To achieve the goals of carbon peaking and carbon neutrality, the development of renewable energies becomes the trend in building a power system with low-carbon emissions and clean energy sources. Analyses of power forecasting errors and improvements in the prediction accuracy of renewable energies are crucial for building new power systems. In this paper, by taking day-ahead prediction of renewable energy power of several southern provinces of China in 2021 as examples, the power prediction characteristics of renewable energies is systematically analyzed and corresponding strategies are proposed to cope with forecasting errors. Firstly, first, existing forecast technologies and the current status of their applications at home and abroad are summarized. Secondly, the common characteristics of the current day-ahead renewable energy power forecasting errors are sorted out. Finally, ideas for coping with renewable energy power forecasting errors are proposed, including the investigation of evaluation metrics for renewable energy power forecasting, research on the ensemble of forecast models, exploration of value ecology cultivation for renewable energy power predictions, etc.