Hydropower Energy Explained: All You Need to Know

Hydropower Energy Explained: All You Need to Know

Grace Smoot

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71% of Earth’s surface is covered by water, making it one of our most abundant natural resources. Harnessing the energy of moving water is a low emissions process that can help ensure a sustainable planet for future generations. So, we had to ask: What is hydropower energy really, and how does it contribute to climate change?

Hydropower energy is the conversion of moving water into energy via hydroelectric facilities. Per kWh produced, hydropower emits 24 grams of CO2 on a life-cycle basis. It combats climate change and has various environmental benefits, but is still responsible for some greenhouse gas emissions.

Keep reading to find out all about what hydropower energy is, its global capacity, its carbon footprint, its environmental benefits and drawbacks, and how it can combat climate change.

The Big Picture of Hydropower Energy

Hydropower contributes to the avoidance of greenhouse gas (GHG) emissions from the burning of fossil fuels (e.g., coal, oil, natural gas). It is classified as a renewable energy source because the resource (water) naturally replaces itself over time. 

How Is Hydropower Energy Defined

Hydropower energy is defined as the conversion of moving water into electrical energy through the use of various types of hydroelectric facilities.

“Hydropower: hydroelectric power (= the production of electricity by the force of fast-moving water)”

Cambridge Dictionary

From Greek water wheels, to Egyptian water screws, to modern water turbines, we have been using water as a source of energy for thousands of years. The principle remains the same, but years of research and development have provided various technologies to more efficiently capture the energy of moving water.

What Are the Different Types of Hydropower Energy 

Hydropower can be divided into three main categories depending on how many megawatts (MW) of power are generated.

Category of HydropowerGenerating Capacity
Micro hydropower100 kilowatts (kW) or less
Low-impact hydropower (low hydro)Between 100 kW and 10 MW
Large hydropower (large hydro)30 MW or more

And those categories can be defined as one of four types of hydroelectric facility:

  • Run-of-river: A facility that channels flowing water from a river through a canal or penstock to turn a turbine which spins a generator to produce electricity.
  • Storage: A large system that stores water in a reservoir via the use of a dam. Water is released from the reservoir to turn a turbine which spins a generator to produce electricity.
  • Pumped storage: A system that harnesses water which is cycled between upper and lower reservoirs by pumps. Water is released from the upper reservoir into the lower reservoir to turn a turbine which spins a generator to produce electricity.
  • Offshore: A system that uses tides or waves to generate electricity from seawater. This is the least established form of hydropower.

Hydropower has been one of the world’s oldest and largest sources of alternative energy and today accounts for more than 50% of all renewable energy generation. So let’s take a closer look at it next.

What hydropower energy isHydropower energy is defined as the conversion of moving water into electrical energy through the use of various types of hydroelectric facilities.
What the different types hydropower energy areThe three types of hydropower energy are micro, low-impact, and large hydropower. 
How hydropower energy worksHydropower energy works by harnessing the energy of moving water which turns turbines and spins generators to produce electricity.
The global capacity of hydropower energyHydropower accounts for over 50% of all renewable energy generation. China, Brazil, Canada, The United States, and Russia are the largest hydropower producing countries in the world. 
The carbon footprint of hydropower energyOn a life-cycle basis, hydropower emits 24g of CO2 equivalent per kWh of electricity produced. 
The environmental benefits of hydropower energyHydropower energy mitigates climate change, promotes energy independence, and creates jobs.
The environmental drawbacks of hydropower energyFish passage difficulties, environmental flow releases, water quality degradation, and GHG emissions are drawbacks of hydropower energy.
Hydropower energy and climate changeHydropower energy combats climate change by mitigating the temperature rise, sea-level rise, ice melting, and ocean acidification associated with global warming.

How Does Hydropower Energy Work

In general, hydropower energy works by harnessing the energy from moving water which turns turbines and spins a generator to generate electricity. 

How Does Hydropower Energy Actually Produce Energy

Hydropower plants generally operate in the following way:

  • Water is temporarily stored in the forebay, a basin-like area commonly referred to as a reservoir.
  • The intake structure, a gate-like structure with trash racks to filter out debris, collects water from the forebay and directs it to the penstocks, large pipes built on a slope.
  • The penstocks, made of either steel or reinforced concrete, transport water from the forebay to the turbines.
  • When water from penstocks hits the turbine blades, it rotates the shaft at the center and causes the generator to produce electricity.

Hydropower plants have had a historical life expectancy of 80 years, but they are known to last around 100 years. And if hydropower plants are properly maintained, the civil engineering infrastructure should last almost indefinitely. This makes them a long-term, reliable source of energy.

What Is the Global Capacity of Hydropower Energy

Globally, hydropower energy is by far the largest modern renewable energy source, accounting for roughly 54% of all renewable energy generation in 2021. Overall hydropower installed capacity reached 1,360 gigawatts (GW), representing year-on-year growth of 1.9%

Illustration of modern renewable energy consumption
Our World in Data: Renewable energy generation, World

26 GW of new hydropower capacity was installed in 2021, an increase from 21 GW the previous year. The scale of that energy generation varies significantly depending on the country, with some generating a lot and others a little.

Illustration of hydropower generation, 2021
Our World in Data: Hydropower Generation, 2021

China, Brazil, Canada, The United States, and Russia are the largest hydropower-producing countries in the world, together accounting for roughly 650 GW of installed capacity. China continues to lead the way in production, adding 21 GW of capacity in 2021. They also possess the largest pumped storage facility in the world which will have 3,600 MW of installed capacity upon completion in 2023.

Hydropower makes up more than half of global renewable energy generation. Because the amount of GHG emissions from hydropower depends on the scale, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

What Is the Carbon Footprint of Hydropower Energy

The carbon footprint is one of the ways we measure the effects of human-induced global climate change. It primarily focuses on the GHG emissions associated with consumption, but also includes other emissions such as methane (CH4), nitrous oxide, and chlorofluorocarbons.

Carbon footprint: the amount of greenhouse gasses and specifically carbon dioxide emitted by something (such as a person’s activities or a product’s manufacture and transport) during a given period

Merriam Webster

Basically, it is the amount of carbon emitted by an activity or an organization. This includes GHG emissions from fuel that we burn directly (e.g., heating a home, driving a car) and GHG emissions from manufacturing the products that we use (e.g., power plants, factories, and landfills). 

On a life-cycle basis, hydropower generally emits 24 grams (g) of carbon dioxide (CO2) equivalent per kilowatt-hour (kWh) of electricity produced. 

Have a look at the illustration below to see the average life-cycle CO2 equivalent emissions of different energy sources and how they compare to hydropower energy.

Illustration of CO2 equivalent per energy source
World Nuclear Association: Average life-cycle CO2 equivalent emissions

On a more specific level, low hydro emits between 0.01 and 0.03 pounds (4.5 and 13.6 g) of CO2 equivalent per kWh, and large hydro emits approximately 0.06 pounds (27.2 g) in arid regions but maybe over 0.5 pounds (226 g) of CO2 equivalent per kWh in tropical regions.

Category of HydropowerCarbon Footprint
Low-impact hydropower (low hydro)4.5-13.6g of CO2 equivalent per kWh
Large hydropower (large hydro)27.2-226g of CO2 equivalent per kWh

When discussing the carbon footprint of hydropower energy, we must take into account carbon emissions across the energy’s building, operating, and building back phases.

The life-cycle stages of hydropower energyEach stage’s carbon footprint
Building of hydropower energyConstruction and transportation of materials, emissions from reservoirs
Operating of hydropower energyLittle to no CO2 emissions or waste products
Building back of hydropower energyNone, if hydropower infrastructure can be maintained indefinitely

It is important to note that hydropower reservoirs are an additional source of CO2 emissions. Reservoirs produce GHG emissions as a result of the decomposition of flooded organic material. A study by the International Hydropower Association found that reservoirs had a global mean GHG emission intensity of 18.5 gCO2 per kWh. However, this is still substantially less than fossil fuels such as coal (820 gCO2 per kWh). 

Because hydropower makes up such a large portion of renewable energy generation worldwide, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

Related: Are you interested in more about the carbon footprint of hydropower? Check it out in this article here: “What Is the Carbon Footprint of Hydropower Energy?

How Environmentally Friendly Is Hydropower Energy

The overall environmental friendliness of hydropower depends on the scale at which it is generated. 

“Environmentally friendly: (of products) not harming the environment.”

Cambridge Dictionary

Micro and Low hydro are more environmentally friendly than large hydro because they produce fewer GHGs and have a minute environmental impact. However, the amount of energy that can be generated from low hydro is less than what can be generated from large hydro. 

Large hydro is less environmentally friendly than micro and low hydro because it produces more GHGs and can potentially alter the natural state of the environment. However, it can contribute significantly higher amounts of energy to the power grid because it operates on a larger scale. 

What Are the Environmental Benefits of Hydropower Energy

Here are three ways in which hydropower energy benefits the environment:

  1. Climate change mitigation: Hydropower has an average life-cycle CO2 equivalent emission value of 24g of CO2, which is significantly less than that of coal, oil, and NG. Hydropower has the potential to reduce overall GHG emissions by 5.6 gigatons by 2050, which is equivalent to the emissions of nearly 1.2 billion passenger vehicles driven in a year. This would also save around $209 billion in damages caused by climate change. 
  1. Energy independence: Being able to produce our own electricity in the U.S. without the aid of foreign countries is an important step to help us become more self-sufficient. Former President George W. Bush signed the Energy Independence and Security Act of 2007 to reduce U.S. dependence on oil, expand the production of renewable fuels (and confront global climate change). 
  1. Employment opportunities: Hydropower supplied more than 2.2 million people in 2020 and is projected to hit 3.7 million by 2050. Renewable energy jobs continue to increase as we start to realize just how beneficial renewable energy is for our environment. 

What Are the Environmental Drawbacks of Hydropower Energy

Some drawbacks of hydropower energy include:

  • Fish passage: Hydropower can affect aquatic organisms by interfering with migration, blocking movement up/downstream, and altering water flow patterns and quality conditions. Fish that move seasonally between large rivers and smaller streams could find their route blocked by hydroelectric dams. 
  • Environmental flow releases: Hydropower reservoirs can retain so much water that the water body below the dam dries up. Diversion projects take water away from the river and return it to the river downstream. In both cases, stream flows and aquatic habitats can be negatively affected.
  • Changes in water temperature: The water released from dams may experience changes in temperature. Warm water may enhance the metabolic rate of aquatic insects and fish eggs, causing them to emerge before their time. Coldwater may do the opposite, slowing the growth rates and reducing fish and invertebrate productivity. It may also lead to the establishment of coldwater fisheries in areas of the river where the natural river is too warm. 
  • Changes in dissolved oxygen concentration: The water released from dams may experience changes in oxygen levels. Thermal stratification causes decreases in dissolved oxygen concentrations because the stagnant water bottom is isolated from the water at the surface. Turbines that remove water from the bottom can discharge water low in dissolved oxygen concentration.
  • GHG emissions: Depending on the age, size, and location of the hydropower facility, vegetation inundation, and decomposition can release GHG emissions in the form of both CO2 and CH4. As a study from Washington State University found, CH4 has a global warming potential 28-34 times that of CO2 and can make up 80% of the emissions from dam reservoirs. 

Hydropower does come with some drawbacks that, if handled properly, can be avoided or at least mitigated. Ways to mitigate both GHG emissions and environmental impacts include installing small turbines in irrigation canals, water-treatment plant outfalls, and existing hydroelectric facilities.

Why Is Hydropower Energy Important to Fight Climate Change

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. Every year, approximately 33 bt of CO2 are emitted from burning fossil fuels. The carbon found in fossil fuels reacts with oxygen in the air to produce CO2. This warms the earth by acting as a heating blanket, and a warmer earth comes with a host of negative side effects. 

Hydropower helps combat climate change because it contributes to the avoidance of fossil fuel combustion. In order to help keep global temperature rise below 1.5C, as outlined in the Paris Agreement, we will need to add 1,200 GW more of hydropower energy by 2050

Utilizing hydropower energy mitigates the following negative effects of climate change:

  • Melting of sea ice: Since 1979, arctic sea ice has declined by 30%. Sea ice plays a major role in regulating the earth’s climate by reflecting sunlight into space and providing habitat for animal species. If all of the glaciers on Earth melted, sea levels would rise by approximately 70 feet, effectively flooding out every coastal city on the planet. 
  • Changing precipitation patterns: Extreme weather events (e.g., hurricanes, floods, droughts) are becoming more common intense. Storm-affected areas will experience increased precipitation and flooding whereas areas located further from storm tracks will experience decreased precipitation and droughts.
  • Ocean acidification: The ocean absorbs 30% of the CO2 released into the atmosphere, which decreases the pH (increases the acidity) of the ocean. In the past 200 years, the pH of oceans has decreased by 0.1 pH units, which translates to a 30% increase in acidity. Aquatic life unable to adjust to this rapid acidification will die off. A prime example of this is coral bleaching, where coral expel the algae (zooxanthellae) living in their tissues as a result of changes in temperature, light, or nutrients. 

The more we reduce CO2 emissions, the more we slow the rate of temperature rise, sea-level rise, ice melting, and ocean acidification. When these rates are slowed, the earth’s biodiversity does not have to struggle to adapt to temperature and pH changes. People will not be displaced due to the flooding of coastal areas. And icebergs will continue to provide climate regulation. 

Final Thoughts

Hydropower energy has been around for thousands of years, and we currently rely on it for more than half of all of our renewable energy generation. Via various types of hydroelectric facilities, flowing water turns turbines and spins generators to produce electricity. Hydropower plants can last indefinitely if properly assembled and maintained, making them a long-term investment in low-carbon energy.

The use of flowing water to generate electricity produces little to no GHG emissions or waste products, unlike coal which produces a lot of both. Hydropower benefits the environment by combating climate change, creating jobs, and promoting energy independence. Environmental disruptions can be addressed by installing smaller turbines in existing hydroelectric facilities.

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