Analysis of DC Government Roof Solar Generation Potential

The analysis in this project was performed in order to determine which DC Government owned buildings have the most potential for generating solar power from solar panels installed on their roofs. The analysis involved using a DC GIS citywide 1 meter DSM derived from LIDAR data and ESRIs Area Solar Radiation tool. The output from the Area Solar Radiation tool is a raster image with solar radiation potential for 1 meter by 1 meter cells across the entire city. The ESRI tool takes into account the position of the sun throughout the course of an entire year and determines any obstructions that may block the suns radiation on every 1 by 1 meter piece of the DSM, throughout the entire city.

The output raster from the Area Solar Radiation tool was clipped to a subset of the DC GIS BldgPly layer, which is a polygon layer of all of the buildings in the District. The subset from the BldgPly layer that was used to clip the Area Solar Radiation raster was all of the DC Government owned buildings. This subset was obtained by joining the ownership information from the DC GIS OwnerPly layer to the BldgPly layer and then querying the building polygons that sit on DC Government property. This layer was than buffered -5 feet, so that the edges of roofs, which are not appropriate for installing solar panels, were eliminated.

Next, the Area Solar Radiation output was clipped to the buffered DC Government owned buildings. ESRIs Zonal Statistics tool was then used to find the sum of each roofs total solar potential. ESRIs Zonal Statistics tool generates statistics for a specific area within a raster layer; In this case, adding all of the solar radiation outputs together for each roof and calculating the total potential solar radiation output for each roof.

The roofs from the analysis are symbolized within the ArcGIS Online map below. The red polygons in the color spectrum represent the roofs with the most solar generation potential and the roofs in blue represent the buildings with the least solar power generation potential. The top 200 DC Government owned roofs for solar power generation are included in this map. The pop up window in the map indicates the rank of each roof in relation to the other top 200 DC owned roofs in the dataset. The pop up window also has the address of the building, when that information is available in the DC GIS OwnerPly layer.

There is an additional layer in the online map that shows the specific areas of the top 200 roofs that are best suited for solar panels according to the Area Solar Radiation tool. These areas are shown with a black outline. These areas were found by dividing the range of solar radiation value outputs on the top 200 roofs into 5 quintiles, using the extract tool to separate the top quintile into a separate layer and converting the Top Quintile raster layer into a polygon feature, so that it could be uploaded to ArcGIS Online. The areas shown on the map below represent collections of raster cells that fall into the top quintile for potential solar energy generation within the top 200 roof dataset. These polygons represent where solar panels should be placed on each roof to get the most possible energy generation and highest return on a solar investment.

This Top Quintile layer has been smoothed into larger and more uniform areas by using ESRIs Boundary Clean tool within the Spatial Analyst extension. This tool helped to eliminate small holes in areas of high solar radiation and small islands of high solar radiation in the middle of larger low solar radiation areas. These results are more visually appealing and are more practical, in that they create larger zones in which to install solar panels.

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