Glossary of hydropower terms

Environmental sustainability is the highest priority in every project. For this reason, planning and implementation are carried out in an interdisciplinary manner and strictly in accordance with the requirements of the Austrian Environmental Impact Assessment (EIA). 

TIWAG collaborates with internationally renowned partners. These include, for example, Ökoteam – Institute for Animal Ecology and Landscape Planning, Geosphere Austria, REVITAL Integrative Natural Resource Planning GmbH, and the peatland experts from Naturraumplanung Egger e.U.

Cooperation with the scientific community is also of great importance to TIWAG. Academic partners include the University of Innsbruck (Faculty of Engineering Sciences – Hydraulic Engineering Unit), the University of Natural Resources and Life Sciences, Vienna (Institute of Hydrobiology and Aquatic Ecosystem Management), the Technical University of Munich (Centre for Geotechnics), and the Austrian Academy of Sciences.
“Close cooperation with science and research brings real added value to our projects. This is how safe and environmentally sound solutions are created that remain viable in the long term.”

More than one hundred highly trained TIWAG employees, including numerous excellently qualified and experienced TIWAG engineers, contribute to the successful implementation of the projects. These specialist departments combine all the expertise required to realise a modern power plant: from conceptual design, submission planning, official approval procedures and procurement of all components, to construction planning, ecological aspects, electrical engineering, mechanical engineering and construction execution. Compared with other Austrian regional energy suppliers, TIWAG’s team ranks among the very best.


How exactly an Environmental Impact Assessment procedure works, what its key features are, and which roles the project applicant, authorities and the public play, can be found here.


Storage and pumped‑storage power plants, such as the Versetz pumped‑storage plant, continue to fulfil their role as flexible energy storage units for stable grids even with reduced runoff volumes. They are therefore ideal and long‑term reliable partners for the energy transition. Their long operational lifetime of at least 100 years is a major advantage.

However, the runoff behaviour of glacial streams is influenced not only by precipitation levels but primarily by the rapid melting of the glaciers:

  • For example, the glacier surface area in the Vent catchment was still around 70 km² in 1969 but had decreased to around 45 km² by 2017.
  • By 2050, a glacier area of about 20 km² can be expected in this region.

Once the glaciers have completely melted in the distant future, the annual runoff of the glacial streams in the Vent catchment will decrease by a maximum of 18%. The increase in annual precipitation in Tyrol due to climate change has not been taken into account here.

The United Nations Intergovernmental Panel on Climate Change (IPCC*) regularly publishes climate change scenarios (RCP**), which are calculated based on global population developments and projected greenhouse gas emissions:

  • For Tyrol, these calculations assume an increase in the annual average temperature of around +2 °C by 2050 compared with the 1971–2000 average.
  • For the more distant future (2071–2100), a temperature rise of +2.3 °C to +4.2 °C is expected, depending on the scenario.
  • These temperature increases influence annual precipitation levels, with projections for the distant future indicating that precipitation in Tyrol may rise by +4.9% to +6.5%.

* IPCC: Intergovernmental Panel on Climate Change
** RCP: representative Concentration Pathways

  • Over the past 40 years, the Platzertal has recorded a temperature increase of more than 1°C (source: Spartacus, Geosphere Austria). This has led to a reduction in glacier areas and to changes in permafrost conditions.

  • According to the climate data applicable to Austria (ÖKS15), temperatures in the period 2071 to 2100 are expected to rise by +3 to +5°C compared with 1971 to 2000.

  • Precipitation levels have remained constant over the past 40 years. However, all projections for the distant future show an increase in winter precipitation in the Platzertal of around 10% and a slight increase in summer precipitation of around 5%.

  • Earlier onset of snowmelt
  • Higher winter runoff
  • Reduced summer runoff

The most likely future scenarios indicate that runoff volumes currently occurring in June/July will shift to April/May. Due to higher winter precipitation, runoff levels in the months of October to December are also expected to rise. The range of runoff changes is between –2% and +4%.

On an annual average, all scenarios show that by around 2080 – despite seasonal shifts – the total volume of water available for the Platzertal reservoir will remain the same as today.

* IPCC: Intergovernmental Panel on Climate Change
** RCP: representative Concentration Pathways


No. To meet the future challenges of the energy supply system, we will need a whole range of storage options.

Battery storage systems can provide significant benefits for system stability in the short‑term range. However, when flexibility is required for more than just a few hours, battery storage becomes unsuitable. Therefore there is no competitive relationship with pumped‑storage power plants. To balance rapid changes in electricity generation and demand, both battery storage systems and pumped‑storage power plants will be necessary, as the European energy system will face major fluctuations within just a few hours in the future.

Pumped‑storage power plants with large reservoirs can generate electricity over extended periods as needed, helping to balance bottlenecks and peaks in both production and demand. They contribute to grid stability and security of supply within Europe’s energy system.

Thanks to the large Platzertal reservoir (with a storage volume of 42 million m³), the Versetz pumped‑storage power plant can operate continuously in either pumping or turbine mode over long periods. The storage duration, which describes how long the reservoir can supply energy, is up to 7 days at full output. Battery storage systems, by contrast, only reach a few hours.

Unlike pumped‑storage power plants, battery storage systems do not reduce the so‑called winter gap. However, the ability to shift stored energy over longer periods is urgently required. Even today, there is a significant energy shortfall when wind does not blow over extended periods or when the sun does not appear for several days. This situation will become even more acute in the future as we phase out fossil fuels, further widening the winter energy gap in Austria and, in particular, in Tyrol.

In the event of a blackout, the expansion of the Kaunertal power plant can make a substantial contribution to securing island operation in Tyrol. This represents another clear advantage over battery storage systems.

Battery storage systems have a very limited service life, which can be well below 15 years depending on the application. Pumped‑storage power plants such as the Versetz plant, on the other hand, have extremely long life cycles – they are typically designed to operate for around 100 years.

Pumped‑storage systems are long‑term and financially viable investments thanks to their proven technology and long service life. Battery storage systems cost at least ten times more than a pumped‑storage system by comparison. This calculation does not even include the significantly greater land requirements of battery installations.

The CO₂ balance of battery storage systems is five to ten times worse than that of pumped‑storage power plants. This is primarily due to the use of rare earth elements such as lithium or cobalt, which must be mined, transported and processed. Pumped‑storage plants, by contrast, use water as their storage medium. Much of the material required to build a dam can be sourced from the immediate surroundings of the construction site. Pumped‑storage power plants are therefore a significantly more climate‑friendly technology.

Battery storage systems cannot replace the Versetz pumped‑storage power plant, as the two storage technologies have entirely different strengths. However, our calculation example clearly shows that the land requirements of battery storage systems must always be taken into account:

  • International large‑scale battery storage facilities require between 80 and 240 square metres to store 1,000 kWh. These figures vary significantly depending on the technical design and the infrastructure required.
  • For comparison: the Platzertal reservoir covers an area of 90 hectares and can store 63 million kWh. The Gepatsch reservoir covers 260 hectares. The Versetz site therefore has a land requirement of 14 square metres per 1,000 kWh.
  • If we use the large Jardelund battery storage facility in the German state of Schleswig‑Holstein as a reference, then to match the amount of energy that can be stored in the Platzertal reservoir, each of Tyrol’s 277 municipalities would need to build battery storage systems covering the area of around three football pitches.
  • If we use the amount of energy processed down to the Prutz power station (149.1 GWh) as the reference, this would equate to more than seven football pitches in each of the 277 municipalities.

Glossary of hydropower terms

In a hydropower station, a turbine converts the kinetic energy of flowing water into mechanical energy. A generator then converts the mechanical into electrical energy. Hydropower allows the power of water in streams and rivers to be used regardless of topographical conditions – from plains to mountain ranges with heads far above 1,000 meters. This wide range of natural conditions requires the use of different, optimised types of power stations.

In a run-of-river power station, the river is dammed slightly using a weir structure upstream of the power plant. The turbines are operated continuously by the inflowing water. The generator converts the power of the flowing water into electrical enery. Energy production depends on the head, the available volume of water and the inflow at a given point in time. Flexible energy production is not possible because there is no storage system for managing the continuous inflow of water.

A pumped storage power station consists of two reservoirs – one higher up, one lower down – and the pumped storage station itself. The water stored in the upper reservoir is used to generate electricity in turbine operation. If there is an energy surplus in the grid (caused, for example, by strong winds), the station switches to pumped operation to pump the water back from the lower reservoir to the upper reservoir, where it is stored for subsequent use. Pumped storage stations thus play an important role in stabilising the power grid. The Kühtai pumped storage station is typical of this type of power station.

In a storage power station, the inflowing water is stored in a natural or man-made lake located above a power station for several hours or even months. The water is drawn off and fed to the machines in the powerhouse for electricity generation as required. The Silz storage station is a typical example of this type.

The water used in hydropower plants mostly originates from vast areas called catchment areas. The natural precipitation in these areas collects in watercourses and flows downhill – some of it directly to the power stations or the water intake structures and reservoirs above the stations. The catchment area as such – the areas above the water intake structures – is in no way affected by the power station.

A water intake is a structure used to draw supply water from a stream. No matter if water is supplied directly to the power station or is fed into a reservoir first, rock, sand, driftwood, leaves and sediment must be removed to prevent operational problems or damage to the subsequent plant sections. The Tyrolean weir, specially developed for Alpine mountain streams, reliably leaves bedload in the stream, thus permitting optimum water drawoff.

In the catchment area of a hydropower plant, water intakes are often far away from the reservoir. Stream adductions guide the water drawn at the weirs to the reservoir via a system of tunnels or pipes. 

A headrace channel is the direct connection from the water intake in a river, stream, lake or reservoir to the powerhouse and on to the outlet channel where the water is returned to the body of water.

In a hydropower station, the turbine and generator are mounted on the same shaft assembly. This combination is called a machine unit.

A generator is a machine for electricity generation that converts mechanical into electrical energy. The generator is connected to a turbine. The kinetic energy of the turbine shaft produces electrical energy in the generator due to the movement of an electrical conductor in a magnetic field.

A turbine is a continuous flow machine that converts the flow of water into a rotary movement. In power stations, turbines are coupled with generators to utilise the rotary motion for electricity generation. The type of turbine chosen depends mainly on the available head and volume of water. The three types of turbines most commonly used today are Pelton, Francis and Kaplan turbines.

The term efficiency describes the ratio of energy output to input in energy conversion processes. In hydropower plants, friction losses occur in the pipelines, hydraulic losses in the turbines, and electrical losses in the generators and transformers. With an efficiency of 90%, hydropower is an extremely efficient way of generating electricity because up to 90% of the energy of water is actually converted into electrical energy.