This thesis analyzes the impact of connecting photovoltaic power plants to the operation of medium-voltage networks, with a particular focus on the technical challenges and opportunities within the distribution system. The introductory section presents the distribution network, emphasizing medium-voltage networks and the criteria for their planning in Croatia. The process of connecting renewable energy sources to the medium-voltage network is then examined in detail, including grid regulations and the procedure for commissioning photovoltaic power plants. Furthermore, the thesis provides an overview of the basic components and operating principles of photovoltaic power plants, as well as the consideration of safety aspects and protection of these systems. Special attention is given to non-integrated photovoltaic power plants in Croatia and the development of substitute load and production curves. The central part of the thesis focuses on analyzing the impact of connecting photovoltaic power plants to the power system, including changes in voltage profiles, power losses, short-circuit currents, and harmonic emissions. Through an example of a real medium-voltage network, load and production curves, power flows, voltage profiles, short-circuit currents, and power losses for a characteristic day of the year are analyzed. In conclusion, the thesis emphasizes the importance of thorough planning and analysis when integrating photovoltaic power plants into medium-voltage networks to ensure the stability and quality of the power system.