Terrain-Driven Wind–Solar Complementarity in Mediterranean Environments: A Spatiotemporal Framework for Albania

Renewable energy systems are increasingly constrained by spatial and temporal variability, particularly in complex Mediterranean environments where terrain exerts a strong control on resource distribution. This study investigates wind–solar complementarity across Albania using a terrain-resolved spatiotemporal framework based on ERA5 reanalysis data (2014–2024). The territory is stratified into coastal, western lowland, and mountainous zones to isolate terrain–atmosphere interactions, and complementarity is quantified using spatial, temporal, and hybrid indices, supported by non-parametric statistical analysis. The results reveal a clear physiographic gradient in spatial complementarity, with values exceeding 0.85–0.90 in coastal areas, decreasing to 0.75–0.85 in lowlands, and further to 0.65–0.75 in mountainous regions, where higher variability is observed. Temporal complementarity exhibits pronounced seasonal variation, with values peaking in autumn (≈0.68–0.69) and reaching minima in summer (≈0.48–0.52). Hybrid suitability also varies spatially, with values of 0.65–0.83 in coastal and lowland areas compared to 0.32–0.55 in mountainous regions. These findings demonstrate that wind–solar complementarity is governed by terrain–atmosphere coupling and seasonal dynamics and provide concrete guidance for renewable energy planning, including the identification of optimal zones for hybrid wind–solar deployment, improved resource balancing strategies, and more efficient integration of variable renewable energy into electricity systems.