How to Compare Solar Module Frame Strength

The frame of a solar module supports the glass and helps transfer wind and snow forces into the clamps and mounting structure. If the frame or mounting method is not suitable, the module may bend too much, move inside the clamps, damage the glass edge or develop cracks inside the solar cells.

Frame strength cannot be judged from one number. A 35 mm frame is not automatically stronger than a 30 mm frame. In the same way, a module marked "5,400 Pa" is not automatically suitable for every roof, wind zone or snow area.

Buyers should compare the complete module, its approved mounting method and the structure supporting it. Tongwei's high-efficiency module range shows that modules can have different sizes, weights, glass structures and frame designs. These differences can affect how the module behaves under load.

What Frame Strength Really Means

Four points need to be considered:

l Strength: Whether the frame, glass and connections can resist bending, cracking, buckling or separation.

l Stiffness: How much the module bends or twists while it is carrying a load.

l Holding ability: Whether the frame stays securely connected to the glass, clamps, rails and corner joints.

l Durability: Whether the module keeps its mechanical performance after years of wind, rain, temperature changes, corrosion and repeated movement.

A frame may not break during a test but may still bend enough to damage cells or seals. For this reason, a simple "passed" statement is less useful than a report that also shows deflection, permanent deformation and the condition of the module after testing.

Start with the Project Load

Do not begin by asking which module has the deepest frame. Begin by finding out what wind and snow pressures the project must resist.

The required load depends on factors such as:

l Local wind speed

l Building height

l Open or sheltered terrain

l Roof edges and corners

l Module angle and mounting height

l Local snow load

l Snow drifting and sliding

l Roof shape

l Local building rules

Tongwei's module application scenarios separate residential, commercial and utility-scale uses. This is useful because a residential roof and a large ground-mounted project do not always use the same module size, support spacing or mounting method.

A practical review should follow this order:

1. Obtain the required project wind and snow pressures.

2. Check the module capacity for the exact mounting method.

3. Check the clamps, rails, fasteners and roof or ground structure.

4. Confirm that the documents match the exact module being purchased.

5. Record the result as Pass, Fail or Unknown.

Pass

The exact module and mounting system have verified capacities equal to or higher than the project requirements.

Fail

At least one verified capacity is below the project requirement, or the proposed mounting method is outside the manufacturer's approved conditions.

Unknown

Important information is missing, the report does not match the model, or it is not clear whether a stated value is a test load or a design load.

Missing information should not be treated as proof that the product is suitable.

Read Load Values Correctly

Mechanical load is normally shown in pascals.

1 Pa = 1 newton per square metre

1,000 Pa = 1 kPa

Pressure Is Not the Same as Total Force

A larger module carries more total force at the same pressure.

Total force = pressure × module area

For a module measuring 2.28 m × 1.13 m:

Area = 2.28 × 1.13 = 2.5764 m²

At 5,400 Pa:

5,400 × 2.5764 = approximately 13,913 N

This force is spread across the full module surface. It does not mean that the same weight can be placed at one point on the glass. A person, tool or block of ice creates a concentrated load and may cause damage at a much lower total force.

Front and Rear Loads Are Different

A datasheet may show one value for the front of the module and another value for the rear.

For example:

This should not be described simply as a "5,400 Pa module."

Front loading commonly relates to pressure acting on the front of the module. Rear loading commonly relates to wind suction or uplift acting in the opposite direction. The exact meaning should always be checked in the manufacturer's installation manual or test report because wording and signs can vary.

For a snow area, the front value may be more important. For an exposed roof, the rear uplift value may control the design.

Test Load and Design Load Are Not the Same

A test load is the pressure applied during a laboratory test. A design load is the value allowed for use when checking a real project.

The highest number shown in a sales sheet may be a test value rather than a design value. Do not convert one into the other unless the manufacturer or the applicable project document clearly explains the method.

The correct comparison is:

Required project design pressure ≤ verified module design pressure

The two values must refer to the same load direction and the same mounting arrangement. If the module document only gives a test value and no permitted design value, the result should remain Unknown.

Compare the Frame and Module Design

Frame Height Is Only One Detail

A deeper frame can reduce bending, but frame height alone does not prove strength. Buyers should also check:

l Frame shape

l Wall thickness

l Internal ribs

l Width of the clamping area

l Glass channel shape

l Corner connection

l Aluminium grade and condition

l Module size

l Clamp and rail positions

A thin-walled 35 mm frame may bend or buckle more than a well-designed 30 mm frame. The full profile drawing and verified module test are more useful than frame height alone.

Check Wall Thickness by Location

A frame does not normally have the same thickness everywhere. The outer wall, glass channel, lower flange and internal ribs may all be different.

Ask the supplier to explain:

l Where the thickness was measured

l The drawing value

l The lowest allowed thickness after production tolerance

l How production thickness is checked

Very thin areas may be more likely to crush under a clamp, bend around a screw hole or buckle under pressure. However, simply adding more aluminium does not always create a better frame. The shape and position of the material also matter.

Check Internal Ribs and the Clamping Area

Internal ribs can help the frame resist bending or local crushing. Their value depends on where they are placed and how they connect to the rest of the profile.

The area under the clamp is especially important because a large module load is transferred through a relatively small contact area. Inspect test samples for:

l Dents in the frame

l Permanent crushing

l Clamp marks

l Frame twisting

l Clamp movement

l Damage close to the glass edge

A longer clamp may spread force over a wider area, but only when its shape properly matches the frame. Clamp length alone does not prove that the connection is stronger.

Check the Glass Channel and Corners

The glass edge sits inside the frame channel. Poor fit, hard metal contact, uneven adhesive or damaged glass edges can reduce module strength.

Check for:

l Enough glass engagement inside the frame

l Even adhesive or sealant

l No sharp contact against the glass edge

l Clear drainage openings

l No loose or open corners

l No frame misalignment

Corner joints connect the four frame sections. A loose corner may allow the frame to twist and may increase stress around the glass and clamps.

Module Size and Glass Type Matter

The same frame does not give the same result on every module. A longer or wider module may carry more total force and may bend more between its supports.

Performance also depends on:

l Front glass thickness

l Rear glass or backsheet

l Single-glass or double-glass construction

l Module weight

l Support spacing

l Manufacturing quality

Double-glass modules are not always stronger than glass-backsheet modules. Thin glass is not automatically weak either. The result depends on the complete module design and the tested mounting method.

Check the Mounting Method

A module's load rating only applies to the mounting arrangements covered by the manufacturer.

The latest installation manual should show:

l Number of clamps

l Approved clamp zones

l Clamp size and overlap

l Rail position and direction

l Module orientation

l Required bolt and torque range

l Allowed mounting holes

l Load value for each installation method

Tongwei's published installation information explains that clamp position can change the module's maximum load capacity. Because module groups and manuals can change, always obtain the latest document for the exact model from the Tongwei download centre.

Clamp Position

Moving the clamps changes the distance between the supports. It also changes the unsupported section at each end of the module.

A clamp installed outside the approved zone can cause more bending, frame twisting, glass-edge stress or clamp movement. Even a small change in position may matter on a large module.

The measurement reference must also be clear. A manual may measure from the module corner, the end of the frame, the clamp centre or one edge of the clamp.

Bolt Torque

Too little torque may allow the module to slip or lift. Too much torque may crush the frame, deform the clamp or damage the thread.

Use the value provided for the approved clamp, bolt and rail system. Do not copy a torque value from another product.

Bolt force can also change because of dirt, lubrication, surface coatings, reused bolts and tool accuracy. A calibrated torque wrench should be used where required.

Rails, Fasteners and the Roof

For a roof system, the load path is:

Glass → frame → clamp → rail → roof attachment → roof structure

For a ground-mounted system, the load continues into the posts and foundations.

A strong module cannot make a weak rail or roof safe. Each part must be checked against the force it actually carries.

Do not directly compare different types of ratings. A module may be rated in Pa, while an anchor may be rated in newtons and a rail may be checked by bending force. Each item needs its own calculation.

Match the Module to Wind Conditions

Wind can push a module toward the roof or pull it away from the roof. Uplift is often stronger around roof edges and corners.

Wind pressure depends on:

l Wind speed

l Building height

l Open or sheltered surroundings

l Roof shape

l Roof edge or centre location

l Module angle

l Array height

l Pressure inside the building

Do not convert a module load rating directly into a hurricane category or a universal wind-speed claim. Two buildings with the same local wind speed may place different pressures on their modules.

A wind check should confirm:

l Required downward pressure

l Required uplift pressure

l Module capacity in both directions

l Approved clamp arrangement

l Rail and attachment capacity

l Roof or ground structure capacity

Match the Module to Snow Conditions

Snow depth alone does not tell you the load. Dry snow, wet snow and ice can have very different weights.

Snow may also collect unevenly because of:

l Wind drifting

l Parapets and roof steps

l Module angle

l Snow sliding from a higher roof

l The lower edge of the module frame

l Melting and refreezing

A uniform laboratory test does not reproduce every real snow condition. IEC 62938 provides a method for testing certain framed modules under inclined, non-uniform snow loading. It is mainly relevant when the lower frame edge can slow or stop sliding snow.

Non-uniform snow testing does not replace the project snow calculation. The engineer must still consider local snow, drifting, ice, roof shape and module position.

Snow removal must follow the manufacturer's instructions. Do not walk on modules, use sharp metal tools or pour hot water onto cold glass.

Check Repeated Loading and Corrosion

Repeated Wind Loading

A static test applies pressure during a set test sequence. Real wind changes direction and pressure repeatedly.

Repeated bending can contribute to:

l Cell cracks

l Loose corner joints

l Clamp movement

l Seal movement

l Electrical connection damage

l Power loss

IEC TS 62782 covers cyclic mechanical loading. When a supplier says that a module passed a dynamic load test, ask for the pressure, number of cycles, mounting method and results before and after testing.

Tongwei publishes module reliability examples from different environments. These examples provide useful manufacturer information, but they do not replace the exact test report and project calculation for the module being purchased.

Coastal Areas

Salt and moisture can affect frames, clamps, rails, bolts, grounding parts and connectors.

Check:

l Salt-mist test evidence

l Test severity

l Frame surface treatment

l Clamp and fastener materials

l Drainage

l Distance-from-coast restrictions

l Warranty exclusions

Passing a salt-mist test for the module does not prove that the complete mounting system is suitable for a coastal project.

Agricultural Areas

Moist air containing ammonia may affect modules and mounting parts in livestock and agricultural buildings.

IEC 62716 is used to evaluate module resistance to ammonia exposure. Ask whether the exact module was tested and whether the manufacturer places any limits on agricultural use.

Mixed Metals

Aluminium frames may touch stainless steel, coated steel or other metals. Moisture and salt can increase corrosion where different metals meet.

Do not add unapproved insulating washers or coatings without checking the grounding design. A part that reduces metal contact may also interrupt the required electrical connection.

Verify the Documents

A datasheet is useful, but it may not contain enough information for a high-value purchase.

Ask for:

l Current product specification

l Current installation manual

l Mechanical-load test report

l Applicable IEC 61215 qualification documents

l Applicable IEC 61730 safety documents

l Frame profile drawing

l Clamp-zone drawing

l Dynamic-load report, where needed

l Non-uniform snow report, where needed

l Salt-mist or ammonia report, where needed

l Confirmation of the current materials and design

Match the Exact Model

Compare the report with the product being purchased:

l Full model number

l Length and width

l Frame profile

l Glass thickness

l Single-glass or double-glass construction

l Manufacturing site

l Clamp and rail arrangement

l Report date and revision

A report for a smaller module does not automatically prove the strength of a larger module from the same product family.

Check for Product Changes

A manufacturer may change the frame supplier, glass, adhesive, corner key or production site. These changes may affect the qualification evidence.

IEC TS 62915 gives guidance on deciding when a changed module design needs additional review or retesting.

Ask the supplier to confirm which report covers the current product and its current bill of materials. The bill of materials is the list of the main parts and materials used to make the module.

Tongwei's module authenticity query can help check product identity. Product authentication is useful, but it does not replace a structural review.

Tongwei also provides global project examples. Project examples can show where modules have been used, but they do not prove that the same module and mounting method are suitable for every new site.

Example Comparison

The following values are only an example and do not describe a real product.

Assume a roof project requires:

l Front design pressure: 3,200 Pa

l Rear design pressure: 2,000 Pa

Module A

l Front test load: 5,400 Pa

l Rear test load: 2,400 Pa

l Design pressures not stated

l Clamp arrangement not clearly shown

Module B

l Front design pressure: 3,600 Pa

l Rear design pressure: 2,400 Pa

l Approved clamp zone shown

l Required mounting method shown

Module A should be marked Unknown because its test loads cannot be compared directly with the project design pressures without a documented method.

Module B passes the module check because both of its design pressures are higher than the project requirements.

The overall project is not yet a Pass. The clamps, rails, roof attachments and roof structure must also be checked.

Claims That Need More Evidence

"The frame is 35 mm, so it is stronger."

Frame shape, wall thickness, module size, glass type and mounting position are missing.

"The module supports 5,400 Pa."

The direction, mounting method and whether it is a test or design value are missing.

"It can survive a Category 4 hurricane."

Hurricane category alone does not give the pressure on a particular roof. Building height, roof zone, terrain, internal pressure and mounting design are also needed.

"It can hold two metres of snow."

Snow density, drifting, ice, module angle and load distribution are missing.

"It passed IEC testing, so it will last 30 years."

IEC qualification testing does not give a direct prediction of service life. Environment, production quality, installation and maintenance also affect long-term performance.

"It passed salt-mist testing, so the whole system is marine-proof."

The rails, clamps, fasteners, connectors and grounding parts must also be suitable for the coastal environment.

Final Decision

The strongest solar module is not simply the one with the deepest frame or the largest number in a brochure.

A reliable decision should confirm:

l The exact product model

l The current module design and materials

l Front and rear design pressures

l Clear separation of test and design values

l The approved clamp and rail arrangement

l Suitable wind and snow evidence

l Suitable corrosion evidence for the site

l Matching test reports and installation documents

l A safe roof, racking system or ground structure

Use Pass, Fail and Unknown consistently. Do not turn an Unknown into a Pass by making assumptions.