*Article* **Comparing 2D and 3D Solar Radiation Modeling in Urban Areas**

**Štefan Koleˇcanský \*, Jaroslav Hofierka , Jozef Bogl'arský and Jozef Šupinský**

Institute of Geography, Faculty of Science, Pavol Jozef Šafárik University in Košice, Šrobárova 2, 04154 Košice, Slovakia; jaroslav.hofierka@upjs.sk (J.H.); jozef.boglarsky@student.upjs.sk (J.B.); jozef.supinsky@upjs.sk (J.Š.)

**\*** Correspondence: stefan.kolecansky@student.upjs.sk; Tel.: +421-55-234-2352

**Abstract:** The use of solar radiation in the urban environment is becoming increasingly important for the sustainable development of cities and human societies. Several factors influence the distribution of solar radiation in urban areas, including urban morphology and the physical properties of urban materials. Most of these factors can be modeled with a relatively high accuracy using 2D and 3D solar radiation models. In this paper, the r.sun and v.sun solar radiation models are used to calculate solar radiation for the city of Košice in Eastern Slovakia to assess the accuracy of both approaches for vertical surfaces frequently found in urban areas. The results were validated by pyranometer measurements. The results showed relatively good estimates by the 3D v.sun model and poor estimates by the 2D r.sun model. This can be attributed to an improper representation of vertical surfaces by a digital surface model, which has a strong impact on solar resource assessments. We found that 3D city models prepared in level of detail 2 (LoD2) are not always adequate in case of complex buildings with morphological structures, such as terraces. These cast shadows on facades especially when solar altitude is high and, thus, assessments, even by a 3D model, are inaccurate.

**Keywords:** 3D city model; renewable energy; solar radiation; urban solar radiation model
