PHOTOVOLTAIC MODULE BACKSHEET COMPRISING POLYOLEFIN LAYERS

Abstract

The present invention relates to a photovoltaic module backsheet comprising, in order: photovoltaic module backsheet comprising a functional layer and a weather-resistant layer, wherein the backsheet is free of fluorinated polymers, characterized in that: i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50 wt. % of the functional layer is polyethylene; and ii) the weather-resistant layer comprises, a first sub-layer facing the functional layer and a second sub-layer, wherein a) each of the first sub-layer and the second sub-layer comprise at least 50 wt. % polypropylene; and b) the second sub-layer has a lowest glass transition temperature (T.sub.g) below 40 C. The present invention also relates to a process for producing the backsheet and a photovoltaic module comprising the backsheet according to the present invention.

Claims

1. A photovoltaic module backsheet comprising a functional layer and a weather-resistant layer, wherein the backsheet is free of fluorinated polymers, characterized in that: i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50 wt. % of the functional layer is polyethylene; and ii) the weather-resistant layer comprises, a first sub-layer facing the functional layer and a second sub-layer, wherein a) each of the first sub-layer and the second sub-layer comprise at least 50 wt. % polypropylene; and b) the second sub-layer has a lowest glass transition temperature (T.sub.g) below 40 C.

2. A photovoltaic module backsheet according to claim 1, wherein the second sub-layer has a lowest glass transition temperature (T.sub.g) at least 20 C. lower than the lowest glass transition temperature (T.sub.g) of the first sub-layer.

3. A photovoltaic module according to claim 1, wherein the weather-resistant layer comprises, in order, a first sub-layer, a second sub-layer and a third sub-layer, wherein the third sub-layer comprises at least 50 wt. % polypropylene.

4. A photovoltaic module according to claim 3, wherein the second sub-layer has a lowest glass transition temperature (T.sub.g) at least 20 C. lower than the lowest glass transition temperature (T.sub.g) of the third sub-layer.

5. A photovoltaic module backsheet according to claim 3, wherein each of the first sub-layer and the third sub-layer comprise from 70 wt. % to 90 wt. % polypropylene.

6. A photovoltaic module backsheet according to claim 3, wherein the first sub-layer and the third sub-layer have an identical chemical composition.

7. A photovoltaic module backsheet according to claim 1, wherein the second sub-layer comprises a blend of polypropylene with a polyolefin elastomer.

8. A photovoltaic module backsheet according to claim 1, wherein the second sub-layer comprises from 20 wt. % to 40 wt. % polyolefin elastomer.

9. A photovoltaic module backsheet according to claim 1, which further comprises a connecting layer, located between the functional layer and the weather-resistant layer.

10. A photovoltaic module backsheet according to claim 1, wherein functional layer comprises a ternary blend of polypropylene, polyethylene and a polyethylene copolymer.

11. A photovoltaic module backsheet according to claim 10, wherein the polyethylene copolymer is an ethylene methacrylate copolymer.

12. A photovoltaic module backsheet according to claim 1, wherein the functional layer has a thickness of from 10 to 50 m.

13. A photovoltaic module backsheet according to claim 1, wherein the weather-resistant layer has a thickness of from 100 to 500 m.

14. A photovoltaic module comprising a photovoltaic module backsheet as defined in claim 1.

15. A process for producing a photovoltaic module backsheet as defined in claim 1 comprising: i) feeding a functional layer composition, a first sub-layer composition, a second sub-layer composition and, where present, a third sub-layer composition to a multi-layer film coextrusion apparatus; and ii) melting and coextruding the compositions, in the multi-layer film coextrusion apparatus, into a photovoltaic module backsheet in the order: functional layer, first sub-layer, second sub-layer and, where present, third sub-layer.

16. A process according to claim 15 comprising: i) feeding a functional layer composition, a connecting layer composition, a first sub-layer composition, a second sub-layer composition and a third sub-layer composition to a multi-layer film coextrusion apparatus; and ii) melting and coextruding the compositions, in the multi-layer film coextrusion apparatus, into a photovoltaic module backsheet in the order: functional layer, connecting layer, first sub-layer, second sub-layer, third sub-layer.

Description

EXAMPLES

Method for Manufacturing a Photovoltaic Backsheet:

[0068] Material of a first sub-layer, second sub-layer and third sub-layer of a weather-resistant layer; a connecting layer and a functional layer were respectively pelletized by an extruder to obtain plastic pellets of respective layers. Pellets of the respective layers were added to multiple inputs of a multi-layer extruder (HRPC-1000 from Tianjin Hengrui Plastic Machinery Co., Ltd.), melt-extruded at 230 C., flowed through an adapter and a die, cooled by a cooling roller and shaped to manufacture the multi-layer back sheet. The layers were, in order, functional layer, connecting layer, weather resistant layer. Where the weather resistant layer comprised multiple sub-layers, the first sub-layer was adjacent the connecting layer and the second sub-layer was located between the first and third sub-layers. The composition of the different layers in the multilayer backsheets are given in Table 1.

TABLE-US-00001 TABLE 1 Connecting Example layer Functional no. Weather-resistant layer (thickness) (thickness) layer (thickness) Ex. 1 Three sub-layers: 70 parts of 55 parts of First sub-layer: 79 parts of polypropylene polyethylene, 10 parts polypropylene copolymer, 10 parts of copolymer, of polypropylene titanium dioxide, 10 parts of talcum 30 parts of copolymer, 25 parts of powder, additives (240 m). polyolefin ethylene copolymer, Second sub-layer: 70 parts of elastomer, 10 parts of titanium polypropylene copolymer, 30 parts of additives dioxide, additives polyolefin elastomer, additives (25 m) (25 m) (30 m) Third sub-layer: 79 parts of polypropylene copolymer, 10 parts of titanium dioxide, 10 parts of talcum powder, additives (30 m). Ex. 2 Three sub-layers: 70 parts of 55 parts of First sub-layer: 75 parts of polypropylene polyethylene, 10 parts polypropylene copolymer, 5 parts of copolymer, of polypropylene polyolefin elastomer, 10 parts of 30 parts of copolymer, 25 parts of titanium dioxide, 10 parts of talcum polyolefin ethylene copolymer, powder, additives (240 m). elastomer, 10 parts of titanium Second sub-layer: 70 parts of additives dioxide, additives polypropylene copolymer, 30 parts of (25 m) (30 m) polyolefin elastomer, additives (25 m) Third sub-layer: 75 parts of polypropylene copolymer, 5 parts of polyolefin elastomer, 10 parts of titanium dioxide, 10 parts of talcum powder, additives (30 m). Comp. Single layer: 79 parts of polypropylene 70 parts of 55 parts of Ex. 1 copolymer, 10 parts of titanium polypropylene polyethylene, 10 parts dioxide, 10 parts of talcum powder, copolymer, of polypropylene additives (300 m). 30 parts of copolymer, 25 parts of polyolefin ethylene copolymer, elastomer, 10 parts of titanium additives dioxide, additives (25 m) (25 m) Comp. Single layer: 75 parts of polypropylene 70 parts of 55 parts of Ex. 2 copolymer, 5 parts of polyolefin polypropylene polyethylene, 10 parts elastomer, 10 parts of titanium dioxide, copolymer, of polypropylene 10 parts of talcum powder, additives 30 parts of copolymer, 25 parts of (300 m). polyolefin ethylene copolymer, elastomer, 10 parts of titanium additives dioxide, additives (25 m) (25 m)

Method for Manufacturing a Photovoltaic Module:

[0069] A module stack was produced by laying the following in the specified order: a sheet of solar glass (1644*985 mm) SM from FSG, a sheet of EVA encapsulant (1644*985*0.45 mm) F406P from Hangzhou First, strings of photovoltaic cells, a second sheet of EVA encapsulant (1644*985*0.45 mm) F806P from Hangzhou First and a photovoltaic backsheet (1654*995 mm). Slits were first cut in the backsheet for electrical contact. The stack was consolidated in a solar module laminator: an SM Innotech Profilam 21-10, equipped with additional oil circulation system and pin lift system. The lamination protocol was 300 s evacuation and melting; 60 s pressure ramp up time; 600 s pressing/curing time at 800 mbar; 60 s pressure release time. A junction box was attached with sealant and an aluminium frame affixed to form a solar photovoltaic module.

Measurements

[0070] Glass transition temperature (T.sub.g) of the material of the sub-layer was measured by differential scanning calorimetry. A heating rate of 10K/minute was used. In Ex. 1, the T.sub.g of the first and third sublayers was approximately 20 C. and the T.sub.g of the second sub-layer was approximately 60 C. In Ex. 2, the T.sub.g of the first sublayer was approximately 20 C. and the T.sub.g of the second sub-layer was approximately 60 C.

[0071] The photovoltaic module was subjected to a thermal cycling test. Thermal cycling was carried out according to IEC 61215:2016, test MQT11 using Votsch VC.sup.3 7018 apparatus. The temperature was cycled between 40 C. and +85 C. with a dwell time of 10 minutes at each temperature. For TC200, 200 cycles were carried out. For TC400 and TC600, 400 and 600 cycles were carried out respectively. The results are presented in Table 2.

TABLE-US-00002 TABLE 2 Observation Observation Example above adjacent No. Test tabbing slit end Comp. TC200 Visible cracks Visible cracks Ex. 1 through through weather-resistant weather-resistant layer layer Comp. TC200 No visible cracks in No visible cracks in Ex. 2 TC400 external layer external layer Visible cracks Not inspected through weather-resistant layer Ex. 1 TC200, TC400, No visible cracks in No visible cracks in TC600 external layer external layer Ex. 2 TC200, TC400 No visible cracks in No visible cracks in external layer external layer

[0072] The backsheets of Ex. 1 and Ex 2. showed no visible cracks in the external layer, either above the tabbing or adjacent to the slit end after TC200, TC400 or (for Ex. 1) TC600. Conversely, Comp. Ex. 1 showed cracking through the weather-resistant layer at both of these locations after TC200. Comp. Ex. 2 showed cracking through the weather-resistant layer above the tabbing after TC400. This indicates an improvement by using a weather-resistant layer comprising three sub-layers, wherein the second sub-layer has a T.sub.g below 40 C. and a T.sub.g which is 40 C. lower than that of the first and third sub-layers.