HSE Expands Prapretno Solar Plant to 9.8 MW with Battery Storage
Slovenia's largest operational solar facility has entered trial operations, tripling its capacity and adding a 7 MW battery system to stabilize grid output.
Holding Slovenske elektrarne (HSE) has completed installation works on the Prapretno 2 and Prapretno 3 solar power plants, bringing the total photovoltaic capacity of the site to 9.8 MW. The facility, located in the Zasavje region, now stands as the largest operational solar park in Slovenia. The expansion was built on remediated land previously used as an ash disposal site for the Trbovlje thermal power plant. Construction for the new sections began in late December 2025 following the initial build of the first 3 MW section in 2022.
Alongside the solar expansion, HSE installed a battery energy storage system with a capability of 7 MW and a storage capacity of 14 MWh. The system consists of four containerized units, two transformers, and two inverters. HSE project manager Nenad Trkulja stated that the facility is currently operating without problems and that tests on the battery storage capacity were successfully conducted last week. The company expects to receive the formal operating permit in the first half of October, at which point the site will transition from trial operation to full commercial status.
Storage System Enhances Grid Flexibility
The battery energy storage system allows HSE to decouple electricity generation from grid delivery, improving the economic viability of the project. Trkulja explained that the output can be continuously adjusted from zero to 7 MW, enabling operators to switch between charging and discharging modes as needed. This flexibility allows surplus energy generated during peak solar hours to be stored and released later when demand or market prices are higher. The facility will be remotely operated from HSE’s generation control center in Maribor.
Investment Cost and EU Funding
The total investment in the expansion of the photovoltaic facility and the installation of the battery system exceeds EUR 11 million. HSE noted that the European Union provided more than EUR 4 million in co-financing. This project is the first Slovenian energy initiative funded through the EU’s Just Transition Fund, a mechanism designed to support the economic transformation of coal-dependent regions. The Prapretno site spans parts of the municipalities of Trbovlje and Hrastnik.
Output Equivalent to 2,300 Households
The expanded Prapretno plant features 11,200 solar modules, each with a rating of 600 W. HSE projects an annual electricity output of 9.8 GWh, which is sufficient to supply the needs of approximately 2,300 Slovenian households. This capacity surpasses the previous national record holder, a 7.1 MW photovoltaic system that entered regular operation in July 2025. The next major project in the pipeline is the 120 MW Družmirje floating solar power plant.
Next Project Targets Waste Site
HSE has also secured a building permit for a new 1.4 MW solar power plant in the municipality of Zagorje ob Savi. This facility will be constructed at the closed Kamnolom Zagorje municipal waste disposal site. The project includes a battery system with an operating power of 1.25 MW and a storage capacity of 5 MWh. Construction is planned to begin next year, with partial funding again sourced from the EU’s Just Transition Fund.
