How Do You Turn Running Water Into Electricity?

Hydropower is one of the oldest and most widely used sources of renewable energy. It is important because it accounts for over 16% of electricity generation worldwide and is a clean, renewable alternative to fossil fuels. Hydropower harnesses the energy of flowing water to generate electricity. Most hydropower plants capture the kinetic energy and potential energy of falling or fast-flowing water to spin a turbine which powers a generator. Some key facts to know about hydropower are that it is renewable, produces very little emissions, is extremely reliable and flexible to operate, and has the highest capacity factor of any renewable source of electricity.

Hydroelectric Power Basics

Hydroelectric power, or hydropower, is a form of renewable energy that utilizes moving water to generate electricity. As described by the U.S. Geological Survey, “Hydropower uses the energy of flowing water to produce electricity or mechanical energy” (USGS). The key principles behind hydroelectric power generation are using the gravity of falling or flowing water and converting its kinetic energy into electricity.

In a hydropower plant, the force of moving water spins a turbine, which powers a generator to produce electricity. The turbine converts the kinetic energy of the water’s flow into mechanical energy, and the generator converts this mechanical energy into electrical energy. The electricity can then be used immediately or fed into a grid to supply homes, businesses, and industries.

Hydropower relies on basic physics – water flowing downhill possesses energy due to gravity and the slope it flows along. A hydroelectric plant captures this energy by channeling water through pipes or tunnels towards the turbines. As the water falls or flows, gravity accelerates it and gives it kinetic energy that gets turned into electricity. This makes hydropower a sustainable and renewable energy source, as the water cycle continuously replenishes the water source.

Hydropower Components

The main components of a hydropower plant include the dam, reservoir, penstock, turbine, and generator (

The dam is built to store water in a reservoir. The dam raises the water level and creates hydraulic head, or pressure. The water from the reservoir is sent through the penstock, a pipe that leads to the turbine (

As the water travels through the penstock, it gains speed and turns the blades of the turbine. This rotational motion causes the shaft connected to the turbine to spin, which then spins the rotor of the generator. The generator uses electromagnetic induction to convert the mechanical energy into electrical energy.

The key components that create the hydroelectric power are the elevated reservouir, the penstock that delivers water to the turbine, the spinning turbine that drives the generator, and the generator itself that produces the electricity.

Turbine Types

There are two main types of hydro turbines: impulse and reaction (1).

Impulse turbines rely on the velocity of water to move the runner and discharges water to atmospheric pressure (1). Common impulse turbines include Pelton wheels and Turgo turbines.

Reaction turbines rely on water pressure acting on the runner blades to generate torque. Water pressure drops as it moves through the turbine and discharges at low pressure. Common reaction turbines include Francis and Kaplan turbines (2).

Other turbine designs include Archimedes’ screw, which use a screw inside a tube to lift water. Gravity causes water to descend through the turbine (1).





Microhydropower refers to hydroelectric systems that generate power on a smaller, individual scale. These systems operate with a “low head” of less than 15 meters and low flow rate, making them well-suited for remote locations, rural or island communities, and private residences.

Microhydropower systems have three main components: a turbine or waterwheel, an alternator/generator, and wiring and controls [1]. The turbine captures the kinetic energy of flowing water and converts it into rotational energy. Common turbine types used are Pelton wheels and Turgo wheels for high heads, and propeller turbines, Francis turbines, and crossflow turbines for low heads [2].

The generator or alternator converts the mechanical power into electrical power. Wiring connects the generator to the load being powered, while controls regulate factors like voltage and load demand. Other components can include pipelines delivering water to the turbine, a penstock, and a powerhouse.

Microhydropower systems generate up to 100 kilowatts of power and can provide electricity for single homes, farms, and even entire villages [3]. They provide a sustainable, renewable power source without producing greenhouse gas emissions.

Pumped Storage

Pumped storage hydropower (PSH) works by using excess electricity to pump water from a lower reservoir to an upper reservoir. When electricity demand is high, the stored water can be released from the upper reservoir through a turbine to generate hydroelectric power on demand (1). This allows energy from intermittent renewable sources, like wind and solar, to be stored and dispatched when needed.

water flowing through a turbine in a hydropower dam to generate electricity
PSH is currently the largest-capacity and most cost-effective form of grid energy storage available (2). The round-trip energy efficiency of PSH ranges from 70-87%, with typical values around 80% (3). This means about 20% of the energy used to pump the water uphill is lost in the process. The main requirement for PSH is having two reservoirs at different elevations, which allows the system to recycle the water. The global potential for new PSH sites is estimated to be over 20,000 GW, providing a vast amount of storage capacity.


(1) EESI Fact Sheet on Energy Storage

(2) Wikipedia on Pumped-Storage Hydroelectricity

(3) Blakers et al., “A review of pumped hydro energy storage”


Run-of-river hydroelectric plants generate electricity by harnessing the natural flow of a river, without the need for large dams or reservoirs. These plants have little to no water storage capacity. Instead, they use the river’s flow to spin turbines connected to generators. The water passes through the plant and returns to the river downstream.

Run-of-river systems take advantage of rivers with consistent, year-round flows. They require a portion of the river to be diverted through a pipe or channel called a penstock to the powerhouse. The moving water rotates the turbines, which spin magnets within coils of wire to generate electricity.

Run-of-river projects have less environmental impact compared to traditional reservoir-based hydropower. They do not substantially alter the surrounding landscape or disrupt natural flow cycles. However, they can affect local wildlife habitats and water quality. Proper siting, design, and mitigation can minimize these effects [1].

Overall, run-of-river provides renewable electricity with lower variability than wind or solar power. It serves as a stable complement to these intermittent resources. Existing dams can sometimes be retrofitted for run-of-river hydropower at low cost and with little additional environmental impact.

Hydropower Pros and Cons

Hydropower is considered a renewable energy source because it relies on the water cycle to replenish the water used to generate electricity. Once a hydroelectric dam is built, the project can generate electricity for decades at a relatively low operating cost. Hydropower is also very flexible – operators can start up, shut down, or otherwise adjust output to respond to changes in electricity demand. This makes hydropower a good complement to other renewables like wind and solar which fluctuate based on weather patterns. Compared to fossil fuels, hydropower emits very low amounts of greenhouse gases.

However, there are some downsides of hydropower that need to be considered. Damming rivers can change natural water flows and affect local wildlife habitats and vegetation. Fish migration can be disrupted without proper design of fish ladders and elevators. Reservoirs created by dams lead to increased evaporation and possible production of greenhouse gases like methane from the decomposition of flooded biomass. Dam failures, though rare, can be catastrophic. There are also limits to the number of suitable hydropower sites that have not already been developed.

Overall hydropower is a mature renewable energy technology that offers flexibility and low emissions, but projects must be designed and operated responsibly to minimize environmental impacts. While not without some downsides, hydropower can play an important role in the transition to cleaner energy systems.

Notable Hydropower Projects

Some of the most notable and largest hydroelectric dams in the world include:

The Hoover Dam on the Colorado River straddling the border of Nevada and Arizona is one of the earliest and most iconic hydroelectric projects in the United States. At the time of its completion in 1936, it was the largest hydroelectric power station in the world with a capacity of 1,345 MW [1].

The Grand Coulee Dam on the Columbia River in Washington state was the largest hydroelectric power station in the United States when completed in 1942 with a capacity of 1,974 MW. It remains the largest power producer in the U.S. today generating over 6,800 MW [2].

The massive Three Gorges Dam in China on the Yangtze River is currently the world’s largest hydroelectric power station. Completed in 2012, it has a capacity of 22,500 MW.

Other major hydroelectric dams around the world include the Itaipu Dam on the Brazil/Paraguay border, the Guri Dam in Venezuela, and the Sayano–Shushenskaya Dam in Russia.

The Future of Hydropower

Hydropower has substantial untapped potential according to recent reports. The International Hydropower Association’s Hydropower 2050 report identified over 850 gigawatts of additional global capacity that could be developed by 2050 through new projects, upgrades, and better integration. The U.S. Department of Energy also sees growth potential, projecting hydropower could expand from 101 gigawatts today to 150 gigawatts by 2050.

Realizing this potential will require new technologies and innovative approaches to overcome challenges. Advances in pumped storage technology, like variable speed turbines, can enable greater grid flexibility. New modular and low-head hydropower designs allow generating electricity from lower water flows. Technologies like hydrokinetic turbines tap the energy of flowing water without dams. Integrating hydropower with floating solar PV, wind, and energy storage creates hybrid renewable systems.

Siting projects to avoid environmental impacts and gaining public acceptance is crucial. Strategic upgrades to existing infrastructure can often increase output while minimizing new impacts. Partnerships with indigenous communities and addressing sustainability issues will pave the way for responsible growth.

Similar Posts