What Resources Are Used To Create Hydro?

Hydroelectric power, as defined by Britannica, is electricity produced from the energy of falling or fast-running water (https://www.britannica.com/science/hydroelectric-power). People have been using water to generate power for thousands of years, but it wasn’t until the late 19th century that hydroelectric power plants began to appear in the United States and Europe. Hydroelectricity was an important early source of electricity in the US. Today, it accounts for just under 7% of total electricity generation in the country (https://www.eia.gov/energyexplained/hydropower/).

Hydroelectric power is considered a renewable energy source because it relies on the water cycle. Rain and snow replenish the water used to generate electricity. Hydroelectric plants provide a stable supply of electricity, as they can quickly respond to peaks and lulls in demand. The ability to store energy by pumping water uphill to a reservoir means hydroelectricity can serve as a giant battery, providing power when solar and wind are unavailable. This makes hydro power an important part of many countries’ energy mix.

Hydroelectric Power Plants

Hydroelectric power plants convert the energy from flowing water into electricity. The key components used are:

  • Dam and reservoir – A dam is built to control the flow of water and create a reservoir. The reservoir stores potential energy by holding back water behind the dam.
  • Turbine and generator – When the water is released from the reservoir, it flows through pipes called penstocks which carry the water to the turbines. The moving water spins the turbine blades which rotate a shaft connected to a generator to produce electricity. Hydro turbines can be Kaplan, Francis or Pelton turbines.
  • Transformer – The electricity generated is stepped up to a higher voltage by a transformer before it is transmitted to the electric grid.

The height of the water behind the dam and volume that can be released determines the amount of electricity that can be generated at a hydro plant. Dams allow control over the water flow to match power production to demand (source).

Types of Hydropower Plants

There are three main types of hydropower plants:

Impoundment (Dam)

Impoundment facilities use a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level. The Department of Energy notes that impoundment facilities are the largest and most commonly used type of hydropower plant in the United States today.

Diversion (Run-of-River)

Diversion hydropower plants channel a portion of a river through a canal or penstock, harnessing the energy of flowing water to spin turbines and generate electricity, without the need for a large dam and reservoir. According to the International Hydropower Association, run-of-river plants provide a continuous supply of energy by utilizing a river’s natural flow and elevation drop.

Pumped Storage

Pumped storage plants pump water from a lower reservoir to an upper reservoir for storage. During periods of high electricity demand, power is generated by releasing the stored water through turbines. Pumped storage enables energy from intermittent sources like wind and solar to be stored and dispatched when needed.

Water Sources for Hydroelectricity

The water sources used for hydroelectric power generation include rivers, lakes, and oceans.

Rivers provide a constant flow of water that can be diverted and channeled through turbines in a hydroelectric dam to generate electricity. Many major hydroelectric plants around the world utilize large rivers with high volumes of water flow, such as the Three Gorges Dam in China which taps into the Yangtze River. Smaller rivers can also be used for small-scale hydro projects.

Lakes serve as reservoirs that can store water and control its release for hydroelectric generation. Often a dam is constructed to form an artificial lake behind it, like the Hoover Dam which created Lake Mead along the Colorado River. Some hydro facilities pump water back into lakes during times of low electricity demand to be released again later at peak demand.

Oceans provide enormous potential for tidal power and wave power. Tidal power harnesses the flow of tides in coastal areas by constructing tidal barrages or underwater tidal turbines. Wave power utilizes the up-and-down motion of waves near shorelines or out at sea, where wave energy converters capture the energy of waves and convert it to electricity.

Advantages of Hydropower

Hydropower offers several key advantages that make it an attractive energy source:

Renewable – Hydropower is considered a renewable energy source because it relies on the water cycle. As long as there is flowing water, hydropower can be generated.

Reliable – Hydropower can generate electricity 24/7 unlike some other renewable sources like solar and wind which rely on weather conditions. Hydroelectric facilities can quickly go from zero power to maximum output, making them useful to meet sudden spikes in demand (1).

Cost-effective – Once a hydroelectric plant is constructed, the generation of electricity is relatively low cost. The cost per kilowatt-hour is lower compared to fossil fuels and competitive with other renewable energy sources (2).

Clean, low emissions – Hydropower does not produce air pollution or greenhouse gases. It has one of the lowest carbon footprints of any energy source (2).

(1) https://www.energy.gov/eere/water/benefits-hydropower
(2) https://www.enelgreenpower.com/learning-hub/renewable-energies/hydroelectric-energy/advantages

Disadvantages of Hydropower

While hydropower offers many benefits, it also comes with some drawbacks. One major disadvantage is the high cost of building large-scale hydroelectric dams and power plants. The initial construction costs are very high compared to other energy sources like solar or wind power (1). Massive dams, spillways, tunnels, and turbines are complex and expensive to manufacture and install.

Hydroelectric dams can also severely disrupt river ecosystems and the habitats of fish and wildlife. The damming of rivers prevents fish migration and spawning, and alters natural water flows and sediment transport (2). This can lead to a loss of biodiversity and extinction of local species. Large areas may be flooded for reservoirs, impacting forests and vegetation.

Hydropower output relies heavily on seasonal precipitation and weather patterns. During droughts and low rainfall periods, power generation can decrease substantially as water levels drop. This makes hydropower generation less reliable than fossil fuels or nuclear power plants (3).

Suitable hydroelectric plant locations are limited by geographical factors like elevation changes, proximity to rivers, and adequate water flow volumes. Not all regions have the right topography and water bodies to support the development of hydropower projects. The best sites are often remote areas far from cities and transmission infrastructure (4).

(1) https://earth.org/pros-and-cons-of-hydroelectric-energy/

(2) https://kiwienergy.us/pros-and-cons-of-hydroelectric-energy/

(3) https://www.greengeeks.com/blog/hydroelectric-energy/

(4) https://www.greengeeks.com/blog/hydroelectric-energy/

Major Hydroelectric Projects

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

Hoover Dam – Located on the Colorado River in Black Canyon on the border between Nevada and Arizona, USA. With a height of 221 meters and a length of 379 meters, Hoover Dam has a generating capacity of 2,080 MW, making it one of the largest hydroelectric power stations in the United States. Construction on Hoover Dam began in 1931 and was completed in 1936.

Three Gorges Dam – Built on the Yangtze River in Sandouping, China, the Three Gorges Dam is the world’s largest power station in terms of installed capacity at 22,500 MW. The dam is 181 meters tall and 2,335 meters long. Construction started in 1994 and was fully operational by 2012. The massive size of the Three Gorges project has drawn criticism in terms of environmental and social impacts.

Itaipu Dam – Located on the Paraná River bordering Brazil and Paraguay, the Itaipu Dam is the second largest hydroelectric power station in the world with a generating capacity of 14,000 MW. At a height of 196 meters and length of 7,919 meters, construction on the Itaipu project began in 1975 and was completed in 1991. Itaipu produces approximately 90% of the electricity consumed in Paraguay and 20% of electricity in Brazil.




Small-Scale and Micro Hydro

Small-scale hydropower systems capture energy from falling or flowing water from small rivers, canals, or streams. They typically have a capacity of 1 to 10 megawatts. Micro hydropower systems have a capacity of up to 100 kilowatts. According to the Wikipedia article on small hydro, small hydro projects can provide clean, renewable energy, especially in rural or remote areas.

Some common types of small-scale hydro projects include:

  • Run-of-river projects – These systems channel a portion of a river’s water through a canal or penstock to turn a turbine. A small weir or dam may be used to divert water, but generally do not require large dams or reservoirs.
  • Small dams/weirs – Small dams or weirs can be built across rivers or streams to raise the water level and create hydraulic head. The water flows through turbines integrated into the dam or weir structure.
  • Community-level hydro – Micro and pico hydropower systems can provide electricity for isolated rural villages and communities. Local materials may be used for civil works and construction.

According to the SSWM.info article, small-scale hydro can be a cost-effective way to provide electricity to remote areas without access to the grid. Projects can often be built and maintained by local communities.

Future of Hydroelectricity

The future outlook for hydroelectricity is positive, with growth expected mainly in Asia and South America. According to the International Energy Agency (IEA), global hydropower capacity is forecast to increase by 17% between 2021-2030, with China and India accounting for half of new capacity. There are major hydro projects underway in countries like Laos, Brazil, and Ethiopia as developing nations seek to expand electricity access.

In existing hydro countries like the United States, focus is on upgrading and modernizing aging infrastructure to boost efficiency and capacity. The U.S. Department of Energy highlights the potential to add power at existing dams that do not currently produce electricity. Retrofitting existing infrastructure is often cheaper than building new capacity.

Pumped storage hydropower is also expected to grow as it offers storage capabilities to complement variable renewable sources like wind and solar. Pumped storage works by pumping water uphill to a reservoir during periods of low electricity demand and then releasing it downhill to generate power when demand is high. The IEA projects global pumped storage capacity will increase by over 50% through 2030, notably in China, Europe, and the United States.


Hydroelectric power has played an important role in energy production for over a century. This renewable energy source utilizes the natural flow of water to generate electricity that powers homes, businesses, and cities. While hydropower only provides about 7% of total US electricity generation, it accounts for over 40% of all renewable power in the country.

As this article outlined, hydroelectric plants rely on flowing water – whether from dams, rivers, or ocean tides – to spin large turbines that activate generators. The different types of hydropower facilities include large hydroelectric dams, pumped storage plants, small run-of-river projects, and emerging technologies like wave and tidal generators. The advantages of hydro include its renewable nature, low operating costs, and ability to quickly adjust output to meet demand. However, building large dams can also carry environmental impacts.

Looking ahead, hydropower will continue providing clean, renewable electricity in the global shift towards sustainable energy. Upgrades and innovations at existing hydro plants, plus small-scale hydropower development, can further grow hydro’s output. With careful siting and management, hydroelectricity can supply emissions-free power to the grids of the future.

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