Kozjak Pumped Storage Hydropower Plant (PSP) Project on the Drava River
The Kozjak Pumped Storage Hydropower Plant (PSP) project on the Drava River and the 2 x 400 kV transmission line to the existing Maribor-Kainachtal international transmission line has been included in the national spatial plan (DPN).
The Kozjak PSP project is included in the "Slovenian Network Development Plan 2023–2032" and in the National Energy and Climate Plan.
The Kozjak PSP project is part of the mission of Dravske elektrarne Maribor, a leading company of HSE Group in green transition. In this respect, and in terms of opportunities for the local environment and the storage of surplus generated electricity, the project is of strategic importance for the entire country.
The project is part of a collaboration between two investors, DEM and ELES.
Dravske elektrarne Maribor, part of the HSE Group, is a leading company in efficient use of renewable energy sources in Slovenia, committed to the development of high-quality energy in an environmentally friendly manner, with the aim of economic efficiency and compatible sustainable development of the environment and the market in which it operates.
The purpose of introducing electricity storage is to increase flexible generation for the purpose of providing balancing services on the electricity market, while at the same time alleviating the burden on the existing generation units in the HSE Group in terms of dynamic operation.
The storage plant (Kozjak PSP) will allow storage and usage when renewable (intermittent) sources are not producing electricity.
A pumped storage hydropower plant belongs to renewable energy sources, which are our allies in reducing the impacts on climate, enabling greater energy security and reducing dependence on imported electricity. The facility will be built safely, professionally and in cooperation with the local environment. The Kozjak PSP plant will store the surplus of the generated electricity, thus reducing energy losses and contributing to a more stable grid.
The expertise of the project is provided by in-house knowledge, cooperation with the most renowned Slovenian institutions in this field, and international cooperation. In addition to Slovenian experts, EU experts and universities are also involved.
One of DEM's missions is the green transition, through which it aims to preserve nature and reduce environmental pollution. DEM is committed to the concerns of the local environment, which is why regular communication and information on the activities of the project will take place.
We will proactively inform stakeholders and the public on the completion of each step, and we are already available to clarify any questions via e-mail chekozjak@dem.si or the toll-free telephone number 080 1140.
What is a pumped storage hydropower plant?
A pumped storage hydropower plant is a type of electricity storage. It is a configuration consisting of two basins of water at different altitudes, which allows electricity to be generated when water flows from the upper to the lower basin through a turbine (discharge). At the same time, a pumped storage hydropower plant is also a consumer of electricity when it pumps water from the lower to the upper pool (recharge). A pumped storage hydropower plant works like a giant battery, as it can store energy and release it when it is needed. In peak demand, a pumped storage hydropower plant acts as a pump, and in peak shortage, it acts as a hydroelectric power plant. Pumped storage hydropower plants are net consumers of electricity, yet they allow for the storage of electricity generated from renewable sources that could not be produced otherwise.
How does a pumped storage hydropower plant work?
The main purpose of pumped storage is not, as in the case of hydroelectric power stations on the Drava River, to continuously harness the water flow and produce electricity. The purpose is to store the surplus electricity generated mainly by intermittent renewable energy sources (sun, wind). When cloudy or windless weather prevents solar and wind power plants from generating enough electricity, the pumped storage hydropower plant begins to transfer water from the upper basin to the lower basin via a turbine, thus ensuring an uninterrupted supply to the electricity grid.
A pumped storage hydropower plant thus has two modes of operation. During peaks, the generator acts as a motor that drives the turbine to pump water. When there is a shortage of electricity, the water flow drives the turbine, which is connected via a shaft to the generator, which mechanically converts the water into electricity.
The importance of pumped storage hydropower plant
Due to the increase in electricity generation from solar and wind power, there are periods when there are peaks of electricity that consumers are not able to consume when it is being generated. Until now, we have had to manage peaks by reducing electricity generation at hydroelectric power stations, which means reducing renewable energy generation and an additional strain on equipment, which accelerates wear. Batteries could be a solution for electricity storage, yet their capacity is currently too small and they are a major environmental burden due to their rare metal contents. A pumped storage hydropower plant is a better solution, as it also acts as an electricity storage device and can store huge amounts of energy. "Green batteries" is a term often associated with pumped storage hydropower plants.
The installation of new and larger pumped storage hydropower plants enables the expansion of renewable energy sources, thereby increasing the share of green energy sources, without sacrificing the reliability of the electricity supply.
Advantages of pumped storage hydropower plants
Presentation of the Kozjak Pumped Storage Hydropower Plant (PSP) project and the accompanying transmission line (TL) connection
Dravske elektrarne Maribor, as the concession holder for the energy use of the Drava River, intends to build a pumped storage hydropower plant, which will operate as part of a chain of hydropower plants on the Drava River. The current use of the Slovenian part of the Drava is a chain of eight large power plants from Dravograd to Ormož. The planned Kozjak PSP is therefore a technically sensible continuation of the energy use of this river. The PSP will produce peak energy during daily peaks, but will also be important for fast reserve needs in the power system and for system services of primary and secondary regulation and voltage regulation.
The key facilities of the project are as follows:
Key dimensions and specifications of the planned Kozjak pumped storage hydropower plant:
The figure below shows a cross-section of the design of the pumped storage hydropower plant with the installation of the powerhouse in the cavern. All the key components of the pumped storage hydropower plant are shown, with the exception of the transmission line.
At the far-left edge of the figure is the lower platform with the lower inlet-outlet structure continuing into the discharge tunnel. At the end of the discharge tunnel (bottom right) is the powerhouse cavern, where the two reversible Francis turbines are installed. The turbines can be used in both turbine and pump mode. A penstock rises vertically from the powerhouse cavern and completes the connection between the Drava River and the upper storage basin. This is shown in the top right of the figure.
The figure also shows the service and access tunnels and the surge tank with the ventilation shaft. The green line shows the terrain profile.
