Assessing micro-scale solar-wind-hydro complementarity in a mountainous catchment through the stability coefficient

• Assesses the performance of the stability coefficient for >2 Variable Renewable Sources (VRES) • The choice of the reference VRES heavily impacts the stability coefficient values. • Single metrics fail to explain the characteristics of complementarity among VRES. Integrating variable renewable energy sources (VRES) into energy systems is challenging due to their non-dispatchability. Recently, complementary renewable generation has been deemed promising for providing smoother VRES integration, typically coupling two VRES; nevertheless, research has shown that coupling three or more VRES could be more effective in some instances. The lack of standardized methods to quantify complementarity among three or more VRES hinders the accurate assessment of hybrid systems’ stability, especially in decentralized and small-scale contexts where optimal combinations are essential for reliability. This study evaluates how the choice of the reference VRES affects the value and interpretation of the stability coefficient ( C stab ) metric, whose original goal is to represent the reduction in the capacity factor ( CF mix ) variability of a hybrid power system compared to a reference VRES. The study also compares the extended C stab with the total temporal complementarity index, discussing similarities and differences. The case study uses multiannual hourly flow, wind, and solar data series from Kłodzko, Poland. The results indicate that the extended C stab metric effectively represents the complementarity among three VRES. For the case study, the scenarios incorporating 3 VRES showed a higher installed capacity and C stab values, with increases ranging from 12.5 % to 45.2 % and from 2.6 % to 40.6 %, respectively. However, these cases also show lower CF mix values, decreasing between 3.2 % and 74.8 % compared to systems with two VRES.