Slovakia: EU Backs €2.1m Study to Hybridise 735 MW Cierny Vah Pumped Hydro with Battery Storage

The European Commission has earmarked €2.1 million under the Connecting Europe Facility (CEF) for Energy to assess adding a battery energy storage system (up to 80 MW/160 MWh) to Slovakia’s 735 MW Cierny Vah pumped-hydro plant and to modernise two of its six units.

The PCI-designated project, launched in October 2024, is coordinated by Slovenské Elektrárne (34% state-owned; Slovak Power Holdings holds 66% through EPH and Enel, with EPH expected to acquire Enel’s stake this year).

Over the next two years, preparations will target converting two pumped turbine units to variable-speed turbines to lift operational efficiency, while studies define the optimal BESS design and controls—covering market simulations, financials, and detailed technical specifications. Branded SE Integrator, the initiative responds to rising variable renewables that drive short-term fluctuations and day-night mismatches; pairing PHES with batteries is intended to improve flexibility and price stability.

Following completion of the EC-funded studies, the project moves to Final Investment Decision (FID). Beyond stabilising Slovakia’s grid, balancing energy could be exported to Hungary, Poland, and the Czech Republic. While battery-plus run-of-river hybrids are emerging in places like the Philippines, Bulgaria, and Germany, direct PHES-plus-battery integrations remain uncommon—though developers SENS and Callio outlined a similar concept in Finland in 2024.