Hydropower: Pros and Cons

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  • 0:07 Hydropower
  • 1:21 Electricity Generation
  • 3:17 Pros
  • 4:41 Cons
  • 5:58 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Hydropower is power generated from moving water. Learn how this energy from water can be harnessed by hydropower plants to generate electricity as well as the pros and cons of this renewable energy source.


If you have ever been whitewater rafting, you certainly noticed that water can generate a lot of energy. The power from moving water, or hydropower, has been recognized for thousands of years. More than 2,000 years ago, civilizations, including the Greeks and Romans, harnessed the power of water to grind wheat into flour and aid in other heavy tasks.

In the early days of the United States, water was used extensively to power lumber and grain mills, and by the late 1800s, water was being used to generate electricity. By the early 20th century, hydroelectric power, which is the use of moving water to generate electricity, accounted for more than 40% of the United States' electricity needs.

This percentage has declined over the years due to the development of new forms of electricity generation, and today, hydropower provides only about 6 or 7% of the United States' electricity needs. Yet, it remains a viable and important energy source. In this lesson, you will learn how the power of water is harnessed and converted to electricity, as well as the pros and cons of this energy source.

Electricity Generation

Because power obtained from moving water is used mainly for electricity generation in our modern age, the terms 'hydropower' and 'hydroelectric power' are often used interchangeably. Remembering that the prefix 'hydro' means 'water' can help you recall these terms. Water is always in motion and moves in a continuous cycle known as the water cycle. The water cycle is the term used to describe the constant circulation of the earth's water.

As water on earth is heated by the sun, it evaporates and then condenses into clouds. When this moisture accumulates, it falls back down to earth as rain or snow, starting the cycle over again. Water takes on different forms as it moves through the water cycle, but its total volume is never reduced or used up, making it a renewable source of energy.

Water is also acted upon by gravity, which causes water to flow from areas of high elevation to areas of low elevation. This flow is what provides the force needed for hydropower and is why hydropower plants are built on rivers with fast moving water or natural waterfalls. Hydropower plants are facilities where electricity is generated using the energy of moving water. A famous hydropower plant is the Hoover Dam, located 30 miles southeast of Las Vegas.

To capture the energy from the flowing water, a dam is typically constructed to create a large artificial lake, or reservoir, behind the dam. Water from this reservoir is channeled through tunnels within the dam. This flowing water causes the blades of turbines, placed in the water's path, to spin. Generators attached to the turbines create electricity, which is transported into the electric grid for use.

Pros of Hydropower

There are many pros to hydropower. Hydropower is renewable energy. This means that as long as the water cycle continues to produce rain and snow, we will have water to drive hydropower. Hydropower is also clean energy, as it produces no air pollutants because it does not involve the burning of fossil fuels, such as coal, oil and natural gas. Hydropower is a cheap energy source. Because most hydropower plants in the United States have already been built, hydropower is one of the cheapest electricity sources in the United States today. After all, flowing water is free to use.

A major plus when it comes to hydropower is the fact that the flow of water through the plant can be controlled, and therefore, hydropower is flexible energy. Water can be stored in the reservoir above the dam and released as energy demands fluctuate throughout the day and seasons. For example, during a heat wave, when air conditioners are creating a high demand for electricity, the output from the plant can be ramped up by fully opening the gates at the top of the dam to let more water flow through the plant. It's also worth noting that the reservoirs that store water above the dam create recreational opportunities, such as fishing, boating and swimming.

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