The connection of Mochovce Unit 4 to Slovakia’s electricity grid marks a major milestone in the completion of one of Central Europe’s most significant energy investments. The new nuclear unit will strengthen Slovakia’s energy security, increase domestic low-carbon electricity generation and support the country’s long-term decarbonisation goals.
Energetický a průmyslový holding (EPH), which indirectly holds a 66 % stake in Slovenské elektrárne through Slovak Power Holding, welcomes the first supply of electricity from Unit 4 of the Mochovce Nuclear Power Plant to Slovakia’s national grid. The milestone, achieved on 15 October 2026, marks a decisive step towards bringing the new nuclear unit into full commercial operation.
At 20:41 on Thursday, 15 October, Slovenské elektrárne successfully synchronized the first of Unit 4’s two turbine generators with the national transmission system. Operating at 20 % reactor power at the time, the unit began delivering its first megawatt-hours of electricity to the Slovak power system.
With an installed electrical capacity of 471 MW, Mochovce Unit 4 is expected to generate approximately 3.5 million MWh of electricity annually once fully operational. This represents around 13 % of Slovakia’s current electricity consumption, significantly strengthening the country’s ability to meet its electricity needs through domestic, low-carbon generation.
A Major Milestone in Slovakia’s Energy Transition
The first synchronization of Unit 4 follows years of development, construction, testing and commissioning. Before the generator could be connected to the grid, specialists had to verify the readiness of electrical circuits, generator protection systems and all equipment involved in the safe and reliable delivery of electricity.
The process requires the generator’s voltage, frequency and phase to match those of the national transmission system precisely. Successful synchronization confirms that the unit has reached an important operational milestone and can begin supplying electricity beyond the power plant itself.
The connection to the grid follows the achievement of first sustained criticality on 6 August 2026, which marked the beginning of a further phase of physical testing and power ascension. Together, these milestones demonstrate continued progress towards the completion of the Mochovce nuclear project.
For EPH, the development of reliable, low-carbon electricity generation is an important part of building a more secure and sustainable energy system. Nuclear power plays a key role in this effort by providing a stable source of electricity that complements renewable generation and supports the integration of an increasing share of intermittent energy sources.
Further Testing Ahead of Full Operation
The first grid synchronization marks the beginning of the next stage of commissioning rather than the completion of the process. The second turbine generator will subsequently be synchronized with the grid, followed by mandatory tests at progressively higher power levels.
Specialists will verify the performance of the unit’s technological, control and safety systems as output increases towards nominal capacity. The commissioning process is being carried out under the supervision of the Nuclear Regulatory Authority of the Slovak Republic.
Once fully operational, Mochovce Unit 4 will further reinforce Slovakia’s electricity supply and reduce the need to rely on external sources to meet domestic demand. Together with Unit 3, which was connected to the grid in 2023, it represents a significant addition to the country’s nuclear generation capacity.