Solar and battery output cushions Romania’s Cernavodă Reactor 2 outage

Stored solar replaces lost nuclear output

Romania maintained power-system stability during Thursday evening’s peak after Cernavodă Nuclear Power Plant’s Unit 2 shut down because of the Danube’s low water level. Adevărul reported that photovoltaic energy stored in batteries supplied almost 700 MW to the grid between 21:00 and 22:00, broadly comparable with the reactor’s output. No major system imbalances were recorded.

Households and companies operating their own storage systems played an essential role in covering the shortfall, according to the publication. The performance demonstrated that distributed solar and batteries can support the national system after sunset, when photovoltaic panels are no longer generating directly and demand must be met from dispatchable production, stored energy or imports.

The contribution continued on Friday, when solar became Romania’s largest electricity source and provided more than 50% of national generation. Transelectrica data cited by Adevărul showed total domestic production at approximately 5,541 MW. The system was operating with a net surplus, allowing electricity to be delivered to foreign markets despite the loss of Unit 2 one day earlier.

Sudden battery contribution raises questions

The almost 700 MW battery injection contrasted with conditions in preceding days, when Romania had been importing more than 2,000 MW each day to cover evening consumption. Eugenia Gusilov, founder of the Romania Energy Center, told Adevărul that the timing had two possible explanations. Storage projects may have received accelerated authorization from energy regulator ANRE after a state of alert was declared at the end of July, or capacity that was already installed may have remained inactive or disconnected until the reactor stopped.

Gusilov said clarification would require ANRE to disclose whether it authorized storage projects in late July or early August. Grid operator Transelectrica could also identify any newly connected battery parks and state when they began supplying electricity. If no significant capacity was recently added, the episode would indicate that previously installed assets had not been operating.

The issue matters for power buyers and traders because earlier use of storage could have reduced at least part of the import requirement. It also raises questions about connection procedures, dispatch incentives and visibility over distributed batteries—resources that can become particularly valuable when nuclear, hydroelectric or thermal generation is constrained.

Hydropower dominance and storage policy

Gusilov linked Romania’s limited progress on alternative storage partly to the position of state-controlled Hidroelectrica. She said the company holds between 80% and 96% of the balancing market and provides substantial dividends to the Romanian state. That model worked while hydrological conditions were favorable, but drought and weaker hydroelectric generation have exposed its vulnerability.

Prime Minister Ilie Bolojan recently said Hidroelectrica would have to invest in storage capacity. The options need not be limited to batteries. The proposed Tarnița-Lăpuștești pumped-storage hydropower plant in Cluj County has planned capacity of approximately 1,000 MW. It would use surplus electricity to pump water uphill and release it through turbines when consumption rises or renewable output falls.

State-owned generation faces a delayed transition

Romania is also developing eight solar parks through joint ventures between Complexul Energetic Oltenia and private companies. The projects, currently at different stages of construction, form part of a restructuring plan that also includes two new gas-fired plants and partial replacement of coal capacity.

According to Gusilov, the company missed the solar expansion of 2013-2015 while relying on coal and state subsidies. After the subsidies ended in 2020, it began diversifying into gas and solar, although coal generation was not fully abandoned. The Reactor 2 outage now provides a practical test of whether Romania can turn rapidly expanding photovoltaic capacity into dependable evening supply through batteries, pumped storage and clearer rules for connecting and dispatching flexible assets.