Why Is It Called Hydropower?

Hydropower is defined as electricity that is generated by harnessing the power of flowing or falling water. It is called hydropower because “hydro” comes from the Greek word for water, and hydropower facilities convert the energy in flowing water into electricity using turbines and generators (https://www.merriam-webster.com/dictionary/hydropower). The term accurately reflects that this form of renewable energy relies on water power to produce electricity.

Hydro Comes from Water

The word “hydro” comes from the Ancient Greek word “hydor” (ὕδωρ) which means water [1]. The prefix “hydro-” is derived from this Greek root and generally means “water” or “of water” in word formations [2]. This Greek root word is found in many English words like “hydrology” (the study of water) and “hydrogen” (an element whose name means “water-former”).

In the term “hydropower”, “hydro” refers specifically to harnessing the power of water. Hydropower uses flowing water to generate electricity or mechanical power, taking advantage of the kinetic energy of water as it moves downwards [3]. So the full term “hydropower” refers to the process of using the power of flowing or falling water to produce energy.

Hydropower Uses Flowing Water

Hydropower plants rely on flowing water as their source of energy. The key is that the water must have kinetic energy from movement in order to be used for generating electricity.^[1]

The flowing water contains kinetic energy proportional to the water’s flow rate and volume. When the water flows through the hydropower plant, this kinetic energy gets converted into electrical energy by turbine and generator equipment. Essentially, the kinetic energy of the flowing water source turns the turbines, which then spin magnets within coils of wire to induce a magnetic field and generate electricity.^[2]

Having water flowing with sufficient kinetic energy is crucial for producing hydropower. This is why hydropower dams are often built along rivers or streams with high volumes. The dams help channel all of this moving water through the turbines to maximize the kinetic energy that gets turned into electricity.

^[1] https://www.energy.gov/eere/water/how-hydropower-works
^[2] https://www.eia.gov/energyexplained/hydropower/

Dams Help Harness Water Power

Dams are a critical component of most hydropower facilities. They help control and harness the power of flowing water to generate electricity. Dams serve two main purposes for hydropower generation:

Dams control and regulate the flow of water. By controlling the flow, dams allow the water to be released through the turbines at the optimal time to generate electricity, such as during peak electricity demand. Dams also ensure adequate water flow even during dry seasons.

Dams create reservoirs to store water above the dam. These reservoirs act like large batteries, storing water that can be released to generate electricity as needed. The reservoirs also provide a constant source of water flow even when natural runoff is low.

Most hydropower dams are built in rivers across their width to control the entire flow of the river. The reservoir stores river water, releasing it in a controlled fashion through intake gates, down tubes called penstocks that lead to the turbines in the powerhouse. After being used to generate electricity, the water is released back into the river downstream.

Some key references:

[1] https://energyeducation.ca/encyclopedia/Hydroelectric_dam

[2] https://www.tva.com/energy/our-power-system/hydroelectric/how-hydroelectric-power-works

Turbines Convert Water Energy

Flowing water is the key to generating electricity at hydropower facilities. The flowing water spins turbine blades, which in turn drive generators to produce electricity. There are two main types of turbines used at hydropower plants:

Impulse turbines are driven by powerful jets of water shooting through nozzles or at the turbine blades. The force of the water applies torque directly to the turbine shaft to turn the generator. Impulse turbines are most often used for high head sites.

Reaction turbines operate by water flowing through propeller-like turbine blades, causing the turbine shaft to turn. The energy from the flowing water is extracted as the water passes through the turbine blades. Reaction turbines are typically used for sites with lower head and higher water flow.

In both impulse and reaction turbines, the rotating shaft turns a generator to produce electricity. The electricity is then fed into transformers and power lines to transmit the energy to homes and businesses.

A Renewable Energy Source

Hydropower is considered a renewable energy source because it relies on the water cycle, which is continuously replenished by the sun. As long as the sun shines, the hydrologic cycle of evaporation, condensation, and precipitation will continue to renew the earth’s water supply. This makes hydropower far more reliable than other renewables like wind and solar power that rely on less predictable weather patterns and availability of sun. According to the U.S. Department of Energy, “The energy generated through hydropower relies on the water cycle, which is driven by the sun, making it a renewable source.”

The renewable nature of hydropower gives it a key advantage over fossil fuels. Coal, oil, and natural gas are finite resources that will eventually be depleted. But the water used to generate hydropower is available year after year. As the Department of Energy states, “As long as we have water, rain, and flowing rivers, we will have hydropower.” This makes hydropower a sustainable energy solution for the long-term.

Low Operating Costs

Unlike fossil fuel power plants, hydropower plants do not require fuel to run. Once built, the force of flowing water spins the turbines to generate electricity. This means hydropower has minimal operating costs compared to other types of generation. According to Statista, the average operating expenses for hydroelectric plants run by major U.S. utilities ranged from $3 to $5 per megawatt-hour from 1998 to 2022.

Hydropower plants also require less maintenance than fossil fuel plants since they have fewer mechanical parts and do not require any fuel input. According to an IEA report, O&M costs for hydropower plants are typically 1.5-2.5% of initial investment per year. This helps keep operating costs low compared to alternatives.

Hydropower is Versatile

One of the main advantages of hydropower is its versatility in electricity production. Hydropower plants can quickly adjust their electricity output to meet changing demands for power across the grid (Department of Energy). This allows hydropower to act as a “buffer” to balance electricity supply and demand. When demand is low, excess electricity can be stored by pumping water uphill into reservoirs. When demand is high, that stored water can be released to generate extra electricity.

This regulating ability gives hydropower a unique flexibility compared to sources like coal or nuclear power that cannot easily adjust their output. Hydroelectric dams essentially act as giant batteries, storing energy in the form of water when supplies exceed demands, and discharging water to produce more power when electricity is needed (Uniper). This versatility and storage capacity make hydropower an important grid resource.

Environmental Considerations

While hydropower is a renewable source of energy, large hydropower projects can have significant environmental impacts (https://www.ucsusa.org/resources/environmental-impacts-hydroelectric-power). Building dams and reservoirs can change natural waterways and negatively affect surrounding wildlife habitats and vegetation.

For example, flooding land to create a reservoir can destroy forests, natural habitats, and agricultural lands. This disrupts local ecosystems and can threaten endangered species. Reservoirs also act as barriers that block fish migration and prevent access to spawning grounds upstream (https://www.eia.gov/energyexplained/hydropower/hydropower-and-the-environment.php).

Additionally, the still waters of reservoirs generate methane, a potent greenhouse gas. Methane bubbles up from the reservoir floor and rises to the surface, contributing to greenhouse gas emissions. There are ways to mitigate these impacts, such as constructing fish ladders to enable fish passage around dams.

Conclusion

As we have seen throughout this article, hydropower is referred to as such because it utilizes the power of flowing water to generate electricity. “Hydro” means water, and hydropower plants harness the kinetic energy of water as it moves downstream to turn turbines and generate power.

Hydropower will continue to play a major role as an important renewable energy source. It offers a flexible, reliable way to generate electricity without carbon emissions. With most suitable dam sites already utilized in developed countries, the future growth of hydropower is likely to be concentrated in emerging economies. While environmental impacts must be carefully managed, hydropower’s ability to provide clean, renewable electricity ensures it will be an invaluable part of the global energy mix for decades to come.