Quantifying the Capacity Credits of Intermittent Renewables: Implications for Power System Planning

The European Union’s objective of climate neutrality by 2050 requires a profound transformation of national power systems. In Poland, this transition involves reducing coal-based generation and expanding variable renewable energy sources (VRES), particularly wind and solar. Between 2020 and 2025, onshore wind capacity increased from 5.9 GW to nearly 11 GW, and solar from 1.6 GW to over 22 GW, while peak electricity demand in 2024 exceeded 28 GW. Although VRES- are essential for decarbonization, their variability poses challenges for system adequacy. This study assessed the adequacy contribution of onshore wind and solar power plants using capacity credit as a key indicator. Two approaches were applied: a deterministic Load Duration Curve (LDC) method and probabilistic methods—Effective Load Carrying Capability (ELCC) and Equivalent Firm Capacity (EFC)—based on historical data from 2021–2024. The results show that capacity credits for onshore wind ranged from 8.08% to 17.27%, and for solar from 1.82% to 6.60%, depending on the method and year. Despite the presence of 1.7 GW of pumped storage and 4.4 GW of battery storage contracted in the capacity market, the relatively low VRES capacity credits underline the continued need for flexible, dispatchable generation. The findings highlight the importance of accurate capacity credit estimation to guide investment in renewables, storage, and backup capacity, thereby supporting a secure and reliable energy transition in Poland.