What Do You Need For Hydropower?
Hydropower, or hydroelectric power, is the use of flowing water to generate electricity. Hydropower is considered a renewable energy source because it relies on the water cycle, which is continuously replenished by the sun.[1] Hydropower has a long history, dating back to the late 19th century, and today generates around 16% of the world’s electricity.[2] As concerns grow over climate change and the need to transition to clean energy, hydropower remains an important renewable energy source with the potential for further growth globally.
Hydropower works by using the energy of flowing or falling water to spin a turbine connected to a generator. The movement of the turbine blades causes the rotor of the generator to spin and produce electricity. The amount of electricity that can be generated depends on the volume of water flow and the height of the water fall. Dams are often constructed to create reservoirs and control the water flow.
Compared to other renewables like wind and solar, hydropower can generate electricity consistently and predictably. It also offers flexibility to generate power when needed. With the ability to store energy via pumped storage, hydropower can help balance electricity supply and demand. Overall, hydropower is a major renewable energy source with the ability to provide clean, flexible electricity globally.
[1] https://www.hydropower.org/iha/discover-facts-about-hydropower
[2] https://www.iea.org/reports/hydropower-special-market-report/executive-summary
Water Source
The water source is one of the most important components of a hydropower system. Hydropower relies on flowing water, so the most common sources are rivers, lakes, and oceans.[1]
Rivers provide a constant flow of water and are often dammed to create large reservoirs for hydropower. Many of the largest hydropower stations in the world utilize major rivers like the Yangtze in China and the Itaipu on the Brazil/Paraguay border.[2]
Lakes, especially large natural lakes, can also provide sustainable water sources for hydropower. Diverting or damming a lake outlet can create the necessary water pressure. Examples include the Krasnoyarsk Dam in Russia which uses the Yenisei River flowing from Lake Baikal.
The ocean provides an immense and powerful water source for hydropower. Tidal power stations rely on the daily flow of the tides to drive turbine generators. Major tidal power facilities include the Sihwa Lake Tidal Power Station in South Korea. Conventional hydropower can also utilize the ocean; for example, Japan’s Kuroshima Ocean Current Power Plant generates electricity from ocean currents.
The key difference between tidal and conventional hydropower is that tidal relies on the predictable ebb and flow of ocean tides rather than an inland water source with a constant flow. Both provide renewable power but have different engineering requirements to harness the water source.
Dam and Reservoir
The dam in a hydropower system serves to create a reservoir by containing and regulating the water flow. The reservoir stores potential energy by holding back water in the elevated reservoir, creating hydraulic head (the height difference between the water source and turbines).
Some of the largest reservoirs in the world by surface area include Lake Kariba in Africa (2,536 square miles), Lake Nasser in Egypt (2,235 square miles), and Lake Volta in Ghana (3,283 square miles) (“List of reservoirs by surface area,” n.d.). By volume, the Three Gorges Dam in China created the largest reservoir in the world, holding 39.3 cubic kilometers of water (“List of reservoirs by volume,” n.d.).
While large reservoirs enable more power generation, they can also have significant environmental impacts. Flooding land for the reservoir may displace people and wildlife. The stagnant water can increase waterborne diseases, and methane emissions from decomposing plant matter underwater may contribute to greenhouse gases. However, dam operators can take steps to mitigate the impacts through resettlement programs, public health initiatives, and greenhouse gas reduction strategies.
Intake
The intake structure is an important component of hydropower projects that controls the flow of water from the water source into the rest of the system. According to the ASCE Guidelines for Design of Intakes for Hydroelectric Plants, the intake “provides for the withdrawal and conveyance of water into the turbine[1].”
Intake gates are used to control the amount of water that enters the system. They allow operators to regulate water flow based on electricity demands and other conditions. Debris screens and trashracks are also installed at the intake to filter out sticks, logs, leaves and other solid objects that could damage equipment downstream[2].
Penstock
The penstock is a large pipe that carries water from the intake to the turbines (Dubai Deep Tunnel Stormwater System). It is usually made of steel or reinforced concrete. The penstock needs to be large enough to supply the water flow required by the turbine and hydroelectric plant.
For example, the Bieudron Hydroelectric Power Station in Switzerland has three Pelton turbines, each with a capacity of 423 megawatts. To supply enough water to these massive turbines, it requires penstocks over 15 feet in diameter (Bieudron Hydroelectric Power Station).
The penstock diameter and materials depend on factors like the water volume and pressure. Larger, high-pressure systems require stronger, thicker penstocks made of steel rather than concrete. Proper design and construction of the penstock is critical to ensure sufficient water delivery and prevent pipe bursts or other failures.
Turbine
The turbine is a critical component of hydropower that turns the kinetic energy of moving water into mechanical energy. There are two main types of hydro turbines used in hydropower plants: impulse turbines and reaction turbines.
Some common types of impulse turbines include Pelton wheels and Turgo turbines. These turbines use the velocity of water to move the turbine blades. The most common reaction turbine is the propeller-type Kaplan turbine, which provides good efficiency and performance over a wide range of flow conditions. Francis turbines are also widely used reaction turbines. They operate with water discharging radially through the turbine. Different turbines are better suited for different situations depending on the head height and flow rate.
Selecting the right turbine type and matching it to the site conditions allows hydropower facilities to maximize power generation efficiency.
Generator
The generator is a critical component of a hydroelectric power plant. It converts the mechanical energy from the spinning turbine into electrical energy. Inside the generator, coils of copper wire rotate around electromagnets, producing an electric current based on the principles of electromagnetic induction.
The generator acts as the powerhouse, generating the electricity that gets fed into transmission lines and distributed to homes and businesses. Larger generators are capable of producing massive amounts of electricity. For example, the 16 turbines at the Three Gorges Dam in China each contain a generator capable of producing 700 megawatts of power, for a total generating capacity of 11,200 megawatts.
The capacity and design of the generator depends on the available water flow and hydraulic head height. More flow and head allows larger, more powerful turbines that can drive bigger generators. State-of-the-art generator designs aim to maximize power output and efficiency.
Transformer
The generator produces electricity at a low voltage, usually around 13,800 volts. This electricity must be stepped up to a much higher voltage for efficient transmission over long distances. Transformers are used to increase the voltage. According to How Power Grids Work, typical transmission line voltage ranges from 155,000 to 765,000 volts. This high voltage enables the electricity to travel hundreds of miles with minimal losses. At the end of the transmission lines, the electricity arrives at a substation, where transformers step the voltage back down for distribution to homes and businesses. The substation connects the power plant to the larger grid.
Transmission
Once the electricity is generated at the hydropower facility, it needs to be transmitted to demanding population centers and connected to the larger electrical grid. Transmission lines carry the electricity at high voltages, typically 115 kV to 765 kV, over long distances up to 300-600 miles from the generation source (1)(2). This allows the electricity to travel efficiently over long distances with minimal power loss.
The transmission system acts as a network, interconnecting various generation facilities and substations using high voltage lines suspended on large steel towers. This creates a grid that allows electricity to flow throughout a region to meet demand. Interconnections between utility control areas also increase reliability by allowing transmission of power across regions in case of excess generation or shortages (2).
Ultimately, the transmission system takes the electricity produced at hydropower facilities and delivers it to distribution substations near demanding population centers. This key step allows consumers access to renewable hydropower from even remote generation sites.
Sources:
(1) https://www.science.smith.edu/~jcardell/Courses/EGR220/ElecPwr_HSW.html
(2) https://www.penlight.org/hydropower-101-transmission-from-dam-to-doorstep/
Environmental Considerations
Hydropower projects can impact wildlife habitats and water quality if not properly mitigated. The construction of dams floods land and forests, altering natural habitats both upstream and downstream. Hydropower projects can also affect water quality by changing water temperatures, oxygen levels, and flow patterns. Strict environmental regulations help minimize these impacts.
In the United States, hydropower projects are regulated by the Federal Energy Regulatory Commission (FERC) under the Federal Power Act. All non-federal hydropower projects must obtain a FERC license which requires a review of environmental impacts and plans for mitigation. FERC regulations include requirements for minimum water flows, fish passage facilities, and monitoring of water quality.
Fish ladders and screens play an important role in minimizing the impact to fish populations. As water is diverted through the dam into the turbines, fish can become trapped or killed. Fish ladders provide a route for fish to safely pass around the dam. Intake screens prevent fish from being drawn into the turbines. Maintaining fish populations is mandated under FERC license conditions. New environmental regulations are raising the standards for fish protection at hydropower facilities.
While hydropower is a renewable energy source, projects must be carefully managed to minimize disturbances to surrounding ecosystems. Strict regulations and mitigation strategies help reduce the environmental footprint of hydropower in the United States.
