Hydroelectricity is electricity generated by hydropower, or the power of moving water.

Like wind power, hydro-power has always been a commonly used form of renewable energy. Even as early as 100 B.C., the energy from moving water has been used for purposes such as grinding of flour. In those days, the mechanisms were relatively simple -- running water in a stream was used to rotate a water wheel which in turn moves gears that would grind the flour. This mechanism was also used in wood and textile mills to drive saws and other tools.

After the industrial revolution in the 1800s and with the development of the electric generator, hydropower started to be used to produce electricity.

In 1881, near the Niagara falls, the Schoenlkoft Power Station No.1 started to operate and in 1882, the first Edison hydroelectric power plant was started. According to the U.S. Department of Energy, by 1907, hydropower accounted for 15% of the country’s electricity generation.

Today, the use of hydro power to generate electricity makes up a substantial proportion of electricity output from the various sources of renewable energies. According to Wikipedia, in 2006, hydroelectricity accounted for around 85% of all renewable energies and was responsible for about 20% of the world’s electricity. And China is the world’s greatest producer of hydro-electricity today, with an annual production of 652 TWh (Terawatts hour), remotely followed by Canada with a production of 369.5 TWh, Brazil with 363.8 TWh and the United States with 250.6 TWh.

Advantages of hydroelectricity

There are many advantages to the use of hydro-energy.

First, the production and use of hydro power does not release carbon dioxide into the atmosphere, and thus, will not contribute to global warming in the way fossil fuels do.

Second, this energy source is ever renewable – so long as there is moving water, there can always be production of hydro electricity. In fact, whether you tap on the energy source or not, the rivers will continue to flow. Third but not least, once the structures for tapping on hydro energy are set in place, generating electricity from hydropower can be very cheap.

How hydroelectricity is produced using turbines

Here’s a quick summary of how moving water is used to generate electricity.

Moving water is used to turn the blades of turbines, and the kinetic energy in the turbine blades is then converter into electricity by generators that are linked to the turbines.

There are two main types of turbines used in producing hydroelectricity. One type is known as the impulse turbine, while the other type is known as the reaction turbine.

The impulse turbine makes use of the velocity of moving water to move the turbine blades. As such, it is more suited for water sources found at higher grounds (i.e. have higher “head” or height of standing water), even with water volume is low (i.e. low “flow”). The running water (sometimes in the form of a water jet spray) hits the blades of the impulse turbines at high speed, and leaves the turbines with reduced speed and at a deflected angle. It is like a ball hitting the ground at high speed and then bouncing off the ground at a lower speed at a deflected angle. The blades of impulse turbines usually have cup-like shapes to capture the water as it flows through the turbines.

On the contrary, the reaction turbine makes use of the pressure of moving water to move its blades. The blades are placed in large volumes of moving water (i.e. high “flow”) and are turned by the water volume flowing past the blades. Because the focus is not on the speed of the moving water, the reaction turbine is suited for water sources found at lower grounds (i.e. have lower “heads”). The reaction turbine blades do not change the direction of the moving water hitting the blades as drastically as the impulse turbine blades. The reaction turbine blades simply spin with the flow of the moving water as the moving water pushes through and flows past them.

Facilities for producing hydroelectricity

When we talk about hydroelectric plants, what usually comes to mind are water dams.

Indeed, impoundment facilities make use of dams to store river water in a reservoir behind the dams. When the reservoir water is released and allowed to flow down a height gradient through a tunnel known as the Penstock, the falling water is channeled to water turbines at the foot of the “waterfall” in order to generate electricity.

Dams as a method of controlling the water levels of a river has been used since ancient Mesopotamia, but dams as a method of generating electricity only began after the invention of the water turbine in 1832. Today there are more than 48,000 dams over 15m high all over the world.

Other than the impoundment facilities that make use of dams, there are two other types of facilities for producing hydroelectricity.

One of these two types of facility is known as the Run-Of-The-River or the diversion facility. Just like the impoundment facilities, water from a river runs through turbines to generate electricity. However, unlike the impoundment facilities, no dams are used to store the river water in a reservoir. In other words, the timing for the flow of water through the turbines cannot be controlled. Diversion facilities are more suited for use with rivers that have minimal dry weather flow.

The third type of facility for producing hydroelectricity is the pump-storage hydroelectric plant. When demand for electricity is low, a pump-storage facility makes use of some of its stored electricity to pump water from a lower reservoir to a reservoir located at higher grounds. As such, when the demand for electricity rises, the water stored in the higher reservoir is allowed to flow to the lower reservoir, and in the process, electricity is produced.

Besides the generation of hydro electricity using river water flows, there are also facilities that generate electricity from tides.

The problem with hydroelectricity

Despite the huge advantages that hydropower offers, it has its disadvantages.

For one, the outputs of hydroelectricity facilities is very much dependent on the water flow in the rivers and climatic conditions. Climatic conditions like drought can reduce the water flow in rivers tremendously, as such drastically reducing the output of the hydropower plants. Power shortages in areas largely dependent on hydro energy may arise. To resolve this issue of reliability of energy supply, cities that make use of hydroelectricity to power their activities might have to couple hydroelectricity with other sources of renewable energy like solar energy or wind energy.

Hydroelectric faclities are costly to build. Not only are large spaces needed, it also involves the construction of massive structures like dams or giant turbines that require substantial resources, expertise and cost. In fact, it is estimated that in the 20th century, around $2 trillion had been spent on the building of dams.

Hydroelectric facilities like dams involve holding back large volumes of water behind thick dam walls. Poor construction or maintenance, earthquakes or other unforeseen events can lead to catastrophes for downstream population and wildlife.

Although the use of dams offers a source of free, green and renewable energy when they’re built, some controversial environmental issues have been associated with the use of dams. Some environmentalists have argued that dams have severe impacts on ecosystems.

One of the often cited examples is that of the Salmon fish -- dam construction have prevented the fish from swimming to rivers upstream to reach their spawning grounds, as such affecting the population of the species and its survival. To address this problem, fish ladders are being employed today to help the fishes swim pass the dam back upsteam. A fish ladder is a structure comprising of a series of relatively low steps that will allow the fishes to leap their way, step-by-step, upstream. With fish ladders, the speed of water flowing over the steps need to be sufficiently great to attract the fishes, at the same time not too great as to prevent the fishes from swimming toward the ladder and leaping up the steps.

Another environmental complaint is that the waters exiting the turbine are usually altered, compared to the waters upstream. For example, the water downstream a dam is usually much warmer than the waters upsteam. This increase in temperature could jeopardize animal life and endangered species living in the waters downstream.

Of the world’s largest rivers, about 60% are fragmented by dams, and between 40 to 80 million people (who used to live beside rivers) have been displaced due to dam construction.

Beyond the facts

If you found the hydro-electricity information this page useful, don’t just use it for your term paper or research thesis. Share the information with those around you to create greater awareness about the pros and cons of such renewable energies like hydro-electricity.


Before we can reduce our dependency on non-renewable energies (e.g. oil and coal) which are highly polluting and contribute substantially to climate change, there first needs to be greater awareness and understanding about the potential benefits of renewable energies and the potential problems they bring.

With greater awareness and attention on the matter, closer examinations of the pros, cons and viability of hydroelectricity would be carried out. And more effort could be put into trying to resolve the shortcomings that this source of energy has. And only then can the use of renewable energies like hydroelectricity, wind power, geothermal energy and solar energy, flourish.

So starting sharing your knowledge with those around you and create awareness about green energy. Make use of the Facebook and Tweeter icons below to help spread the message.

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