## 7 Conclusions and Policy Recommendations  
The results of this research demonstrate that the growing integration of renewable energy sources (RES), particularly wind and solar generation, significantly affects electricity price dynamics in the European day-ahead wholesale market. High-resolution data from the period 2015 to 2025 revealed systematic relationships between RES generation intensity, the occurrence of extreme price events (including negative prices), and year-on-year changes in the predictive power of statistical models. The findings confirm that the relationship between hourly RES generation and electricity prices is clearly negative in several countries. This supports Hypothesis H1. The strongest effects were observed in Germany and Poland, where the correlation coefficients between wind generation and price reached \(-0.57\) and \(-0.47\), respectively, during years with a high share of renewables. Hypothesis H2, which assumed the existence of a threshold level of RES generation beyond which the likelihood of extreme prices sharply increases, was also confirmed. In Germany, for instance, negative prices began to appear frequently once the combined RES output exceeded 65,000 MW, and in ranges above 195,000 MW, the share of hours with negative prices approached 100%. This non-linear trend indicates that the system reaches structural limits under certain conditions, resulting in a breakdown of price equilibrium. The analysis of annual regression models confirmed Hypothesis H3: In crisis years such as 2022, the coefficient of determination (R\({}^{2}\)) increased significantly, meaning that the relationship between RES generation and electricity prices becomes more predictable during periods of market stress. Hypothesis H4 was confirmed through comparison between countries with different levels of system flexibility. Nations such as France, which benefit from higher demand-side responsiveness or stronger interconnections with neighbouring markets, showed lower price volatility at comparable levels of RES generation compared to more isolated countries such as Estonia or Slovakia. The final Hypothesis H5, concerning the statistical identification of predictive patterns for negative price events, was also validated. Using segmented production intervals, it was demonstrated that the combination of high RES output with temporal factors (e.g., summer weekend afternoons) significantly increases the probability of negative prices. These findings confirm that electricity price volatility is becoming a feature of evolving generation mixes. This transformation calls for fundamental changes in energy policy and market design. It is essential to strengthen system flexibility through targeted investments in energy storage technologies, support for flexible consumption (e.g., dynamic pricing schemes), and expansion of cross-border transmission capacity. Regulators should also introduce tools that allow market participants to proactively identify risk periods with a high likelihood of price extremes. This may include the mandatory publication of short-term RES generation forecasts, the implementation of adaptive auction mechanisms, and the development of shared European capacity reserves. The findings of this study are consistent with previous research that highlighted the correlation between increased RES penetration and greater price volatility, including more frequent occurrences of extreme pricing. For example, [PERSON] and [PERSON] in [27] emphasised the need to reform market mechanisms as price signals increasingly decouple from underlying costs due to zero-marginal cost generation. Similarly, [27; 28] reported over 200 h of negative prices in Germany in 2020, which aligns with our observed frequency of negative pricing above 195,000 MW of RES generation. From a market perspective, such dynamics present significant investment uncertainty and challenge the functioning of existing pricing frameworks.