The process of designing an off-grid photovoltaic system located in Rašćane Gornje will be presented. The task is to ensure a sufficient amount of energy for all devices in a cottage that does not have access to the electrical grid. An analysis of the building's energy consumption, battery capacity, and the efficiency of the photovoltaic modules needs to be conducted. Special emphasis is placed on the depth and number of battery discharge cycles, as these parameters define the lifespan of the batteries. Based on the obtained data, an optimal system configuration has been determined, allowing the energy needs of the building to be met throughout the year. The results showed that the system can produce enough energy. However, in the case of cloudy days, the system provides only one day of autonomy, and a complete battery discharge may occur. It is necessary to properly size the components of the photovoltaic system for optimal and reliable operation in an off-grid setup.