PHOTOVOLTAIC MODULE WITH INCREASED RESISTANCE AGAINST POTENTIAL INDUCED DEGRADATION

Abstract

The present invention relates to a photovoltaic module comprising a protective front layer element, an encapsulation layer element, a photovoltaic cell element and a protective back layer element, whereby at least one of theprotective elements comprises glass; wherein the encapsulation layer element comprises a polymer composition (I) comprising at least the following components: (A) 90 to 99.8 wt.-% based on the overall weight of the polymer composition (I) of a polymer selected from a polyolefin elastomer or a polymer of ethylene (a) selected from (a1) a copolymer of ethylene which bears functional groups containing units; (a2) a copolymerof ethylene comprising one or more polar comonomer unit(s) selected from (C1-C6)-alkyl acrylate or (C1-C6)-alkyl (C1-C6)-alkyl acrylate comonomer units, and optionally bears functional groups containing units different from said polar comonomer unit(s); (a3) a copolymer of ethylene comprising one or more alpha-olefin comonomer unit(s); and optionally bears functional groups containing units different fromsaid polar comonomer unit(s) of polymer (a2); or mixtures thereof; and (b) silane group(s) containing units; (B) 0.2 to 10 wt.-% based on the overall weight of the polymer composition (I) of a copolymer of ethylene, which bears functional group containing units originating from at least one unsaturated carboxylic acid and/or its anhydrides, metal salts, esters, amides or imidesand mixtures thereof, whereby component (B) is different from component (A) Furthermore, the present invention refers to the use of an encapsulation layer element comprising polymer composition (I) according to the invention for increasing the Pmax determined after 96 h according to IEC 60904, by applying the foil method with a temperature of 85° C. and relative humidity of 60% and a potential differenceof 1500 V, of a photovoltaic module comprising besides the encapsulation layer element a protective front layer element, a photovoltaic cell element and a protective back element, whereby at least one of the protective elements comprises glass.

Claims

1. A photovoltaic module comprising a protective front layer element, an encapsulation layer element, a photovoltaic cell element and a protective back layer element, whereby at least one of the protective elements comprises glass; wherein the encapsulation layer element comprises a polymer composition (I) comprising at least the following components: (A) 90 to 99.8 wt. % based on the overall weight of the polymer composition (I) of a polymer selected from a polyolefin elastomer or a polymer of ethylene (a), wherein the polymer of ethylene (a) is selected from (a1) a copolymer of ethylene which bears functional groups containing units; (a2) a copolymer of ethylene comprising one or more polar comonomer unit(s) selected from (C1-C6)-alkyl acrylate or (C1-C6)-alkyl (C1-C6)-alkyl acrylate comonomer units, and optionally bears functional groups containing units different from said polar comonomer unit(s); (a3) a copolymer of ethylene comprising one or more alpha-olefin comonomer unit(s); and optionally bears functional groups containing units different from said polar comonomer unit(s) of polymer (a2); or mixtures thereof; and (b) silane group(s) containing units; (B) 0.2 to 10 wt. % based on the overall weight of the polymer composition (I) of a copolymer of ethylene, which bears functional group containing units originating from at least one unsaturated carboxylic acid and/or its anhydrides, metal salts, esters, amides or imides and mixtures thereof, whereby component (B) is different from component (A).

2. The photovoltaic module according to claim 1, wherein component (A) comprises (a1) a copolymer of ethylene which bears silane group(s) containing units (b) as functional groups containing units; or (a2) a copolymer of ethylene comprising one or more polar comonomer unit(s) selected from (C1-C6)-alkyl acrylate or (C1-C6)-alkyl (C1-C6)-alkyl acrylate comonomer units, and optionally bears silane group(s) containing units (b) as functional groups containing units different from said polar comonomer unit(s).

3. The photovoltaic module according to claim 1 wherein component (A) is different from a polyolefin elastomer.

4. The photovoltaic module according to claim 1, wherein component (B) is a copolymer of ethylene and a C.sub.4 to C.sub.10 alpha olefin comonomer; whereby said copolymer before introducing the functional group has (i) a density in the range of 850 kg/m.sup.3 to 920 kg/m.sup.3 measured according to ISO 1183; and/or (ii) an MFR.sub.2 in the range of 0.1 to 20.0 g/10 min measured according to ISO 1133 at 190° C. and a load of 2.16 kg.

5. The photovoltaic module according to claim 1, wherein the copolymer of ethylene for component (B) is a copolymer of ethylene and methyl acrylate or a copolymer of ethylene and butyl acrylate.

6. The photovoltaic module according to claim 1, wherein component (B) bears functional group containing units originating from a compound selected from the group consisting of maleic anhydride, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, fumaric acid anhydride, maleic acid, citraconic acid and mixtures thereof; and/or component (B) is obtained by copolymerising and/or grafting a copolymer of ethylene with a compound selected from the group consisting of maleic anhydride, acrylic acid, methacrylic acid, crotonic acid and mixtures thereof.

7. The photovoltaic module according to claim 1, wherein the content of the functional group containing units originating from unsaturated carboxylic acids or carboxyl acid anhydrides in component B) is in the range of 0.01 to 2.0 wt. %.

8. The photovoltaic module according to claim 1, wherein polymer composition (I) comprises at least one additive (C) selected from the group consisting of antioxidants, UV light stabilizers, metal deactivators, nucleating agents, clarifiers, optical brighteners, acid scavengers, slip agents, pigments, fillers and flame retardants, tackifiers, plasticisers, crosslinking agents, crosslinking boosters, wavelength-shifting agents and mixtures thereof.

9. The photovoltaic module according to claim 1, wherein the content of component (A) in polymer composition (I) is in the range of 95.0 to 99.5 wt. % based on the overall weight of the polymer composition (I); and/or the content of component (B) in polymer composition (I) is in the range of 0.5 to 5.0 wt. % based on the overall weight of the polymer composition (I).

10. The photovoltaic module according to claim 1, wherein the photovoltaic module comprises a front encapsulant layer element and rear encapsulant layer element, whereby at least one of these encapsulant layer elements comprises polymer composition (I) and/or polymer composition (I) is not cross-linked in the presence of a peroxide or a silanol condensation catalyst selected from carboxylates of tin, zinc, iron, lead or cobalt or aromatic organic sulphonic acids.

11. The photovoltaic module according to claim 1, wherein the protective front layer element is a rigid protective front layer element; and/or the protective back layer element is a rigid protective back layer element.

12. The photovoltaic module according to claim 1, wherein the protective back layer element is a polymeric backsheet.

13. The photovoltaic module according to claim 1, wherein the retained P.sub.max determined according to IEC 60904 of the photovoltaic module is above 95%.

14. The photovoltaic module according to claim 1, wherein polymer composition (I) comprises the following components: (A) 97 to 99 wt. % of a terpolymer of ethylene (a2) with methyl acrylate comonomer units and vinyl trimethoxysilane comonomer units; and (B) 1 to 3 wt. % of a copolymer of ethylene and 1-octene grafted with maleic acid anhydride having a density in the range of 860 to 880 kg/m.sup.3 measured according to ISO 1183 and a MFR.sub.2 in the range of 0.5 to 3 g/10 min measured according to ISO 1133 at 190° C. and a load of 2.16 kg.

15. Method for retaining the P.sub.max determined after 96 h according to IEC 60904 of a photovoltaic module comprising besides the encapsulation layer element comprising polymer composition (I) according to claim 1, a protective front layer element, a photovoltaic cell element and a protective back element, whereby at least one of the protective elements comprises glass, the method comprising the step of applying a foil method with a temperature of 85° C. and relative humidity of 60% and a potential difference of 1500 V.

16: Method of retaining the P.sub.max determined after 96 h according to IEC 60904 of a photovoltaic module comprising besides the encapsulation layer element comprising polymer composition (I) according to claim 14, a protective front layer element, a photovoltaic cell element and a protective back element, whereby at least one of the protective elements comprises glass, the method comprising the step of applying a foil method with a temperature of 85° C. and relative humidity of 60% and a potential difference of 1500.

17. The photovoltaic module according to claim 8, wherein the content of said additive (C) based on the overall weight of the polymer composition (I) is in the range of 0.0001 to 10 wt. %.

18. The photovoltaic module according to claim 1, wherein the content of said component (B) based on the overall weight of the polymer composition (I) is in the range of 1.0 to 3 wt. %.

19. The photovoltaic module according to claim 7, wherein the content of the functional group containing units originating from unsaturated carboxylic acids or carboxyl acid anhydrides in component B) is in the range of 0.02 to 1.5 wt. %.

20. The photovoltaic module according to claim 7, wherein the content of the functional group containing units originating from unsaturated carboxylic acids or carboxyl acid anhydrides in component B) is in the range of 0.20 to 1.0 wt. %.

Description

Preparation of Polymer 1

[0188] Copolymer of ethylene with methyl acrylate comonomer and with vinyl trimethoxysilane comonomer

[0189] The copolymer of ethylene with methyl acrylate comonomer and vinyl trimethoxysilane comonomer (polymer 1) was produced in a commercial high pressure tubular reactor at a pressure 2500-3000 bar and max temperature 250-300° C. using conventional peroxide initiatior. Ethylene monomer, methyl acrylate (MA) polar comonomer and vinyl trimethoxy silane (VTMS) comonomer were added to the reactor system in a conventional manner. Chain transfer agent was used to regulate melt flow rate as well known for a skilled person. After having the information of the property balance desired for the final polymer 1, the skilled person can control the process to obtain polymer 1. The amount of the vinyl trimethoxy silane units, VTMS, the amount of methyl acrylate, MA, and MFR.sub.2 are given in the Table 1.

[0190] The properties in Table 1 were measured from the polymer 1 as obtained from the reactor.

TABLE-US-00001 TABLE 1 Product properties of Polymer 1. Properties of the polymer obtained from the reactor Polymer 1 MFR.sub.2.16, g/10 min 4.5 Methyl acrylate content, mol % (wt %)  8.6 (22) Melt Temperature, ° C. 90 VTMS content, mol % (wt %) 0.38 (1.7) Density, kg/m.sup.3 946 SHI.sub.0.05/300, 150° C. 52

[0191] In above Table 1 and below MA denotes the content of Methyl Acrylatecomonomer present in the polymer and, respectively, VTMS content denotes the content of vinyl trimethoxy silane comonomer present in the polymer.

[0192] Polymer a (Copolymer of Ethylene with 1-Octene)

[0193] Queo™ 7007LA is an ethylene based 1-octene elastomer produced in a solution polymerization process using a metallocene catalyst with a MFR.sub.2 (2.16 kg, 190° C.) of 6.6 g/10 min and a density of 870 kg/m.sup.3 and is commercially available from Borealis AG, Austria.

Preparation of Polymer B (polymer A grafted with maleicanhydride)

[0194] The extruder used for the MAH-grafting was a Werner & Pfleiderer ZSK 30 co-rotating extruder with L/D of 38 with 12 barrels. The temperature control of the extruder barrels was divided into 6 control sections. Barrel 1 was the feeding section. Barrels 2&3, 5&6, 7&8, 9&10 15 and 11&12 share the same control loop in pairs and only took measurement from one barrel per pair. Barrel 4 was the only one with its own control loop. The barrels were heated with electrical heaters and cooled with closed loop water-glycol circulation if necessary, or were not cooled (in normal operation typically no cooling is necessary). In addition to the temperature measurements from the barrels, the melt temperature and pressure at the die 20 plate were also measured. The following temperatures of the different zones of the extruder as listed below were targeted for the examples:

[0195] Temperature Feeding zone [° C.]<40

[0196] Temperature Control zone 1 [° C.] 180

[0197] Temperature Control zone 2 [° C.] 200

[0198] Temperature Control zone 3 [° C.] 200

[0199] Temperature Control zone 4 [° C.] 200

[0200] Temperature Control zone 5 [° C.] 200

[0201] Temperature Control zone 6 [° C.] 200

[0202] Temperature die plate [° C.] 200 Queo 7007LA was grafted by adding various amounts of maleic anhydride (MAH).

[0203] The peroxide initiator (0.1 wt.-% POX-Perkadox 14S-fl, Akzo Nobel) was fed as a 10% isododecane solution.

[0204] A dry blend of Queo 7007LA and MAH was fed through the hopper into the feeding section of the extruder. The POX solution was fed into a side feeding entrance into the feeding section of the extruder. The screw speed was 200 rpm and the throughput was 8 kg/h.

[0205] The residence time was 60 seconds. This resulted in a content of grafted maleic anhydride grafting of 0.22 wt.-%, as determined by FTIR.

[0206] C. Manufacturing of PV Modules and Testing

Preparation of the polymer compositions for the encapsulation layers of photovoltaic modules 1 to 6

[0207] For the encapsulation layers of photovoltaic modules 1 and 2 only polymer 1 was used.

[0208] For the encapsulation layers of photovoltaic modules 3 and 4, 90 wt.-% of Polymer 1 and 10 wt.-% of polymer A was premixed prior to film extrusion.

[0209] For the encapsulation layers of photovoltaic modules 5 and 6, 88.5 wt.-% of Polymer 1 and 1.5 wt.-% of polymer B was premixed prior to film extrusion.

Preparation of the Encapsulation Layer Element

[0210] The encapsulation layer elements of the inventive and comparative examples, with dimensions of 995 mm width and 0.45 mm thickness were prepared in a Breyer CellProtect film line, using a melt temperature of 150° C. and at lines speeds of 20 mpm (meter per minute).

Preparation of the Photovoltaic Modules

[0211] PV Module Elements:

[0212] Protective front layer element: Glass layer, structured solar glass, soda-lime, low iron glass, supplied by Hemelaers Glas, length: 200 mm and width: 200 mm, total thickness of 3.2 mm.

[0213] Front and rear encapsulant element: films of the polymer compositions as described above, with same width and length dimensions as the protective front and back layer element, each had the total thickness of 0.45 mm.

[0214] PV cell element: 1 soldered bifacial solar cell, cell dimension 156*156 mm from LightWay Solar, pseudosquare, 5 busbars, total thickness of 200 micron.

[0215] Protective back layer element: Glass layer, structured solar glass, soda-lime, low iron glass, supplied by Hemelaers Glas, length: 200 mm and width: 200 mm, total thickness of 3.2 mm.

Preparation of PV Module (1-Cell Solar Module) Assembly for the Lamination

[0216] Two PV module assemblies were prepared for each encapsulation layer element as follows. The front protective glass element was cleaned with isopropanol before putting the first encapsulation layer element film on the solar glass. The solar glass element has the following dimensions: 200 mm×200 mm×3.2 mm (b*l*d). The front encapsulation layer element was cut in the same dimension as the solar glass element. After the front encapsulation layer element was put on the front protective glass element, then the soldered solar cell was put on the front encapsulation layer element. Further the rear encapsulation layer element was put on the obtained PV cell element and the back protective glass element was cleaned with isopropanol before it was put on said rear encapsulation layer element. The obtained PV module assembly was then subjected to a lamination process as described below.

[0217] Lamination Process of the Solar Modules:

[0218] Laminator: Incapcell 18-11, supplied by SM InnoTech GmbH.

[0219] Each PV module assembly sample was laminated in an Incapcell 18-11 laminator from SM InnoTech GmbH with a laminator temperature setting and pressure setting adapted to the encapsulation layer elements. The lamination settings are given in Table 2.

TABLE-US-00002 TABLE 2 Lamination settings for photovoltaic modules 1 to 6. Module 1 Module 2 Module 3 Module 4 Module 5 Module 6 Encapsulation Polymer 1 Polymer 1 Polymers 1 Polymers 1 Polymers 1 Polymers 1 layer elements & A & A & B & B Temperature, ° C. 165 165 165 165 165 165 Pressure, mbar 700 700 700 700 700 700 Total time of 1380 1380 1380 1380 1380 1380 steps, s

[0220] A 1-cell photovoltaic module prepared according to the lamination process as described above is shown in FIG. 1 illustrating the layer elements (separated) of the photovoltaic module, namely a protective front layer element (1), a front encapsulation layer element (2), a photovoltaic cell element (3), a rear encapsulation layer element (4) and a protective back layer element (5).

[0221] PID Testing

[0222] The 1-cell PV modules underwent PID stress testing according to the foil method as described in IEC62804-1: “Test methods for detection of potential-induced degradation of crystalline silicon photovoltaic (PV) modules”. The foil method was applied, with a temperature of 85° C. and relative humidity of 60% being the (controlled, stable) environmental stress conditions throughout the test duration, using a Vötsch climate chamber. A 1500 V potential difference was applied between the aluminium (Al) foils and the short-circuited solar cell. During PID stress, the solar cell was at a negative potential (−1500 V) with respect to the Al foils (0 V). Hence, driving positive charges towards the solar cell. The 1-cell modules laminates were put under bifacial PID stress, i.e. Al foils at high voltage difference to the solar cell attached to both the front and the rear SLG covers. The test duration for the PID-test was 96h.

[0223] Flash Test

[0224] The PV power loss under PID stress was quantified using a pv-tools LOANA PV analysis system for all 1-cell modules. All characterization measurements were conducted from both the front side and the rear side of the single-cell laminates using monofacial illumination and a black cloth underneath the laminate to reduce the reflected irradiance. The power output loss was calculated as the relative difference in P.sub.max before and after the 96h PID test. All IV-characterisation was done in accordance with the IEC 60904 standard.

TABLE-US-00003 TABLE 3 Retained power Pmax for modules 1 to 6. Module 1 Module 2 Module 3 Module 4 Module 5 Module 6 (CE1a) (CE1b) (CE2a) (CE2b) (IE1a) (IE1b) Encapsulation 100 wt.-% 100 wt.-% 90 wt.-% 90 wt.-% 98.5 wt.-% 98.5 wt.-% layer elements Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 1 10 wt.-% 10 wt.-% 1.5 wt.-% 1.5 wt.-% Polymer A Polymer A Polymer B Polymer B Retained P.sub.max 96 h 91.5 94.4 74.5 80.9 97.5 98.2 (front side) [%] .sup.a Retained P.sub.max 96 h 78.5 80.4 20.9 32.3 91.7 93.4 (back side) [%] a .sup.a average of 3 measurements

[0225] D. Discussion of the Results

[0226] From Table 3, it can be concluded that the photovoltaic modules including a front and rear encapsulation layer element comprising polymers 1 and B show only minor losses of P.sub.max after the PID test (IE1a and IE1b).

[0227] Surprisingly, the addition of polymer A to polymer 1 accelerates the PID of the modules, as is seen by the lower retained power for CE2a and CE2b, whereas the addition of polymer B-being the same base polymer, but grafted with maleic anhydride-to polymer 1 reduces the power drop compared to the modules having an encapsulant consisting solely of polymer 1 (see the comparison CE1a and CE1b with IE1a and IE1b). Further, the conclusion is valid both for the power retention on the front and the rear side of the bifacial module.