Let’s calculate the shadow length of building ‘B’ on building ‘A’. Height of building B is 8 m and height A is 5 m. Distance between buildings in 2 m. Buildings are located in Delhi, India.
Step 1: Altitude and Azimuth Angles
Since the shadow creating object (i.e. Building ‘B’) is on South side of proposed solar roof (i.e. Building ‘A’). Hence, it will cause shadow during both morning and evening hours. (Since, noon time shadow length is always small when compared to morning and evening time shadow lengths, we have not calculated the noon time shadow).
Therefore, Altitude and Azimuth angles were considered for morning hours i.e. 10 am and for evening hours i.e. 4 pm for Delhi location and 21st December (Winter Solstice).
Using www.sunposition.info, Altitude and Azimuth Angles were derived:
At 10 am, Altitude Angle: 28 degree, Azimuth Angle: 142 degree
At 4 pm, Altitude Angle: 16 degree, Azimuth Angle: 230 degree
Step 2: Relative height of Shadow creating object
Height of shadow creating object (Building B) is 8 m. Height of building where solar PV array is proposed (Building A) is 5 m.
Hence, Relative Height of shadow creating object = 8 – 5 = 3 m
Step 3: Shading Length (m) Morning Time
Using below formula, for North – South shadow profile:
Shadow Length (m) = H (m) x [ Cos (Azimuth) / Tan (Altitude) ]
Shadow Length (m) = 3 x [ Cos (142) / Tan (28) ] = 4.5 m
Step 4: Shadow Length (m) Evening Time
Shadow Length (m) = 3 x [ Cos (230) / Tan (16) ] = 6.9 m
Since, Evening time shadow length (i.e. 6.9 m) is more than Morning time shadow (i.e. 4.5 m). Hence, we will consider Evening time shadow length, i.e. 6.9 m and leave this distance from Building B in North direction.
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