SOLAR PANELS SELECTION IN BUILDING USING CITYGML FOR ENVIRONMENT PLANNING By A.Subathra

CONTENTS: 1.AIM 2.OBJECTIVE 3.DATA USED 4.ASSUMPTIONS 5.METHODOLOGY 6.ILLUSTRATIONS 7.SOURCE CODE 8.CONCLUSION

AIM: To build an interactive system for user to specify parameters and to identify eligible surfaces in building models beased on citygml for installing solar panels in urban environment.

OBJECTIVE: 1.Locate all planar surfaces where solar panels can be placed for PV or for Thermal absorption. 2.Classify the planes according to the exposure to sun more than ’n’ number of hours at the ‘d’ degree of inclination Where ‘n’ may be 5 to 6 hours and ‘d’ may be normal to the plane. 3.The value of ‘n’ and ’d’ to be decided after modelling and analysis for a given geography and depending on cost and utility. 4.Given the location in latitude and longitude find the solar orientation of inbound solar rays. 5.Calculate shadows of the building and surrounding objects and thus shortlist the panels that are exposed3 to sun. 6.Calculate for each panel, the number of hours for exposure and angle of exposure.

DATA USED: 1.CityGML Building model in LOD2 In LOD 2, a building has a Solid geometry as well as Boundary Surfaces: Ground Surface, Wall Surface, Roof Surface, and some special cases. 2.Sun path with azimuth and elevation in each hour in CSV format from

ASSUMPTIONS: 1.Surface eligibility : Eligible if the solar rays incident angle ‘N’ to be (+/-)> Imax ( 60° ) to the surface normal over more than ‘H’ hours (to be 6 hours in a day) 2.No shadows assumed to be caused by objects other than building itself 3.No bounce effect of rays considered. Only direct sun rays are considered

METHODOLOGY: To calculate the inclination of sun rays wrt the surfaces of the building to choose where to place solar panels. CITYGML Geometry with surfaces in CSV Extract Surface orientation Cross product Sun path (Spherical coordinates) Sun orientation (Cartesian coordinates) Conversion Dot product Angle of inclination Fig: Find solar ray incident angle to the surface normal

WORKFLOW: 1.Input valid citygml model 2.Specify parameters for eligibility of surface for solar use 3.Get Coordinates of surfaces from the citygml 4.Calculate the normal vectors of surfaces using vector algebra(plane orientation) 5.Calculate solar orientation 6.Calculate angle between the surfaces and sun rays, over time of the day by vector algebra

ALGORITHMS : Plane orientation: Plane orientation is to be done by cross product of two vectors.

Contd.. Solar Orientation: (Spherical to Cartesian Coordinates) X = Cos (“elevation” )* Cos (“azimuth” ) Y = Cos (“elevation” ) * Sin (“azimuth”) Z = Sin (“elevation”) Ange of inclination: (calculate angle between the surfaces and sun rays, over time of the day by vector algebra)

ILLUSTRATION : Consider a surface of a building,

Contd.. 1.Distance vector of wall side is to be calculated as follows AX = A1X – A2XBX = B1X – B2X AY = A1Y – A2YBY = B1Y – B2Y AZ = A1Y – A2YBZ = B1Z – B2Z Where, A1and B2 is upper left corner of wall surface A2 is bottom left corner of wall surface B1 is upper right corner of wall surface AXi+AYj+AZk is distance vector of wall sides A1 & A2 BXi+BYj+BZk is distance vector of wall sides B1 & B2

Contd.. 2.Cross product used to calculate normal to the (wall) surface. AB = (AY*BZ – BY*AZ) i+( AX*BZ – BX*AZ)j+ ( AX*BY – AY*BX)k 3.Calculate the unit vector of sun orientation and plane orientation and then find angle of inclination by dot product. Cos(angle of inclination)= sun orientation. Plane orientation sun orientation plane orientation

Coordinates From CityGML: coordinates from postgis: COPY(SELECT ST_AsText(geometry),parent_id from surface_geometry where parent_id in(SELECT lod2_multi_surface_id from thematic_surface)) TO '/tmp/COORDINATES.csv' DELIMITER ',' CSV HEADER; surfaces from postgis: COPY(SELECT type,lod2_multi_surface_id from thematic_surface where lod2_multi_surface_id in (SELECT parent_id from surface_geometry)) TO '/tmp/SURFACES.csv' DELIMITER ',' CSV HEADER;

>>> import csv >>> from itertools import product >>> def main(): with open('E:/SUN.csv', 'rb') as f1, open('E:/PLANE.csv', 'rb') as f2: reader1 = csv.reader(f1, dialect=csv.excel_tab, delimiter=',') reader2 = csv.reader(f2, dialect=csv.excel_tab, delimiter=',') header1, header2 = next(reader1), next(reader2) with open('E:/OUTPUT.csv', 'wb') as out: writer = csv.writer(out, dialect=csv.excel_tab, delimiter=',') writer.writerow(header1 + header2) writer.writerows(row1 + row2 for row1, row2 in product(reader1, reader2)) PYTHON SCRIPT: Cartesian product of sun and plane orientation:

POSTGIS: Output file to be stored in postgis for further querying. Create Table: create table output(ID numeric,Surfaces character varying(50),Planex float,Planey float,Planez float,Hourtime time,Sunx float,Suny float,Sunz float,Orientation float,Inclination float) Output to Postgis table: COPY output(ID,Surfaces,Planex,Planey,Planez,Hourtime,Sunx,Suny,Sunz,Orie ntation,Inclination) From 'E:/output.csv' WITH DELIMITER ',' CSV HEADER

ONWARD RESEARCH: Testing on increasingly more complex cityGML models 1.Multiple buildings with shadows on each other 2.Trees and other obstructions 3.Use as solar thermal or as Photovoltaic use 4.Compare this for some real buildings using solar enegy: interact with energy department 5.Explore insight and Photosynth toolkit to create 3d models from digital photos, point clouds 6.Create the workflow for inputs as any of selected forms, create valid citygml models and provide evaluation of surfaces for use as solar panels and calculate possible energy capture