Is hydropower a word


Lexicon> Letter W> Hydropower

Definition: the extraction of electrical (or sometimes mechanical) energy from water

Alternative term: hydro energy

More general terms: renewable energy

English: hydroelectric power

Categories: Renewable Energy, Basic Terms

Author: Dr. RĂ¼diger Paschotta

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Original creation: July 18, 2010; last change: 16.01.2021


The Hydropower (also Hydro energy) is the use of the kinetic or potential energy of the water. It is an indirect use of solar energy, as the high-altitude water reservoirs used are constantly being renewed. B. is evaporated in the sea with the help of solar energy and can thus reach high-altitude regions via precipitation. Very little solar energy can be used in this way, but in a concentrated and particularly well usable form.

In most cases, hydropower is used with the help of hydropower plants. The article on hydropower plants discusses the specific aspects of such plants, while here the more general aspects are discussed. Most of the world's hydropower generation comes from large hydropower plants; Small power plants make little contribution.

In some cases, osmotic power plants are also referred to as hydropower plants. They take advantage of differences in the concentration of salt (salt gradients) between river and sea water.

Importance of hydropower

Hydropower (or Hydro energy) was of importance for the generation of electrical energy practically at all times. Today it covers a good 15% of the world's electricity demand - a little more than nuclear energy - at often very low costs, especially for larger systems. Although the investment costs are usually quite high, the operating costs are very low and the service life (sometimes over 100 years, with occasional renovations) can be much longer than the payback period.

In Germany, hydropower only covers 3% of electricity generation (as of 2008), as the country's topography offers only limited possibilities. In contrast, mountainous regions are particularly well suited for the use of hydropower, in Europe in particular the Alps. In Switzerland and Austria, over 50% of electrical energy (not about the entire primary energy requirement) is generated with hydropower, in Norway even 98.5% (as of 2010). Since a large part of the power plants in question are storage power plants, a significantly larger proportion can be obtained as valuable peak load electricity than is required in the country. Such countries therefore use the opportunity to export excess peak loads using the European network system at high prices and to import cheaper medium loads (less base load). In countries like Germany, investments in peak load power plants (e.g. with gas turbines or compressed air storage) can be correspondingly lower. For the purpose of greater use of such capacities z. In Norway and Sweden, for example, the European power grids are being expanded step by step, for example with submarine cables in the North Sea. Once a European supergrid is in place, the importance of Nordic hydropower in the energy industry will continue to increase.

In particular, because of the need for climate protection (see below) and the scarcity of fossil fuels, hydropower is likely to be expanded further in some countries, while other countries (e.g. Germany and Switzerland) have few expansion options and the use of remaining potential would often be ecologically problematic.

In principle, it would be beneficial in Germany to be able to make greater use of water storage power plants in order to be able to better compensate for the increasing and strongly fluctuating feed-in of wind and solar power. Unfortunately, there are hardly any suitable locations for this. That is why such an increased use of hydropower is practically only possible via increased power grids, especially to Norway (see above).

Ecological aspects

Climate-neutral power generation

What is very welcome is that, ideally, electricity from hydropower almost equates to CO2-free and therefore not harmful to the climate, i.e. generally almost climate-neutral. It would therefore be in the interests of climate protection to further expand global hydropower generation in order to be able to reduce the use of fossil-fuel-fired power plants accordingly. However, it should be noted that the establishment of reservoirs can at least temporarily lead to high emissions of carbon dioxide and methane if rural areas with high carbon soil (possibly even primeval forests) are flooded. In extreme cases, the climate-damaging emissions can be as high as with coal-fired power plants - most likely in power plants in tropical rainforest regions, but hardly in colder regions, and in any case, with increasing usage time, to a decreasing extent.

In the case of pumped storage power plants, it must of course be taken into account that the pumping power often comes from coal-fired power plants that are very harmful to the climate (but sometimes also from nuclear power plants). The corresponding part of the generation is of course not regarded as actual hydropower generation and is to be assessed accordingly from an ecological point of view. For comparison, other methods of generating peak loads must be considered (such as gas turbines or combined cycle power plants), and possibly also methods of load management to reduce peak load requirements.

Interventions in the landscape

A large hydropower plant requires greater interventions in the landscape than a small one - but usually less than a large number of small power plants with overall the same output!

The construction of hydropower plants often requires major interventions in the landscape. In particular, when building dams for storage power plants in mountain regions, the effects are massive; considerable and partly ecologically valuable areas have to be sacrificed for the construction of the water reservoir. Some major projects also require the relocation of large numbers of people, often with corresponding social consequences.

In ecological terms, however, large (and correspondingly deep) reservoirs may perform better than smaller ones. Essentially, this is due to the fact that much more water can be stored per square meter of reservoir or water surface, i.e., conversely, less space is required for the same amount of stored energy. In contrast, the ecological interventions related to the small production quantities in the case of small hydropower are often particularly strong.

Today, ecological compensation measures are also often carried out, for example the renaturation of rivers or the establishment of protected areas to compensate for flooded regions.

Climate-damaging methane emissions

When large water reservoirs are created, considerable amounts of biomass are sometimes washed over by the water, and then when the biomass rots under a lack of oxygen, the climate-damaging methane can be formed. The extent to which this calls into question the climate neutrality of hydropower electricity, however, depends very much on the respective conditions. These dangers are particularly great when the soil contains a lot of carbon - for example when forests are flooded. In contrast, such effects are weak on rocky ground.

Effects on fauna in rivers

River hydropower plants (run-of-river power plants) can have negative effects on fauna and flora, especially on fish. Older structures are often very difficult for fish to migrate, and fish can be killed if they get through the turbines. In newer river power plants, carefully planned fish ladders (fish ladders, e.g. also fish lifts) can enable fish to migrate. But there are also other ecological effects such as B. Changes in the transport of gravel and nutrients and the general flow dynamics, e.g. B. no longer occurring flooding of certain areas. In some cases, power plant structures are optimized to minimize such effects.

Problems can also arise with too little Residual water occur. Sometimes water is taken from a river at one point and fed back into it at another place (further downstream), so that the section of the river in between carries correspondingly less water. In times of low water levels, rivers and streams can then fall completely dry if certain residual amounts of water are not observed, which of course reduce the amount of energy that can be recovered. There are similar problems when the water runoff from storage power plants fluctuates very strongly in the context of peak load generation; the Surge operation can affect the habitat of numerous aquatic animals and plants. Of these are z. For example, around 30% of rivers in Switzerland are already affected.

In the case of storage power plants, additional problems arise due to the flushing of the storage space, with which deposits such. B. digested sludge must be removed from the reservoir. The flushing of the storage space can particularly damage the fish population if it is not planned and carried out very carefully.

In the context of water usage concessions, residual water quantities, restrictions on surge operation and rules for flushing reservoirs are prescribed, which usually represent a compromise between the needs of energy generation and water protection. Similar compromises are also necessary in connection with other technologies, such as the irrigation of fields in agriculture and the cooling of large thermal power plants and industrial plants.

Assessment of the ecological impact

The ecological effects of the use of hydropower therefore depend very much on the respective circumstances and the efforts made. In any case, the ecological effects should be assessed in a differentiated manner for each system and compared with the respective potential use. (Comparisons of ecological damage that do not take into account the size of the production are, of course, improper.) The ecological comparison with other methods of electricity generation is difficult, since z. For example, it is difficult to weigh up the climatic dangers of burning fossil fuels against landscape interventions in the use of hydropower.

Ecological improvements are often possible by using electricity produced in environmentally friendly hydropower plants as Green electricity can be marketed, whereby the higher revenues enable additional investments or, if necessary, can also compensate for a certain reduction in the amount of electricity generated.

Questions and comments from readers


In the article, I miss the importance of hydropower plants in view of the challenges posed by extremely rapidly changing load requirements in the grids as a result of feed-in from photovoltaics in particular, but also from wind power. As far as I know, the hydropower plants are particularly suitable for compensating for these fluctuations, as their output can be regulated much more quickly than with gas, coal or nuclear power plants operated with steam turbines. The systems of Vorarlberger Kraftwerke / Illwerke, designed as peak load power plants, have been proving this for decades.

Water-fed small power plants, which were previously classified as relatively uneconomical, would be well suited as regional regulators from this perspective in order to compensate for load changes regionally. In this case, the assessment of their economic efficiency shows a different picture, since they are not to be viewed in isolation as a single system, but in their systematic importance.

Answer from the author:

It is true that water storage power plants are very useful as a supplement to wind and solar power. However, this does not apply to run-of-river power plants, as their output can usually hardly be regulated. Small hydropower plants in particular usually do not have a water reservoir with which they could produce as needed.

For Germany, the only possibility of significantly greater use of hydropower for these purposes is to expand the power lines, especially to Norway (and of course also within Germany) in order to be able to use the huge storage capacities that already exist there.

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See also: hydropower plant, run-of-river power plant, water storage power plant, pumped storage power plant, storage for electrical energy, renewable energy
as well as other articles in the renewable energy categories, basic concepts