New developments of transparent plastic materials in frontsheets and backsheets as valid alternatives to glass.

The new challenges of the ultralight bifacial modules

The strong development of new types of cells and modules, like bifacial ones, has on the one hand been accompanied by glass-glass solutions and on the other has

encouraged many manufacturers of plastic films to develop new products that are able to compete with glass, providing a number of advantages.

In fact, by making use of both surfaces of the cells, almost twice as much can be produced for the same cost. One thing is certain: the photovoltaic bifacial cell allows more clean energy to be produced, lowering the cost of the kW produced.

To be competitive with the glass-glass solutions, the polymer based transparent laminates have been developed to avoid any problems with the structures of the glass/glass modules, such as premature fractures

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duration including cells breakage, reduced thermal conductivity, high logistics, transport and installation costs, as well as improving resistance to physical phenomena like hail, sand and UV rays.

So described below are the innovative new solutions designed and implemented by Coveme, to make plastic films the best solution for protecting not just the back part (backsheet), but also the front part (frontsheet) of the new generation panels. These flexible ultralight can be installed on roofs with limited load capacity, or used for new integrated solutions (BIPV) and those compatible with thin film technologies (CIGS, OPV).

More detailed information will also be provided on the development of the new coatings to improve resistance to abrasion and scratching, with a discussion on test procedures and the standards needed to ensure the guaranteed performance is achieved.

Description of the innovation, principal advantages and characteristics

Coveme has recently developed two totally transparent polyester based materials as a valid alternative to glass, that act as back support (dyMat® Clear BACK) and front support (dyMat® Clear FRONT) in the new generation PV modules, such as the bifacial, light and semi-flexible examples.

The final applications, grid and off-grid, are utility, rooftop and BIPV, as well as commercial and special applications including automotive and nautical.

The use of the new dyMat® clear as a transparent backsheet in the bifacial modules, as already mentioned above, provides a number of advantages listed below:

• Notable reduction in the weight of the module compared with the glass/glass configuration, with a consequent reduction in transport and installation costs

• Improved productivity of the module itself for the same cost, and less fractures of the cells during the production of the module

• Exceptional thermal conductivity reducing the operating temperature of the NOCT module

• Reduced weight, especially in the 1500 VDC configuration, and the use of the standard ALU frame which both reduce the cost of the BOS for the assembly system whether fixed or not

• Increase in the production of energy thanks

to the special diffusive coating which enables the light to be caught and diffused on the cells even at low angles of radiation, at sunrise and sunset

Main features of the backsheet for 1500VDC

• TLT > 89%

• Abrasion Taber test > 200 cycles

• Resistance to UV > 150kWh

• DHT > 2500hrs

• WVTR < 1.9

The use of dyMat® Clear as the frontsheet on the light modules, as an alternative to glass, gives the following advantages:

• This new transparent frontsheet consists of the revolutionary opaque coating, which is highly transparent and resistant to UV rays, with exceptional anti-scratch and anti-reflection characteristics

• Its special anti-abrasive coating avoids the degradation of the polymer that would otherwise become opaque over time reducing the performance of the module

Main features of the frontsheet for 1000VDC

• TLT > 89%

• PET produced for resistance to UV

• Texturised version – for anti-reflection and high efficiency for low angles of radiation

• Hard-coat and scratch resistance

PRIMER Transparent

PET Transparent PET,

Hydrolysis Resistant (HR)Electrical Grade

PET Transparent PET, UV Stable

Hydrolysis Resistant

AIR SIDE

CELL SIDE

1500 VDC

PROTECTIVE COATING OR TRANSPARENT TEDLAR®

UV Resistant

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Taber test

This test, conducted according to the ASTM D4060 standard, enables a number of types of surface to be tested assessing the abrasion resistance of a large number of types of materials and coatings.

The abrasive action is obtained by rotating the test sample, cut in the shape of a disc, while two abrasive wheels turn above it. The Coveme dyMat® clear backsheet compared with a competitor’s shows loss of transparency of only 0.5 after 100 cycles.

Erichsen 413 scratch hardness test

The Erichsen 413 is a scratch hardness tester.

It is a motorised test instrument used to measure the resistance to scratches and cuts on plastic or painted surfaces. Panels of different thicknesses are tested by making single, parallel and transverse cuts.

The sample has to be mounted on a rotating table (number of turns in the standard

version: 5 min-1). The test instrument is connected to a load arm, with an adjustable weight that enables the pressure of the tool on the sample, to be set (load range from

0 to 10 N with increments of 0.1 N and load range from 0 to 1 N with increments of 0.01 N).

The resistance of the sample to this treatment is assessed visually using the zero trace.

Coveme’s sample has a scratch resistance that is ten times greater than that of the competitor.

The results of the test, shown in the table in Figure 2, again confirm the excellent anti-abrasion and anti-scratch properties of the coating in the case of the FS, and it’s the same in the texturised version.

Field test

PV bifacial modules using transparent backsheet and installed in the field for more than 3 years show no yellowing, cracking, chalking or bubbling.

All the above tests results show why dyMat® clear products are durable and the ones to use.

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Technical details

Coveme has developed a new type of innovative coating that protects the polymer films from UV rays and abrasion. This technology enables the coating itself to act as an anti-reflective surface and to increase the amount of light that reaches the cells with low angles of incidence.

These new materials have been tested and validated internally using international standards. The tests include tests on resistance to abrasion and resistance to scratching to guarantee long life.

The anti-dazzle surface of the new frontsheet has shown an increase in power of about 10% in field trials with an angle of inclination of 10-15°, with respect to the standard backsheet.

In support of this the tests conducted on the dyMat® clear products are described below.

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Figure 2 Erichsen 413 scratch resistance values for the frontsheet samples of the competitor vs Coveme dyMat FS 1000VDC

Scratch Hardness Test

COMPETITOR 1 matt < 0,5 N

COMPETITOR 2 matt < 0,5 N

COMPETITOR 2 matt < 0,3 N

COVEME CLR UV matt < 3,2 N

Figure 1 Values of loss of haze after 100 cycles- dyMat clear FS 1000VDC- comparison between samples subjected to the Taber test

H

COVEME CLR UV-matt

T0 85

100 cycles 86

H

COMPETITOR 2 – TPT matt

T0 28,6

100 cycles 33,5

H

COMPETITOR 1 – TFB matt

T0 45,8

100 cycles 49,5

H

COMPETITOR 3 –KPF matt

T0 45,2

100 cycles 54,1

∆H 1 ∆H 9

∆H 3,7∆H 4,9

Abrasion Resistance Tests (comparison with competitors)

Scratch Resistance Tests (comparison with competitors)

ULTRA PROTECTIVE COATING

CELL SIDE

AIR SIDE

UV PET Transparent PET,

UV Stable

PRIMER Transparent

1000 VDC

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