The National Electricity Company (NEK) has signed contracts with Japanese corporation Toshiba and Austrian consortium Voith-ABB for the repair and rehabilitation of Hydro Units 1 and 3 at the Chaira pumped storage hydropower plant in Bulgaria. These agreements mark a significant step forward in the restoration of the largest pumped-storage hydropower plant in the Balkans, with both units slated for repair in parallel during 2025.
NEK has engaged Toshiba Corporation, the designer and original equipment manufacturer of the plant, to repair Hydro Unit 1. The signing ceremony, attended by Energy Minister Vladimir Malinov and Japanese Ambassador H.E. Hisashi Michigami, highlights the successful conclusion of negotiations demonstrating professionalism and expertise.
The contract aims to ensure the safe medium-term operation of Hydro Unit 1, which has remained in its original condition since its commissioning in 1995. Toshiba’s high technical expertise is expected to deliver the optimal solution, with works commencing as soon as possible. The unit is projected to return to operation in 2026.
For Hydro Unit 3, NEK signed a contract with the Austrian consortium Voith-ABB, represented at the signing by Minister Malinov and Philipp Kupfer, Commercial Counsellor at the Austrian Embassy in Bulgaria. The rehabilitation of Hydro Unit 3 will incorporate a special engineering solution similar to the one used for Hydro Unit 2, which successfully re-entered service in late 2024 following the completion of its 72-hour testing. Preparatory work is already underway, with NEK having completed the dismantling of Hydro Unit 3’s generator section.
Recent progress at Chaira pumped storage plant
In December 2024, NEK announced the successful rehabilitation of Hydro Unit 2, a project that utilized an innovative technical solution to restore the turbine. The unit’s completion marked a milestone in the project = and demonstrated NEK’s ability to manage complex modernization projects.
“From the very beginning, the scale, complexity, and lack of similar accidents in global practice exceeded the usual engineering challenges,” said NEK CEO Martin Georgiev. “Innovative approaches and non-standard solutions were required. I am confident that this pioneering solution will leave a lasting mark on the history of engineering excellence.”
The successful rehabilitation of Hydro Unit 2 has set a precedent for the ongoing modernization efforts. In addition to the works on Hydro Units 1 and 3, NEK has initiated a procedure for the complete replacement of Hydro Units 1 and 4 to ensure sustainable, long-term operation.
Strategic impact
The parallel rehabilitation of two hydro units in 2025, along with the planned modernization of the remaining units, is a critical component of NEK’s strategy to fully restore Chaira pumped storage plant. This large-scale project will significantly enhance the integration of renewable energy across the region and contribute to Bulgaria’s and Europe’s decarbonization goals.
Bulgaria is poised to strengthen its position as a regional leader in green energy storage, with Chaira playing a pivotal role. NEK’s modernization program also extends to other hydropower projects, including the rehabilitation of the Belmeken-Sestrimo-Momina Klissura hydropower cascade and plans for new pumped-storage facilities at the Batak and Dospat dams.
Broader modernisation initiatives
NEK is advancing its strategy to integrate innovative energy solutions, such as hybrid hydropower plants. A pilot project at Vacha 1 hydropower plant will combine generation and storage technologies, making it Bulgaria’s first hybrid hydropower plant. Similar systems are planned for four additional facilities.
