Renalfa starts construction of 269 MW Horia 2 solar-storage site in Romania

Renalfa Solarpro Group has commenced construction of the Horia 2 solar power plant located in Arad county, Romania. Featuring 269 MW of grid injection capacity, the project represents an initial phase of a larger renewable generation complex that integrates photovoltaic panels with battery storage facilities. EPC services for the site are being undertaken by Solarpro Holding.

The development of large-scale hybrid solar and storage projects introduces distinct technical challenges for transmission and distribution network operators across South-Eastern Europe. Unlike conventional standalone photovoltaic installations that generate energy along a predictable daily parabolic curve, utility-scale battery integration enables complex charge and discharge cycles. Energy is stored during peak generation windows or periods of grid congestion and injected back into the transmission system during evening demand peaks or system balancing events.

For substations and step-up transformers, these operational dynamics produce severe cyclic stress. High ramp rates and sudden shifts between energy absorption and generation trigger rapid thermal variations within transformer tanks. This repeated expansion and contraction accelerates paper insulation degradation and accelerates moisture movement within the oil-paper system. Furthermore, high concentrations of solid-state power conversion equipment introduce harmonic currents that increase stray losses, heat hot spots in transformer windings, and strain reactive power compensation equipment.

Additionally, frequent load shifts demand more dynamic regulation from tap changers, raising mechanical duty cycles far beyond historical operational baselines for solar collector assets. Protection coordination also becomes significantly more complex, as fault current contributions vary depending on whether the battery storage arrays are active, charging, or idling. Utility engineers must adapt protective relaying schemes to ensure reliable fault isolation across all operating modes.

What this means for asset owners in the Balkans and the Black Sea region: Asset owners and transmission system operators in Romania handling co-located renewable projects must specify step-up transformers built to withstand high harmonic distortion and continuous thermal cycling. The rapid load fluctuations characteristic of battery integration increase tap changer wear and accelerate winding insulation ageing, making continuous oil condition monitoring essential to manage failure risks and avoid costly unscheduled outages.