Installation works on solar power plants Prapretno 2 and Prapretno 3 and a battery energy storage system have been completed, and the facilities, in Slovenia’s Zasavje region, have entered trial operation. State-owned power utility Holding Slovenske elektrarne (HSE) said that, together with the first section, it is currently the largest operational solar park in the country.
The Prapretno solar power plant, with a capacity of 3 MW, was built in 2022 in a former mining area, on remediated land previously used by the Trbovlje thermal power plant as an ash disposal site. Preparations for its expansion began in 2025, while the construction of Prapretno 2 and Prapretno 3 started in late December.
The works have recently been completed, bringing the photovoltaic system’s total capacity to 9.8 MW. In addition, a battery energy storage system with a capability of 7 MW and a capacity of 14 MWh has been installed alongside the solar power plant.
The new sections have entered trial operation. HSE expects to obtain the operating permit in the first half of October. The company said Prapretno is now the largest operational solar power plant in Slovenia. The site spans parts of the municipalities of Trbovlje and Hrastnik.
Prapretno will produce enough electricity to supply around 2,300 households
“The solar power plant is operating without problems, and last week we also tested the capacity of the battery storage system. We are gradually bringing the entire system to full operational status,” Nenad Trkulja, HSE’s project manager, told Naš stik.
The previously largest photovoltaic system in Slovenia, with a capacity of 7.1 MW, entered regular operation in July 2025. The biggest project is for the 120 MW Družmirje floating solar power plant.
Prapretno 2 and Prapretno 3 together consist of 11,200 solar modules, each of 600 W. The expected annual electricity output is 9.8 GWh. According to Trkulja, it is equivalent to the needs of around 2,300 Slovenian households.
The investment in the expansion of the photovoltaic facility and the installation of the battery system exceeds EUR 11 million. HSE pointed out that the European Union provided more than EUR 4 million and that it is the first Slovenian energy project co-financed through the EU’s Just Transition Fund. It is a tool primarily intended to support the transformation of coal regions.
Energy storage improves the project’s economic viability
The battery energy storage system consists of four containerized units, two transformers and two inverters.
“We can continuously adjust the storage system’s output from zero to 7 MW. At any moment, we can stop discharging and start charging or switch to another operating mode. This significantly increases the flexibility of the entire facility,” Trkulja explained.
The storage system enables electricity generation and sale to be separated in time, improving the economic viability of the entire facility, he added. When the solar power plant generates large amounts of electricity, it can be stored and delivered to the grid later, when demand or prices are higher.
The facility will be remotely operated, from HSE’s generation control center in Maribor.
Solar power plant to be built at former municipal waste disposal site
HSE recently obtained a building permit for another solar power plant in the Zasavje region, in the municipality of Zagorje ob Savi. The 1.4 MW facility will be located at the closed Kamnolom Zagorje municipal waste disposal site.
The company said it would also install a battery system of 1.25 MW in operating power and a storage capacity of 5 MWh.
The Slovenian power utility plans to begin construction next year. As with Prapretno, part of the funding has been secured from the EU’s Just Transition Fund.
