Assessment of photovoltaic potential in urban areas using open-source solar radiation tools Jaroslav Hofierka * , Ja ´n Kan ˇuk Department of Geography and Regional Development, Faculty of Humanities and Natural Sciences, University of Pres ˇov, 17. novembra 1, 081 16 Pres ˇov, Slovak Republic article info Article history: Received 27 March 2008 Accepted 22 February 2009 Available online 31 March 2009 Keywords: Photovoltaics Solar resource assessment Solar radiation Urban areas Open-source Geographic information system abstract This study presents a methodology for the assessment of photovoltaic potential in urban areas using open-source solar radiation tools and a 3-D city model implemented in a geographic information system (GIS). The solar radiation tools are represented by the r.sun solar radiation model and PVGIS estimation utility. The applicability of the methodology has been demonstrated on a selected urban area of a small city in eastern Slovakia. The relevant attributes of buildings have been mapped and implemented in a GIS database. The selected urban area consists of various urban zones characterized by different morphology and functionality. The photovoltaic potential of buildings has been assessed using the PVGIS estimation utility. The analysis has shown a high photovoltaic potential that could cover about 2/3 of current electricity consumption in the city. However, this potential exhibits large spatial and temporal variations caused by global and local factors. This study has also shown that national assessments of photovoltaic potential can be improved by extrapolation of local assessments using spatial databases of urban areas. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction It is assumed that future massive photovoltaic (PV) applications will involve mainly urban (built-up) areas. More than 80% of inhabitants of the most developed countries live in urban envi- ronments. In these areas, the energy is being consumed and, at the same time, a large portion of green-house gases is being produced. Some authors (for example, [1]) point out that, in theory, the electricity consumption in many countries could be completely covered by utilization of solar radiation from a relatively small area (e.g., using only 1% of the territory in some countries). Among the key problems affecting the wider use of solar energy are strong spatial and temporal variations in solar radiation patterns influenced by many factors. For example, the basic patterns of seasonal and daily variations given by astronomic factors are strongly modified by changing atmospheric conditions (e.g., clouds, aerosols, water vapor, and ozone). At local scales, the patterns are modified even more due to varying local conditions (for example, sky-view obstructions, temperatures, etc.). Currently available global or regional solar resource databases and services provide only approximate estimates based on aver- aged values [2]. While spatially and temporally averaged solar radiation data offer approximate values of available solar energy, estimates at local scales may significantly deviate from the general trends [3]. Thus the assessment of solar energy resource in urban areas at local scales requires a combination of a general/regional solar resource database and analysis of local conditions that modify the actual availability of solar energy. Various models and computer programs have been used to simulate solar irradiance on buildings and increase the uptake of solar energy systems in urban areas. However, Robinson and Stone [4] note that these programs are rather weakly coupled with complex problems of the urban environment. Therefore the dynamics of solar radiation and complexity of urban areas require sophisticated modeling approaches and tools. S ˇ u ´ ri et al. [5] suggest that geographical information systems (GIS) could contribute to the effective assessment of solar resources at supra-national, national or regional levels. GIS presents an impor- tant tool for complex processing of spatial information. The inter- action of solar radiation with natural and human environments requires the use of complex spatial database with relevant factors as well as GIS tools for processing spatial information. While the solar radiation models implemented in GIS have been extensively used in environmental applications, only a few studies have focused on coupling GIS technology and solar radiation models in urban areas. Gadsden et al. [6] described a prototype of a GIS-based approach to assist planners and energy advisers in hot water applications. S ˇ u ´ ri and Hofierka [7] have developed the r.sun solar radiation model included in the open-source GRASS GIS [8] and proposed its application to regional PV assessments. S ˇ u ´ ri et al. [1,9] * Corresponding author. Tel.: þ421 51 7570613; fax: þ421 51 7725547. E-mail address: hofierka@fhpv.unipo.sk (J. Hofierka). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2009.02.021 Renewable Energy 34 (2009) 2206–2214