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The Bulgarian hydroelectric plant portfolio was acquired by Akuo in 2018. CHB comprises two hydropower plants (HPP), Passarel and Kokalyane, which are the energy production components of the Iskar cascade complex strategically located on the Iskar River near Sofia, with an installed capacity of 53 MW.


The Iskar reservoir has a volume of 655.3 million m³ and is connected to the Passarel HPP by a 5-km tunnel belonging to and operated by a third-party service provider.

Thanks to a pressurized pipeline, the water is channeled to the Passarel HPP, and then to the Kokalyane dam, from where it is transferred to the Kokalyane HPP.


Water for the city of Sofia’s drinking water network runs through the Passarel HPP’s small turbine, which operates 24/7. Annual production is volatile and depends on weather conditions and on the global management of the Iskar cascade’s water level. These two hydroelectric plants play a strategic role in regulating the Iskar cascade’s level.

chb akuo projet

Akuo independent on the energy market

This hydroelectric production and reservoir project is directly optimized by selling electricity to wholesale markets (with no long-term sales contract). This is a first for the Akuo group that thus emphasizes the flexibility of its facilities, steering production in accordance with market demand.

En Bulgarie, Akuo transforme l’eau en énergie

The project team

When Akuo bought this asset from EDF in 2018, the retention of the employees formerly affiliated with EDF was a no-brainer. Their expertise and knowledge of the site without doubt contributed to making this hydraulic plant effective.

chb projet akuo

Our CSR commitment

Drinking water

Akuo’s number 1 mission with this plant is to maintain the dam’s water level in order to ensure the safety of Sofia’s residents who live downstream from it. Thanks to this project, Akuo is participating not only in making Bulgaria’s energy mix greener, but also in the quality and the supplying of drinking water to Sofia, thus providing a response to a major local challenge, as this capital city is prone to regular water cuts affecting its residents’ quality of life.

eau potable rse projet akuo

Local agricultural production

In Pasarel and Kokalyane, Akuo has made the most of its land to grow fruit trees (pears, apples, plums, cherries, hazelnuts), but also plants such as rhubarb. To maintain these orchards, a retired former employee of the plant enthusiastically takes care of these old trees. Located in the middle of a park that locals like to stroll through, these organic fruits and nuts are regularly offered to them free of charge, and the plant’s employees enjoy eating them too.

poires projet chb akuo

Historical heritage

Constructed in 1956 during the Soviet era, the Kokalyane plant is a building of great historical value. Staff frequently welcome pupils and students from the city’s schools and university to share this heritage. Treasuring the plant’s first operating manual, we are intent on supplying it with the very latest equipment by, for example, installing four new wheels for the turbines in 2023, integrating them in a way that visually preserves the plant’s historical character.

Diversification et vente de l’électricité

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