Calculation of the illuminance coefficient and energy performance of buildings in the design of urban development.

The use of solar panels as a source of energy supply, not only for industrial enterprises but also for private buildings, began in Ukraine in the early twenty-first century. Widespread adoption became evident approximately a decade later, when the number of households equipped with solar power systems increased rapidly following the introduction of the so-called “green tariff”. The necessity for autonomous energy supply for individual houses has become even more acute in the context of the ongoing war.The object of this research may be considered the aspect (orientation) of the slopes of gable roofs in the spatial planning of residential areas, while the aim is to determine the amount of solar radiation incident on roof surfaces of different orientations equipped with photovoltaic panels.The article sets the task, based on the principles of geodetic astronomy, of determining optimal parameters for the orientation of solar panels installed on building roofs in order to maximise electricity generation. The calculations were performed for the day of the summer solstice under the conditions of the city of Ivano-Frankivsk. The value of the optimal roof pitch angle was adopted from existing literature sources. The conducted study illustrates how roof orientation affects the potential for solar energy utilisation. The calculated values of the solar energy coefficientKand the amount of solar energyEₛfor different orientation scenarios of gable roofs enable the formulation of relevant conclusions.The results of the study indicate that the optimal orientation of roof slopes for the installation of small-scale energy systems is the east–west configuration, which allows for maximising solar energy generation throughout the daylight period. In this case, the east-facing slope is active from sunrise until noon, while the west-facing slope is active from noon until sunset. In contrast, with a north–south roof orientation, the southern slope exhibits increased activity only for a relatively short period around midday, which is insufficient to ensure high efficiency throughout the entire daylight period. As expected, the northern slope receives the least solar radiation and, consequently, demonstrates the lowest efficiency in electricity generation. Roofs with diagonal orientations (north-west–south-east or north-east–south-west) provide a more uniform distribution of solar radiation throughout the day.Received: 28.04.2026;Accepted: 15.05.2026;