Jesenice, Slovenia - 12 MW / 24 MWh

The battery was built in 2019 on land next to the SIJ Acroni steelworks in Jesenice and opened on 10 October that year. It was Slovenia's first grid-scale battery and, at the time, the largest Tesla Powerpack system in Europe. Construction started in April and the first operational tests were completed by the end of August, just over a year after NGEN was founded.

Jesenice became the template for every project that followed. From its first day of operation, the battery ran on NGEN's own software and never operated separately from the rest of the portfolio. NGEN managed industrial consumers with flexible demand in the same portfolio, so the battery and demand response acted as a single resource. NGEN has applied this model in every market since.

Generation and consumption must be balanced at every moment. To cover sudden changes, the transmission system operator ELES procures reserve capacity that must be available at all times and follow its signal when activated. Until then, conventional power plants had provided this service. They are reliable, but they change output more slowly and must keep running to hold reserve.

A battery can do the same job faster and without burning fuel. In 2019, however, no battery in Slovenia had been prequalified for the service. With its first project, NGEN set out to show that a battery run by its own software could meet ELES's availability requirements as reliably as a power plant.

The battery has 12.6 MW of connected power and 22.2 MWh of storage capacity. It consists of Tesla Powerpack units on about 800 m² of land next to the steelworks. The system is liquid-cooled and contains more than two million cells. The hardware sets the physical limits; NGEN's platform makes the decisions.

In January 2020, NGEN contracted 14 MW of automatic frequency restoration reserve (aFRR, also known as secondary frequency control) with ELES. The battery does not meet the obligation alone: NGEN also manages industrial consumers with demand response in the same portfolio. The obligation is demanding. The capacity must be available every hour of the year and follow the operator's setpoint when activated. The battery and demand response respond together, which in practice made the portfolio an early virtual power plant.

The platform links the battery to the markets and the grid, forecasts system needs and adjusts operation accordingly. The battery is monitored around the clock from the control centre in Žirovnica.

Secondary frequency control for ELES

Since January 2020, NGEN has provided aFRR to the transmission system operator ELES. Before that, only conventional power plants provided this service.

Zero-emission availability

The battery provides reserve capacity with the availability the system expects from a power plant and the response time of a battery.

Room for more renewables

At launch, NGEN estimated that the battery would allow around 250 MW of additional renewable generation to be integrated into the Slovenian power system.

A template for the whole portfolio

The software-led approach proven in Jesenice is now used on NGEN projects in Austria, Poland, Croatia and elsewhere.