BUILDING ROOFTOPS EXTRACTION FOR SOLAR PV POTENTIAL ESTIMATION USING GIS-BASED METHODS

Green energy is increasingly used due to the lack of traditional resources and the increase in environmental pollution, which badly affects our planet in all aspects of life including air, plant life, seas, oceans, etc. In this context, buildings’ rooftops extraction approach for photovoltaic (PV) potential estimation is presented into two main phases. First, rooftops detection from satellite images using image pre-processing techniques and a machine learning algorithm. The pre-processing steps include gamma correction, shadow, vegetation masking, kmeans, and connected components. Support Vector Machine (SVM) algorithm is then applied to extract rooftops. Second, using two GIS-based methods, PVGIS and Solar Analyst Tool in ArcGIS, for PV estimation. Satellite images for a part of Madinaty city in Egypt were used to evaluate our approach. The accuracy assessment of SVM expressed by the precision and recall were 95.7% and 90%, respectively. The identifiable rooftops in the image were 112 rooftops with a total area of 26,131 m2. The annual PV potential area was estimated to be 9.3 and 8.7 MWh/year using PVGIS and Solar Analyst Tool, respectively. PVGIS was more accurate as it uses more recent data from solar databases that exist in Africa. On the other hand, Solar Analyst Tool was less accurate as it depends on a digital elevation model with a resolution of 30 m. According to our calculations, the electric energy and the amount of CO2 emission were compensated by an annual average value of 48% for using solar panels instead of the traditional sources of energy.

Obstrução do horizonte calculada a partir de modelo digital de elevação

O objetivo deste trabalho foi avaliar a exatidão do cálculo da obstrução do horizonte, a partir de um modelo digital de elevação (MDE), em diferentes situações topográficas. O material utilizado incluiu um MDE disponível para a região da Serra Gaúcha, RS, receptores GPS, câmera digital, lente grande‑angular e os programas Idrisi, Arcview/ArcGIS e Solar Analyst. Foram adquiridas fotografias hemisféricas, e coletadas as coordenadas de 16 locais na área de estudo. As coordenadas e o MDE foram utilizados para calcular a obstrução do horizonte com uso do algoritmo Solar Analyst. Foram comparadas a fração aberta do céu calculada e a obtida pelas fotografias hemisféricas. O coeficiente de determinação foi de 0,8428, tendo-se observado superestimativa média de 5,53% da fração aberta do céu. Os erros são atribuídos principalmente à obstrução pela vegetação, que não pode ser identificada pelo MDE. A obstrução do horizonte, causada pelo relevo na Serra Gaúcha, pode ser calculada satisfatoriamente pelo Solar Analyst, a partir de um MDE interpolado de cartas topográficas na escala 1:50.000.