pumped storage power plant

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Dam of the Ottenstein power plant with the power house, in which two pumps with 9 MW each and four turbines with 12 MW each are housed

A pumped storage power plant , also Pumpspeicherwerk abbreviated, PSW , one is storage power plant , the electrical energy in the form of potential energy (potential energy) in a reservoir stores. The water is lifted into the storage tank by electric pumps so that it can later be used again to drive turbines to generate electricity. Pumped storage power plants are currently the only way to store electrical energy on a large scale under economic conditions. In times of low demand, they take in an oversupply of electrical energy in the power grid and release it back into the grid at peak loads .


Pre-industrial predecessors

The basic principle of storing water as a positional energy was already used in the late phase of the solar-agrarian age - shortly before the beginning of industrialization . Windmills , which were more volatile in production than watermills , pumped water into a reservoir at a higher level, from which in turn watermills were continuously fed; a process that v. a. was used in the textile industry, where a finely adjustable, regular movement of the mechanically driven looms was particularly important . This made it possible to increase the working capacity of the water power, which was particularly valuable and therefore heavily used at this time, through wind power.

First modern PSP

One of the oldest pumped storage plants was installed in Gattikon on the Sihl . With a Jonval turbine, the system transported one cubic meter of water per second into the artificially created forest pond . When the water level in the Sihl was low, the water was drained from the pond and fed to a low - pressure run-of-river power station , which mechanically drove the transmissions of a weaving mill . The plant was in operation from 1863 to 1911. When the weaving mill was connected to the power grid, the pumping operation was discontinued, the system components were only removed in the 1980s to make space for residential developments.

Development since the 1920s

Modern pumped storage power plants were first implemented on a small scale in the 1920s. Arthur Koepchen was one of the German engineers who developed the technology for large-scale pumped storage power plants as a worldwide pioneering achievement . The PSW Koepchenwerk of RWE AG in Herdecke an der Ruhr , which went into operation in 1930, was named after him. A compilation can be found in the list of pumped storage power plants .

Originally, pumped storage power plants were primarily used for the short-term provision of expensive peak loads and for better utilization of base load power plants such as nuclear power plants or lignite power plants . These provide the most constant possible power and, apart from emergencies such as load shedding , can only be started up and shut down economically within hours or days. At the same time, there is strongly fluctuating electricity consumption over the course of the day and week, which must always be met exactly. Pumped storage power plants offered a possibility to z. B. at night or at times of day with low sales, to convert base-load electricity fed into the grid, which was available at comparatively low prices, into significantly more expensive electricity for peaks in demand. The sales price in this business can be many times the purchase price, which made the operation of pumped storage power plants economically viable. It was clear from the start that this system would work technically, but the economic benefit was only proven when the Koepchenwerk went into operation . The existence of pumped storage power plants thus also hedged some of the economic risks of thermal base load power plants, which were able to feed electricity into the grid that was practically unnecessary at night.

energy transition

With the expansion of renewable energy in the course of the energy transition , the operating pattern of pumped storage power plants has changed significantly. Especially in summer, when photovoltaics feed large amounts of electrical energy into the grid during the day, the midday peak and often also large parts of the medium load are covered by photovoltaic systems, so that the operating times of pumped storage systems are shifted more into the morning and evening hours. At the same time, the expansion of wind and solar energy will lead to an increasing need for storage in the long term in order to be able to compensate for volatile generation. This is why storage power plants, including pumped storage power plants, are expected to become increasingly important in the future. The storage requirement reaches a relevant dimension from a renewable share of 60–80% of the power supply; If the proportions are lower, the flexibility options such as load management , flexible operation of conventional power plants and the expansion of the power grid are economically more expedient options to compensate for the fluctuations.



Basic structure of a pumped storage power plant with a ternary machine set in generator or pump operation
Detailed cross-sectional
drawing using the Raccoon Mountain pumped storage plant as an example

In principle, every pumped storage power plant, as shown in the sketch opposite, consists of at least one upper storage basin (upper water basin) and one lower deep basin (also called underwater basin). There are one or more pressure pipes between the two basins . In the simplest case, the machine hall of the power plant contains a water turbine , a pump and a rotating electric machine , which can be operated either as an electric generator or as an electric motor and is shown in red in the sketch. In the case of larger pumped storage power plants, several such units are available in parallel operation.

The turbine, the electrical machine and the pump, including auxiliary equipment such as clutches and the launch turbine, are mounted on a common shaft . As in other power plants, the electrical machine is usually designed as a three-phase synchronous machine with an exciter . Since synchronous machines in motor operation for starting the pumping operation cannot start safely from standstill by themselves due to the mass moment of inertia , auxiliary devices such as a smaller launch turbine are provided, depending on the power plant, in order to be able to bring the motor up to speed for pumping operation. Alternatively, in some pumped storage power plants, dedicated three-phase asynchronous machines are provided as drive motors for pump operation , which have no start-up problems. The synchronous machine is then operated exclusively as a generator.

While the electric machine can work in both generator and motor mode, turbines usually cannot also work as a pump. For this reason, the pump is separated from the turbine, designed as a Francis turbine or free-jet turbine , as an independent unit and, depending on the operating mode, connected to the pressure pipeline via gate valves . The turbine is idle-proof, which means that in pumping operation the turbine runs idle without any function. Idling would cause damage to the pump in generator mode, which is why the pump must be separated from the shaft by means of a coupling in generator mode .

To avoid cavitation , the power plant hall is usually provided below the geodetic suction height of the deep basin and designed as a so-called cavern power plant , as shown in the second sketch using the Raccoon Mountain pumped storage plant. In some pumped storage power plants, such as the Blenheim-Gilboa pumped storage power plant , the machine hall is located entirely in the lower deep basin.

Next it comes when closing the gate valve in the pressure lines, z. B. when switching from generator to pump operation, to pressure surges . To compensate for this, a water lock is provided which compensates for pressure surges and thus prevents damage to the pressure lines. Pumped storage power plants can also be operated with very high heads of up to 1000 m.

In the case of a storage power plant, the lower deep basin and the pumping device are not required. The upper storage basin in a storage power plant inevitably requires an inflow. In the case of pumped storage power plants, a distinction is made between those with an inflow in the upper storage basin and those without an inflow.

In addition to this classic design, pump turbine power plants are also built for smaller outputs, which are equipped with so-called pump turbines instead of the turbine and the pump . The pump turbine is a fluid flow machine that can flow through in both directions and works as a pump or turbine, depending on the direction of rotation.

The amount of energy, usually expressed in megawatt hours in this context , depends on the amount of water that can be stored and the usable height difference between the upper basin and the turbine. In purely pumped storage plants, the storage capacity is usually designed so that the generators can produce electrical energy for at least 4 to 8 hours under full load .

In some storage power plants, the storage basins are enlarged by a natural lake using a dam or dam , for example at Schluchsee . Some storage basins are natural lakes without such enlargements, a few storage basins were created exclusively artificially, for example Hornberg basin , Eggberg basin and at the Geesthacht pumped storage power plant .


Power plant cavern with turbine (in blue, rear) and pump (in blue, front right) and electric machine painted in yellow

In principle, more electricity is required for pumping up in every pumped storage power plant than can be recovered when flowing down. Losses occur during the loading and unloading process due to the friction losses of the flowing water (liquids have a flow resistance ; water is also referred to as water resistance and hydraulic losses), through the efficiency of the pump (loading process) or turbine (unloading process), through the efficiency of the motor or the generator as well as transformer losses and, to a lesser extent, the pumped storage plant's own requirements. The overall efficiency of a pumped storage power plant is 75–80%, in exceptional cases a little higher. The overall efficiency is lower than with storage power plants, since in a pumped storage power plant the efficiency for the pumps is added.

In addition, there are further transmission losses for the transport of electrical energy there and back. These depend on the geographical distance between the energy producer, pumped storage and energy consumer.

Energy density

The volume-related density of potential energy of a pumped storage power plant is calculated by the following equation.

With the density of the water , the acceleration due to gravity and the difference in altitude .

This results in a normalized energy density of


Energy-economic importance

Daily cycle of a pumped storage power plant. Green means power consumption from the network by pumps, red means power output into the network by the turbine.

The ability of the pumped storage power plants to both absorb and deliver energy is used to optimize the use of the storage power plants. The high flexibility of their use makes them particularly suitable for providing control power . The generated power is available as storage hydroelectric power plants as needed within minutes and can be controlled flexibly in a wide range. The pumping operation can also be flexibly adapted to different power surpluses in the network if there are two separate riser and downpipes ( Schluchseewerk ), the principle of hydraulic short-circuit is applied ( Kopswerk II ) or asynchronous machines drive the pumps ( PSW Goldisthal ).

Thanks to their so-called black start capability , pumped storage power plants can be used to start other non-black start power plants such as coal-fired power plants in the event of large-scale power outages .

In its special report "100% renewable electricity supply by 2050: climate-friendly, safe, affordable" from May 2010, the German Federal Government's Advisory Council for Environmental Issues assumes that the capacities of the storage power plants, especially in Norway (almost 85  TWh water basin capacity of the pumped storage facilities there expandable storage hydropower plants) and Sweden are by far sufficient to compensate for fluctuations in the renewable energies that will be fed in in the future. However, this requires a considerable expansion of the north-south network connection. The current capacities in Germany (more recent estimates in connection with wind and solar gas speak of approx. 0.6 TWh) are too low for this. The contracts for the construction of the first direct HVDC connection between Germany and Norway ( NordLink ) were awarded at the beginning of 2015 (planned commissioning 2019).

Pumped storage power plants play an important role in Austria to compensate for fluctuations in Germany. In 2014 the electricity export from Germany to Austria was 39.2 TWh, the import from Austria to Germany 17.0 TWh. The maximum storage capacity of all Austrian (pump) storage power plants is currently around 3 TWh; No data is available for pumped storage power plants alone. In a study by the Energy Economics Group of the Vienna University of Technology , it is assumed that the majority of new pump storage power plant installations are merely extensions / upgrades of existing systems and that no or only a negligible increase in storage capacity is to be expected in the future.

Storage costs

The full costs of storing electrical energy in a pumped storage power plant for one day are 3 to 5 cents / kWh. The storage duration influences the costs: the longer the storage, the higher the costs, the shorter the storage, the lower the costs. Since power plants are legally treated like end consumers and therefore have to pay high fees for network use, according to the power plant operators, pumped storage plants are currently (as of August 2014) almost uneconomical. (Only newly built systems are exempt from the network usage fee for the first 10 years.) At the same time, income falls because the difference in electricity prices over the course of the day is less than it used to be. This is due, on the one hand, to the shutdown of nuclear power plants, which mainly caused the nocturnal overload, and, on the other hand, to the solar power that is only available during the day.

Economy (Germany)

In 2009 the Federal Court of Justice ruled : The operator of a pumped storage power plant, which draws electricity from the grid for its operation, is the end consumer i. S. of § 3 No. 25 EnWG and thus chargeable network users according to § 14 para. 1 sentence 1 StromNEV.

In the purchase case, an energy supply company had lodged a complaint. Before 2009, grid usage fees were only due for the electricity supplied, not for energy that was transported to storage facilities in the course of the production chain. After the Federal Network Agency deviated from this practice, the case went to the BGH; there, pumped storage power plants were denied their status as power plants at the highest level.

As a result, the cost-effectiveness of electricity storage systems, which are required in the course of the energy transition to cover the base load from renewable energy sources, has been drastically reduced.


Above-ground pumped storage power plants

There are pumped storage power plants around the world with an installed capacity of around 130 GW. The world's most powerful pumped storage power plant is the Bath County Pumped Storage Station with a capacity of 3,003 MW.


Pipelines of the Wendefurth pumped storage power plant at the Wendefurth dam in the Harz Mountains

In Germany , a pumped storage power of about 7 GW (gigawatts) is installed (see the pumped storage power plants in Germany List ). The power plants are designed to deliver electricity for 4–8 hours a day. This results in a total storage capacity of around 40 GWh (as of 2010). In 2006, the German pumped storage power plants generated 4,042 GWh of electrical energy; this is a share of around 0.65% of electricity generation. This contrasted with pumping work of 5,829 GWh, so that the average efficiency was around 70%.


A storage capacity of around 7.2 GW (gigawatts) is installed in Austria; 3.4 GW of this is available in the form of pumped storage power plants. (see list of Austrian power plants , especially pumped storage power plants).


In Switzerland, the Federal Office of Energy distinguishes between pumped storage plants and pure circulation plants . Pump storage plants are storage power plants whose reservoir can be enriched with additional pumped water. In the case of pure circulation systems, the upper reservoir only contains water that was previously pumped up from a lower reservoir. The largest circulation plants in Switzerland are the Limmern headquarters of the Linth-Limmern power plant , which went into operation in 2016 and has an output of 1 GW, and the Veytaux power plant , which stores the water from Lake Geneva in the Lac de l'Hongrin . In 2019, the Nant de Drance circulation plant is due to go into operation, with an output of 900 MW.

Most power plants that can pump are considered to be circulating plants. The only two large pumped storage power plants are the Grimsel 2 headquarters of KWO and Tierfehd of the Linth-Limmern power plant. In addition, there is the Engeweiher pumped storage plant in Schaffhausen , the oldest plant in Switzerland from 1909, which was revised in 1993 and can now generate 5 MW.

According to official statistics, of the 121 storage power plants with an output of more than 300 kW, only the 3 above-mentioned power plants are regarded as pumped storage power plants and a further 18 plants as circulating plants. The total installed pump capacity is 3.6 GW.

Special design: ball pump storage under water

Main article: Ball pump storage

In order to enable energy to be stored in the vicinity of offshore wind farms in the future, the Fraunhofer Institute for Wind Energy and Energy System Technology Kassel is developing a concrete hollow-sphere storage system in the StEnSEA (Storing Energy at Sea) project. Promising test runs took place in Lake Constance in 2016.

The principle is similar to that of conventional pumped storage power plants, except that here it is not the difference in height between two storage tanks that is used, but the difference between the water pressure outside the spherical storage system and the empty interior of the sphere: Inflowing water drives a turbine, whose attached generator generates electricity. If there is an excess of electrical power, the water is pumped out of the ball again. Both the power and the amount of energy that can be stored depend on the volume and immersion depth of the hollow sphere.

Electricity storage in pumped storage power plants in Europe

The upper basin of the Wehr pumped storage power plant, the Hornberg basin in the southern Black Forest, when empty, May 2008
Net electricity generation in GWh
country 1990 1995 2000 2005 2010 2011
Belgium 624 889 1,237 1,307 1,348 1,127
Bulgaria 0 0 0 0 0 0
Denmark 0 0 0 0 0 0
Germany 2,342 4.187 4.176 7,015 6,785 6,099
Estonia 0 0 0 0 0 0
Finland 0 0 0 0 0 0
France 3,459 2,961 4,621 4,659 4,812 5,074
Greece 228 253 418 593 25th 264
Ireland 283 252 301 340 175 0
Iceland 0 0 0 0
Italy 3,372 4,057 6,603 6,765 3,290 1.934
Croatia 0 0 18th 105 106 129
Latvia 0 0 0 0 0 0
Lithuania 0 358 287 354 741 564
Luxembourg 746 743 737 777 1,353 1,069
Malta 0 0 0 0 0 0
Macedonia 0 0 0 0 0 0
Netherlands 0 0 0 0 0 0
Norway 223 838 396 734 378 1,240
Austria 988 1,037 1,369 2,319 3.163 3,504
Poland 1,877 1,947 1.991 1,566 560 422
Portugal 140 107 381 376 391 564
Romania 0 0 0 0 360 218
Sweden 525 57 35 67 103 122
Switzerland 1,134 769 1,357 1,820 1,738
Slovakia 558 300 318 103 394 368
Slovenia 0 0 0 0 184 143
Spain 702 1,493 3,490 4,552 3.152 2,275
Czech Republic 288 272 555 647 591 701
Turkey 0 0 0 0 0 0
Hungary 0 0 0 0 0 0
United Kingdom 1,892 1,502 2,603 2,776 3.139 2,895
Cyprus 0 0 0 0 0 0
Value not available


The construction of pumped storage power plants means a considerable intervention in the ecology and the landscape. Opponents of pumped storage power plants consider the encroachment on nature and the landscape to be unjustifiable. Since the storage basins have to withstand the regular stress and erosion caused by changing water levels, they are partially concreted or asphalted, which means that no natural vegetation can form. The frequent water changes with a complete mixing also prevents the setting of a natural limnology in the water body. If the basins are dammed by dams, there is little risk of dam bursting . For example, the Taum Sauk pumped storage power plant in the USA suffered a disaster in 2005. Due to the very large pipe diameter, a pipe break could also cause considerable damage and flooding.


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