Czech utility ČEZ has completed investments worth CZK 840m (US$40.7m) at the Dlouhé Stráně pumped storage hydropower plant, concluding a two-year modernisation program focused on safety, reliability, and service life extension.
The work was finalised with the replacement of the stator winding on the TG1 generator set. Following a successful 72-hour trial run, the unit has returned to commercial operation. The completion of this upgrade marks the end of a series of planned major repairs across the facility.
According to ČEZ, both generating units underwent stator winding replacement and alignment over 2023 and 2024. Additional work included modifications to the main ball valve, upgrades to control system hardware, modernization of the excitation system, repairs to hydraulic motors, and continued refurbishment of internal coatings in the water conduits between the upper reservoir and the turbines.
Further investments were carried out across the plant site. These included upgrades to camera and security systems, refurbishment of the protective mastic coating on the inner walls of the upper reservoir to improve UV resistance, and restoration of water-level monitoring stations on the Desná River that were damaged during flooding.
Dlouhé Stráně will mark 30 years of operation in 2026. Alongside public outreach events, ČEZ plans additional technical work, including bridge repairs, construction of a second weir on the Divoká Desná River, replacement of frequency converters for backup power supply, and other smaller upgrades.
ČEZ said the primary objective of the modernisation programme is to ensure long-term reliable operation. The role of Dlouhé Stráně has grown in importance as the Czech power system integrates higher shares of renewable energy. In addition to covering morning and evening demand peaks, the plant is increasingly used for energy storage to support grid balancing.
The Dlouhé Stráně facility operates with its powerhouse and key technologies located deep underground. It provides large-scale energy storage, black-start capability, and voltage regulation services. In recent years, ČEZ has increased investment in the plant, spending CZK 111m (US$5.4m) in 2023 and CZK 60m (US$2.9m) in 2022 on safety and reliability improvements. In 2021, the operating level of the upper reservoir was raised by 70cm, increasing storage capacity per cycle by about 6%.
Dlouhé Stráně holds several national and European records, including Europe’s largest reversible turbine at 325MW, the highest hydraulic head in the Czech Republic at 510.7m, the country’s largest installed hydropower capacity at 2 × 325MW, and the highest reservoir water level in the Czech Republic at 1350m above sea level.
