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A Student’s Guide to Hydroelectric Energy

Hydroelectric energy is among the safest, most reliable forms of power in existence today. Many countries are working toward having hydroelectricity be their primary form of power. With a long list of advantages and relatively few disadvantages associated with the power source, hydroelectric energy has been at the forefront of alternative energy sources for over a hundred years and continues to be well thought of and immensely important today.


Though it was not originally a means of generating electricity, flowing water has been used to assist with tasks for thousands of years. Water wheels were built near rivers and large streams by the Greeks and Romans and many cultures after them. The flowing water would turn the wheel, which would then rotate a mechanism inside a building to grind grain. Later on, additional tasks were completed using hydropower, such as cutting lumber or to assist in the production of steel. The first true hydroelectric power plant was built in Appleton, Wisconsin in 1882. Within 10 years, there were 200 plants producing hydroelectric power in the United States alone, and by 1920 40% of the electricity in the US was hydroelectric. Many massive dams were constructed throughout this period; most notably the Hoover Dam. At the time of construction, the Hoover Dam produced more electricity than any other hydroelectric source, though it was surpassed just 6 years later by the Grand Coulee Dam and by several other dams since. Today, the United States has over 2000 hydroelectric power plants which supply 49% of its renewable energy.

How It Works

One of the most essential features of a hydroelectric plant is its water reservoir. Water gathers in this reservoir in front of the power plant by the natural flow of the river. Water then enters the intake tunnel at the base of the dam’s wall, and then passes through a small channel called the penstock. At the end of this channel is the turbine. The part of the turbine that stays in the water resembles a plane’s propeller, and is spun rapidly by the flow of water passing it. Attached to this propeller-like structure is a steel shaft which also spins around, and above that is the electric generator which produces electricity using electromagnets. The power generated then goes out on power lines to supply electricity to houses just like yours.

Once the water passes the turbine and has done its job of spinning the structure, it passes out of the facility and on to rejoin the river. In pumped-storage facilities though some of the water is stored, and is pumped back up to the reservoir during hours when less electricity is used to be run through the turbine again during peak hours. For example, not much electricity is used in the middle of the night, so the hydroelectric plant doesn’t need to produce as much electricity during this time. But at 3 pm the next day, much more electricity will be used to power lights and TVs and air conditioners. During these peak hours, the water that was pumped back up the channel into the reservoir during the night when only a small amount of electricity needed to be generated is run back through the intake and the penstock to power the electric generator once again. In this way, hydroelectric power plants are able to use completely renewable and reusable “fuel” to generate a constant source of power and to quickly and easily adapt to fluctuations in electricity demand.

How It’s Used

Today, hydroelectric power plants produce only about 7% of the power generated in the United States. However, about 16% of the world’s power is hydroelectric, and that number is expected to steadily and significantly rise over the next 25 years. China has been one of the biggest supporters of hydroelectric power, and finished construction on the Three Gorges Dam in 2008. The Three Gorges Dam is currently the largest hydroelectric power source in the world and produces about 10 times more energy than the Hoover Dam. Much of the potential for hydroelectric power production is still unrealized, and about 2/3rds of viable locations for hydroelectric power plants aren’t currently being used. There are some disadvantages to building new hydroelectric power plants though. Naturally flowing rivers must be dammed up to form the reservoirs that these plants rely on. This means that formerly habitable areas become submerged by this new body of water, which can displace local people and animals. It also can have negative impacts on the fish and other creatures living in the river, and indeed these dams have caused many species of aquatic wildlife to become endangered. And while these hydroelectric facilities do wonders for controlling natural flooding, there’s always the risk that a dam will break, with devastating consequences. However, it cannot be overstated that the advantages to hydroelectric power far outweigh the drawbacks:

  • Hydroelectricity is produced using not only a renewable resource, but a free one.
  • Hydroelectricity is not nearly as affected by market fluctuations as other sources of energy. What this means is that while your parents likely complain about the rising price of gasoline, they would rarely have cause to complain about the rising costs of hydroelectricity.
  • Hydroelectric power plants don’t directly produce any pollution whatsoever, meaning they lead to cleaner air for everyone and reduced emissions of greenhouse gasses.
  • These power plants have very low operating and maintenance costs, making them a much more affordable source of energy all around.
  • Due to their high reliability as an energy source, hydroelectric plants actually increase the production of other alternative sources of energy by providing a safe fall-back or a supplementary source for less reliable sources like solar or wind energy.
  • New hydroelectric plants help provide jobs and better living situations for the local populace in the same way that fossil-fuel powered plants do, but with much cleaner energy.

Hydroelectric power was one of the first sources of electricity explored, and one of the most reliable and sustainable sources to this day. It’s already immensely important to the United States and the rest of the world, and will only become more so in the future. Click the links below for even more information on hydroelectric power.

  • Timeline of hydropower – This timeline shows the major events in hydroelectric power history from ancient civilizations up to the early 2000s.
  • Full hydropower history – This link is a much more detailed history of hydroelectric power, with more than just the major events covered.
  • Hydroelectric dam explained – This page gives a detailed description demonstrating how hydroelectric dams actually work, complete with easy to understand full-color diagrams.
  • Tour of a dam – An interactive walkthrough of a dam and its internal components.
  • Background information – A clear and concise description of hydroelectric power.
  • Hydroplant description – A very detailed look at hydroplants and their benefits and drawbacks.
  • Renewable energy – A description of all forms of renewable energy in the United States.
  • Greenhouse gases – Data on greenhouse gas emissions and their causes.
  • Electricity cost graph – A graph displaying the average costs of all current forms of energy production.
  • Dams in the US – A list of dams, hydroprojects, and reservoirs in the United States and their statistics.
  • Pumped storage – An in-depth look at pumped storage facilities.
  • World Commission on Dams – A framework and guide for the construction of new dams to minimize damage to the local ecosystem and human population.
  • Global usage – An article on the rapid increase in global reliance on hydroelectric power.
  • Hydropower in China – An article on the future of hydroelectric power in China.
  • Hydropower in the UK – An overview of hydropower in the UK and information on the installation of micro-hydro units on smaller properties.
  • DRC hydropower – Information on current and future hydroelectric projects in the Democratic Republic of the Congo.
  • Hydropower Facts – A bulleted list of facts on hydropower which includes information on the countries that produce the most hydroelectric power.
  • Advantages & Disadvantages of Hydroelectricity – A list of the advantages and disadvantages of producing hydroelectricity.
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