PULS

The pumped storage project is designed to strengthen security of supply as an integral part of the European interconnected grid.

Vattenfall is planning the construction of the PULS pumped storage facility in southern Thuringia. The project complements Vattenfall’s existing high-performance pumped storage sites. The PULS facility will be developed from scratch to support grid stability and help integrate renewable energy sources by providing large scale electricity storage and flexibility.

Overall, PULS is expected to support the energy transition by ensuring grid stability and providing rapid flexibility in electricity generation. The project benefits from the specific conditions of the selected site in southern Thuringia, including an existing grid connection, suitable topography and geological conditions, and a favourable location for providing flexibility to support the integration of renewable electricity. 

Key facts about PULS

PULS is an acronym formed from the initial letters of the surrounding towns:

  • Probstzella
  • Unterloquitz
  • Leutenberg
  • Schweinbach

A pumped storage plant is a type of hydropower facility that stores electricity as potential energy by moving water to an upper reservoir and can release that stored energy to generate electricity when needed.

The project includes, among other elements, the construction of an upper and lower reservoir as well as an underground powerhouse cavern, and it is planned to be connected to the existing 380 kV transmission line.

Subject to the necessary approvals, PULS is expected to go into operation in the mid-2030s.

Map with localization of upper and lower reservoir in Thuringia

Contribution to Energy Security

The PULS project contributes to supporting the European electricity grid. Its integration into the existing grid enables PULS to support the transition towards a fossil-free energy system by providing storage capacity, improving the use of renewable electricity and helping balance fluctuations in supply and demand:

  • Flexibility for renewable energy: The project provides additional storage capacity to help balance fluctuations in electricity generation from renewable sources.
  • Fast power availability: Pumped storage plants enable the rapid provision of electricity within 90 seconds and help stabilize the grid when needed.
  • Black start capability: Some pumped storage plants can independently restart the grid after a power outage. PULS will also have this capability.

Technical Design and Functionality

The underground powerhouse cavern forms the technical core of the pumped storage plant. It houses the key mechanical equipment needed for power generation and energy storage, including the generator and pump turbine. Together, these components enable water to be moved between the upper and lower reservoirs. A surge tank protects the system against pressure surges.

  • Energy storage: When there is excess electricity, water is pumped from the lower reservoir through a tailrace tunnel and pressure shaft via the pump turbine into the upper reservoir.
  • Power generation: When electricity is needed, water flows from the upper reservoir through the pressure shafts into the pump turbine, which drives the generator to produce electricity. The water is then discharged back into the lower reservoir via a tailrace tunnel.
Technical cross section of pumped storage plant PULS

Project of Common Interest (PCI)

The expansion of renewable energy and the transition away from fossil fuels also require, at a European level, the promotion of facilities that make a significant contribution to securing energy supply. For this reason, the EU has granted the PULS project the status of a Project of Common Interest (PCI), recognising it as an energy infrastructure project of European relevance.

Projects of Common Interest are key cross-border infrastructure projects that connect the energy systems of European countries. They strengthen the EU internal energy market and security of supply, while supporting sustainability and a climate-friendly energy system.

PCIs benefit from accelerated permitting and regulatory procedures and may gain access to European funding.

European Commission: Key cross-border infrastructure projects

Project timeline

In 2011, a potential study was conducted on behalf of the Free State of Thuringia to identify and analyze possible new sites for pumped storage plants. The study aimed to provide a foundation for the development and expansion of energy storage capacities in Thuringia and to stimulate investment. As part of this study, the site for the PULS project was identified.

In 2012, the project company WSK Puls GmbH, under the leadership of STRABAG SE, initiated the pumped storage project PULS. An important first step was the launch of the spatial planning procedure (“Raumordnungsverfahren”), which aimed to assess the fundamental feasibility and regional planning compatibility of the site.

At the same time, the grid connection was reserved with the transmission system operator 50Hertz – an essential prerequisite for the later integration of the power plant into the electricity grid.

In 2016, the project achieved a major milestone with the completion of the spatial planning procedure (“Raumordnungsverfahren”), representing a key hurdle in the subsequent permitting process.

This means that the overall spatial compatibility of the project was assessed and positively approved, thereby confirming the fundamental feasibility of the selected site.

In 2023, Vattenfall acquired WSK Puls GmbH from STRABAG SE. This step marked a key milestone in the project’s development. Since then, Vattenfall has continued the project under the name Vattenfall Wasserkraft Puls GmbH.

In 2024, the PULS project was granted Project of Common Interest (PCI) status. This European designation underlines the importance of the pumped storage plant for the European energy transition and infrastructure.

In 2025, a comprehensive feasibility study was completed. A particular focus was placed on the hydrology of the site and the detailed assessment of historical mining activities in the region, with all relevant geological and water management aspects thoroughly analyzed.

In the second half of 2025, the pumped storage project entered the crucial phase of the approval planning process. During this phase, comprehensive planning documents and expert reports were prepared, detailing the technical aspects of the project, its environmental impacts, and the measures planned to mitigate them. The outcome of this phase was the application for planning approval (“Planfeststellungsantrag”).

Towards the end of this decade, the planning approval procedure (“Planfeststellungsverfahren”) is expected to begin, marking a key milestone for the project.

This comprehensive approval process involves a detailed assessment of the project, taking into account all relevant aspects such as environmental and nature conservation as well as public interests. It also includes the collection of required statements and feedback from authorities and the public.

If the approval process concludes with a positive planning approval decision (“Planfeststellungsbeschluss”), a final investment decision will be made. If this decision is positive, the construction phase of the PULS pumped storage plant is expected to begin in the early 2030s.

From that point onwards, a pioneering pumped storage facility will be constructed step by step.

If everything proceeds as planned, commissioning of the PULS pumped storage plant is expected in the middle of the next decade. From that point onwards, the plant is intended to make an active contribution to grid stability and to the integration of renewable energy in Germany.

Vattenfall Wasserkraft Puls GmbH

Vattenfall Wasserkraft Puls GmbH, based in Berlin, is developing the PULS pumped storage project in Thuringia. As part of the Swedish energy group Vattenfall AB, the company is one of the largest producers and suppliers of electricity and heat in Europe. Vattenfall is an integrated energy company with a strong focus on its customers.