ČEZ completes modernisation of Czech pumped-storage plant Dlouhé stráně for CZK 840 million

ČEZ Group has completed a two-year modernisation of the Dlouhé stráně pumped-storage hydropower plant in the Šumperk region, investing 840 million crowns. Following an uneventful 72-hour trial run, the plant’s generating unit has entered normal operation. The modernisation will improve safety and extend the life of the pumped-storage plant, which is important for stabilising the energy system in Czechia. ČTK was told today by ČEZ Group spokesman Vladislav Sobol.

Technicians focused the modernisation mainly on refurbishing important parts of the turbine-generator units, which have been in service for almost 30 years. “Last year and this year, we gradually replaced the stator windings and aligned both units. We also modified the spherical valve, upgraded the control system hardware, modernised the excitation system, repaired the hydraulic motors and continued applying internal coatings to the water conduits from the upper reservoir to the turbine,” said ČEZ hydropower plant director Róbert Heczko.

The Dlouhé stráně pumped-storage plant began operating in 1996. Its machine hall and other technology are located deep underground. At the turn of September and October, technicians reinstalled the repaired stator and rotor in generating unit TG1 at the pumped-storage plant. This was one of the key milestones in this year’s modernisation. The stator weighs 280 tonnes and the rotor 410 tonnes. For each operation, the technicians had to use two overhead cranes, each with a lifting capacity of 250 tonnes.

Investment and repairs took place throughout the plant site. “We modernised the camera and security systems. In the summer, we worked on renewing the mastic coating on the inner walls of the upper reservoir, which improves UV protection for the asphalt lining. We also managed to restore the limnigraphs—stations that measure the water level of the Desná River—which were washed away by floods,” said plant director Ludvík Štrobl.

In 2023, ČEZ invested 111 million crowns in improving the plant’s operational safety and reliability; in 2022, the figure was CZK 60 million. A year earlier, the energy company raised the operating level of the upper reservoir by 70 centimetres, enabling it to store approximately six percent more energy than before.

The Dlouhé stráně pumped-storage hydropower plant serves as a huge battery. In the Czech energy system, it is used both to absorb surplus energy, which is then used to pump water from the lower reservoir to the upper one, and during periods of energy shortage, when it generates electricity and sells it at a higher price. The plant is important for balancing the intermittent supply from renewable energy sources.