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Hydroelectric power plant (definition, principle, usage, types and layout)

March 29, 2018
Diesel power plant (Principle, Component, Layout, Applications)

What is hydroelectric power?

Hydroelectric power plant;  also we can define as water power is the power produces from the falling water, the fast running water; rain or metaled snow. And it’s one of the oldest and cheapest renewable energy sources used for producing energy, and also used for irrigation and operation of various mechanical devices like gristmill, textile mills, domestic lifts, trip hammers and dock cranes.

hydroelectric power plant

10% of the nation’s energy generated by hydroelectric power plants which make us inquires how this hydroelectric plant works, but at first, we will deep in the history of the hydroelectric power plant, let’s start.

History of hydropower:

Humans use the hydroelectric energy for centuries as the ancient Greeks used water wheels to grind wheat into flour as the water wheels pick up the flowing water in buckets located around the wheel and the kinetic energy from this water turns the wheel to convert it into mechanical energy to run the mill.

There are some rumors said that in the 4th-century water wheels; and water mills were built in India although records of that era are spotty.

The Roman Empire Used Water_powered mills to produce flour from grain and for sawing timber and stone; also they used water mill pumps in China since the Han dynasty to raise water into crop or irrigation canals.

And a team led by project managers of renewable energy developed the first electric generator by the late nineteen century which now could be coupled with hydraulics.

The hydropower becomes a source for generating electricity in the late 19th century as in 1879 the first hydroelectric power plant built at Niagara Falls, then in 1881 they powered the street lamps in the city of Niagara Falls by hydropower, and the United States in 1882 began  operating of the world’s first hydroelectric power plant in Appleton, Wisconsin.

The hydropower was used in the early Peak in the US canal_building in the 1830s; to provide the energy to transport barrage traffic up and down steep hills using inclined plane railroads.

And in 1848 the open  water moved wheel turned to  an enclosed turbine (water motor) by James R.Francis while working as a head engineer of Lowell’s locks and canals company then they  improve these designs to create  a turbine with 90% efficiency, and in 1870 Laster Allan Pelton developed a high_efficiency Pelton wheel impulse turbine which utilized hydropower from the high head streams characteristics of the mountainous California interior.

How to generate electricity from water:

Electricity produced by hydroelectric power plant is simply similar to electricity produced by coal power plants in both plants we use a power source to turn the turbine,  which in turn turns the metal shaft connected to an electric generator to produce the electricity, then this electricity carried by the power lines connected to the generator to homes and mines, but the difference between hydroelectric and coal power plants is the water which is an easily renewable source which keeps flowing.

There are also once_through cooling systems which use cooling systems to draw water from a lake, river, aquifer or ocean to cool steam and then return virtually all of it to the source although at a higher temperature.

How to generate Electricity from Water

And where there is a hydroelectric dam water is used as the power source to turn the turbine, and the dams are constructed with special passageway sloped downward to create a flow of the falling water, so the turbine turns by the force of this flowing water then the turbine, in turn, spins the metal shaft of the electrical generator to produce the electricity.

There are also unexpected ways which illustrate that water plays a vital role in the modern energy production which are:

  • Rain power: of course the energy in the falling raindrop isn’t a lot to produce electricity, so a team at the French Atomic Energy Commission think to build a device with special plastic to convert the vibrational energy of the raindrop hitting it into electricity not huge electricity but an enough electricity to power a couple standard laser pointers.
  • Hydrogen fuel: we can turn hydrogen fuel into electricity with a fuel cell, also it isn’t easy to get pure hydrogen researchers work on ways to split hydrogen from water without using more energy.
  • Seawater_derived jet fuel:

    the U. S. Navy developed a method for turning the seawater into jet fuel and that begins when they use electricity to split water into hydrogen and oxygen then combine the hydrogen with carbon dioxide and dissolved in the water to produce a hydrocarbon (aka jet fuel),

  • Solar_wind hybrid: this method was patented back in 1975 as they built a really tall tower with an upper lip and over this lip there would be a fine mist of water which absorbs heat from the air and evaporates so a dense, cool air flow to the bottom of the structure to drive a huge turbine that produces electricity, and this method works best in hot, arid places where there are a lot of water.
  • Geothermal: it isn’t a new word in our minds as we said that we produce power in geothermal from the heat from inside the earth, so we can exploit sites where there are deeper rocks below the surface and pump down cold water through wells to be heated then extract this water from other wells and under special conditions of pressure and temperature turned into steam which used to drive generators and produce electricity.
  • Biofuels: the difference for biofuels is that they don’t need any additional application of water before being harvested and by the year 2030 8% of U. S.Freshwaterr may go to biofuel production.
  • Freaking: we pump water in hydraulic fracturing deep underground to create cracks to allow access to trapped oil or natural gas, and in some countries diverting water for freaking is depleting already stressed supplies.

How does hydroelectric power work:

We simply illustrate how hydroelectric power works by  the parts of the hydroelectric power plant which are:

  • Dam: which is used to raise the level of water of the river to create the falling water, and controls the flow of water and the reservoir store the energy.
  • Turbine: the turbine spins as a result of the force of the falling water to convert the kinetic energy of this water into mechanical energy.
  • Generator: the generator is connected to the turbine by shafts and gears so it spins when the turbine spins and convert the mechanical energy into electrical energy, and the generator based on its work on the principle of Faraday which says when a magnet is moved to past a conductor it’ll cause electricity to flow.
  • Transmission lines: which transmit electricity stepped up by transformers from hydropower plants to homes, hospitals, and business.

parts of hydroelectric plant


Types of hydropower plants:

1- We can simply classify hydropower plant, according to facilities for generating hydropower (the way of operation of the plant) into four main types:

  • Impoundment plant (storage hydropower plant):

This facility is a large hydropower system which uses dams to store river water in a reservoir, then we use this water to turn turbines which in turn rotate the generator to produce the electricity.

Impoundment plant

And this cross-section illustrates that we use transmission lines to conduct this electricity to homes, hotels, hospitals & businesses; and the dam store water until we need for usage; penstock is the way to carry water to the turbines, and generators connected with turbines which are turned by the force of the water  to automatically turn to generate  electricity.

  • Diversion hydro plants:

Diversion plants or run-of-river plants don’t require dams to store water as they divert portions of the water into the canals from the river; and we use them to supply power to the base load.

run of river plants

The main advantage of this plant is that it reduces the need for constructing large reservoirs; as they use small water pond to meet the immediate loads and that also reduced initial cost compared to storage plant.

  • Pumped storage plants:

It’s the most common type of hydro plants and it fairly works like a battery as it stores the energy produced by solar, wind, nuclear and other power sources, and this plant requires a dam to store the water in a reservoir then this water carried by penstocks to turn turbines to generate electricity.

pumped storage plants

We use the pumps to cycle harnessing water between a low and upper reservoir to surplus energy at times of low demand; and release back the water to the lower turbine when the demand is high.

And the pumped storage plant is capable to supply the peak load with low cost. So, the efficiency of this plant varies between 70_80 % and that increase the revenue.

  • Tide (tidal) power hydroelectricity:

Tide power hydroelectricity or offshore hydroelectricity is a technology which uses the power of the waves or the tidal currents from seawater to generate electricity.

Tide (tidal) power hydroelectricity

and the main advantages of this technology:

  • We can stop the generation of electricity on the basis of requirement.
  • We use water wheels instead of dams which decrease investments
  • It gives us constant power supply.
  • It’s cheaper than many other types.

There is also an unknown type of hydroelectric power plant which is:

  • Underground hydropower plant:

We construct this plant below the upper level of the water; and it works on the basis of the natural height difference generated by the use of two waterways (waterfall or mountain lake).

underground hydropower plant

This plant is safe against any external factors (rock or earth slips or snow avalanches); and they don’t affect the site scenic beauty.

2- We can also classify hydroelectric power plant according to size to:

  • Large hydro plants:

They are plants capable to produce more than 30MW.

  • Small hydro plants:

They are plants produce 10MW or less of power which enough to supply home, farm, ranch or village.

  • Micro-hydro plants:

They are plants capable to produce up to 100KW and they also supply village, home, ranch or farm.


Layout of hydropower plant:

The layout of the hydroelectric power plant is simply the all main and assistance components of the hydroelectric power plant; and the importance of each component as we have:

  • Water reservoir: it’s very necessary for the hydroelectric power plant to have continuously available water so we use the reservoir to store water collected from watersheds or catchment areas during the rainy season.
  • Dam: it’s used to increase the height of the water level behind it and increase the working head of the power plant. And it also controls the outing run of the water.
  • Control Gate: we use the control gate penstock to control the water flows from the reservoir through the penstock to the turbine, as a maximum amount of water released through the penstock when the control gate is fully opened.

Layout of hydro power plant

  • Spillway:it’s a way used to provide a release of flood water from a dam, prevent over toping of the dams which may cause a damage or failure of dams, and this spillway may be an uncontrolled type which starts releasing water upon water rising above the particular level or controlled type with a possible regulation of the water flow.
  • Surge tank: it’s a small reservoir or tank opened at the top, and we usually provide this surge tank with high or medium head power plants when we require long penstock and we fit it between the reservoir and the powerhouse. We use the surge tank to reduce the sudden rise of pressure in the penstock; and provide excess water needed when we suddenly open the control gates to meet the increase in load demand.
  • Pressure tunnel: it’s used to facilitate the flow of water from the reservoir to the surge tank.
  • Penstock:

    it’s a huge reinforced concrete or steel pipe used to carry water from the reservoir to the turbine; and as a result of gravity and flowing down of water through the penstock; the potential energy of the water converted into kinetic energy.

  • Water turbine: water turbine or hydraulic turbine is used to convert the water-energy into mechanical energy, and it is mechanically coupled to an electrical generator by a shaft to produce electricity, and there is an impulse turbine which used for large heads and reaction turbine which used for medium and low heads.
  • Electrical generator: it’s mounted in the powerhouse and mechanically coupled to the turbine shaft and it rotates when the turbine blades are rotated to generate the electricity then we use transformers to step up this electricity for the transmission purposes.
  • Draft tube: it’s connected to the outlet of the turbine to allow it to be placed over tailrace level, and it’s used to exchange the kinetic energy of the water into pressure energy to return to the atmosphere.
  • Tailrace level: it’s a waterway (path) used to lead the water discharged from the turbine to the river.
  • Powerhouse:   it accommodates the turbine, generator, transformer and the control room.
  • Step up transformer: which is used to raise the voltage produced at the generator terminal to be transmitted to the power consumers.

And to achieve the highest  benefits of these components when we select a site for a hydroelectric power plant; we should take into account:

  • The availability of water.
  • Location of the dam.
  • The distance from the load center.
  • Transport facilities.
  • Storage of water.
  • And the head of water.

What is hydroelectricity used for:

After we almost know everything about the hydroelectric power plant and how it works to produce the electricity; we should know the other benefits of hydroelectricity:

  • We should start with the major use;  which is producing electricity as hydroelectricity is the most important; cheapest and non-polluting sources of energy; and big countries like China, Brazil, Russia; India and South America completely depend on hydroelectricity for their massive need of energy.
  • We also use it in the industry as from earlier time we use it for driving bellows in small blast furnaces; and also for the extraction of metal ores.
  • We also use hydro-power for agriculture as we use for producing flour from grain; and also for sawing timber and stone to raise water into irrigation canals.
  • Hydroelectricity also used for storing energy as we use pumped hydro storage for grid energy storage; and because hydroelectricity is a cheap option for storing energy there is already 90 GW of global hydro storage; and with the increase of solar and wind energy usage this capacity will grow.

Biggest countries using hydropower:

It’s the time to know that hydroelectric power plants are the backbone of many countries for producing electricity;  as it produces about:

200GW in China.

89GW in Canada.

80GW in the USA.

70GW in Brazil.

45GW in Russia.

33GW in India.

27GW in Norway.

27GW in Japan.

15GW in Venezuela.

And we can’t ignore Paraguay which produces almost 100% of its electricity supply from hydroelectric power.

biggest countries using hydropower

Advantages of hydroelectric power plant:

When we focus on all details of hydroelectric power plant we will discover great advantages as:

  • We use water and don’t burn fuels so it produces minimal pollution.
  • The water used for running the hydro plant is free; and it will never run out as a result of the natural water cycle.
  • It’s a clean renewable source which helps to reduce the greenhouse gas emission.
  • The operation and maintenance cost is relatively low and the parts of the plant need minimal replacement.
  • It’s a reliable source of energy; as the construction of the dams long-lasting and capable to produce hydroelectric power for 50-100 years.
  • We can control the use of the energy according to the requirements; we can reduce the flow of water from the dam if we require less energy; and when we require huge energy; we can maximize the water by uncovering water tunnels in a very short space of time.
  • Also, we can use the built dam also as providing a supply of water to the surrounding towns and cities to use for drinking, washing, bathing and also irrigation.
  • Imagine that or not; the hydroelectric dams can be a landmark in the country and bring large volumes of tourists. (as we can use it for fishing, boating and aquaculture purposes) which will provide a boost to the local economy.

Disadvantages of hydroelectric power plant:            

Nothing is perfect,  so it’s ordinary to meet some drawbacks of hydroelectric power plant like:

  • The investment and upfront capital cost is high, it reaches 20 billion $.
  • Time needed to build and finish a hydroelectric plant is too long it may take 18 years.
  • Creating dams may affect the fish habitats which depend on the water current, water level, and its access to food.
  • Floods created by the flow of the water from the dam affect the organisms living; as the temperature of the water may increase; and the organisms which don’t adapt to this new environment conditions will die.
  • The hydroelectric energy also can affect the residences living near the dam; and force them to relocate to another way of living.
  • Producing hydroelectric energy depends on the weather conditions and the availability of water.
  • The flow of the water may reduce; as a result of the sedimentation in dams and that affects the generation of the hydroelectric energy.
  • We need a large area of land to construct a dam, install power production unit, and transformers.
  • Hydroelectric plants only built in areas with perfect conditions like landscape and precipitation levels.