This work compares the energy production of different types and orientations of photovoltaic systems under the equal outdoor conditions over the 4-yr period in Slovenia. The following photovoltaic systems were analyzed: the fixed photovoltaic system oriented to the south tilted at 30 deg, the fixed photovoltaic system oriented to the east tilted at 30 deg, the single axis photovoltaic tracking system tilted at 30 deg, and the fixed photovoltaic system oriented to the south tilted at 15 deg. The same monocrystalline silicon (mc-Si) solar modules are used in the compared systems. The systems are installed in a radius of 20 m. This provides the same meteorological parameters during the measured period. The impact of orientation and inclination on energy production are evaluated. The analysis of the data obtained shows that the energy production of the photovoltaic systems depends on the solar irradiation, temperature of solar modules, efficiency of solar modules, and efficiency of dc-ac inverters. Based on the analysis and measurements for different photovoltaic systems, the optimal orientation and inclination are presented. The results for Slovenia show that the optimal orientation and inclination facing south tilted at 45 deg.