Machine Vision Lens for Solar Cell and PV Module Inspection: How to Check Cell Alignment, Edge Chips, Busbar Position and String Spacing

Solar cell and photovoltaic module manufacturing requires accurate control of repeated geometry across large inspection areas. A production system may need to verify whether individual solar cells are positioned correctly, whether cell-to-cell spacing remains within specification, whether a visible edge chip is present, whether busbars follow the expected position, and whether completed strings remain straight and consistently spaced before further module assembly. These requirements create a demanding optical problem because a complete cell, string or module section can occupy a relatively large field of view while the smallest positional or edge defect may be only a fraction of that physical area. Selecting the correct machine vision lens for solar cell inspection therefore requires balancing FOV, focal length, sensor format, working distance and optical resolution so that the complete required photovoltaic geometry remains visible without sacrificing critical pixels on small features.

Buyers searching for machine vision lens for solar cell inspection, PV module inspection camera lens, solar panel manufacturing machine vision, solar cell alignment inspection, solar cell edge chip detection, busbar position inspection, or solar string alignment camera are generally trying to solve this field-of-view versus feature-resolution problem. An industrial camera may show an entire solar cell clearly while a slight edge defect or small busbar-position shift remains represented by too few sensor pixels for reliable automated inspection. Similarly, a wide view can make an entire string visible but reduce the sampling available to measure narrow cell-to-cell gaps. The Machine Vision Lens should therefore be selected around the smallest required defect or positioning tolerance, not simply the overall cell or module dimensions.

Kyptec Automation® provides a broad Machine Vision Lens portfolio covering conventional 5 MP, 10 MP and 25 MP lens classes across multiple focal lengths and camera formats. The current collection includes 8 mm, 12 mm, 16 mm, 25 mm, 35 mm and 50 mm conventional Machine Vision Lens options across several 2/3", 1" and larger-format families, giving OEM machine builders and system integrators flexibility to design wider solar-cell inspection fields as well as tighter high-detail views.

Start With the Smallest Solar Cell Defect or Alignment Error That Must Be Rejected

Solar inspection can contain several levels of difficulty. Detecting a completely missing cell is relatively straightforward. Identifying a cell shifted several millimetres from its expected location is also easier than detecting a small edge chip or a slight difference in string spacing. Likewise, recognizing that a busbar exists is less demanding than measuring whether its visible position has moved by a small amount relative to the cell.

The Machine Vision Lens should therefore be selected around the smallest physical variation that determines production acceptance. If a small edge chip is the most demanding visible defect, that feature should drive the spatial-resolution requirement. If cell alignment tolerance is tighter, the displacement should be converted into pixels at the final FOV. This creates a much stronger optical basis than selecting a focal length only because the complete solar cell fits inside the image.

Cell Alignment Inspection Requires a Stable Geometric Reference

A solar cell can be fully present and undamaged but still be positioned incorrectly relative to its neighboring cells, transport reference or intended string axis. Cell alignment inspection therefore requires both the cell boundary and a stable reference system.

The vision system can locate cell corners or edges, establish the expected cell center and compare actual position with the intended coordinate system. A machine vision lens for solar cell alignment inspection should provide enough full-cell geometry for translation and rotation to be measured while retaining sufficient pixels for the minimum allowed position error.

Translation and Rotation Should Be Measured Separately

A cell can shift sideways while remaining parallel to neighboring cells, or it can rotate slightly while its center remains near the correct position. These are different assembly conditions.

Lateral displacement can be measured from cell center or edge location. Angular error can be determined from the orientation of opposite cell edges. The Machine Vision Lens should preserve enough of the complete cell profile to differentiate translation from rotation instead of relying on only one local corner.

Calculate Pixels per Millimetre Before Choosing the Lens

A useful starting relationship is:

Pixels per millimetre = sensor pixels across the measurement direction ÷ physical FOV in millimetres

If a camera provides 4,000 horizontal pixels across a 200 mm physical field, simplified sampling is approximately 20 pixels/mm. A 0.5 mm cell-position shift would therefore correspond to approximately 10 pixels before other system effects are considered.

If the same camera covers a 400 mm field, sampling falls to approximately 10 pixels/mm and the same positional variation becomes approximately 5 pixels.

This simple calculation explains why unnecessary surrounding area can reduce solar cell alignment measurement accuracy even when the camera resolution remains unchanged.

Cell-to-Cell Spacing Should Be Measured From Corresponding Edges

In a solar string, neighboring cells are normally expected to maintain consistent spacing.

The inspection system can measure the distance between corresponding edges of adjacent cells and compare the gap against expected limits. If the required gap tolerance is small, the Machine Vision Lens must provide enough pixels across that spacing.

A large image containing many cells may reduce per-gap sampling substantially. The number of cells that need to remain visible simultaneously should therefore be part of the optical design.

String Spacing Creates a Repeated-Geometry Inspection Problem

A solar string contains multiple cells arranged along a consistent direction. This repetitive structure is useful because neighboring cells provide natural references, but it also distributes sensor resolution across many repeated features.

If ten cells are captured in one image, each individual cell and inter-cell gap occupies a smaller fraction of the sensor than if only two cells are captured. For solar string inspection, the buyer should therefore consider both total string FOV and pixels available to each individual cell boundary.

A 16 MM 10 MP Lens Can Support Broader Cell Coverage

For compatible 2/3" camera systems, the Kyptec Automation® KL-1226 16 MM Machine Vision Lens With 10 MegaPixel & 2/3" Format Lens provides a 16 mm focal length, 10 MP resolution, C-mount, 2/3" image format and an F2.8–16 aperture range.

This type of configuration can be evaluated where a complete solar cell, multiple cell boundaries or a broader string region needs to remain visible within the available working distance. Final suitability should be determined from actual camera sensor dimensions, cell size, inspection FOV and minimum visible defect.

A 25 MM 10 MP Lens Can Provide More Controlled Cell Framing

Where the required solar-cell region can fit within a tighter physical field, the Kyptec Automation® KL-1228 25 MM Machine Vision Lens With 10 MegaPixel & 2/3" Format Lens provides a 25 mm, 10 MP option for compatible 2/3" systems. The current Kyptec Automation® product page describes the lens family for high-resolution industrial inspection and dimensional-analysis applications.

A tighter legitimate FOV can allocate more sensor pixels to cell corners, narrow inter-cell gaps, busbars and edge defects. This can be useful where small positional variations matter more than capturing a very broad module area.

Edge Chip Detection Should Be Based on Minimum Rejectable Chip Size

A large broken corner is easy to identify. A small edge chip is much more demanding because it changes only a short portion of the otherwise straight solar-cell boundary.

The optical specification should therefore identify the smallest visible chip that must trigger rejection. That physical dimension should then be translated into pixels at the final FOV.

A machine vision lens for solar cell edge inspection should provide sufficient edge sampling around the complete perimeter, including the corners where local defects may occur.

Cell Corners Can Be More Demanding Than Long Straight Edges

A long straight cell edge gives the vision system many pixels from which to establish an expected line. A small corner defect affects a much shorter geometric region.

For this reason, qualification should include small corner chips and localized edge defects rather than testing only gross dimensional differences.

The Machine Vision Lens should also preserve useful detail at all four corners if the complete cell occupies most of the image.

Edge Position and Edge Damage Are Different Inspection Conditions

A solar cell can have an undamaged edge but be shifted from the correct assembly position. Another cell can be positioned correctly while containing a localized chip.

The first is an alignment problem; the second is a contour-defect problem.

The vision system should therefore evaluate global cell geometry and local edge variation separately where both are required. The Machine Vision Lens needs enough full-cell context for alignment and enough local resolution for edge-defect inspection.

Busbar Position Inspection Requires a Cell-Based Reference

A visible busbar should be evaluated relative to the solar cell, not simply against fixed camera coordinates.

If the complete cell moves slightly inside the inspection station, the busbar moves with it. Comparing the busbar only with fixed image coordinates could therefore create a false position error.

A stronger approach is to locate the cell edges or center first and then measure busbar position relative to that cell reference.

Busbar Presence Is Easier Than Busbar Position

A busbar can be visually obvious yet still be slightly displaced.

Presence detection only needs enough information to determine whether the expected feature exists. Position inspection requires much finer localization of its visible centerline or boundaries.

If a single image must perform both functions, the Machine Vision Lens should be selected according to the tighter busbar-position requirement.

Busbar-to-Busbar Spacing Can Be Checked Across One Cell

Where several parallel busbar features are visible on one cell, the system can compare their relative spacing.

This creates another repeated-feature measurement. The entire cell needs to remain visible, but each busbar must still receive adequate sampling.

The combination of whole-cell coverage and narrow-feature localization is one reason higher-resolution Machine Vision Lens systems can become useful in photovoltaic inspection.

High-Resolution Larger-Format Lenses Can Help When Whole-Cell Coverage and Fine Detail Must Coexist

Some solar-cell inspection stations cannot reduce FOV because the complete cell or several neighboring cells must remain visible.

In these cases, increasing total optical resolution can provide more spatial samples across the same required physical area.

For compatible larger-format systems, the Kyptec Automation® KL-1238 16 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides a 16 mm focal-length option within the current 25 MP Machine Vision Lens family.

This type of configuration can be evaluated where broader solar-cell or string coverage must coexist with high total image resolution.

A 25 MM 25 MP Lens Can Balance Cell Coverage and Local Feature Detail

For compatible larger-format systems requiring more controlled high-resolution framing, the Kyptec Automation® KL-1240 25 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides 25 mm focal length, 25 MP resolution, C-mount and an F2.8–22 aperture range. The official product title uses the 1.1" format designation.

This type of lens can be considered where a complete cell or selected multi-cell region should remain visible while edge chips, cell gaps or busbar positions need stronger sampling.

More Megapixels Should Increase Pixels on the Solar Cell

Higher camera and lens resolution is most useful when the extra pixels remain concentrated on the actual photovoltaic features.

If the physical FOV is expanded at the same time, much of the potential improvement can disappear.

The stronger design method is to establish the minimum legitimate cell or string FOV first, then use higher resolution to increase pixels per edge, pixels per busbar and pixels across each inter-cell gap.

Cell String Straightness Can Be Evaluated Over a Longer Baseline

A string may contain individually acceptable cell-to-cell gaps but still drift gradually from the intended assembly axis.

A longer inspection field can reveal cumulative lateral deviation because the first and last cells can be compared with the expected string direction.

This requires enough FOV to establish the long baseline while preserving sufficient cell-edge resolution throughout the image.

Local Cell Spacing and Overall String Alignment Should Both Be Checked

Two neighboring cells can maintain correct spacing even if the entire pair has shifted away from the expected string path.

Likewise, a string can remain globally straight while one local gap is incorrect.

The Machine Vision Lens should support whichever combination of local and global geometry the machine needs to verify.

This can influence whether one wide high-resolution view or several localized views provide the stronger optical design.

Multiple Strings in One Image Reduce Pixels per Cell

PV manufacturing equipment may process several cell strings or lanes simultaneously.

Capturing multiple strings in one image increases the total physical field, reducing sensor pixels per cell.

The smallest edge chip, busbar shift or spacing error should therefore be calculated against the complete multi-string FOV.

If sampling becomes insufficient, higher-resolution optics or fewer strings per camera can provide a stronger inspection margin.

Cell Orientation Should Be Established Before Measuring Spacing

If an individual cell rotates slightly, its corner-to-corner projection and neighboring gap geometry change.

The vision system should determine cell orientation before making precise spacing comparisons.

The Machine Vision Lens should therefore preserve enough cell-edge information to calculate both center position and angle.

A 35 MM 1-Inch Lens Can Support Greater Inspection Stand-Off

PV manufacturing machinery can contain transfer systems, handling tools and fixtures that limit how close the camera can be positioned.

For compatible 1" camera systems, the Kyptec Automation® KL-1218 35 MM Machine Vision Lens With 10 MegaPixel & 1" Format Lens provides a 35 mm, 10 MP Machine Vision Lens option. Kyptec Automation® currently lists this model within its 1" format lens family.

This focal-length class can be evaluated where a controlled solar-cell inspection region must be viewed from additional stand-off because closer camera positioning is mechanically difficult.

Local Edge or Busbar Inspection Can Benefit From Longer Focal Lengths

Not every inspection station needs the complete solar module or string in one image.

A dedicated station may inspect one cell edge, one busbar region or a smaller group of cells.

In such cases, tighter framing can allocate substantially more sensor pixels to the critical feature.

Where sufficient working distance is available, a longer focal length can therefore provide a stronger local inspection view than a very broad lens.

A 50 MM 25 MP Lens Can Support Localized High-Detail Inspection

For compatible larger-format systems requiring tighter high-resolution framing, the Kyptec Automation® KL-1244 50 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides 50 mm focal length, 25 MP resolution, C-mount and an F2.8–22 aperture range.

This focal-length class can be evaluated where a localized cell edge, busbar region or tight cell-spacing area should occupy more of the sensor while complete-module coverage is unnecessary.

Cell Height and Handling Flatness Affect Measurement Repeatability

Solar cells and strings should be presented as consistently as practical during dimensional inspection.

If part of the cell sits closer to the camera because of handling variation or local bowing, apparent scale and edge position can change in a conventional perspective imaging system.

Where tight alignment and spacing measurement are required, stable object presentation should therefore be treated as part of the optical design rather than assuming that calibration alone will remove all variation.

Focus Should Be Qualified Across the Complete Cell Plane

A large solar cell can occupy a significant image area.

If the inspection plane is not sufficiently parallel to the sensor, one side of the cell may lie at a different working distance than the other.

The operating focus and aperture should therefore be tested using features at several positions across the cell or string. The smallest required edge and busbar features should remain adequately resolved throughout the entire production field.

Aperture Should Balance Depth Tolerance and Fine Edge Detail

Stopping down the aperture can increase usable depth of field when cell height varies slightly.

However, excessively small apertures can reduce fine spatial detail through diffraction.

The operating aperture should therefore be established using the smallest actual edge chip, busbar shift or spacing variation across the expected object-height range rather than simply maximizing depth of field.

Outer Cells and Outer Corners Require Separate Qualification

When a multi-cell field occupies much of the sensor, cells near the edges and corners of the image can be just as important as central cells.

Minimum edge defects and alignment errors should therefore be tested at central and outer image positions.

The Machine Vision Lens should be approved based on the entire production inspection field rather than only one conveniently centered solar cell.

Digital Zoom Cannot Restore Missing Solar Cell Detail

Software enlargement can make a cell edge or busbar appear larger on screen, but it cannot create additional physical sensor information.

If a small edge chip occupies only a few original pixels, digital zoom simply enlarges those pixels.

The correct solution is sufficient physical sampling through suitable FOV, camera resolution, focal length and Machine Vision Lens selection.

Qualification Should Use Borderline Alignment and Edge Samples

A heavily damaged cell or dramatically misaligned string is useful for early setup but should not define final qualification.

Production validation should include the smallest rejectable edge chip, minimum cell-position shift, busbar-position variation and cell-to-cell spacing error.

These conditions should be tested across different cell positions, outer image regions and valid production orientations so the complete optical system is qualified rather than only the easiest sample.

Why Kyptec Automation® Is a Practical Choice for Solar Cell and PV Module Inspection

Kyptec Automation® provides a broad Machine Vision Lens collection spanning conventional 5 MP, 10 MP and 25 MP lens classes and several focal lengths across different industrial camera formats. The current collection provides wider focal-length options for larger photovoltaic inspection areas as well as 25 mm, 35 mm and 50 mm choices for more controlled or localized fields.

For compatible 2/3" systems, Kyptec Automation® KL-1226 16 MM Machine Vision Lens With 10 MegaPixel & 2/3" Format Lens provides a broader 16 mm, 10 MP option, while Kyptec Automation® KL-1228 25 MM Machine Vision Lens With 10 MegaPixel & 2/3" Format Lens provides tighter framing when more sensor pixels are required on individual cells, edges or busbar regions.

For compatible larger-format high-resolution systems, Kyptec Automation® KL-1238 16 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens can be evaluated where wider cell or string coverage needs high total resolution, while Kyptec Automation® KL-1240 25 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides more controlled high-resolution framing. Where localized high-detail inspection and additional image scale are priorities, Kyptec Automation® KL-1244 50 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides a longer-focal-length option.

This portfolio breadth gives solar-production OEMs and system integrators practical flexibility to select Kyptec Automation® Machine Vision Lens configurations according to actual solar-cell size, cell count, smallest edge defect, spacing tolerance, busbar geometry, sensor format and machine working distance.

Frequently Asked Questions About Machine Vision Lenses for Solar Cell and PV Module Inspection

1. What is the best Machine Vision Lens for solar cell inspection?

The correct Machine Vision Lens depends on solar-cell dimensions, smallest visible edge defect, cell-position tolerance, busbar dimensions, sensor format, camera resolution and available working distance. A complete-cell inspection normally requires enough FOV for the full cell plus positioning tolerance, while local edge inspection can use tighter framing. Kyptec Automation® provides multiple focal lengths across 10 MP and 25 MP Machine Vision Lens families, allowing the optical system to be selected according to actual photovoltaic inspection geometry rather than focal length alone.

2. How much resolution is needed to detect solar cell edge chips?

Start with the smallest edge chip that must cause rejection. Calculate pixels/mm from the final physical FOV and determine how many pixels represent that defect. A large cell can appear perfectly sharp while a small chip remains under-sampled, so minimum defect size rather than overall cell size should drive the optical-resolution requirement.

3. Can machine vision measure solar cell alignment?

Yes. The system can locate cell edges or corners, calculate cell center and orientation, and compare those values with the expected string or module position. The Machine Vision Lens should preserve enough of the complete cell boundary to distinguish lateral shift from rotation while providing adequate sampling for the minimum permitted alignment error.

4. Can machine vision measure the gap between adjacent solar cells?

Yes. The system can locate corresponding cell edges and convert their pixel separation into a physical spacing after calibration. Reliable measurement requires adequate pixels/mm and stable cell presentation. When many cells share one image, the total FOV should be checked carefully because each inter-cell gap receives fewer pixels.

5. Is a 16 mm Machine Vision Lens suitable for solar cell inspection?

It can be when the resulting FOV matches the cell or string region. For compatible 2/3" systems, Kyptec Automation® KL-1226 16 MM Machine Vision Lens With 10 MegaPixel & 2/3" Format Lens provides 16 mm focal length, 10 MP resolution, C-mount, 2/3" image format and an F2.8–16 aperture range. Final suitability should be calculated from actual sensor dimensions, cell size and working distance.

6. When should a 25 mm Machine Vision Lens be considered for PV inspection?

A 25 mm focal length can be useful when the required solar-cell region fits inside a more controlled FOV and additional pixels per millimetre are valuable. Kyptec Automation® KL-1228 25 MM Machine Vision Lens With 10 MegaPixel & 2/3" Format Lens provides a current 10 MP option for compatible 2/3" systems. It can be evaluated where cell-edge, busbar or spacing detail is more demanding than broad scene coverage.

7. Can machine vision check solar cell rotation or skew?

Yes. By detecting multiple cell edges or corners, the system can calculate cell orientation and compare it with the expected string direction. This requires enough full-cell geometry to distinguish rotation from simple lateral translation. A lens framed only around one corner may therefore provide insufficient orientation information.

8. How can machine vision inspect busbar position on a solar cell?

The system can first establish the cell coordinate system from its edges and then locate the visible busbar relative to that geometry. This avoids interpreting normal whole-cell movement as busbar misalignment. The Machine Vision Lens should provide adequate sampling across the busbar feature and enough surrounding cell geometry for a stable reference.

9. When should a 25 MP Machine Vision Lens be considered for solar inspection?

A 25 MP configuration becomes particularly useful when a complete solar cell, several neighboring cells or a broader string field must remain visible while small edge, busbar or spacing tolerances still require substantial image sampling. Kyptec Automation® currently lists several 25 MP Machine Vision Lens focal lengths for compatible larger-format systems.

10. Which Kyptec Automation® lens can support broader high-resolution solar-cell inspection?

For compatible larger-format systems, Kyptec Automation® KL-1238 16 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides a 16 mm option within the current 25 MP Machine Vision Lens family. It can be evaluated when broader cell or string coverage and high total optical resolution need to coexist.

11. Which Kyptec Automation® lens can provide tighter high-resolution solar-cell framing?

For compatible larger-format systems, Kyptec Automation® KL-1240 25 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides 25 mm focal length, 25 MP resolution, C-mount and an F2.8–22 aperture range. This can be considered when a cell or selected multi-cell region should occupy more of the sensor while retaining high total image resolution.

12. Can a 35 mm Machine Vision Lens be useful when the camera must be mounted farther from the cell?

Yes. For compatible 1" camera systems, Kyptec Automation® KL-1218 35 MM Machine Vision Lens With 10 MegaPixel & 1" Format Lens provides a current 35 mm, 10 MP option within the Kyptec Automation® portfolio. This focal-length class can be evaluated where handling equipment or production machinery requires greater camera stand-off.

13. Can a 50 mm Machine Vision Lens be used for detailed solar cell edge inspection?

Yes, when a localized region is being inspected and sufficient working distance is available. Kyptec Automation® KL-1244 50 MM Machine Vision Lens With 25 MegaPixel & 1.1" Format Lens provides 50 mm focal length, 25 MP resolution, C-mount and an F2.8–22 aperture range for compatible larger-format systems. Tighter framing can allocate more sensor pixels to a cell corner, edge or local busbar region.

14. Can one camera inspect several solar cells at once?

Yes, provided the complete multi-cell area fits within the FOV while each cell edge, busbar and spacing feature still receives sufficient sensor sampling. Every additional cell increases the physical field and reduces pixels per individual feature. The smallest required edge or spacing defect should therefore be calculated against the complete multi-cell view before lens selection.

15. Why can a vision system detect a missing solar cell but miss a small edge chip?

A missing cell creates a very large visual difference, while a small edge chip modifies only a short section of the cell contour. The chip therefore needs far greater local spatial resolution. Lens selection should be based on the smallest edge defect if edge-chip detection is part of the inspection requirement, rather than on simple cell presence.

16. Does solar cell height or flatness affect machine vision measurement?

It can. In a conventional Machine Vision Lens system, changes in object distance can affect focus and apparent scale. If cells bow or are presented at varying heights, precise alignment and spacing measurements can change. Stable material handling and qualification across the real height range therefore improve measurement repeatability.

17. What information should I provide before buying a Machine Vision Lens for solar cell or PV module inspection?

Provide solar-cell width and height, number of cells that must fit within one image, smallest edge chip to detect, permitted cell-position and rotation error, required cell-to-cell spacing tolerance, visible busbar dimensions, camera sensor format and resolution, available working distance and expected object-height variation. These inputs allow a Kyptec Automation® Machine Vision Lens to be evaluated according to actual FOV, pixels per millimetre and pixels available to each critical photovoltaic feature.

Design Solar Cell Inspection Around the Smallest Cell-Level Feature, Not Only Module Size

Reliable solar cell and PV module inspection requires recognizing that complete-cell presence, alignment, edge-chip detection, busbar-position measurement and string-spacing verification operate at different physical scales. A complete photovoltaic cell can appear clearly visible while a small edge chip or slight busbar displacement remains inadequately represented. Likewise, an entire string can appear straight while one local cell-to-cell gap lies outside tolerance. The Machine Vision Lens should therefore be selected around the smallest required cell-level or string-level variation rather than only the overall module dimensions.

The strongest optical design begins with cell size, number of cells in the inspection field, smallest edge defect, alignment tolerance, busbar geometry and allowed string spacing. The minimum legitimate FOV is then established from those dimensions plus actual product-position tolerance. Pixels per millimetre can be calculated from camera resolution, after which sensor format, focal length and working distance are selected so the photovoltaic features use the available sensor efficiently. Final qualification should include borderline edge chips, minimum alignment errors, busbar-position variations and spacing errors at central and outer image locations.

Kyptec Automation® provides a comprehensive Machine Vision Lens portfolio spanning multiple focal lengths and conventional 5 MP, 10 MP and 25 MP resolution classes across several industrial camera formats. By matching the appropriate Kyptec Automation® Machine Vision Lens to solar-cell dimensions, smallest visible defect, string geometry, camera sensor format and available machine working distance, OEM machine builders and system integrators can establish a stronger optical foundation for automated solar cell alignment inspection, visible edge-chip detection, busbar-position verification, cell-spacing measurement and PV module assembly quality control.