Hydroelectric power generation is the act of using moving water to generate power. Historically this was done using paddle wheels in streams to turn grinding stones for making grain flour. Today, most hydroelectric dams are of a larger scale. A hydro dam location is chosen because it has a large amount of flowing water that can exit the dam at a much lower height than it was taken at. As in a waterfall, the waters falling through the dam generators speed up and drive turbines, generating power. Hydroelectricity is a renewable energy resource.

A dam is a large cement wall anchored to the land around it so at to resist the force of the river. It forms the structure which contains the turbines and also forms one of the walls of the reservoir.

A reservoir is an area behind the dam on the ‘high’ side, where water pools into a lake. The water in a resevoir can be used by allowing it to run down through a turbine, creating power. In this way, water stored in a resevoir is a form of energy storage, because we can use it when we want to. This is a novel feature amongst renewable energy sources, since most others do not have built-in energy storage capability.



Hydroelectricity is the largest contributor to low carbon electricity world wide, currently producing around 20% of worldwide electricity. Large amounts of hydro power are still being constructed in the world, chiefly in developing Asia. The vast majority of hydroelectric sources have been exploited in the west and in some cases is in decline due to flow shortages.

Small Scale

Many notable small scale water turbines have been built in the last decade or so. These generators more resemble modern versions of their wooden water wheel parent than the large scale dams we are familiar with. These smaller systems are a relatively inexpensive form of small scale power that cause minimal to no harm to the waterways they draw upon.

They cause less harm in that they minimally disturb the plants and animals in the area. For instance, it is much easier to include ecological features such as a fish ladder in these small generators.

There are also many more locations suited to small scale hydroelectric generators because they do not require large amounts of fast water or convenient natural forms to be made into reservoirs. They do not have the social and environmental impacts of traditional hydro dams, but do not produce nearly as much power in one location as the larger scale dams, as expected.

Implementation Issues

A reservoir is carved into the land behind the dam to hold a large supply of water. In some cases, natural land forms are simply flooded with water to form the reservoir. This has led to the flooding of large amounts of fertile river-side farmland worldwide, and the relocation of substantial populations of both animals and humans.


As previously stated, hydroelectricity is generally considered a green, sustainable form of electricity. It has no fuel costs once constructed and require relatively little maintainance when compared with other forms of non-carbon based power such as wind, solar, and nuclear. Hydroelectricity is one of the cheapest forms of power, even in modern times. Water can be retained behind dams to be converted into electricity during peak demand hours, have a relatively quick ability to start or stop generating power, and the ability to generate less than maximal power by only utilizing a fraction of total turbines at a time. Hydroelectric facilities can be constructed in stages, such as the Three Gorges Dam, to provide a fraction of total power before final completion.


Hydro dams disrupt the natural flow of water. This includes flooding of natural land forms for use as reservoirs and restricting of fish such as the salmon to swim upstream to spawning grounds. While by no means perfect, it is generally agreed that most of the hydro dams built during the 20th century had far fewer ecological consequences than generating that power through fossil fuel based means. Newer dams being considered are generally in spots less suited to hydroelectric power because the best spots have already been taken.

Adaptations and Variants

Large Scale Variation

A reservoir on the lower end can be included in the design. This allows water sitting in the lower reservoir to be pumped back up to the higher reservoir using power generated during the night.

The reason extra power is generated during the night is twofold. Firstly, demand typically hits it’s daily low during the night because people typically consume less power when they are asleep. Secondly, some types of power generation cannot be scaled easily according to demand. What this means is if we are using an old 800 megawatt coal power plant, it quite likely has to run at full power all the time. It would take many hours or even days to bring it down to a lower output.

It also makes sense to use intermittent power sources to pump water from the lower side of the dam to the reservoir on the higher side. For instance, if we had a wind turbine powering a pump, it would pump hard while the wind is blowing hard, and very little when the wind is relatively calm. It would be able to contribute to the stored energy in the reservoir at it’s own pace. Since we can turn on and off hydroelectric turbines at our discretion, this allows us greater control over our energy production, and additional safety since we have a larger amount of stored energy for later use.

Small Scale Variation

Vortex generator: Type of generator that is more expensive initially than standard small scale hydro, but has ecological and repair advantages. Reliability and minimal environmental impact are the design goals.

Kyle Laskowski

I am a graduate from the University of Regina’s Honours Physics program from rural Saskatchewan. After taking a keen interest in the Saskatchewan Uranium Development Partnership consultation effort, I have become interested in studying and writing about a diverse range of topics, as you seen on Vision Of Earth now. Recent additions to my interested include machine learning, space flight and our future relationship with Mars.

8 thoughts to “Hydroelectricity”

  1. I’d love to know how many megawatts a small scale watermill like the one you describe would generate. Could cities like Prince George (which has 2 rivers, the Thompson and the Nechako), Ottawa, Quebec and Montreal power themselves this way without completely blocking their rivers?

    (Never mind that PG will be powering itself with biomass from their pulpmills in the relatively near future anyways)

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