Buzz
Hydropower plants account for roughly 24% of global electricity production, providing power to over a billion people. These plants collectively generate 675,000 megawatts, equivalent to the energy of 3.6 billion barrels of oil, according to the National Renewable Energy Laboratory. With more than 2,000 hydropower facilities in the United States alone, hydropower is the nation's leading source of renewable energy.
In this article, we will explore the process of how falling water generates power and delve into the hydrological cycle that drives the flow of water necessary for hydropower. Additionally, you'll discover a fascinating application of hydropower that could influence your everyday life.
The Power of Water
When observing a river's current, it's difficult to grasp the immense power it holds. If you've ever experienced the thrill of white-water rafting, you've sensed a small portion of the river's strength. White-water rapids form when a large volume of water is forced down a narrow passage, intensifying its flow. Floods offer another striking example of the overwhelming force exerted by vast quantities of water.
Hydropower stations capitalize on the energy contained in water and employ basic mechanical systems to convert this energy into electricity. These plants operate on a straightforward principle: water flowing through a dam rotates a turbine, which subsequently drives a generator.
Below are the key components found in a traditional hydropower facility:
The shaft connects the turbine to the generator, enabling their synchronized operation.- Dam - The majority of hydropower plants utilize a dam to store water, forming a vast reservoir. Often, these reservoirs double as recreational lakes, like Lake Roosevelt located at the Grand Coulee Dam in Washington State.
- Intake - Gates in the dam open, allowing gravity to pull water through the penstock, a large pipe leading to the turbine. As water travels through the pipe, pressure builds up.
- Turbine - The water impacts and spins the blades of a turbine, which is connected to a generator above it via a shaft. The most common turbine used in hydropower plants is the Francis Turbine, which resembles a large disk with curved blades. These turbines can weigh up to 172 tons and rotate at speeds of up to 90 rpm, according to the Foundation for Water & Energy Education (FWEE).
- Generators - As the turbine blades spin, a series of magnets inside the generator rotate, generating alternating current (AC) by passing over copper coils and moving electrons. (More on how the generator operates will be discussed later.)
- Transformer - The transformer within the powerhouse increases the voltage of the alternating current (AC) produced by the generator.
- Power lines - Every power plant sends out four wires: three for the phases of electricity being generated and one neutral wire that serves as a common ground for all three phases. (For more details on power line transmission, refer to How Power Distribution Grids Work.)
- Outflow - The used water flows through pipelines known as tailraces and returns to the river downstream.
The water stored in the reservoir is regarded as potential energy. Once the gates open, the flowing water moving through the penstock transforms into kinetic energy as it is set into motion. The amount of electricity generated is influenced by a number of factors, two of the main ones being the volume of water flow and the hydraulic head. The head is defined as the vertical distance between the water's surface and the turbines. As both the head and flow increase, so does the electrical output. The head generally depends on the water volume in the reservoir.
While hydropower reached its peak usage in the mid-20th century, the concept of generating power from water dates back thousands of years. A hydropower facility is essentially an enlarged water wheel. Over 2,000 years ago, the Greeks are credited with using a water wheel to grind wheat into flour. These ancient water wheels were similar to the turbines used today, spinning as the water flowed over their blades. The gears of the wheel ground the wheat into flour.
Pumped-Storage Hydropower Systems
The massive generators at Hoover Dam generate over 2,000 megawatts.
Photo credit to the U.S. Bureau of ReclamationAnother variation of hydropower plants is the pumped-storage plant. In a traditional hydropower facility, water flows from the reservoir through the plant, then exits and moves downstream. A pumped-storage plant, however, utilizes two reservoirs:
- Upper reservoir - Similar to a conventional hydropower plant, a dam creates a reservoir. The water in this reservoir is directed through the hydropower plant to generate electricity.
- Lower reservoir - After passing through the plant, the water flows into a lower reservoir instead of returning to the river to continue downstream.
By utilizing a reversible turbine, the plant is capable of pumping water back into the upper reservoir during off-peak hours. Essentially, the second reservoir is used to refill the first. This process allows the plant to store water, ensuring that more electricity can be generated during times of high demand.
The Generator
At the core of the hydroelectric power station is the generator. Most hydropower plants are equipped with several generators to meet the demand for electricity.
As you might expect, the generator is responsible for producing electricity. This is achieved by rotating a set of magnets within coils of wire, which causes electrons to move and generates electrical current.
The Hoover Dam is equipped with 17 generators, each capable of producing up to 133 megawatts of electricity. The total generating capacity of the Hoover Dam hydropower facility is 2,074 megawatts. Each generator consists of several essential components:
- Shaft
- Excitor
- Rotor
- Stator
As the turbine rotates, the excitor sends an electrical current to the rotor. The rotor consists of large electromagnets that spin inside a tightly coiled copper wire, known as the stator. The interaction between the magnetic field and the coil generates an electric current.
At the Hoover Dam, an electrical current of 16,500 amps is generated and sent from the generator to the transformer, where it is increased to 230,000 amps before being transmitted.
The Hydrologic Cycle
The hydrologic cycleHydropower plants harness the power of a continuous, natural process — the same one that causes rainfall and river levels to rise. Each day, our planet loses a small amount of water as ultraviolet rays from the sun break apart water molecules in the atmosphere. Simultaneously, new water is emitted from the Earth’s interior through volcanic activity, balancing the amount of water lost with the amount created.
At any given moment, Earth's water exists in several different forms. It can be liquid, as in oceans, rivers, and rain; solid, as in glaciers; or gaseous, as in the unseen water vapor in the air. Water constantly changes its state as it is transported around the Earth by wind currents, which are driven by the sun. The sun shines more intensely on the equator than on other regions, which creates these air-current cycles.
Air-current cycles propel Earth’s water supply through its own cycle, known as the hydrologic cycle. As the sun heats liquid water, it evaporates into vapor in the atmosphere. The heat causes the air to rise, but as it moves higher, the air cools. This cooling causes the water vapor to condense into droplets. Once the droplets accumulate enough, they may fall back to Earth as precipitation.
The hydrologic cycle is crucial for hydropower plants because they rely on water flow to generate power. If there is insufficient rainfall near the plant, water won't accumulate upstream. Without this water, less water flows through the hydropower plant, resulting in a decrease in electricity production.
Sources: U.S. Bureau of Reclamation and the National Renewable Energy Laboratory
- The largest hydroelectric power plant in the world is the Itaipu power plant, a joint venture between Brazil and Paraguay. Itaipu can generate 12,600 megawatts.
- The second largest hydroelectric power plant is the Guri power plant, located on the Caroni River in Venezuela, with a capacity of 10,300 megawatts.
- The largest hydroelectric power plant in the U.S. is the Grand Coulee power station on the Columbia River in Washington State. It currently produces 7,600 megawatts and is undergoing an upgrade to reach 10,080 megawatts. (NREL)
Hydroelectric Footwear
Image from patent No. 6,239,501: Footwear with hydroelectric generator assembly
Photo courtesy U.S. Patent and Trademark OfficeThe core concept of hydropower is to harness the energy of flowing water to turn a turbine. Usually, this requires building a large dam across a river. A recent innovation, however, is applying this principle on a smaller scale, using it to power portable electronic devices.
Inventor Robert Komarechka from Ontario, Canada, has developed a novel idea of embedding small hydropower generators into the soles of shoes. These micro-turbines are designed to generate enough energy to power almost any portable gadget. In May 2001, Komarechka was granted a patent for his innovative foot-powered device.
Walking follows a simple yet essential principle: each step involves a motion from heel to toe. When your foot strikes the ground, force is applied through the heel. As you get ready for the next step, your foot rolls forward, shifting the force to the ball of your foot. Komarechka recognized this basic walking motion and has come up with an idea to capture the energy produced by this natural action.
Komarechka's 'footwear with hydroelectric generator assembly,' as detailed in his patent, consists of five key components:
- Fluid - The system utilizes an electrically conductive fluid.
- Fluid sacs - One sac is positioned in the heel and another in the toe section of the shoe.
- Conduits - These connect each fluid sac to a microgenerator.
- Turbine - Water moving within the sole drives the blades of a tiny turbine.
- Microgenerator - Placed between the two fluid sacs, it includes a vane rotor that drives a shaft to power the generator.
When the person walks, the compression of the fluid in the heel's sac forces the fluid through the conduit into the hydroelectric generator. As walking continues, the heel lifts and pressure is exerted on the sac beneath the ball of the foot. This movement of fluid powers the rotor and shaft to generate electricity.
An external socket will be available to connect wires to a portable device. Additionally, a power-control output unit, possibly worn on the user's belt, will be provided. This unit will allow electronic devices to be connected, ensuring a consistent supply of electricity.
"As the number of battery-powered portable devices increases," the patent states, "there is a growing demand for a reliable, adaptable, and efficient power source." Komarechka envisions his invention being used to power laptops, mobile phones, MP3 players, GPS devices, and two-way walkie-talkies.
