The variable generation characteristics of renewable energy sources present new operational challenges in terms of power system balancing, grid frequency control, backup capacity planning, and transmission system constraint management. In recent years, Turkey's electricity system has undergone a transformation with the rapid increase in wind and solar energy capacity. The rapid expansion of variable renewable energy sources (vRES) is transforming the operational structure of Türkiye’s electricity system and introducing new challenges related to system flexibility, balancing, and grid stability. By the end of 2025, the share of solar power in installed electricity capacity reached 25 109 MW, or 20.5%, while the share of wind power reached 14 774 MW, or 12.1%. The total installed solar and wind power capacity reached 39.8 MW in 2025, representing 32.6%. According to preliminary data, Türkiye's total electricity production in 2025 was 362.9 TWh and in certain operating periods, the instantaneous share of renewable energy production has exceeded 55%. The rapid integration of renewable resources has intensified operational challenges such as steep evening ramp requirements reaching 8–10 GW within 3–4 hours, increased forecasting uncertainty, regional transmission congestion, and reduced system inertia. This study analyzes the operational impacts of high renewable penetration using real transmission system data and evaluates key system-level challenges, including frequency control, net-load variability, and balancing reserve requirements. The findings indicate that maintaining system reliability in a high-renewable environment requires coordinated investments in flexible generation resources, energy storage systems, advanced forecasting technologies, and smart grid infrastructure. Türkiye’s experience provides valuable operational insights for large interconnected power systems undergoing rapid renewable energy transitions.
Bulut et al. (Tue,) studied this question.