- Photovoltaic
- PVT110 (S/N: TF21-UP)
- PVT115 (S/N: TF51-UP)
- PVT117 (S/N: TF71-UP)
- PVT120 (S/N: GH81-UP; TF81-UP)
- PVT115 (S/N: TF51-UP)
Introduction
This Special Instruction provides field shading guide for certain photovoltaic modules.
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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Failure to follow all safety guidelines prescribed in this document and by governing authorities and regulatory agencies may result in severe injury or death of personnel or machine damage. |
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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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Do not operate the machine if any guards or covers are missing or inadequately secured. Personnel could be seriously injured or machine damage may occur. |
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Observe the safe working load limits of all lifting and blocking devices and keep a safe distance from suspended/blocked loads. Personnel may be seriously injured or killed by falling loads. |
Background
Cat® PVT 110, and PVT 110 ARC modules are tested and certified by an accredited third party laboratory to be compliant to IEC 61646 Edition 2.0 Thin Film Terrestrial Photovoltaic (PV) Modules – Design qualification and type approval. This is the international standard governing thin film module performance testing. Section 10.9 of IEC 61646 details the “Hot Spot Endurance Test”. The purpose of the test is to verify that modules are capable of withstanding certain reverse bias events, caused by localized shading, which may occur in certain field deployment conditions.
The concern of device damage due to shading is unrelated to reverse current, but is driven by localized areas of reverse bias (negative voltage / positive current). This happens when modules are shaded in only very specific patterns. However, when the shading geometry is suitable for damage to occur, it can happen in very short durations (seconds to minutes) and under a wide range of irradiance (as low as 150 W/m2). Reverse bias is generated by 1 or more series-connected cells being shaded while the rest of the cells are fully illuminated. However, no damage is seen when greater than 45 percentage of series-connected cells are shaded. All cells in series connected modules are included.
The illuminated cells push forward current through the shaded cells. As a result, the shaded cells operate in reverse bias, because they are not generating voltage from sunlight exposure. An example of prohibited shading is shown in Illustration 1.
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| Illustration 1 | g06361093 |
While there exist countless ways to shade a module, a few typical field scenarios are discussed to clarify the impact of common behaviors relative to a PV system using Cat® modules.
No Risk Shading
- "Row-to-Row" shading, where modules are oriented in landscape and exposed to uniform shading pattern as a result of low sun angles, poses no risk to long term reliability or performance.
- Shading while modules are in Open Circuit (OC) conditions poses no risk to long term reliability or performance. Open circuit is defined as the condition when modules, strings, or arrays are electrically open and not actively driving current flow. Open circuit conditions are common during storage, unboxed transport, installation, or when inverters (or loads) are off or disconnected. Any shading during these open circuit conditions, regardless of how many cells are shaded or at what contrast or intensity, will not create reverse bias events because no current is flowing through the module. With no reverse bias, there is no risk.
- Shading of active area under typical module mounting clips mounted on long edges of modules poses no risk to reliability or performance.
- Diffuse shading (no crisp edge to the shadow) cast as a result of faraway objects like overhead power lines, meteorological towers, utility towers, etc. poses no risk to reliability or performance.
Low Risk Shading
- Repeatedly walking or standing closely in front of operating modules between rows during highly illuminated times can create highly irregular shading difficult to predict and test. Best practice is to stay as close to the back side of the rack as one walks down a row of operating modules. These irregular actions present very low risk of high contrast shading, and should be systematically avoided.
- Repeated parking or driving of vehicles or equipment closely in front of operating modules can potentially create undesirable high contrast partial shading of complete cells, and should be systematically avoided.
High Risk (Prohibited) Shading
- Resting or adhering slender objects (tools, brooms, clothing, wires, tape) on sunny side of operating modules, or within inches above operating modules, especially when shadow oriented parallel to cells, can create high risk of undesirable shading.
- Fixed objects within 5 to 7 feet above operating modules that cast a shadow over the long dimension of the cell should be avoided. Close objects like posts, ropes, signs, fences, or equipment can begin to increase risk of partial shading of full cells when nearer than 5 to 7 feet from the sunny side of operating module.
- Working continuously with outstretched arms or tools over operating modules can create high risk of undesirable shading.
- A support frame or mounting method on the short edges of modules that fully shades the entire length of a cell (either partially or completely) can create a high risk of undesirable shading.
- Cleaning apparatuses, including cleaning robots and other mechanisms that traverse the module repeatedly while the system is operating (unless evaluated and approved by Cat®).