The effect of shadow on photovoltaic cells and a methodology 
for detecting shadow from direct radiation has been explained 
in section 2. Then result has been shown applying the 
methodology and some brief idea about the future work of this 
research has been presented in section 3 and 4. 
2. METHODOLOGY 
The simulation of the shadow effect is based on the 3D data. To 
consider the shadow effect a model has been developed, which 
determines the exact shadow projected onto each of the surfaces 
of the analyzed area for direct radiation. For photovoltaic 
potentiality analysis knowing incident radiation on each cell is 
important, because partial shading cause different results in 
different cases. Effectiveness of a cell depends on amount of 
incident sunlight and its intensity. Photovoltaic cells electricity 
production is proportional to the intensity of sunlight only until 
the entire module is exposed to the sun, but this does not 
happen simultaneously. In a module photovoltaic cells are 
connected in series. Dart or shadow significantly reduces the 
performance. The weakest link cell in the chain limits the 
amount of energy production. Therefore it is important to know 
the exact shadow location. The amount of power loss also 
depends on the size and darkness of shadow. But darkness of 
shadow depends on diffuse radiation and many other 
parameters. At this phase of the research only direct radiation 
has been considered but other parameters will be considered in 
future phases. 
The 3D models are mostly consisting of polygons. First step is 
to read these sets of polygons and then triangulate each of them. 
Shadow will be calculated for specific points distributed over 
the surface, which will represent the whole surface. So to 
achieve a fine resolution each triangle is further triangulated 
and middle point of each side is connected and thus the triangle 
is divided into four smaller triangles, the process is repeated 
until the length of the smallest side is larger than the desired 
resolution. This resolution represents the maximum distance 
between two points. Then the centroid of the triangle is 
measured and a line towards the sun’s direction is calculated 
representing the sun’s ray. Here the real time sun information is 
used. The next step is to look if the sun’s ray intersects any of 
the surfaces. For this purpose it is checked if the line intersects 
with any of the triangles found in the second step. As light 
always follow straight line, a simple line plane intersection 
check will give shadow information. If any intersection point is 
found then the triangle can be declared as a shaded triangle and 
joining the shaded triangles together will help to find the 
shadow polygon on any surface. The process may face problem 
with thin triangles. So, for triangles with very narrow angles 
triangulation can be done by dividing the triangles according to 
the longest side. Thus the problem with thin triangles can be 
avoided and a high quality result can be obtained. The 
transparency of the obstacle in this case has an impact. This 
approach is only applied for direct or beam radiation. For 
diffuse radiation surrounding buildings and objects should also 
be considered. Any reflective surface in surrounding area would 
cause an increase in diffuse radiation. The procedure has to be 
applied for every time step of the simulation due to the 
changing solar position. The complete process has been 
illustrated in Figure 1. 
SA 
KA ) X | 
Figure 1. Workflow of shadow detection (Alam et al, 2011) 
Only the roof surface and facades were taken into account. The 
steps has been discussed below: 
2.1 Sun angles detection 
In this step, sun’s azimuth and zenith are calculated with the 
simulation engine INSEL (Schumacher, 1991) at any specific 
time. Azimuth is measured from north and zenith is measured 
from ground level. Approximately at noon azimuth will be close 
to 180 degree in northern hemisphere and close to zero degree 
in southern hemisphere shown in Figure 2. This depends upon 
the direction of sun from any point on earth. 
   
FS 
Figure 2. Direction of the sun at different hemisphere measured 
from north 
2.2 Potential surface filtering 
Then tilt and orientation are calculated from the surface by 
extracting the surface normal. Angular distance of surface 
normal from the ground and north were measured. The motion 
of sun has a great impact on the amount of power received by 
the PV system. The availability of direct radiation is the most 
when the surface normal and the sun's ray is parallel and it is 
near to zero when the surface normal and sun's ray has an angle 
more than 90 degree. So, the surface filtering must pass these 
two conditions: 
a-—o i90? (1) 
z—t>-+90° 
where a = azimuth 
0 = orientation 
z = zenith 
t= tilt 
An additional filtering for surface dimension is applied to avoid 
the narrow surface not suitable for PV installation. So, for 
surface dimension filtering, requirements for minimum length 
     
   
  
  
  
  
  
  
   
    
    
    
   
    
   
    
   
    
   
   
     
   
   
    
    
   
   
   
   
   
   
   
    
   
    
    
   
   
    
   
    
  
   
    
   
   
    
  
     
    
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