The paper presents the results of empirical studies of the energy sector in Poland in the period 2005–2020. The main research problem was the impact of gross savings of changes in gross investment levels in this sector. To this end, we used a formula determining the value of private investments from the theory of the economic dynamism of M. Kalecki. First, we checked its adjustment to the economic reality of the energy sector and analysed the impact of individual independent variables on gross investment levels. We calculated linear regression and correlation coefficients in two variants due to delays between investments and investment decisions. The results of the studies justified the hypothesis. According to it, gross investments in the Polish energy sector are determined by the level of gross savings of companies.