Module Characterization Response of Certain Cat® PVT 110 and PVT 110 ARC Photovoltaic Modules to Partial Shading {1471} Caterpillar


Module Characterization Response of Certain Cat® PVT 110 and PVT 110 ARC Photovoltaic Modules to Partial Shading {1471}

Usage:

PVT110 TF2
Photovoltaic
PVT110 (S/N: TF21-UP)
PVT115 (S/N: TF51-UP)
PVT117 (S/N: TF71-UP)
PVT120 (S/N: GH81-UP; TF81-UP)

Introduction

This Special Instruction provides supplemental information about response of Cat® PVT 110 and PVT 110 ARC Photovoltaic Module due to partial module surface area shading.

Do not perform any procedure in this Special Instruction until you have read the information and you understand the information.

Safety Section

Work safely. Most accidents that involve product operation, maintenance, and repair are caused by failure to observe basic safety rules or precautions. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs.

A person must be alert to potential hazards. This person should also have the necessary training, skills, and tools to perform these functions properly.

Safety precautions and warnings are provided in this instruction and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons. Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard.

Therefore, the warnings in this publication and the warnings that are on the product are not all inclusive. Ensure that any tool, procedure, work method, or operating technique you use that is not recommended by Caterpillar is safe.

Ensure that the product will not be damaged or the product will not be made unsafe by the operation, lubrication, maintenance, or repair procedures used.

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Do not operate or work on this product unless you have read and understood the instruction and warnings in the relevant Operation and Maintenance Manuals and relevant service literature. Failure to follow the instructions or heed the warnings could result in injury or death. Proper care is your responsibility.


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When removing a major component or attachment, ensure that it is properly blocked or secured before removing mounting hardware. An assembly that is disconnected without proper blocking may shift or fall, resulting in serious injury or death of personnel or machine damage.


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Personal injury or death can result from improper maintenance procedures. To avoid injury or death, follow the procedures exactly as stated below.


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Personal injury can result from improper handling of chemicals.

Make sure you use all the necessary protective equipment required to do the job.

Make sure that you read and understand all directions and hazards described on the labels and material safety data sheet of any chemical that is used.

Observe all safety precautions recommended by the chemical manufacturer for handling, storage, and disposal of chemicals.


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Climbing equipment may be required to access this service point. Refer to the Operation and Maintenance Manual, "Mounting and Dismounting" topic for safety information.


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Before servicing/performing maintenance on the machine, electrical power must be physically disconnected; battery plugs must be disconnected from the batteries, or the trailing cable must be unplugged, and warning tags and padlocks shall be applied by a certified electrician. Certified electricians shall perform or direct any electrical work, including any energized testing, repair work in controllers, motors, or other approved compartments, and shall insure that all compartments are properly closed and inspected prior to re-energization. All applicable lock out and tag out procedures must be followed.


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Module Characterization Response of Photovoltaic Modules to Partial Shading

Purpose

The information contained in this document provides supplemental information about the response of CAT PVT 110 and PVT 110 ARC due to partial module surface area shading and its dependence on the orientation of the shading. The data is intended to support the proper design of systems using these CAT PVT 110 and PVT 110 ARC modules as well as the development of more accurate models for energy prediction. The data is representative of all power bins of CAT PVT 110 and PVT 110 ARC Modules, although some variation among the modules is normal and to be expected.

Shading Parallel to Cells



Illustration 1g06361104
Shaded along 600 mm (23.6 inch) dimension.


Illustration 2g06361108
I(V) Characteristic, Partially shaded Cat PVT 110 and PVT 110 ARC module with entire cells shaded.

Illustration 2 shows how the IV curve of a single Cat PVT 110 and PVT 110 ARC module changes as entire cells are shaded. In this case, shading occurred along the 600 mm (23.6 inch) dimension of the module, completely obscuring some cells. The number of entirely shaded cells increases with the total shading percentage. The shaded cells act to limit the current and power produced by the module. The maximum power PMAX and maximum power voltage VMP are significantly reduced upon shading of the first 5-10% of the module surface area, but do not vary much as the amount of shading increases from 10% to 30%. In this range, the PMAX value is approximately one half of the value for an un-shaded module. Beyond the 10-30 percentage range, additional reduction in PMAX and VMP occurs with increased shading.



Illustration 3g06361110
P(V) Characteristic, Partially shaded Cat PVT 110 and PVT 110 ARC module with entire cells shaded.

This effect is also evident in Illustration 3, which shows P(V) curves corresponding to the I(V) curves shown in Illustration 2. Response of the relative module power output to shading percentage is shown in Illustration 7, which indicates that the module ceases producing power when more than half of the cells are entirely shaded.

Shading Perpendicular to Cells



Illustration 4g06361105
Shaded along 1200 mm (47.2 inch) dimension.


Illustration 5g06361115
Partially shaded Cat PVT 110 and PVT 110 ARC module with equal portions of all cells shaded.


Illustration 6g06361116
Partially shaded Cat PVT 110 and PVT 110 ARC module with equal portions of all cells shaded.


Illustration 7g06361117
Relative power output vs shaded portion of module.

The response of the module to shading along the 1200 mm (47.2 inch) dimension is shown in Illustration 5. In this case, all cells of the module remain partially illuminated and the un-shaded portions of the cells function normally. Thus the resulting power loss from shading scales proportionately with percentage of shaded module surface area. In this case, the maximum power voltage VMP is only slightly affected by the degree of shading, shifting by about 3 V (or about 7 percentage) from the fully illuminated case to the 75 percentage shaded case. The weak dependence of VMP on 1200 mm (47.2 inch) shaded area percentage is also shown by the approximate vertical alignment of the maximum power points in Illustration 6.

The maximum power current IMP varies directly with un-shaded (active) cell area. Since this dependence is linear, and since the VMP response is only weakly dependent upon shaded area, the resulting dependence of module power is nearly linear with shaded area percentage. This behavior is clearly shown in Illustration 7. A linear fit to the relative power versus shading percentage in the 1200 mm (47.2 inch) dimension shows good agreement with the data.

Conclusion

Cat PVT 110 and PVT 110 ARC module respond differently to partial shading depending on shading orientation. If the shading occurs along the 600 mm (23.6 inch) dimension of the module, output power of the module initially drops to approximately half of the un-shaded value for shadings of 10 to 30 percentage of module surface area. Beyond 30 percentage shading, the output power drops further, eventually reaching zero when more than 50 percentage of the module is shaded. VMP can vary appreciably over the entire range, but remains nearly constant when 10 to 30 percentage of the module’s surface area is shaded.

If the module is shaded along the 1200 mm (47.2 inch) dimension, output power of the module varies essentially linearly with the percentage of un-shaded module surface area, and VMP remains essentially unchanged with less than 50 percentage of the module surface area shaded.

Based on these behaviors, module power loss due to shading will be minimized when shading can be restricted to occur along the 1200 mm (47.2 inch) dimension of the module (ensuring no cells are entirely shaded). In a typical free-field application where modules might be affected only by row-to-row shading, mounting modules in a landscape orientation would result in minimization of power loss due to shading.

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