How to determine the module inter-row spacing for flat rooftop solar PV systems?

Example 1

Let’s calculate the minimum Inter-Row spacing required between two rows of PV modules to avoid the effect of Inter-Row Shadow. Module Lenght is 1.956 m (as taken from Module datasheet), the tilt angle proposed is 25 degrees and a single portrait module configuration is planned. The system is planned over a flat roof in Delhi, India.

Solution:

Step 1: Calculate height of solar PV module

Using the formula mentioned in above section:

Module Height (m) = Module Length (m) x Sin (Tilt Angle)

Module Height (m) = 1.956 x Sin (25) = 0.83 m

Step 2: Altitude and Azimuth Angles

Since the shadow creating object (i.e. Row 1) is on South side of the rear row (i.e. Row 2). 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 3: Inter-Row Distance (m) Morning Time

Using below formula, for Inter-Row Distance:

Inter-Row Distance (m) = H (m) x [ Cos (Azimuth) / Tan (Altitude) ]

Inter-Row Distance (m) = 0.83 x [ Cos (142) / Tan (28) ] = 1.23 m

Step 4: Inter-Row Distance (m) Evening Time

Inter-Row Distance (m) = 0.83 x [ Cos (230) / Tan (16) ] = 1.83 m

Since, evening time inter-row distance (i.e. 1.83 m) is more than morning time inter-row distance (i.e. 1.23 m). Hence, we will consider evening time inter-row distance, i.e. 1.83 m and leave this distance from Row 1 to Row 2.

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