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What is Hydroelectric Power? (Pros, Cons and how it Works)


Hydroelectric power, also known as hydroelectric energy, hydroelectricity or hydropower, is a type of energy that uses the power of water in motion - such as water flowing downhill—to produce electricity. This type of water power has been used by people for millennia, such as in Ancient Greece where moving water was used to turn a mill wheel to grind wheat into flour.

Hydroelectric power is the most commonly-used form of renewable energy, accounting for over 18% of the world’s total power generation capacity and 71% of the renewable electricity that is generated. This type of power uses the potential energy of water flowing downwards to drive turbines that power generators to produce electricity.

Large producers of hydroelectricity include Brazil, Canada, India, Russia and the United States. The largest producer of hydroelectric power is China, who also have the largest hydroelectric dam in the world; the Three Gorges Dam that holds back the Yangtze River is 2,335 metres (7,660 feet) long and 185 metres (607 feet) tall, with the capacity to produce 22,500 megawatts of power.


The power of falling water is one of the three main sources of electricity generation currently in use, along with fossil fuels and nuclear power. However, hydropower is a renewable resource that doesn’t produce thermal pollution and is a preferred energy source for areas with high rainfall and in hilly or mountainous areas close to main load centres to reduce transmission costs.


TWI provides our Industrial Members with support for a range of services related to renewable energy sources, including hydroelectric power. Our expertise in this area has been used to help manage the structural integrity of hydropower assets as well as improving operating efficiencies and inspection methods, including the use of drones to inspect hydroelectric dams

TWI is an Industrial Membership based organisation who can provide your company with an extension to your own resources. Our experts are dedicated to helping industry improve safety, quality, efficiency and profitability through all aspects of materials, joining, and allied technologies. Industrial Membership of TWI currently extends to over 600 companies worldwide, embracing all industrial sectors.

Contact us today to find out more:

How Does Hydroelectric Power Work?

Hydroelectric power works by harnessing the potential energy of water held at a higher elevation before it flows downhill or spills from the top of a dam. This potential energy becomes kinetic energy as the water flows, turning turbines to generate electricity that can then be distributed to customers.

The majority of hydroelectric power plants use a reservoir of water alongside a gate or valve that controls the flow of water, as well as an outlet or place to collect the water once it has flowed downwards through the turbines to generate electric power. The difference in elevation between the top reservoir and the lower elevation is known as the head while the structure that houses the turbines and generators is known as the powerhouse.

Most hydroelectric power plants are located at dams on rivers that raise the level of the water to create a high head. The higher the location of the head, the less water is required to produce power. Some dams have the powerhouse installed on one side of the dam, allowing the other side to be used to manage the discharge of excess water during times of flood. Where the dam is situated in a narrow, steep gorge, the powerhouse can be located in the dam itself.

Hydropower is reliant on the water cycle, which has three steps as follows:

  1. Solar energy heats water on the surface of rivers, lakes, and oceans, causing the water to evaporate
  2. The evaporated water vapour condenses into clouds before falling as rain and snow
  3. The precipitation collects in streams and rivers, which flow into oceans and lakes, where the cycle begins again

The amount of precipitation draining into rivers and streams determines how effective an area is for producing hydropower, with seasonal variations and long term environmental changes also having an impact on the availability of hydroelectric production.

The power of water is also harnessed in coastal areas such as the Rance River estuary in Brittany, France. This type of hydroelectric production uses the rise and fall of tides to create energy. At high tide, water flows into reservoirs before being released at low tide, where the water can drive hydraulic turbines and power electricity generators. This type of hydropower is known as tidal power and is distinct from other types of hydroelectric production.

Types of Hydroelectric Plant

Excluding tidal power, there are three types of hydropower facilities, as follows:

  1. Impoundment: Impoundment facilities are the most common of hydroelectric energy plants. This is where a dam is used to arrest the flow of water in a pool or reservoir. This water is released from the dam when energy is required and gravity causes the water to flow down through a turbine to power a generator.
  2. Diversion: A diversion facility uses a series of canals rather than a reservoir to channel river water towards the turbines.
  3. Pumped Storage: Pumped storage hydropower can collect energy produced by other means, such as solar or wind, and store it for future use. Some of the energy is used for pumping water uphill to a higher elevation where it is collected in a reservoir. This stores the latent energy, which can then be drawn upon by releasing the water when there is a demand for electricity.


Hydroelectric power has a number of inherent advantages:

  1. Flexible: Hydroelectric power is incredibly flexible as the turbines can be pushed from a cold start-up to full load in just 60-90 seconds, which is much faster than steam plants or gas turbines. Equally, power generation can be reduced quickly when there is a surplus.
  2. Low Cost/High Value Power: Hydroelectric dams are able to store water and thereby potential energy at a low cost. They also deliver a higher value than base power and than intermittent energy sources. The cost of construction is also quickly recouped by the sale of electricity and these stations have long economic lives, with plants still in service after 50-100 years. Operating labour costs are also low, with much of the operation being automated.
  3. Suitable for Industrial Applications: Hydroelectric facilities are also able to provide power for industrial applications, such as aluminium electrolytic plants.
  4. Reduced CO2 Emissions: Hydroelectric dams do not produce carbon dioxide (other than during construction). While some methane is released by reservoirs, this is still much less damaging to the environment than the burning of fossil fuels and even other energy sources such as wind, nuclear and solar.
  5. Additional Uses: Hydroelectric reservoirs can also be used for other purposes, such as supporting agriculture, irrigation, water supply and flood control. These dams can also be used for water sports and other leisure activities.


Despite the advantages, there are still a few disadvantages associated with hydroelectric power:

  1. Ecosystem Damage and Displacement: Creating large reservoirs for hydroelectric power stations can lead to large areas of land being submerged, which can destroy ecosystems such as marshlands, forests or grasslands. These large bodies of water often displaces people and wildlife from the region. Hydroelectric dams can also impact the downstream environment, reducing the amount of suspended sediment and causing the scouring of downstream riverbeds and eroding riverbanks. Dams can also interrupt the migration of spawning fish.
  2. Water Loss through Evaporation: Evaporation of the water from reservoirs is also a problem for hydroelectric plants, with losses being greater than those seen for generation technologies that use cooling towers, including concentrated solar power, nuclear energy or natural gas.
  3. Flow Shortage and Siltation: The normal flow of a river will carry particles downstream, but a dam will collect these particles and lead to siltation in the reservoir. Siltation can fill reservoirs and render them useless or lead to water flowing over the top during periods of flooding. As the water flow is reduced, so the amount of energy that can be produced also lessens. This flow reduction can lead to power shortages. Reduced flow can also result from climate change as higher temperatures reduce precipitation and the subsequent river run-off that hydropower relies on.
  4. Methane Emissions: Power plant reservoirs can produce substantial amounts of methane, especially in rainforest areas. This is caused by plant matter decaying in the anaerobic environment and forming the greenhouse gas, methane.  These emissions can even exceed those from an oil fired thermal generation plant if the reservoir is large compared to the generating capacity and there is no forest clearing in the area. This can be mitigated against by underwater logging that targets drowned areas of forest to prevent plant and tree decay.
  5. Failure Risks: The large volumes of water contained in dammed hydro facilities can pose a risk due to construction failures, natural disaster or even sabotage. Downstream flooding caused by excessive rainfall or a compromised dam structure can destroy homes, ecosystems, and lives. Smaller dams pose less risk but even decommissioned dams can fail years later and lead to a loss of life downstream.


Are Hydroelectric Power Plants Expensive?

Smaller hydropower plants can be expensive when compared to their maximum installed power output, but these relative costs reduce as the size and thereby the output increases.

Are Hydroelectric Power Plants Bad for the Environment?

Hydroelectric power plants do not pollute the water or air with emissions like fossil fuels, but they can have an environmental impact by changing land use and natural habitats around the area of the dam. The reservoirs can also release methane into the atmosphere, which is a greenhouse gas.

Is Hydroelectric Power Renewable?

Hydroelectric power is a renewable energy resource, since the plants use the energy of running water to produce electricity.

Is Hydroelectric Power Sustainable?

Hydroelectric power is a sustainable source of energy as it uses the natural flow of water to produce electricity.

Can Hydroelectric Power be used in Homes?

Hydroelectric power, like electricity generated through other means, can be used to power appliances in homes.

Can Hydroelectric Power Replace Fossil Fuels?

Hydroelectric power can replace the use of fossil fuels and is actually the largest single renewable energy resource in use in the world today.

Can Hydroelectric Power be Stored?

Hydroelectric power can be stored on a grid as with other energy. In addition, hydropower can be used to store latent energy by pumping water uphill until the energy is needed and the water released.

What Can Hydroelectric Power be used for?

Hydroelectric power can be used to power homes and industrial applications alike. It can also be used to store potential energy to be used later with the release of water from a dam.

Where Can Hydroelectric Power be Found?

Hydroelectric power is used around the world, with China being the largest producer of hydroelectricity, followed by Canada, Brazil, and the United States.

When was Hydroelectric Power Invented?

The power of water has been used by humans for thousands of years, but the advent of modern hydroelectric power came in 1831 when Michael Faraday invented the first electric generator, paving the way for modern hydroelectric power plants.

Where are Hydroelectric Power Stations Located?

Hydroelectric power stations are generally built on hillsides to exploit gravitational forces that allow the water to flow downwards and turn turbines to power generators and create electricity.

How will Hydroelectric Power be used in the Future?

Hydroelectric power looks set to continue to grow as an energy resource in the future with the move away from fossil fuels. It is likely to be used in conjunction with other renewable energy sources to provide an energy mix for the future.

How long will Hydroelectric Power Last?

Hydroelectric power plants can operate safely for decades, meaning that hydroelectric power is likely to be part of the energy mix around the world for years to come.


Hydroelectric power is a renewable energy resource that looks set to continue being an important part of the future clean energy mix. Widely used around the world, hydropower has many advantages but also a few challenges, including being potentially hazardous and also leading to the release of methane into the atmosphere. However, it is still an important renewable resource with wide use in countries such as China, Brazil and the United States.

Hydroelectric power has the advantage of being controllable, meaning that it can be used to store potential energy with the water being released when power is required at peak times.

With a relatively low cost per output, hydroelectric power is a flexible resource that can also aid other areas such as irrigation, flood control and agriculture.

Related Frequently Asked Questions (FAQs)

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