How to use sun path diagram to estimate the effect of shading on the PV array?

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Shading plays a very important role on the performance of a solar PV system and many of the system designers unfortunately do not take shading in to consideration while analyzing there system  performance. Some of the software such as PVsyst is quite capable of simulating shading and estimating energy losses due to shading of the PV array.  Below figures shows typical sunpath of New delhi.

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In fact the first requirement is to understand sun path diagram of a given location which shows the path of the sun across sky from the summer to winter solstice. PVsyst is capable of generating sun path diagram for a given location and energy production can be simulated for each hour during  winter and summer seasons and accordingly the system design can be optimized for annual yield basis, summer yield basis or winter yield basis depending on the design criteria . It is possible to estimate the reduction of energy generation of a soar plant due to shading from a individual object for example following figure shows simulation of a Tree and inverter room in PVsyst through which the energy reduction due to shading of these objects on array output can be analyzed while shading simulation a percent loss due to shading for each hour is calculated and accordingly the annual losses can be derived for the shadings through these objects . A typical analysis conducted by our team ,the output of a 5MW system can have shading losses as high as 2-3% due to shading from the near objects .the below figures highlights the shading effect due to inverter rooms and a tree beside a roof top PV .

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A case study conducted by first green of a typical 5MW plant reveals that there is a loss of 163.3 MWh of energy due to effect of shading on the plant during morning and evening hours resulting in a revenue loss of approximately INR 19  lacs.The shading losses are of the order of 1.73%. These losses are expected to be further higher as the array face the shading during the morning hours due to differential leveling of array structures.

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Article by,

Dr Sanjay Vashishtha & Rishikesh Muthyal

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