Due to unfavorable factors, dangerous conditions occurred in the delivery of electric energy in Poland. This was the most serious incident of its kind since the 1980’s. Such a serious incident raised concern about the safety of the electric power system in the summer and led to the formulation of conclusions for the future. In this article, the author analyses the conditions, which caused that situation. Poland was experiencing a doubt in August 2015, which along with an extremely high maximum daily temperature created remarkably unfavorable conditions for power plants and decreased the capacity of overhead power lines. Such unfavorable metrological conditions occurred not only in Poland, but also in Central-Eastern and Western Europe. It is worth emphasizing that the safety of electric energy delivery was endangered only in Poland. The improper renovation and upkeep policies, as well as unplanned outages in power plants caused a significant decrease of available power in the National Electric Power System. Unscheduled flows between Germany and Poland ruled out the possibility of importing electric energy at such a critical time. The author presents the correlation between the maximum daily air temperature in the sweltering heat and an increase in the demand for electric energy. Overall, unfavorable conditions posed a threat in the delivery of electric energy in Poland. In this article, the author draws attention to the report from the Supreme Audit Office (Najwyższa Izba Kontroli – NIK) from 2014, which predicted such a dangerous situation. Unfortunately, that report remained unnoticed. The author formulated appropriate solutions in order to increase the safety of electric energy delivery in the summer and to prevent such occurrences in the future.

The overriding objective of the National Electric Power System (KSE) is to ensure the security of electricity supply. In summer, the upward trend in the demand for electric energy is caused by, among others, the proliferation of air conditioners. Therefore, the upward trend in summer’s on-peak demand is expected to be maintained. Examples from 2015, 2016 or 2018 indicate that National Electric Power System needs a summer’s on-peak source that will be able to produce electricity regardless of the hydrological conditions. Photovoltaics is a source of energy that can cover the peak demand during sweltering heat. This article briefly characterizes the problem of increasing demand for electricity in summer and uses examples that have taken place in recent years. The main conclusion is the postulate for the extension of photovoltaic power in the National Electric Power System, the purpose of which will be the production of electricity during sweltering heat, covering the peak load in the system. This article presented both the advantages and disadvantages of such a solution. Unfavorable weather conditions (high air temperature, low water level, lack of wind) limit the production of electricity from wind farms or conventional power plants, and also increase transmission losses, which is why photovoltaics is a desirable source from the National Electric Power System’s point of view. The article refers to examples from the Czech Republic and Germany, where a significant installed capacity of photovoltaics enables the stable operation of the power system during sweltering heat. It was also pointed out that the role of photovoltaics in the National Electric Power System is growing, which is consistent with the assumptions of the Polish Energy Policy Project until 2040.