What is Hydro energy?

Hydro energy definition

hydro energy definition

Hydro energy definition is – The kinetic energy process by flowing water can be converted into electricity. The power is then used for direct mechanical purposes or more frequently, for generating electricity.

Hydropower is the most established and widely used in a formal resource for electricity generation. Hydropower now accounts for about 20% of the world’s electricity generation. Output depends on rainfall and the land. Hydroelectric generation for various countries and regions indicates the Global increase. In about one-third of the world, hydropower produces more than half of the total electricity.

In general, the best sites are developed first on a national scale, so the rate of exploitation of total generating capacity tends to diminish with time. By the 1940s, most of the best sites had already been exploited. Almost all the increase in hydroelectric generation is in developing countries, notably India, China, and Brazil.

However, Global estimates can be misleading for local hydropower planning, since the potential for hydro generation from the run-of-river scheme ( i.e. with only very small dams) is often underestimated. In a hydroelectric power plant, a dam on the river is used to store water in a reservoir. Water released from the reservoir spins the turbine, which in turn activates a generator to produce electricity. 

But all hydroelectric power does not require a large Dam. Some of them just use a small canal to channel the river water through a turbine. 

Another type of hydroelectric power plant is called a pumped storage plant. The power is sent from a power grid into the electric generator. The generator then spins the turbine backward, which causes the turbine to pump water from the lower reservoir to an upper reservoir, where the water is stored.

The water is released from the upper reservoir back down into the river or lower reservoir. This spins the turbine forward, activating the generator to produce electricity.


A volume per second, Q, of waterfalls down a slope. The density of the fluid is p. Thus the Mass falling per unit time is pQ, and the rate of  potential energy lost by the falling fluid is

                                        P0 = pQgH

Where g is the acceleration due to gravity,  P0  is the energy change per second (watts) and H is the vertical component of the water path.

The purpose of a hydropower system is to convert this power to shaft power.

Assessing the resources for small installations

Suppose we have a stream available, which may be useful for hydropower. At first, only approximate data, with an accuracy of about + – 50%, are needed to estimate the power potential of the site. Then, a detailed investigation will be necessary involving data, for instance, rainfall, taken over several years. To estimate the input power  P0  we have to measure the flow rate Q and the available vertical fall H (usually called the head).

Measurement of head H

For early vertical falls, the trigonometric method (perhaps even using the length of shadows) is suitable; Whereas for a more gently sloping site, the use of label and Pole is straight forward. Note that the power input to the turbine depends not on the geometric (or total) head Ht as measured this way but on the available head Ha

                                                           H= Ht – Hf 

where there Hf allows for friction losses in the pipe and channel leading from the source to the turbine. By a suitable choice of pipework, it is possible to keep what Hf < Ht /3 increases in proportion to the total length of pipe, so that the best site for hydropower has a steep slope.

A brief history of Hydropower

 The power of falling water has been used to produce electricity for over 135 years. Some of the earliest innovations in using water power were conceived in China during the Han Dynasty between 202 B.C. and 9 A.D.

Some of the key development in hydropower Technology happens in the first half of the 19th century. In 1827 French engineer Benoit Fourneyron developed a turbine capable of producing around 6 horsepower. In 1849, British American engineer James Francis developed the first modern water turbine named as Francis turbine. 

In 1870, the American inverter, Lester Allan Pelton developed the Pelton wheel, an impulse water turbine, which he patented in 1880. In the 20th century, Australian professor Viktor Kaplan developed the Kaplan turbine in 1913. It was a propeller-type turbine with adjustable blades.

The first hydroelectric generation

The world’s first hydroelectric project was used to power a single lamp in the crag side country house in Northumberland, England, in 1878. Four years later, the first plant to serve a system of private and commercial customers was opened in Wisconsin, USA, and within a decade, hundreds of hydropower plants but in operation.

By the term of the 20th century, the technology was spreading around the globe, with Germany producing the first three-phase hydroelectric system in 1891, Australia launching the first publicly owned plant in the southern hemisphere in 1895. 

In 1895, the world’s largest hydroelectric development of the time, the Edward DNean Adams Power Plant, was created at Niagara fall. 

In 1905, a hydroelectric station was built on XIndian Creek near Taipei, with an installed capacity of 500 kilowatts. This was quickly followed by the first station in Mainland China, the Shillong plan in the Yunnan province, which was built in 1910 and put into operation in 1912.

In the first half of the 20th century, the USA and Canada led the way in hydropower Engineering. At 1,345 MW, the Hoover Dam on the Colorado river become the world’s largest hydroelectric plant in 1936.

It was surpassed by the Grand Coulee Dam with a capacity of 1,974 MW in Washington In 1942, which is upgraded to a capacity of 6,809 MW today.

From 1960 through to 1980, large hydropower development was carried out in Canada, The USSR, and Latin America.

Over the last few decades, Brazil and China have become a world leader in hydropower. The Itaipu Dam, straddling Brazil and Paraguay, opened in 1984 at 12600 MW. It has since been enlarged and upgraded to 14000 megawatts and is today only dominated in size by the 22500 megawatts China Three Gorges Dam., which opened in 2008.

Hydroenergy potential of India

In the 21st century, hydropower continues to play a major role in growth around the world. For example, it has played a key role in transforming the Indian economy. 

India is the 5th largest producer of hydroelectric power. Hydroelectric power potential of 148700 megawatts at 60% load factor is one of the largest in the world. The present installed capacity as on 31st March 2016 is 42783 megawatt which is 14.35% of total utility electricity generation capacity in India. in addition, 4274-megawatt small hydropower units are installed as on 31st March 2016.

During the year 2014 to 2015, the total hydroelectricity generation in India was 129 billion KWh which works out to be 24500 megawatts at 60% pasta factor.

 Basin wise potential

BasinPotential for Hydroelectric power (MW)
Indus Basin33832
Ganga Basin20711
Central Indian river system4152
Western flowing rivers of South India9430
Eastern flowing rivers of south India14511
Brahmaputra Basin66065

Hydroelectric potential in Himachal Pradesh

Himachal Pradesh has a big potential for hydroelectric power generation, the state is having 25% of total potential of India. The projected capacity of the hydroelectric power of the state is 27435 MW out of which 3934.7 MW is exploited out which of which 7.6% is under control of Himachal Pradesh. This power is the biggest source of income in state.

Some of the working hydro project in Himachal Pradesh are Nathpa 

Jhakri, Parvati Pariyojana, Malana Project, Bassi project, Binwa project, Sanjay Vidyut pariyojana and many more.

Hydropower Technologies

 there are three types of hydropower technology in use

  1. Impoundment
  2. Diversion
  3. Pumped storage


Impoundment plant is the most common type of hydroelectric plant power plant. An impoundment plant is a large hydropower system in terms of its size and capacity. It uses a Dam to store river water in a large reservoir. Water released from the Reservoir flows spins the turbine, 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.


In divergent Technology, a portion of a river is channeled through a Canal which flows through a turbine, spinning it, which in turn activates a generator to produce electricity. It may not require the use of a dam.

Pumped storage

Pumped storage stores the electricity generated by other power resources like solar, wind, and nuclear for later use. It stores energy by pumping water to a reservoir at a higher place from a second reservoir at a lower place. When the demand for electricity is low, water is pumped from the lower reservoir to an upper reservoir. During periods of electricity demand, the water is released back to the lower reservoir and turn a turbine, generating electricity.

Hydroelectric power plants can be also be classified on the basis of their size

 Large hydro power plant

 Large hydropower has a capacity of more than 100 megawatts. Large hydropower developments involve large dams and huge water storage reservoirs. They are typically grid-connected supplying large grids. Preference for large hydro is on the decline due to the high investment cost, long payback period, and huge environmental impact (losses of arable land, forced migration, diseases, and damage to biodiversity). Many social and environmental impacts are related to the impoundment and existence of a Reservoir and therefore are greater for ‘large hydro’ plants with a reservoir.

Small hydro power plant

Small hydropower plant has a capacity of 1 megawatt to 10 megawatts. Small hydropower plant station are typically run-of-the-river. They combine the advantages of hydropower with those of decentralized power generation, without the disadvantage of large scale installation.

Advantages include

Low distribution cost, no/low environmental cost as with large hydro, low maintenance, and local implementation and management. Power generated with a small hydro station can be used for Agro-processing, local lightning, water pump, and small businesses. 

Small hydro can be further subdivided into Mini micro and Pico.

Micro hydropower plants

The micro hydro power plant has a capacity of up to 100 KW. A small or micro-hydroelectric power system can produce enough electricity for a home, farm, ranch or village.

Classification of a hydropower plant on the basis of their size

Hydro CategoryPower RangeNo. of Homes Powered
Pico0 kW – 5 kW0-5
Micro5 kW – 100 kW5-100
Mini100 kW – 1 MW100-1,000
Small1 MW – 10 MW1,000-10,000
Medium10 MW – 100 MW10,000-100,0000
Large100 MW+100,000+

 The generation and transportation of hydroelectricity

 The steps to generate electricity from a dam and how it is transported are outlined below:

  1.  Hydroelectric Dam:  potential energy store in a water reservoir behind a dam is converted to kinetic energy when the water start flowing from the dam. the kinetic energy is used to turn a turbine.
  2. Generator:  The falling water strikes a series of blades attached around a shaft which converts kinetic energy to mechanical energy and causes that avoid rotating. The shaft is attached to a generator, so that when the turbine generator is driven. The generator converts the turbine mechanical energy into electrical energy. 
  3. Step Up Transformer:  Generator usually produces electricity with a low voltage. In order for a transmission line to carry the electricity efficiently over long distances, the lower generator voltage is increased to a higher transmission voltage by step-up Transformer. The higher voltage reduces the magnitude of current (I) therefore heat losses are reduced to a significant value. There is more loss at a Higher voltage between earth and transmission line. This loss in Corona discharge, however, this loss can be minimized if diameter of the transmission line is increased and the problem-related weight can be reduced by making conductor hollow.

*Corona discharge is a process in which the surrounding air becomes conductive due to ionization of the gas at high voltage and these iron conduct electric current to the earth.

  1. Grid High Voltage transmission line:  Grid transmission lines, usually supported by tall metal Tower, carry High Voltage electricity over long distances. The long thick cable of the transmission line is made of copper or aluminum because they have low resistance. As we know that the higher the resistance of a wire, the warmer is it gest. So, some of the electrical energy is lost because it is changed into heat energy thus, in spite of high current, High Voltage transmission lines are used to carry electricity over long distances to a substation.
  2. Terminal station:  Terminal station control power flow on-grid transmission line and reduce the great voltage to sub-transmission voltage.
  3. Sub transmission lines:  Sub transmission lines go into substation near businesses, factories, and homes. Here, the Transformer can change the very High Voltage electricity back into lower voltage electricity.

Environmental impact of hydropower sources

Hydropower does not pollute the water or the air. however, these facilities can have a large environmental impact on land wildlife and life cycle.  

Land impacts

The size of the reservoir used by a hydroelectric project can vary widely. It depends largely on the size of the hydro-electrical generator and the topography of the land. Hydroelectric plants in flat areas tend to require much more land than those in the hilly area or Valley where deeper reservoir can hold more volume of water in a small space.

Land used for a hydroelectric reservoir has severe environmental impacts: it destroys forest, wildlife habitat, agricultural land, and Scenic land. 

Wildlife Impacts

  1. Direct impact on aquatic (Sea, river) ecosystem: Hydroelectric reservoir are used for multiple purposes, such as agriculture irrigation, flood control, and Recreation, etc. Thus, not all wildlife impacts associated with them can we directly attributed to hydroelectric power. However, hydro-electric facilities can have a major impact on aquatic ecosystem. For example, fish and other underwater organisms can we injured and killed by turbine blades. 
  2. Indirect impact on the aquatic (Sea, river) ecosystem: Apart from direct contact, there can also be an impact both within the dammed reservoir and downstream from the dam. Water within the reservoir is usually more stagnant than normal river water. As a result, the reservoir can have higher quantity of sediments and nutrients, which can cultivate and excess of algae and other aquatic plants and animals. These aquatic plants and animals can crowd out other river animal and plant life. They must be controlled by manual harvesting or by introducing fish that eat these plants.
  3. Impact on the rate of water loss: Water is lost through evaporation in dammed Reservoir at a much higher rate than inflowing rivers. 
  4. Impact on downstream river segment: If two much water is store behind the Reservoir, segments of the river downstream from the Reservoir can dry out. Thus, most hydroelectric operators release a minimum amount of water at a certain time of year. if not released approximately, water levels downstream will drop and animal and plant life can be harmed.
  5. Impact on quality of water storage reservoir:  Reservoir water is typically low in dissolved Oxygen and colder than normal river water. When this water is released, it can have negative impacts on downstream plants and animals. To lessen these impacts, aerating turbines can be installed to increase dissolved oxygen. In addition to this, water is released from the Reservoir that comes from all levels of The Reservoir, rather than just from the bottom (which is coldest and has the lower dissolved oxygen). 

Life-cycle global warming emission

Global warming emission (i.e. carbon dioxide and other greenhouse gases) are produced during the installation and dismantling of hydroelectric power plants. These emissions can be significant during hydroelectric power generation operation. Such emission can vary depending on the size of The Reservoir and the nature of the land that was flooded by the Reservoir.

Small plants emit between 0.01 and 0.03 pounds of carbon dioxide equivalent per kilowatt-hour. 

Lifecycle emissions from large scale hydroelectric plants built in the semi-arid region are also modest: approximately 0.06 pounds of carbon dioxide equivalent per kilowatt-hour. 

The vegetation and soil in areas related by Reserve oil decomposed and release both carbon dioxide and methane. 

The exact amount of emission depends greatly on site-specific characteristics. However, current estimates suggest that life cycle emission can be over 0.5 pounds of carbon dioxide equivalent per kilowatt-hour.