What Is The Basics Of Hydropower Engineering?

Hydropower is a form of renewable energy that utilizes moving water to generate electricity. The term hydropower generally refers to the production of electricity using the energy from falling or fast-moving water. Hydropower has been used as a source of energy for thousands of years. Ancient civilizations used hydropower to turn paddles on various machines. The modern hydropower turbine was invented in the mid-1800s and the first hydroelectric power plant began operation in 1882 in Appleton, Wisconsin.

Today, hydropower is one of the most important and widely-used renewable energy sources in the world. In 2020, hydropower accounted for over 16% of total electricity generation globally, avoiding over 3 billion metric tons of carbon emissions. The main advantage of hydropower is that it is a clean, renewable energy source that produces minimal emissions and relies on the water cycle rather than fossil fuels.

Hydropower is considered an extremely reliable and flexible energy supply that helps balance electricity systems by providing energy storage and grid stabilization services. With advanced pumped storage technology, water can be pumped uphill and stored for later use, functioning like a giant battery. Overall, hydropower offers a sustainable way to generate electricity from a replenishable resource.

Sources: https://www.energy.gov/eere/water/hydropower-basics, https://www.nrel.gov/research/hydropower.html

Table of Contents

Hydropower Components

The key components of a hydropower plant include the dam, reservoir, turbine, and generator. The dam stores river water in the reservoir and controls the water flow. The water in the reservoir has potential energy. The reservoir water flows through an intake and pushes against turbine blades that spin a shaft connected to the generator, converting the potential energy of the water into mechanical energy. The generator then converts this mechanical energy into electrical energy using electromagnetic induction. The key hydropower components work together to convert the potential energy of water into electricity.

The dam serves as a barrier to create the reservoir and control the water flow. Common types of dams used in hydropower include embankment dams made of earth and rockfill, concrete gravity dams that rely on their weight and shape for stability, arch dams that are curved in shape, and buttress dams that have supporting structures on the downstream side. The reservoir stores potential energy in the form of water held at an elevation above the turbines. It also allows control over the water flow.

The turbine is the component that converts the potential energy of the water into mechanical energy by spinning when hit by a high-pressure flow of water. The most common types of turbines used in hydropower plants are Kaplan, Francis and Pelton turbines. Kaplan turbines have adjustable blades and are used in low-head sites. Francis turbines have fixed blades and are suitable for medium-head sites. Pelton turbines use spoon-shaped buckets attached to the wheel and are used for high-head sites.

The generator converts the mechanical energy from the turbine spinning a shaft into electrical energy using electromagnetic induction. The spinning turbine turns electromagnets within the generator, which generates a magnetic field that pushes and pulls electrons in the wire windings around the magnets to produce electricity.

By harnessing the potential energy in water with dams and controlling water flow to spin turbines, the mechanical energy produced turns generators to convert that energy into electricity in a hydropower plant.

Hydroelectric Power Generation

Hydroelectric power generation relies on harnessing the potential energy of water. As water flows from higher to lower elevations, such as in rivers or through dams, it carries kinetic energy. Hydropower plants convert this kinetic energy into electricity by routing the moving water through hydro turbines connected to electric generators (1).

The amount of available energy in moving water is determined by its flow rate and the change in elevation it experiences. The greater the flow rate and height difference, the more energy can be generated. The water flows through an intake and pushes against blades in the turbine, causing them to spin. The turbine spins a shaft connected to the generator, which then converts the mechanical energy into electrical energy using electromagnetic induction (2). The electricity is then fed into transmission lines and distributed.

Hydropower is considered a renewable energy source because it relies on the water cycle to continuously replenish the water used. However, the availability of hydroelectricity can vary based on precipitation patterns.

Types of Hydropower Plants

There are three main types of hydropower plants:

Impoundment

Impoundment hydropower facilities use a dam to store river water in a reservoir. The water is then released through the dam to spin a turbine and generate electricity (https://www.energy.gov/eere/water/types-hydropower-plants)

Diversion

Diversion facilities channel a portion of a river through a canal or penstock, spinning turbines that generate electricity. They do not require dams or impoundments (https://www.hydropower.org/iha/discover-types-of-hydropower).

Pumped Storage

Pumped storage plants pump water from a lower reservoir to an upper reservoir when electricity demand is low. During peak demand, water is released back down to spin turbines and generate power (https://www.enelgreenpower.com/learning-hub/renewable-energies/hydroelectric-energy/hydroelectric-plants).

Hydraulic Considerations

Hydraulic considerations are key factors in hydropower engineering as they determine the amount of power that can be generated. The three main hydraulic factors are head, flow rate, and water pressure.¹

Head refers to the vertical distance between the reservoir surface and the turbine.² The greater the head, the more potential energy is available to drive the turbine. Flow rate is the volume of water flowing per unit time, usually measured in cubic meters per second. Higher flow rates result in more kinetic energy to rotate the turbines. Water pressure, which increases with depth, must be high enough to avoid cavitation damage to turbine blades but not so high as to require excessively robust turbines.

Optimizing these three hydraulic factors – head, flow rate, and pressure – is critical in hydropower plant design and operation to maximize power generation. Head and flow rate directly influence the available power, while pressure affects equipment durability and longevity. Careful analysis of site hydrology and selection of appropriate turbines are key engineering considerations.

Turbine Types

There are two main types of hydro turbines: impulse and reaction [1]. Impulse turbines are activated by water jets striking its blades, while reaction turbines operate fully submerged in water. The three most common types of hydropower turbines are:

Pelton turbine: An impulse turbine that uses the velocity of water to move its buckets mounted around a wheel. Pelton turbines are used for sites with a large head of water.
Francis turbine: A type of reaction turbine that contains guide vanes to control water flow onto the runner blades. Francis turbines are suitable for sites with medium head ranges.
Kaplan turbine: Designed like propeller blades, Kaplan turbines have adjustable blades and are used in low head hydropower sites. They are the most widely used turbines.

Pelton turbines operate best with high head water sources, while Kaplan turbines are ideal for low head sites. Francis turbines fall in the middle range and are a jack-of-all trades design. The runner design and number of blades makes each turbine type more suitable for certain head ranges and flow rates [2].

Environmental Considerations

Hydropower can have significant environmental impacts, especially on rivers and the wildlife that depend on them. Building a dam floods large areas of land, which destroys habitat and disrupts ecosystems. For example, according to the U.S. Energy Information Administration, “Reservoirs may cover important natural areas, agricultural land, archeological sites, and scenic lands” (https://www.eia.gov/energyexplained/hydropower/hydropower-and-the-environment.php).

Damming a river also alters its natural flow, temperature, and sediment transport downstream, negatively affecting native plants and animals. As the Union of Concerned Scientists explains, “Flooding land for a hydroelectric reservoir has an extreme environmental impact: it destroys forest, wildlife habitat, agricultural land, and scenic lands” (https://www.ucsusa.org/resources/environmental-impacts-hydroelectric-power). Fish populations can be impacted by barriers to migration and insufficient water flows.

To mitigate these impacts, hydropower projects can be designed to maintain sufficient downstream flows, install fish ladders, and preserve riparian buffers along shorelines. However, projects in sensitive ecological areas may be avoided altogether. Overall, careful siting, design, and operation are necessary to reduce the environmental footprint of hydropower.

Economic Factors

Hydropower can have high capital costs due to the complex civil works required for dams, tunnels, pipelines and powerhouses. However, operating costs are typically low since hydropower does not require fuel. According to the Institute for Water Resources, “Because hydroelectric powerplants burn no fuel, operating costs are low and are immune to rising fossil fuel prices.”

This makes hydropower very cost competitive compared to other energy sources over the long term. The U.S. Department of Energy states “Hydropower is an affordable source of electricity that costs less than most.” The low operating costs offset the high initial investment over time.

Hydropower also provides economic benefits beyond just power generation. According to the Department of Energy, “Hydropower creates jobs in rural locations and boosts local economies. To local economies, dams and reservoirs can mean recreation, tourism, irrigation, and transportation.”

Sources:

https://www.iwr.usace.army.mil/Missions/Value-to-the-Nation/Hydropower/Hydropower-Economic-Impact/

https://www.energy.gov/eere/water/hydropower-basics

https://www.energy.gov/eere/water/benefits-hydropower

Hydropower Around the World

Some of the largest hydroelectric plants in the world are located in China, Brazil, Canada, and the United States. The Three Gorges Dam in China is currently the world’s largest power station with a capacity of 22,500 MW according to Wikipedia. The Itaipu Dam, located on the border of Brazil and Paraguay, is the second largest at 14,000 MW of capacity. Some other major projects include the Robert-Bourassa Hydroelectric Generating Station in Canada with a capacity of 5,616 MW, and the Grand Coulee Dam in the United States at 6,809 MW.

China has developed massive hydropower infrastructure and leads the world in hydropower capacity according to Power Technology. The country has over 352 GW of installed hydro capacity. Other top countries for hydroelectric power generation include Brazil, Canada, the United States, and Russia. Large dam projects provide renewable energy but also carry environmental and social impacts that must be carefully managed.

Future of Hydropower

Hydropower is poised to continue growing as an essential renewable energy source for the future. With global energy demands rising, many countries are investing in new hydropower projects to expand renewable electricity generation capacity. Some key trends shaping the future of hydropower include:

Growth Potential

Many regions of the world still have untapped capacity for new hydropower development, especially in Asia, Africa, and South America. Large-scale projects on major rivers as well as micro-hydropower plants for rural electrification can increase clean energy access. With support through policy incentives and technological innovations, hydropower could feasibly grow 1.5 to 2 times by 2050.

New Technologies

Advances in hydropower technologies like pumped storage, floating turbines, and small modular hydropower systems create new opportunities. Pumped storage facilitates grid integration of other renewables. Floating turbines allow electricity generation without dams. Modular hydropower enables distributed renewable energy access. Continued research and development can improve efficiency, flexibility, and sustainability.

Sustainability

Making hydropower more sustainable remains crucial. Upgrades to existing infrastructure, adaptive management for ecological flows, and strategic environmental assessments for new projects can reduce impacts. Bottom-up inclusive planning, benefit sharing, and compensation mechanisms can address social equity concerns. With proper safeguards, hydropower can play an expanded role in carbon-free energy systems.