What Is The Most Common Way To Generate Hydropower?

Hydropower is a renewable form of energy that harnesses the power of moving water to generate electricity. The most common and widely-used form of hydropower is hydroelectric power, which uses the energy from flowing water to spin large turbines inside a dam. These turbines then activate generators to produce electrical power. Today, hydroelectric power provides approximately 16% of the world’s electricity and is considered one of the largest and least expensive sources of renewable energy. Most hydropower facilities rely on dams and reservoirs to control water flow and direct it through the turbines in a controlled manner.

This article provides an in-depth look at how hydroelectric dams produce clean electricity through hydropower generation. It explores the basics of dam and turbine operation as well as the advantages and challenges of hydroelectric power. With climate change driving the need for clean energy, understanding hydropower and its role in the renewable energy landscape is increasingly important.

History

The first known use of hydropower was in the late 1870s, when the world’s first hydroelectric power scheme was developed at Cragside in Northumberland, England. In 1878, a hydroelectric system was used to power a single lamp in the country house, making Cragside the first house in the world to be lit using hydroelectric power. Just a few years later in 1882, the first hydroelectric power station opened on the Fox River in Appleton, Wisconsin, United States. This station powered a paper mill and lit up two streets with 12.5 kilowatts of power.

Types of Hydropower

Hydropower plants can harness the energy of flowing water in rivers, streams, and canals to generate electricity. There are three main types of hydropower plants:

• Hydroelectric – Hydroelectric plants store water in a reservoir behind a dam. The water flows through an intake and turns blades in a turbine to spin a generator to produce electricity. Hydroelectric power provides almost 7% of U.S. electricity generation. ¹
• Pumped-storage – Pumped-storage plants pump water from a lower reservoir to an upper reservoir for storage. During periods of high electricity demand, the water is released from the upper reservoir through a turbine to generate power. Pumped-storage makes up about 93% of utility-scale energy storage in the U.S. ¹
• Run-of-river – Run-of-river plants channel a portion of a river’s water through a canal or penstock to turbines that generate electricity. These plants do not require dams or reservoirs for water storage. Run-of-river provides a more constant supply of electricity than hydroelectric or pumped-storage. ²

Hydroelectric Power

The most common type of hydropower generation is hydroelectric power. Hydroelectric power utilizes the energy from flowing water to generate electricity. A hydroelectric dam is constructed on a large river to control water flow and create a reservoir. The dam gates allow water to flow through at high pressure to spin turbines connected to power generators (National Geographic). The mechanical power from the spinning turbines gets converted into electrical energy by the generators. Hydroelectric power accounts for over 90% of utility-scale electricity generation from hydropower in the United States (Energy.gov). It is considered a renewable energy source because it relies on the water cycle to replenish the water in the reservoir. However, hydroelectric dams and reservoirs can also have negative environmental impacts on local ecosystems and communities.

Hydroelectric Dam Construction

Hydroelectric dams are large infrastructure projects that require extensive engineering and construction. The key components involved in building a hydroelectric dam are:

The dam structure itself, which is built to hold back and control water in the reservoir. Dams are typically made of concrete or a combination of rock, earth and clay (Energy.gov, 2022). The size and design of the dam depends on factors like the terrain, water volume, and power output goals.

The reservoir formed upstream, which stores potential energy in the form of water held at high elevation. Reservoirs can be very large, flooding existing valleys and landscapes (Energy Education, 2022).

The water intake manages water flow into turbines. This includes intake gates, screens, and passages like tunnels or penstocks.

Hydraulic turbines convert the water’s potential energy into mechanical energy. Common types are Kaplan, Francis and Pelton wheels. The number and size of turbines will determine electricity generating capacity.

Spillways, concrete channels release excess water to control reservoir levels. Pipes and valves manage water downstream of the turbines.

Building a large dam is a major civil engineering project that can take many years. Strict planning, design, environmental review and safety precautions are essential.

Turbine Operation

The most common type of turbine used in hydropower plants is the hydroelectric turbine. Hydroelectric turbines convert the energy of flowing water into mechanical energy that then spins a generator to produce electricity. The amount of available energy in moving water is determined by its flow rate and fall height from the dam or reservoir.

There are two main types of hydroelectric turbines: impulse and reaction turbines. Impulse turbines, like Pelton wheels, use the velocity of water to move the turbine blades. Reaction turbines, like Francis and Kaplan turbines, use water pressure in addition to velocity. In both cases, the moving turbine blades spin a shaft connected to the generator (source).

The most common reaction turbine is the propeller-shaped Kaplan turbine which has adjustable blades that can change their pitch to maintain optimal efficiency as water flow changes. Francis turbines have fixed blades but can still operate efficiently across a range of water flows (source). The generator converts the mechanical power from the spinning turbine into electrical power using electromagnetic induction.

Output and Distribution

The main purpose of hydropower systems is to generate electricity. The amount of electricity that can be generated depends on several factors like the volume of water flow and the height from which it falls. According to the U.S. Department of Energy, the power generated by falling water is directly proportional to the product of head and flow (https://www.energy.gov/eere/water/hydropower-basics).

The electricity generated by the hydroelectric plant is then connected to electrical grids for transmission. High voltage transmission lines are used to transmit the electricity from the power plant to substations near demand centers. The voltage is stepped down at these substations before distribution to homes, businesses and industries (https://www.energy.gov/eere/water/hydropower-basics).

Hydropower plays an important role in electricity transmission grids by providing reserve generating capacity to meet peak load demands. Hydroelectric generators can start up quickly to help meet sudden rises in electricity demand. In some regions, pumped storage hydropower provides most of this peaking capacity (https://www.energy.gov/eere/water/hydropower-basics).

Advantages

Hydropower is considered a renewable source of energy because it relies on the water cycle. As long as the water cycle continues, hydropower will be available. Hydropower is also very reliable once the dam and power plant equipment are constructed. It can quickly go from zero power to maximum output, allowing it to efficiently meet sudden peaks in electricity demand. Additionally, after the initial capital cost of construction, hydropower is relatively inexpensive to operate and maintain. The fuel, water, is free and a hydropower plant has a much longer lifespan than most power plants.

According to the U.S. Department of Energy, hydropower is a “cost-effective, reliable, flexible, and sustainable solution for our nation’s electricity needs.” Hydropower accounted for over 7% of total electricity generation and 44% of the total renewable electricity generation in the United States in 2020. The ability for hydropower to store energy as water behind dams adds to the value and flexibility of the hydropower resource.

Disadvantages

While hydropower can provide clean renewable energy, there are some notable disadvantages as well. One major concern with hydropower dams is their impact on rivers and wildlife. Building a dam drastically alters the natural flow of a river, which can harm native plant and animal species that rely on the river’s natural rhythms and flow levels (Source). Dams disrupt fish migration routes, block sediment transport downstream, and change water temperatures. This damages local ecosystems that have evolved around a river’s natural state.

There are also concerns around greenhouse gas emissions from reservoirs created by hydroelectric dams. As vegetation decomposes underwater it releases methane and carbon dioxide. Some studies have found certain hydroelectric reservoirs emit more greenhouse gases per unit of electricity generated than power plants running on fossil fuels (Source).

Sedimentation buildup behind dams is another issue, as it gradually reduces the storage capacity of reservoirs. Eventually sediment fills reservoirs and reduces the operational life of hydroelectric facilities. Periodic dredging and dam removal is often needed to mitigate this problem.

Conclusion

In summary, hydropower is an important renewable energy source that provides clean, flexible baseload power to electricity grids around the world. The most common type of hydropower generation involves damming a river to store water in a reservoir, which is then released through turbines to generate electricity.

While hydropower development faces environmental challenges regarding river ecosystems and habitat loss, technological advances and more strategic site selection for new projects can help mitigate these impacts. Existing hydropower facilities are also being modernized and upgraded for increased efficiency and flexibility.

Looking forward, hydropower will continue serving as a major source of renewable electricity globally. With greater integration of variable renewables like wind and solar onto grids, hydropower can provide grid balancing services thanks to its storage capabilities. Developing countries still possess significant untapped technical hydropower potential to expand access to clean electricity.

With care taken to consider environmental impacts, hydropower can be a sustainable solution as part of a diversified clean energy portfolio that displaces fossil fuel generation and helps decarbonize electricity systems worldwide.