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.