Chaira Hydro Power Plant, Pumped-storage power station in Belovo Municipality, Bulgaria

The Chaira Hydro Power Plant is a large pumped-storage facility in Belovo Municipality, Bulgaria, situated about 100 kilometers southeast of Sofia in the Rila mountain range. It operates with two reservoirs - the upper Belmeken Dam and the lower Chaira Dam - connected by tunnels roughly 4 meters in diameter, using four reversible turbines that can both generate electricity and pump water back uphill to store energy.

Construction began in 1980 and stalled for financial reasons; units 1 and 2, supplied by Toshiba, entered service in April 1995. The second stage, financed 74% by the World Bank, added units 3 and 4 in August 1999. In March 2022 a turbine failed during a test after overhaul, and the plant has been offline since.

Chaira is named after the Chaira reservoir, the lower equalizing basin of the plant, which sits above the village of Sestrimo. The plant belongs to the Belmeken–Sestrimo–Chaira hydropower cascade on the Rila range, and its two 1.7 km penstocks, 4.4 to 4.2 m in diameter and about 50 m apart, drop 689 m to the machine hall. The hall itself is a cavern 22.5 by 11.5 m and up to 43 m high, 350 m underground, with the transformers in a side cavern.

The machine hall lies 350 m underground in a cavern 22.5 m wide, 11.5 m long and up to 43 m high, reached by access tunnels; the site is a working industrial facility, not a visitor attraction. The lower Chaira reservoir allows 8.5 hours of continuous generation or 11 hours of pumping. The plant has been out of service since a turbine failed in March 2022.

The turbines were built by Toshiba and assembled in Bulgaria under Japanese supervision, a rare technical feature for a Southeast European project in the 1990s. Since 2022, the facility has been offline due to turbine failure, making repairs a priority to restore its energy storage and generation capability.