BOLOGNA SOLAR CITY, A WEB APPLICATION FOR THE ANALYSIS OF POTENTIAL ENERGY: FROM ESTIMATING SOLAR RADIATION TO THE REALIZATION OF THE APPLICATION

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1 17 th Building Services, Mechanical and Building Industry Days Urban Energy Conference, October 2011, Debrecen, Hungary BOLOGNA SOLAR CITY, A WEB APPLICATION FOR THE ANALYSIS OF POTENTIAL ENERGY: FROM ESTIMATING SOLAR RADIATION TO THE REALIZATION OF THE APPLICATION Andrea MINGHETTI, Dr., Paola AFRICANI, Eng., Elisa PASELLI, Eng. Municipality of Bologna Unit Territorial Information System (SIT); sitadmin@comune.bologna.it KEYWORDS: solar radiation, web application, GIS, Flex. Abstract: In order to provide useful services to citizens in the environmental field and to reduce energy consumption, the SIT of the Municipality of Bologna has developed a web application that identifies renewable energy systems which have already been constructed in the municipal area and assesses the benefit of installing solar panels on the roof of your home. The concept of the Bologna Solar City application, (available at: is based on estimating the amount of solar energy available on the roofs of buildings. Assessment of the total amount of direct and indirect solar energy is possible through the use of Solar Radiation instruments provided with the Spatial Analyst extension of ArcGIS Desktop. This web application provides the total solar radiation value for each building, showing an estimate of the solar energy produced and the subsequent reduction of CO 2 atmospheric emissions from fossil fuels. 1. Introduction In recent years Italy has seen an increase in solar energy production brought about by the installation of solar (thermal and photovoltaic) systems on the roofs of our homes. In order to increase the public's awareness about the use of "clean" energy and efficient energy to reduce the environmental impact of human activities, the SIT unit of the Municipality of Bologna is committed to creating a web application that spatially represents the solar energy potential of our city. This web tool makes it possible in just a few simple steps to assess the potential of using the solar energy available on the roofs of houses and to identify the most suitable areas for the installation of solar systems. 2. Estimate of global solar radiation Global solar radiation is a major source of energy which cones through the atmosphere and lands on a surface, it consists of three different types: direct beam, diffuse and reflected. Direct beam radiation follows a straight line directly from the sun to the Earth's surface; diffuse radiation is scattered/absorbed by atmospheric elements such as clouds or dust, while reflected radiation consists of the albedo or reflection coefficient of solar radiation being further reflected by surfaces. The amount of solar radiation depends on a number of factors, the most important of which is land contour or topography. Other determinants include microclimatic conditions such as air and soil temperature, evapotranspiration, the trend of melting snow, soil moisture and light available for photosynthesis, but also geographic location (latitude, longitude), elevation, the position of the sun throughout the day and the changing of the seasons. 25

2 17th Building Services, Mechanical and Building Industry Days Urban Energy Conference October 2011, Debrecen, Hungary The Solar Radiation tool provided in the Spatial Analyst extension of ArcGIS Desktop 9.3 is used to calculate the global solar radiation of all the buildings in the municipality. The Solar Radiation algorithm requires, among other things, a digital surface model (DSM) input. 2.1 Processing the DSM Processing of the data available on the CTC (the 1:2000 digital technical map of the municipality), provided two high-precision products, the Digital Terrain Model (DTM) and the Digital Surface Model (DSM). The Digital Terrain Model was made from processing a series of CTC information by the Spatial Analyst extension of ArcGIS: spot elevations, contour lines in 2 and 10 meter resolutions, and the elevations at the bases of all buildings. The DTM, although quite accurate, does not meet the requirements of the model needed to calculate global radiation because it does not take into account either anthropogenic aspects, such as roads, buildings and bridges or natural features, such as ground cover. For this reason, a three-dimensional DSM model was generated which, in addition to the morphology of the land, includes the building masses (roofs were considered flat and not pitched, because the CTC does not have this information). The DSM was obtained from the DTM and from the DEM of the buildings 1 by using Map Algebra's Con (condition) statement. The latter is an ArcGIS Spatial Analyst analysis language, whose simple syntax using a conditional statement of the 'if, then, else' type, permitted a bitmap to be generated with pixels showing the elevations obtained from the DEM or DTM depending on whether these were inside or outside of the buildings. 2.2 Calculation of solar radiation and data processing In order to calculate the global solar radiation, once the DSM had been generated, it was necessary to insert some parameters into the tool Area Solar Radiation, like the proportion of diffuse radiation, the transmittance, latitude, longitude and the time period (year, month, etc.). The Area Solar Radiation tool allows the global solar radiation on a surface to be calculated for any time of day for each month of the year, investigating in every direction whether there are any obstacles (natural and artificial) and cross referencing this information with the map of the sun and the sky map. The first is based on the position of the sun and calculates direct beam radiation; while the second is based on the atmosphere and calculates diffuse solar radiation (reflected solar radiation is excluded from the calculation). This process produced 12 bitmaps each representing monthly solar radiation. To connect this information to each building of the CTC a sequence of operations was performed limited to the geometry of buildings, in order to shorten the computation time. 1 The DEM of the buildings is a bitmap of the CTC shapefile wherein each pixel shows the eaves height of the building located in it. Where there is no building, the value is 0. 26

3 A. Minghetti et al. Bologna Solar City, a Web Application for the Analysis of Potential Energy... Fig. 1: Global Solar Radiation of an area over twelve months of the year Using the Mask tool Extract included among those available with the ArcGIS Spatial Analyst extension ArcToolbox interface, a bitmap of only the areas concerned was produced, whose pixels were converted into points, showing only their monthly global solar radiation as an alphanumeric indication. So, to get the average global solar radiation for every roof in the city, the join space function in ArcToolbox was used to aggregate data spatially. Given the time needed for processing and the need to repeat this step twelve times (for each month of the year), the workflow was designed using a template created with the Model Builder tool of the ArcGIS Desktop. Fig. 2: Flow of operations using Model Builder This allowed a one-time process that produced the twelve bitmaps in sequence, providing the same number of shapefiles with information about the global solar energy for individual buildings in different months of the year. 27

4 17th Building Services, Mechanical and Building Industry Days Urban Energy Conference October 2011, Debrecen, Hungary 3. Map Services In order to make the results of these calculations easily accessible to the public and technical experts in the field, the GIS decided to create a web application with an "attractive" and extremely easy to use graphic user interface, which includes basic maps advanced computing functions, but that does not require special knowledge of GIS instruments. The global solar radiation and complimentary thematic maps were published as map services on a ArcGIS Server 9.3.1, and incorporated in the web application using the REST protocol. The map services are of two types: dynamic and cached. A cached map service allows clients to have a quick view as each zoom or move of the pointer by the user brings up small images (tiles) covering portions of the territory which are already on the server. A map cache provides the utmost in terms of performance and scalability achievable in a web application. The advantage of using the dynamic services, however, is that the information displayed is updated in real time, i.e. the data changes are immediately visible when the web application is refreshed, even though this requires relatively longer waiting times. In general, a criterion was used whereby a dynamic service was created for data that need continuous updating, while a cached service was created for data that do not require frequent updating, and in any case not in real time. For this reason there was a moment during the design of the application when it was decided which data would use cached services and which would use dynamic services, since good performance of a web application depends on this; the majority of the layers that make up the map or a general basic map were set up in the cached services, while only a percentage of data (those that undergo changes more rapidly and therefore must be updated more frequently) were handled as a dynamic service. 4. The web application The Bologna Solar City web application is designed to provide the user with easy, fast, dynamic territorial navigation that is rich in content. This has been made possible by the integrated use of ArcGIS Server and Flex by using ArcGIS API for Flex. Bologna Solar City offers highly specialized GIS functionality (on and off levels of information, street and house number searching, searches, etc.) together with a quick and easy to use streamlined interactive interface offered by the Flex framework. This solution has increased the productivity of the application because all of the functions that the traditional WebGIS devolved to the server, are now in part performed on the Flex client. The application can be seen using the Flash Player plug-in, available on most browsers, regardless of operating system installed on the computer station. The web application was developed using the Sample Flex e Viewer 1.3, a sample web application developed by ESRI to show the significant potential of the ArcGIS platform in a Web 2.0 interface. The Sample Flex Viewer, in its source code version, was used by customizing its configuration files and adding/changing the different tools or widgets. In particular, using the Solar Radiation widget, shows the monthly and annual global solar radiation values of all the rooftops, and based on this, annual energy production in kwh per m 2 and the reduction of CO 2 consumption. The analysis tool requires the user to define, by means of a scroll bar, the percentage area of the roof that can actually be used and to be considered in the calculation. 28

5 A. Minghetti et al. Bologna Solar City, a Web Application for the Analysis of Potential Energy... In fact, the model does not consider aspects related to the slope of the roof, but the usable portion of the roof may be determined according to its inclination and the space occupied by objects, chimneys, aeration systems, other structures or equipment, and any trees that may provide shade. The orientation of the roof considered by the algorithm is always 0 South, and with a flat roof (0 incline), while the annual production estimate is made on the basis of the percentage of the roof that is usable and on the basis of available annual solar radiation, considering a production type of W/m 2, typical of a system of crystalline silicon modules with standard efficiency. The annual production is then used for the reduction of greenhouse gas emissions, specifically CO 2, considering a conversion factor equal to Conclusions Fig. 3: Bologna Solar City web application Bologna Solar City is not a final stop, but only an intermediate step of a broader project; the GIS department is already looking for new ways to provide the public and technicians with instruments that are best suited to meet their needs. Several improvements to the web application are planned, with Web 2.0 tools such as online editing, integration with popular social networks, and many other instruments. As regards the calculation of global solar radiation, further experiments are planned that will refine the accuracy of the model, which underlies everything, perhaps even through the use of different data such as LIDAR data or data from direct measurements. Bologna Solar City is an example of how, by coordinating and combining various data streams from different subjects, it is possible to create a simple, fast and dynamic product for the public at large. 29

6 17th Building Services, Mechanical and Building Industry Days Urban Energy Conference October 2011, Debrecen, Hungary Acknowledgement The author would like to say thank for the fund of the Central Europe Programme. The paper was elaborated within the EnergyCity project. References Casini C., Lombardo S. (2009). Valutazione della potenzialità di utilizzo dell energia solare termica in ambito urbano, AISRe, Atti della XXX Conferenza Scientifica Annuale, Firenze