solar, geothermal, tidal power, wave power, and wind power

When the flowing water is captured and turned into electricity, it is called “hydroelectric power” or “hydropower.” 

There are different types of hydroelectric facilities all over the world, and they are powered by the kinetic energy of flowing water as it moves downstream. 

Generators and turbines convert the energy into electricity, which is then passed into the electrical grid to produce energy for use in homes, businesses, and industries. 

Hydroelectric power has played a key role in developing the electric power industry in most countries. 

Small, as well as large hydroelectric power productions, were instrumental in the early expansion of the electric power industry. 

Hydropower has water as its resource, which continually moves through evaporation from lakes and oceans, forming clouds. Then the water comes down as rain or snow and then flows back down to the ocean. 

Hydropower uses water, which never gets reduced or finishes in the process. The water cycle is an endless, constantly recharging system. This is why hydropower is renewable energy.


Water, especially falling water, had been used as a source for generating power over the ages.

Americans identified the advantages of mechanical hydropower as early as the 1700s and used it for milling and pumping. 

In 1878, the first hydroelectric power facility was established to generate electricity for a single arc lamp. 

By 1881, Schoellkopf Power Station Number One near Niagara Falls started producing electricity on a mass scale. 

During the 20th and early 21st centuries, technological innovations helped set up hydroelectric power as a core resource to find renewable energy solutions.

In the early 1900s, hydroelectric power comprised more than 40% percent of the electricity supply in the US. 

In 1909, a 4,500-kW power plant was set up with five generators were in operation. They started generating power to pump irrigation water and electricity to the Phoenix area.

In the 1940s, hydropower provided nearly 75% of all the electricity consumed in the West and Pacific Northwest. 

Figure. 2: Major Purposes of Constructing US Dams (Source: wvic.com)

Later, the US Federal Government took initiatives to produce hydropower due to its commitment to provide water in the dry Wester part of the country. 

Subsequently, the waterfalls of the Reclamation dams became significant producers of electricity. 

Also, power plants were installed at the dam sites to complete construction camp activities. 

Hydropower was used for lifting, moving, and processing materials to construct the dams and dig canals,  to run sawmills, cableways, concrete plants, giant shovels, and draglines. 

Work at night was possible because of the lights powered by hydroelectric power. 

Hydropower also drove pumps that provided drainage or passed water to elevated lands.  

Surplus electricity was sold to existing power distribution systems. 

The low-cost electricity generated benefited local industries, towns, and farms. Also, irrigators in the dry western lands benefited by the surplus power.

The first hydroelectric power plant for Reclamations was built to help in constructing the Theodore Roosevelt Dam on the Salt River, located about 75 miles northeast of Phoenix, Arizona. 

Also, surplus power was sold to the community, and citizens started supporting to increase the dam’s hydroelectric capacity. 

The production of hydropower, however, came down to about 10 percent due to the increasing production of other forms of electric power. 

How Hydroelectric Power Works?

Hydroelectric power is generated from water in motion. It can be perceived as another form of solar energy, as the sun provides power to the hydrologic cycle, which gives the earth its water. 

In the hydrologic cycle, atmospheric water reaches the earth’s surface as precipitation. 

Some part of this water evaporates, but a large portion of it is absorbed into the soil or becomes surface runoff. 

Water that comes down through rain and melting snow eventually reaches ponds, lakes, reservoirs, or oceans where evaporation is continually happening.  

Similar to coal-powered plants, a turbine is used, which then turns a metal shaft in an electric generator to produce electricity. 

The difference is, a hydroelectric plant uses falling water to turn the turbine instead of steam.

The sizes of hydropower plants range from “micro-hydros” that power only a few households, to giant dams like Hoover Dam that provide electricity to millions of people.

The concept is about building dams on large rivers that have a drop in elevation.

The dams have the capacity to store plenty of water behind them in the reservoir. Near the bottom of the dams’ wall, there is the water intake. 

Due to gravity, the waterfalls through the penstock inside the dam. At the end of the penstock, there is a turbine propeller which is turned by the moving water. 

The shaft from the turbine goes up into the generator, which generates electricity. Power lines are connected to the generator that carries electricity to homes and businesses.

A Hydroelectric Power Generator Produces the Electricity

When generating hydroelectric power, no new energy is created, just one form of energy is converted into another form. 

The flowing water turns blades in a turbine, and the form changes into mechanical energy. 

In order to generate electricity, water must be in motion, which is called “kinetic (moving) energy.” 

Some of the hydropower plants are located on rivers, streams, and canals. However, for a steady water supply, dams are required. 

Water is stored in dams to be released later for irrigation, domestic/industrial use, and also for power generation.

A hydraulic turbine converts the energy of flowing water into mechanical energy. 

The operation of a generator is based on the principles discovered by Michael Faraday. He found that when a magnet goes past a conductor, it causes electricity to flow. 

In a large generator, electromagnets are made by circulating direct current through loops of wire coiled around a bunch of magnetic steel laminations. These are called “field poles,” and are mounted on the perimeter of the rotor. 

The rotor is attached to the turbine shaft and rotates at a specific speed. 

When the rotor starts rotating, the field poles or the electromagnets move past the conductors mounted in the stator. 

In this way, electricity starts flowing, and a voltage develops at the generator output terminals.

Once the electricity is generated through hydroelectric plants, it is delivered to homes, offices, schools, and factories. 

All the electricity produced at a power plant first goes through transformers, which increase the voltage so it can travel long distances through power lines. 

At local substations, transformers reduce the voltage so that electricity can be distributed in an area. 

Reusing Stored Water for Peak Electricity Demand

Demand for electricity fluctuates during day time or night. It goes up during peak time and down overnight when there is less demand for electricity in households, businesses, and other facilities.

Hydroelectric plants have more efficiency at providing electricity during peak hours compared to fossil-fuel and nuclear power plants. 

Pumped storage is a method where water is reserved for peak period electricity demands by pumping water that has already passed through the turbines. 

The water is then allowed to flow back through the turbine-generators at times during peak demand, and a heavy load is placed on the system.

The reservoir works similar to battery storage. It stores power in the form of water when demands are low and generating maximum power during daily peak periods. 

A major advantage of pumped storage is that hydroelectric plants can start up quickly and make rapid adjustments in output. 

They operate efficiently for one or several hours. 

Also, because pumped storage reservoirs are relatively small, the costs of construction are usually low compared with traditional hydropower facilities.

Advantages of Hydroelectric Power

  • Hydroelectric plants do not burn fuel, so there is minimal pollution;
  • The costs of operating and maintaining hydroelectric plants are relatively low;
  • Water is used to operate the power plants, which is nature’s unlimited resource;
  • Hydropower uses a reliable and proven technology;
  • Hydropower plays a major role in reducing carbon footprints;
  • Hydroelectric power is renewable as rainfall replenishes or refills the water in the reservoir, so the fuel to operate the plants is always there.

Disadvantages of Hydroelectric Power 

  • Hydropower has high investment costs;
  • This power is dependent on hydrology (precipitation);
  • Hydropower facilities can displace local populations;
  • Stored water in dams when released can inundate lands and wildlife habitats;
  • Deploying hydropower may result in loss of fish habitat or fish entrainment (passage restriction);
  • The quality of water in the reservoir and stream often changes.

The Future Ahead

Hydroelectric power is undoubtedly one of the major renewable resources along with solar, wind, tidal energy, and others. 

There are, however, many questions that have remained unanswered about maintaining the economic viability of hydropower amid the increasing demands to protect fish and other environmental resources.

Hydropower is clean energy and does not discharge pollutants into the environment. Still, this energy may have some adverse environmental effects. 

Over the years, especially in the US, efforts have been made to minimize the environmental issues associated with hydropower operations, including creating safe fish passages and improved water quality. 

If the environmental issues are sorted out, there is a huge potential for hydropower due to its renewable nature. 

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