Od stopni Celsjusza do megawatogodzin: prognozowanie zapotrzebowania na energię elektryczną przy użyciu publicznie dostępnych prognoz pogody [From Celsius to megawatt hours: Forecasting electricity demand using publicly available weather predictions] Dawid Linek (Faculty of Management, PWr, Wrocław) Current weather conditions significantly impact electricity generation and consumption. However, it is unclear whether publicly available short- and medium-term weather forecasts can improve the accuracy of electricity demand predictions up to seven days ahead. In this study, we evaluate the predictive power of variables such as temperature, wind speed, cloud cover, and atmospheric pressure. We identify the most informative variables, discuss methods for processing weather predictions, and highlight key considerations for incorporating these variables into forecasting models. ---------- Prognozowanie cen energii elektrycznej na rynku dnia następnego: uśrednianie prognoz a wykrywanie punktów zmiany [Electricity price forecasting in the day-ahead market: averaging forecasts vs breakpoint detection] Piotr Zaborowski (Doctoral School - Management, PWr, Wrocław) The profitability of a battery energy storage system (BESS) in the day-ahead market is determined by the precise timing of buying (charging) and selling (discharging) electricity. The latter requires reliable electricity price forecasts for the next day. In this paper, two approaches are compared using regression-based models. The first averages forecasts across calibration windows of varying lengths, balancing short-term responsiveness with long-term stability. The second uses structural break detection with the pruned exact linear time (PELT) algorithm, calibrating models only within homogeneous segments. The approaches are evaluated using both statistical (MAE, RMSE) and economic criteria (average opportunity cost of a BESS trading strategy and the Sharpe ratio) on four European day-ahead markets: Germany, Finland, Poland, and Spain. The test period includes the COVID-19 pandemic and the 2022 energy crisis. The results show that averaging-based models outperform breakpoint-based approaches in both accuracy and profitability.