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Pros & Cons of Hydropower

Below, we'll be covering the pros and cons of hydropower. There are a lot of benefits of hydropower; however, recent scientific studies have shed new light on an energy source that is also being pushed by several countries as environmentally friendly.

For centuries, hydropower from many kinds of water mills has been used for irrigation and to operate various machines and technology, including gristmills, sawmills, textile mills, trips hammers, dock cranes, and ore mills. In the late 1800's, hydropower became a source for generating electricity. The first commercial hydropower dam was built at Niagara falls in 1879.

What Is Hydropower?

Hydropower, also known as water power, is derived from the energy of falling water or fast running water.

How Energy Is Made

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Energy from conventional hydroelectric dams comes from the potential energy of dammed water driving a turbine and generator. The amount of extracted power depends on the volume of the water and the difference in height between the source and the water's outflow. A large pipe, known as the penstock, delivers water to the turbines from the reservoir.

What Determines How Much Energy Is Made?

The farther the water falls, the more power it generates. Usually, the distance the water falls depends on the size of the dam. The power of the falling water is directly proportional to the distance it falls, essentially water falling twice as far has twice as much potential energy. Additionally, the power is also directly proportional to river flow.

Types of Hydropower

Hydropower plants range in size from micro-plants, that power only a few homes, to giant dams that generate enough electricity for millions of people.

Pump-Storage Method

The Pump-storage method creates electricity to supply high peak demands by moving water between reservoirs at different elevations. This method is the most commercially important means of large-scale grid energy storage and improves the daily capacity factor of the generation system. At night, when the demand for electricity is low, water is pumped back up into the dam so it can be released again the next day when electricity demand is higher.

Run-of-the-River Stations

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Run-of-the-river stations have no reservoir capacity, are powered only by the water coming upstream, and any oversupply must pass unused. There must be a constant supply of water from a lake or an existing reservoir upstream for a significant advantage in choosing this type of hydropower.

Tide Power Stations

A tide power station makes use of the rise and fall of tidal waves, a highly predictable, dis-patchable source of electricity (electricity on demand at the request of power grid operators).

Large-Scale Plants

Large-scale hydropower plants are more commonly seen as the largest power producing facilities in the world. Some facilities are capable of generating more than double the installed capacities of the current largest nuclear power stations. Currently, only four facilities over 10,000 megawatts are in operation worldwide, two of which are in China, while the others are in Brazil and Venezuela.


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Small-scale development of hydropower, also known as micro-plants, typically serves a small community or an industrial factory. The definition may vary, but it is generally accepted that a small hydro station produces under 10 megawatts, although some may produce as much as 30 MW in Canada and the United States. Small-scale stations can be built in isolated areas that would be uneconomic to serve from a network or in areas where there is no national electrical distribution network. These projects typically have minimal reservoirs and civil construction work. They have a relatively low environmental impact compared to large hydropower plants. The decreased environmental impact depends strongly on the balance between stream flow and power production.

How Hydropower Works

Hydropower plants use turbines to convert the kinetic energy of falling water into mechanical energy, then a generator converts it the electrical energy.

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                                                                               Photo by Matthew Henry via Unsplash

Making Electricity

The energy from flowing water is captured and turned into electricity. The most common type of hydropower uses a dam on a river to store water as a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. However, hydropower doesn't always require a large dam. There are some hydropower plants that only use a small canal to channel the river water through a turbine. The turbine propeller is turned by the moving water.

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                                             Photo by Anna JimĂ©nez Calaf via Unsplash

Spinning Turbines

When water levels of the river rise, the force of falling water pushes against the turbine's blades and causes the turbine to spin. Much like a windmill, the turbine "collects" the kinetic energy of falling water, and then causes the shaft that connects to the generators to spin also, converting the mechanical energy to electricity. Then, the electricity is sent through transmission lines to either the power grid, homes, or businesses.

Pros and Cons of Hydropower

Hydroelectricity is the most popular and one of the most used forms of renewable energy as compared to other energy forms such as solar, tidal, or wind energy. But, as we use hydropower more, we learn more about the potential effects it has on our environment. In a recent study, hydropower stations from around the world are responsible for more methane and carbon dioxide emissions than previously assumed. The balance of the pros and cons of hydropower have shifted since the study was published in 2016.

While hydropower can generate electricity, it can cause environmental and social harm. Damage to wildlife habitats, impaired water quality, impeded fish migration, reduced sediment transport, along with diminished cultural and recreation benefits of rivers were reported due to the hydropower plants effects on the waterways.

Pros of Hydropower


Hydropower is generally available when needed. Engineers control the flow of water through turbines to produce electricity on demand. The time required to shut down and restart a hydropower station is far less than other power stations. Other types of power stations can take up to eight hours to restart. A hydropower station can restart in just a few minutes.


Hydropower is also less expensive than solar power, and it can provide power and water to communities in northern climates better than solar energy.

Recreational Opportunities

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Impoundment hydropower creates reservoirs that provide a variety of recreational opportunities: fishing, swimming, and boating. Other benefits may include water supply and flood control.

Cons of Hydropower

Greenhouse Emissions

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While hydroelectric power is completely free of fossil fuels, or other perishable resources, it does not involve any combustion or burning of fuel, like coal. Many countries consider hydroelectricity a clean source of power, due to the lack of burning fossil fuels. However, the study from 2016 shows that the world's hydroelectric dams' greenhouse gas emissions are responsible for as much as Canada.

The study from Washington State University finds methane, which is at least 34 times more potent than other greenhouse gases. In addition to methane, carbon dioxide makes up 80 percent of emissions from water storage reservoirs created by dams.

As of 2016, 100 studies on greenhouse gas emissions, from 267 large reservoirs around the world, find that methane and carbon dioxide make 80 percent of the emissions from large-scale reservoirs. None of which, are currently included in global greenhouse gas inventories.

These greenhouse gas emissions vary according to a wide variety of indications: air and water temperature, season and time of day, vegetation and soil types in both the reservoir and the upstream watershed, and watershed management practices.

Hydropower dams manipulate water levels to make electricity. When the water levels decline, the hydrostatic pressure on submerged soils also lowers, and it allows gas bubbles to escape. Some gas bubbles can stay trapped in the water while others surface and get released into the atmosphere.

Ecological Effects

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Additionally, constructing a river dam, at a particular location, can lead to adverse ecological effects on its immediate surroundings. A proper land examination is a must prior to hydropower station construction. Earthquakes are also a major concern when it comes to hydroelectricity generation. It has been observed, that in China and India in particular, large dam constructions are responsible for massive earthquakes that occurred in those regions. Globally, there are over 100 identified cases of earthquakes that scientists believe were triggered by reservoirs. Scientists believe that earthquakes related to dams are caused by the extra pressure in micro-cracks. This pressure, coupled with the water, acts as a lubricant on fault lines. These fault lines were already under pressure but were stopped from slipping by the friction of rocky surfaces.

Fish Migration

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Fish populations can be affected if they cannot migrate past impoundment to spawning grounds. An upstream fish passage can be achieved using fish ladders, also known as a fishway. Another option would be trapping and hauling fish upstream by truck. A downstream fish passage can be achieved by diverting fish from turbines using screens, racks, or underwater lights and sounds.

A fish ladder is a structure built on or around dams to help fish pass artificial barriers while migrating. The construction of the ladder allows the fish to swim over low steps to reach the other side.

Water Flow and Quality of Water

Hydropower can also impact water flow and quality. Hydropower plants can cause low dissolved oxygen levels in the water. This is addressed by aeration techniques to oxygenate the water to help improve riparian (riverbank) habitats. Hydropower facilities are also impacted by drought; when there is not enough water available, it cannot power electricity.



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About a decade ago, not much was known about water storage reservoirs. Nobody knew the pros and cons of hydropower. It was thought that shallow reservoirs in hot climates were more likely to heat up and emit greenhouse gases. On the contrary, researchers found that biological activities, like nutrient runoff and dying fauna, are major indicators of gas emissions. While the nutrient runoff can also be due to naturally occurring processes, it is usually found in regions affected by farming, logging, and land development. The 2016 study concluded that all 267 water reservoirs, worldwide, contributed to 1.3 percent of all man-made greenhouse emissions. Unfortunately, when comparing the pros and cons of hydropower the disadvantages are starting to outweigh the advantages. 

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