The primary objective of this thesis is to analyze the impact of different distributed energy sources on the conditions within the power system and to compare them. The second chapter provides a brief overview of distributed generation, the main reasons for introducing this new type of energy production, its positive and negative impacts, and methods that can enhance the stability of the power system. It defines the connection points depending on the type of power plant (installed capacity), connection technologies, and the impact on the grid at the connection point, as well as explaining the concept of integration levels. The third chapter offers a theoretical basis for understanding the impact of distributed sources on the conditions within the power system and describes the transition from a passive to an active distribution network, along with the future transition to a smart grid. The first subsection provides a detailed explanation of the impact of distributed generation integration on voltage conditions, covering the basic concepts of voltage control, permissible voltage deviations in distribution and transmission networks, mathematical expressions for approximate voltage rise, and methods for increasing integration levels. The second subsection describes in detail the impact of distributed generation integration on current conditions in the distribution network, defining key concepts in power system design and presenting methods for reducing current loads and increasing integration levels. The final chapter models and describes the power network of the island of Vis, which is used in simulations. Simulations were conducted under minimal and maximum load conditions, both with and without battery energy storage systems. The simulations varied the type of distributed source (photovoltaic plant, wind farm, small hydroelectric plant, wave energy plant). Voltage and current conditions were monitored throughout the simulations. The last subsection presents a comparison of the impacts of different distributed sources on the network under minimal load, both with and without battery storage.