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Three Gorges Dam in China

Hydropower (also: hydro-energy ) is a regenerative energy source . The term describes the conversion of potential or kinetic energy of the water into mechanical work by means of a water power machine .

Until the beginning of the 20th century, water power was mainly used in mills . Today, electricity is almost always generated with the help of generators . With a share of 15.58% of global electricity generation , hydropower was the third most important form of electricity production in 2011 after the generation of electricity from coal and natural gas and before nuclear energy .


Run- of
-river power plant from 1892 in Schöngeising

The history of hydropower goes back a long way. Historians estimate that it was used in China 5000 years ago. Other ancient cultures on the Nile , Euphrates and Tigris and on the Indus used the first water-powered machines in the form of water paddles to irrigate fields 3500 years ago. In the times of the Romans and Greeks , water was then used in a wide variety of ways as a drive for working machines. Around the 2nd century BC The Archimedes' screw was invented and is still in use today.

In the 9th century AD, the undershot water wheel was used. The next decisive development followed five centuries later with the use of the overshot water wheel. Here, not only the kinetic energy of the water but also its weight was used.

In 1767, the English civil engineer John Smeaton manufactured the first cast iron waterwheel , which was an essential prerequisite for the industrial revolution , as its enormously higher load capacity also enabled greater performance. The associated increase in productivity led to an economic upswing and gave the waterwheel an outstanding position as a source of power until the 19th century.

At the end of the 18th century there were around 500,000 to 600,000 water mills in Europe, which served as a drive source for (grain) mills and other working machines. The average output of these mills was between 3 and 5 kW, the largest systems achieved up to over 40 kW.

In 1842, the French engineer Benoît Fourneyron developed the forerunner of the Francis water turbine . This technology made it possible to use larger amounts of water and higher gradients, which led to an increase in performance compared to water wheels. When Werner von Siemens invented the electrodynamic generator in 1866 , it became possible to convert hydropower into electricity.

In 1880 the first hydropower plant was put into operation in Northumberland, England, and in 1896 the world's first large-scale power plant was built at Niagara Falls in the USA. With the Reichenhall electrical works , the wood pulp manufacturer Konrad Fischer built Germany's first hydroelectric power station in Bad Reichenhall , which went into operation on May 15, 1890. It is the first AC power plant in Germany and the first electric plant in Bavaria.

In 1902, the Congrès de la houille blanche took place in Grenoble - with an additional exhibition in 1914 and 1925, then in Lyon and again in Grenoble . The term “white coal” shows the weight that was attached to this energy source compared to conventional coal. The term is derived from the melted ice of the mountain regions, which mostly pours white-foaming down into the valley. Hydropower received a substantial boost from the electrification of the railway lines, which required particularly powerful thrust in the mountain regions where hydropower could be generated locally. The power plants were often built as a building for the railway companies. That is why electricity is often referred to as “the little sister of the railroad”.



Hydropower has great potential for generating electricity, although the respective potentials vary greatly depending on the amount of precipitation and the topographical or geographical conditions. The technically usable potential is estimated at approx. 26,000  TWh per year, of which 21,000 TWh could also be used from an economic point of view. The potential that can actually be developed is around 16,000 TWh, which roughly corresponds to the global electricity demand in 2005.

In 2016, hydropower plants with a cumulative capacity of around 1096 GW were installed worldwide, which produced around 4100 TWh of electrical energy. Thus, hydropower provided 16.6% of the world's electrical energy requirements and around 2/3 of the total electricity generated from renewable sources, which covered 24.5% of the world's electricity demand. This corresponds to a little more than 1.7 times the production of the nuclear power plants , which delivered 2,346 TWh in 2012. A good half of global production takes place in the five countries of China, Brazil, Canada, the USA and Russia. In 2014, it was assumed that around 180 GW of hydropower capacity would be added globally in the next decade, mainly in China, Turkey, Brazil and India.

Ten of the largest hydropower producers in 2009.
country Annual
( TWh )
( GW )
Share of total
electricity production
in that country in%
China People's RepublicPeople's Republic of China People's Republic of China 652.1 196.790 0.37 22.25
CanadaCanada Canada 369.5 88.974 0.59 61.12
BrazilBrazil Brazil 363.8 69.080 0.56 85.56
United StatesUnited States United States 250.6 79.511 0.42 5.74
RussiaRussia Russia 167.0 45,000 0.42 17.64
NorwayNorway Norway 140.5 27.528 0.49 98.25
IndiaIndia India 115.6 33,600 0.43 15.80
VenezuelaVenezuela Venezuela 86.0 14.622 0.67 69.20
JapanJapan Japan 69.2 27.229 0.37 7.21
SwedenSweden Sweden 65.5 16.209 0.46 44.34


At the end of 2006, 7,300 plants were active in Germany and in 2007 they contributed 3.4% to total electricity generation. In Austria it is approx. 56.6% and in Switzerland approx. 52.2%. In Germany, hydropower plants currently cover around 4% of Germany's electricity demand; In 1950 it was still around 20%. The reason for this decline was the sharp rise in electricity consumption since 1950, which is why the relative contribution of hydropower fell in the period mentioned despite the construction of new hydropower plants.

Among the member states of the European Union , Sweden , Italy and France contribute most with energy from hydropower: In 2011 Sweden supplied 66 TWh, followed by Italy and France with around 45 TWh each.

Since hydropower plants can be regulated and thus easily adapted to the electricity demand, they can represent an important addition to other renewable energies that are not suitable for base loads, such as wind power and photovoltaic systems.

country Electricity generation (GWh, 2013) Electricity generation from hydropower (GWh, 2013) Share in% (2013) Hydropower potential (estimate 1950) (summer / winter)
Belgium 81900 380 0.5 -
Bulgaria 27500 4080 14.8 2000
Denmark 31200 13 0 -
Germany 518100 22998 4.4 20000
Finland 79800 12838 16.1 10,000
France 439200 70489 16.0 40000
Great Britain 317500 4699 1.5 3000
Ireland 24400 578 2.4 1000
Italy 287400 52773 18.4 40000
(Yugoslavia) 61400 24637 40.1 8000
Slovenia 12600 4849 38.5
Croatia 15100 8001 53.0
Serbia 26900 10203 37.9
Macedonia 6800 1584 23.3
Netherlands 106200 114 0.1 -
Norway 109300 128477 117.5 80000
Austria 62900 41977 66.7 35000 30000
Poland 124100 2439 2.0 5000
Portugal 45300 13730 30.3 1000
Romania 40300 14957 37.1 3000
Sweden 125000 61361 49.1 65000
Switzerland 69633 39308 56.4 10,000 7000
Spain 231700 36780 15.9 30000
(Czechoslovakia) 116600 7796 6.7 6000
Czech Republic 56700 2734 4.8
Slovakia 25100 4849 19.3
Hungary 34800 213 0.6 1000

Hydropower plants


There are a number of different types of hydropower plants. Their classification is not always completely clear and can be made according to different aspects. The following classifications can be made:

Approach Classification
Effective head Low pressure system (fall height <15 m)
Medium pressure system (fall height <50 m)
High pressure system (fall height> 50 m)
Energy industry Base load power plant
load power plant Peak load power plant
Installed capacity Small hydropower plants (<1 MW)
medium-sized hydropower plants (<100 MW)
large hydropower plants (> 100 MW)
topography Upper course (storage power plant)
Middle course (run-of-river and storage power plant)
Lower course (river power plant)
Sea (tidal power plant)
Operating mode Island operation
interconnected operation
medium Waters
drinking water
other pipeline medium (oil: TAL )

Plant types


Impeller of a Pelton turbine


As with the power plant types, turbines can be differentiated according to various aspects: According to the loading (partially or fully loaded), the wheel shape (radial, diagonal, axial), the design (vertical or horizontal to the shaft position) and the mode of operation, which is most common differentiator. Accordingly, there are constant pressure turbines and positive pressure turbines .


Depending on the turbine type and operating point, there is a risk of damage from cavitation .

general basics


Energy comes in different forms. Taking into account the laws of thermodynamics , energy can be converted into work . Kinetic energy and the potential energy are decisive for the use of hydropower . Water above the sea level, has the potential energy and undergoes through the force of gravity an acceleration , whereby a part of the initial energy is automatically converted into kinetic energy. This fluid mechanical energy is converted into mechanical energy ( rotational energy ) by turbines in hydropower plants and ultimately transformed into electrical current by generators .

In order to determine the maximum transformable energy, a calculation must be made according to the extended Bernoulli equation , in which all losses due to turbulence or due to friction on system parts are taken into account. Losses during energy conversion escape in the form of thermal or acoustic energy.

The performance, also called energy flow, is influenced by the height of the water falling, the amount of water, the density of the water and the efficiency of the system, with the overall efficiency including all losses of the turbines and the generator. For hydropower plants, the overall efficiency is 80% or higher. Compared to other types of power plants, this value is the largest. From an energy point of view, hydropower is a primary energy source , as it comes directly from a natural source of energy.


The hydrological cycle is of great importance for hydropower . It describes the movements of water on a regional and global level. Driven by the radiant energy of the sun, the water passes through different physical states . In principle, the cycle works as follows: Water evaporates from surface waters (seas, lakes, rivers) and rises into the atmosphere in the form of water vapor. There it condenses, whereupon it mainly comes back to the earth's surface as rain or snowfall. Topographical conditions create catchment areas in which precipitation enriches rivers with water.

The amount of water carried by a river is subject to strong fluctuations, mainly caused by seasonal fluctuations in precipitation and by climatic and meteorological conditions. The runoff is a very important parameter for the dimensioning of hydropower plants. Above all, extreme values ​​have to be taken into account so that e.g. B. no damage occurs during floods . Long-term measurements of the runoff of a catchment area help here. Useful of these are in addition to the hydrograph of a river, the flow duration curve, the sum line and the filling line, all of which are described in a runoff-day chart.

  • The hydrograph, the starting point for hydrological discharge studies, indicates the corresponding discharge volume for time intervals (e.g. days, hours).
  • The duration curve is arranged according to its discharge values ​​and thus indicates on how many days in a year a certain discharge value is exceeded or not reached.
  • The sum line is important for the dimensioning of hydropower plants with storage. It is created by adding up the chart over time.
  • The fill line is used to describe the discharge during flood events. If there is not enough data for a particular location to be tested, statistical methods can be used to collect the data. From the knowledge of the discharge data, the type of the planned power plant, the choice of turbine and other planned uses of the water, such as shipping or ecologically-related minimum water output, the expansion flow designed for the particular power plant can be determined. With it , the performance should be at its maximum with a simultaneously favorable efficiency . Depending on the size of the power plant, the expansion flow is designed so that it is exceeded on around 100 days a year.

Whether a hydropower plant is profitable depends on the costs, the quantities and the electricity prices that can be achieved for it (see also cost-benefit ratio ).


In Germany, the Water Management Act (WHG), the Environmental Impact Assessment Act (UVPG) and the Renewable Energy Sources Act (EEG) deal with hydropower.


The costs for a hydropower plant are made up of the plant and operating costs . The system costs, also known as investment costs, are made up of all expenses for the construction of the system. In contrast to combustion power plants , when generating energy from hydropower, little or no financial means have to be paid for the respective resource, as it is available almost indefinitely. This means that the operating costs - with the exception of pumped storage power plants - for fully functional hydropower plants are very low compared to the system costs.

The question of profitability depends on the relationship between the plant and operating costs and the gross profit. Overall, it can be said that the decisive factors are the system costs and the useful life . For the energy industry, hydropower is mostly base load capable . In these cases, electricity can be produced almost continuously, which means that a profit calculation can be carried out using the remuneration rates specified in the EEG. Basically, hydropower plants usually have a very long service life and amortize very well over their lifetime.

Use of hydropower and ecology

Although the use of hydropower for energy generation is usually recognized as being particularly ecological , it is sometimes associated with considerable interventions in nature and the landscape. One of the most important natural monuments on the Rhine, the Kleine Laufen near Laufenburg, was blown up for the first power plant to cross the Rhine. The power plant went into operation in 1914. For the Rhine Falls of Schaffhausen (also Großer Laufen ), from 1887 onwards, several efforts were made to use the unused falling water masses to generate energy; Concerns about the interference in the landscape prevented the implementation until today. A current example in which the generation of energy through hydropower simultaneously means a serious intervention in an ecosystem is the Three Gorges Dam on the Yangtze River in China.

The European Water Framework Directive (WFD), which applies to European countries, defines the compatibility of interventions in local rivers. In addition to maintaining or improving the chemical-biological quality of these aquatic habitats, the WFD is specifically dedicated to the morphological parameters. The target status was defined as the good ecological status or the good ecological potential, which should be achieved by 2027 at the latest. This has a major impact on the definition of the expandable hydropower potential . Thus, the use of hydropower is only possible if all ecological parameters are taken into account, including ensuring that there is sufficient residual water in the body of water. Hydropower projects can only be implemented in compliance with these ecological requirements. These requirements create a field of tension between the energy industry and ecology, as existing systems are technically matched to the approved intake water volume and residual water requirements are associated with corresponding energetic and economic losses. The creation of continuity at existing locations is also associated with high investment costs and causes, v. a. in small hydropower, often economically critical situations.

Advantages and disadvantages of hydropower

In reservoirs , gases such as CO 2 and methane (with 25 times the global warming potential than CO 2 ) are produced. The amount depends in particular on the vegetation before the damming and the age of the lake; it decreases from the time of flooding. The use of hydropower releases around 48 million tons of carbon in the form of carbon dioxide and 3 million tons of carbon in the form of methane every year. These are small amounts compared to the total annual carbon emissions caused by human use (approx. 10 billion tons of carbon in CO 2 and 400 million tons of carbon in methane), which means that hydropower plants do not play a major role as carbon emitters globally. Under certain conditions , however, significant amounts of carbon can be released in some regions, for example the tropics . On the other hand, the large bodies of water can also make a positive regional contribution to the climate through evaporation (effect of evaporative cooling).


  • Water is one of the regenerative raw materials, i. i.e., it is not used
  • Fossil energy resources such as coal, oil and gas are conserved
  • Independence from conventional energy sources
  • Climate protection as it is low in CO 2
  • Parts of the system can be recycled after the end of the operating time
  • Flood protection for those lying below
  • Reservoirs are also reservoirs for drinking water and for irrigation in agriculture
  • Hydropower and variable renewable energies complement each other, which can reduce the need for storage or shadow power plants


  • By diverting water, the amount of water in the stretch of water between the accumulation and the re-introduction below the turbines is reduced. This reduction to the so-called residual water quantity represents an intervention in the water balance , whereby large-scale changes in the ecological balance can occur in individual cases.
  • Ecological barrier: fish and microorganisms can no longer carry out their usual migrations, or they die if they are drawn into the turbines.
  • Decreased flow rate due to water accumulation leads to decreased oxygen concentration and an increase in water temperature.
  • The water table in the area of ​​the lower reaches can decrease sharply, while it increases in the area of ​​the impoundment. Depending on the nature of the composition of flora and fauna, this can have adverse effects on their coexistence.
  • With the sediment retention is a sedimentation above and increased erosion below the barrage connected.
  • When areas in warm regions and with a lot of vegetation are flooded, digestion processes lead to the emission of the greenhouse gases methane and carbon dioxide .
  • If the dam breaks, there is a risk of habitat destruction for people and nature.
  • When the storage space is created, huge areas are sometimes flooded, whereby the living space for people is also lost.

possible solutions

There are various ways of observing the interests of nature and water protection. The easiest way to protect nature from interference is to refrain from interference. For this reason, existing hydropower plants should primarily be expanded and new ones only built where there are already dams. Innovative technical improvements to the system components can increase performance and at the same time improve the ecological situation. The further development consists in the replacement and modernization of existing systems. The Renewable Energy Sources Act in Germany regulates the remuneration of new or modernized systems in such a way that the ecological condition of the water body must improve with the construction or modernization.

In addition, nature and water protection must always be observed. As long as the environmentally relevant aspects are taken into account, nothing stands in the way of building new hydropower plants. Various design and compensation measures make it possible to improve the ecology of a body of water.

  • It is imperative to ensure a minimum water release to the lower reaches and the bed load passage.
  • Fish ladders are aids to ascending and descending or bypass channels for fish. They are among the decisive construction measures.
  • There are now also technically improved turbines that make it possible for fish to pass them mostly unharmed.
  • The problem of the low oxygen content can be solved by so-called "air" turbines, which bring oxygen into the water.
  • A design of water bodies as natural as possible with structural diversity in the storage area , for example through deep and shallow water zones, oxbow lakes and gravel banks, leads to a natural water profile and improves the habitats of flora and fauna.
  • In order not to destroy the landscape, the systems should be integrated harmoniously into the landscape.

Small hydropower plants

In many cases, small hydropower plants are viewed as ecologically compatible . Proponents argue that systems that are professionally built according to the latest standards do not pollute the waters and that some of them are "ecologically upgraded" through the construction of fish ladders or accompanying measures. Critics, on the other hand, often argue that small hydropower plants and associated interventions such as damming, barriers or reduced residual water volumes represent severe cumulative interventions in the affected ecosystems, especially due to their large number and scattered distribution in a river basin.

Electricity from sewers

A completely new approach to the ecologically largely harmless use of hydropower is the use of specially designed turbines for generating electricity in sewers, which, even when retrofitted in existing sewers, do not interfere with the landscape or impair fishways. In addition, through the use of sewers, electricity can be generated in a decentralized manner and therefore close to potential consumers due to the extensive distribution of sewers.


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Web links

Renewable energy
Commons : Hydro  - collection of pictures, videos and audio files

Individual evidence

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