The aim of the paper was to analyse selected aspects of the energy sector in Poland. We analysed conventional methods of electric power production and provided an overview of conventional main activity electricity producers in Poland. The work contains a presentation of selected modernisation projects from the energy sector, characterisation of distribution system operators and analysis of the thermal power sector in Poland. Additionally, the article describes an enterprise operating in the thermal power engineering sector. The case study presented encompasses characterisation of a district heating plant located in Skierniewice, analysis of the heat generation process and description of the heat network programme. The study was based on literature, research and statistical data as well as on data provided by a thermal energy company LLC seated in Skierniewice. Additionally, employees of the company were interviewed during a site visit in the plant. The analysis of the thermal energy company LLC in Skierniewice allows us to conclude that the operation of undertakings specialising in the production of heat, which is to be used to heat buildings and supply hot water, differs depending on the quarter of the year, with 2 quarters of intense production (quarter I and IV - heating season) and 2 quarters of a reduced demand (quarter II and III - summer season).What is more, the company is required to comply with stringent standards for air pollutant emission. As a result of the above, there is a need for investments, which will have lower impact on the environment and will be performed in accordance with applicable regulations. In addition, the investments and modernisations aim to improve the efficiency of the equipment, reduce losses in the transmission of heat energy and enhance reliability of devices, all with a positive effect on the financial condition of the company.