This paper summarises the ongoing transformation in the structure of Polish power system. This is a very complex process which fits into global megatrends in this matter. It needs to take into account such crucial elements like socially responsible investments, life cycle assessment, policy changes and investments strategies. United Nations climate policy urges to take certain actions to combat climate change and its impact. It highlights new record high levels of greenhouse gases content in the atmosphere. Presented graphs contain data extracted from the Polish power system showing intra-day, monthly and annual load distribution. Particular attention is paid to the variability of wind energy sources and their efficiency (full load equivalent operating hours factor). Discussed aspects does not address any issues related to the stability of the power system. Additionally, it does not contain any polemic with the cited research results. On their basis it can be pointed out that wind farms contribute to a local temperature and precipitation increase. The nature of this phenomenon (positive or negative) in the context of global warming is currently the subject of worldwide research. Nevertheless, it can be said with certainty that the environmental impact of renewable sources usage is significantly lower than in the case of classic power plants based on fossil fuels.