Photovoltaic module

Abstract

Described herein is a photovoltaic module, which includes PV cells capable of converting light incoming from a front side and from a rear side (3) and a transparent rear side including a rear surface carrying a structured layer (9), where the lower surface of the structured layer (9) is the lower surface of the module, and where the surface of layer (9) is structured by parallel V-shaped grooves of depth h2 or less than h2, where the lateral faces of the grooves of depth less than h2 form a groove angle beta and adjacent faces of neighbouring grooves form a peak of apex angle alpha, characterized in that h2 is from the range 5 to 200 micrometer, and each pair of neighbouring grooves includes one groove of depth h2 and one groove of depth (h2−h1), where h1 ranges from 0.1 h2 to 0.9 h2.

Claims

1. A photovoltaic module comprising one or more bifacial PV cells (3), which module comprises a front side and a rear side, wherein the front side is designed for receiving direct sunlight, and the rear side is made of a transparent material and comprises a rear surface carrying a structured layer (9), wherein the rear surface of the structured layer (9) forms the rear surface of the module's rear side or a fraction of said rear side and is structured by parallel V-shaped grooves, characterized in that each pair of neighbouring V-shaped grooves comprises one groove of depth h2 and one groove whose depth equals h2−h1, h2 is from the range 5 to 200 micrometer, h1 ranges from 0.1 times h2 to 0.9 times h2, and wherein the lateral faces of said grooves of depth h2−h1 form a groove angle beta and adjacent faces of neighbouring grooves form a peak of apex angle alpha.

2. The photovoltaic module of claim 1, wherein beta is larger than alpha.

3. The photovoltaic module according to claim 1, wherein the parallel V-shaped grooves of the structured layer (9) extend along the module's length intended for mounting parallel to the ground.

4. The photovoltaic module according to claim 1, which module comprises more than one bifacial PV cell and a gap area between said bifacial PV cells, and wherein the structured layer (9) covers at least 90% of the gap area between cells.

5. The photovoltaic module according claim 1, wherein the structured layer (9) comprises neighbouring grooves of depth h2 and of depth equaling h2−h1, wherein h1 ranges from 0.3 times h2 to 0.7 times h2.

6. The photovoltaic module according to claim 1 comprising a plurality of PV cells and a gap area between said bifacial PV cells, wherein the structured layer (9) covers the module's rear surface at least below said gap area.

7. The photovoltaic module according to claim 1, wherein the cells are embedded in an encapsulant (2) and positioned between a transparent front sheet (1) and a polymer film (10) and an optional rear plane (7), and wherein i) the structured layer (9) covers the polymer film (10), which stands in optical contact with the encapsulant (2) or, if present, the rear plane (7), or ii) the structured layer (9) directly covers the rear plane (7) in optical contact, where the module's rear plane is formed by the same material as the encapsulant (2) or is a glass sheet (7) or a polymer layer (7) in optical contact with the encapsulant (2).

8. The photovoltaic module according to claim 7, wherein, apart from the structured layer (9) and an optional adhesive layer, any further polymer film or layer, if present, is made from a thermoplastic polymer material.

9. The photovoltaic module according to claim 1, whose PV cells (3) are crystalline silicon cells.

10. The photovoltaic module according to claim 1, wherein the structured layer (9) comprises a resin cured by actinic radiation or an embossed polymer material.

11. A method for the manufacturing of a photovoltaic module comprising bifacial PV cells, a front side designed for receiving direct sunlight, and a rear side made of a transparent material, as described in claim 1, which method comprises the step of structuring the module's transparent rear side with parallel V-shaped grooves, characterized in that each pair of neighbouring V-shaped grooves comprises one groove of depth h2 and one groove whose depth equals h2−h1, wherein h2 is from the range 5 to 200 micrometer, and h1 ranges from 0.1 h2 to 0.9 h2, and wherein the adjacent lateral faces of grooves of depth h2−h1 form a groove angle beta, and adjacent faces of neighbouring grooves form a peak of apex angle alpha.

12. The method of claim 11, wherein the step of structuring the module's transparent rear side comprises (a) applying a transparent radiation curable resin layer to a polymer film, (b) structuring said radiation curable resin layer by imprinting with a suitably structured molding tool to obtain V-shaped grooves, (c) curing the structured layer obtained by irradiation, thus obtaining a polymer film comprising a structured and a non-structured side, and (d) applying the polymer film obtained in step (c) with its non-structured side to the back sheet (7), or directly applying said polymer film with its non-structured side onto the encapsulant (2), step (d) optionally comprising application of an adhesive.

13. The method of claim 11, wherein the step of structuring the module's transparent rear side comprises (a) applying a transparent radiation curable resin layer to a back sheet (7), (b) structuring said radiation curable resin layer by imprinting with a suitably structured molding tool to obtain V-shaped grooves, and (c) curing the structured layer obtained by irradiation.

14. A method of using the transparent structured layer (9) as described in claim 1, the method comprising using the transparent structured layer (9) on a rear surface of a photovoltaic module comprising bifacial PV cells for improving the module's energy gain.

15. The photovoltaic module of claim 1, wherein h2 is from the range 10 to 60 micrometer.

16. The photovoltaic module of claim 1, wherein h1 ranges from 0.1 times h2 to 0.8 times h2.

17. The photovoltaic module of claim 1, wherein beta is larger than 40°.

18. The photovoltaic module of claim 1, wherein both alpha and beta are from the range 40° to 120°.

19. The photovoltaic module of claim 1, wherein the structured layer (9) covers at least 90% of the surface of the module's rear side.

20. The photovoltaic module of claim 1, wherein h1 ranges from 0.4 times h2 to 0.7 times h2.

Description

EXAMPLES

(1) 1. Structured Layer on PV Module

(2) A structured layer is prepared utilizing a carrier foil (substrate) and a UV-curable coating in combination with an imprinting process. The substrate is in this case a PET-foil of 175 μm total thickness (Mitsubishi Hostaphan GN 175 CT 01B), which is primered on both sides. A UV-curable coating (based on an urethane acrylate, acrylate monomers, photoinitiators, and respective additives) is applied on the substrate and subsequently brought into contact with an imprinting tool bearing the negative structure of the desired final structure. The imprinting tool and the substrate are pressed against another in a way that the UV-curable coating fills the cavities of the imprinting tools negative structure. While the imprinting tool and the coated substrate are in contact, the coating is cured using UV-radiation. After curing, the imprinting tool and the coated substrate are separated, releasing the substrate with a cured, structured coating layer. During the whole imprinting process, the coating is in contact with the substrate.

(3) A layer consisting of parallel grooves of alternating depth of 20 micrometer (h2) and of 9 micrometer (h2−h1; “W-type cross section”) with groove angle 89° (beta) and apex angle 83° (alpha) is obtained as shown in FIG. 3; the base length (B) between two adjacent grooves of depth h2 is 50 micrometer.

(4) The PV module used is full sized comprising bifacial cells, front glass sheet, and polymer backside comprising the sealed cells without glass backsheet (as shown in FIG. 6), 1.68 m (x-axis intended for mounting parallel to the ground)×1.0 m (y-axis intended for mounting tilted to the ground), 60 cells of edge length 156 mm, gap between cells on each side 3 mm resulting in a relative cell area of 96.26% and a relative gap area of 3.74%. The substrate film containing the layer thus structured is applied to the back side of a photovoltaic (PV) module; the length of the structure (L) extends along the module's x-axis over the whole module width of 1.68 m.

(5) For the purpose of comparison, test modules are provided whose backside is covered by the PET substrate film alone (plane, unstructured backsheet), and further by PET substrate films carrying structured layers known from prior art (“V-type” cross section as of U.S. Pat. No. 4,235,643 with groove angle same as apex angle 110°).

(6) 2. Modelling

(7) Efficiency of the modules of Example 1 is simulated for the following conditions: For the module (including the structured backside layer), a constant refractive index of 1.5 is set, and a refractive index of 1 for the ambient atmosphere. The module is mounted with its y-axis tilted by 28.56° southwards and irradiated from its front side by a light source following the solar path over the year in Phoenix, Ariz., and from its backside by a light source of Lambert angular distribution simulating diffusive ground reflection. Both light sources are simulated providing light of 550 nm wavelength. Radiation reaching the cells after transmission through, or reflection by, the module's back sheet (following light paths as shown in FIG. 2, percentage of incident radiation after reflection or transmission by back sheet) is calculated using the software LightTools.

(8) (Synopsys, USA). Results for light paths II-IV shown in FIG. 2 are shown in the below Table 1; the calculations show that contributions by light path I are negligible for the present module construction (distance between lower cell surface and structured layer 9 from the range 300-500 micrometer).

(9) TABLE-US-00001 TABLE 1 Percentage of incident radiation reaching the solar cell via light paths II-IV for various module back sides Portion (%) in Light Path Backsheet structuring II III IV none (comparison) 5.5 0.5 91.8 “V-type” (comparison) 43.9 23.2 92.9 “W-Type” (invention) 68.4 19.7 94.2

(10) The software Wafer Ray Tracer (accessible at:

(11) https://www.2.pvlighthouse.com.au/calculators/wafer%20ray%20tracer/wafer%20ray %20 tracer.html) is used to calculate the fraction of radiation energy transmitted through or absorbed by a standard cell arrangement comprising: Embedding material EVA [Mcl09a], front film SiNx 75 nm PECVD [Bak11], substrate 200 micrometer Si crystalline 300 K [Gre08], rear film 100 nm SiO2 thermal [Pal85e]; wavelength range 300-1200 nm, wavelength interval 20 nm, 5000 rays per run, max total rays 50000, 1000 bounces per ray, intensity limit 0.01). Further considered are 3 typical types of PV cells (crystalline Si) differentiated by their surface morphology (planar, structured with micropyramids, and planar on backside with pyramid structuring on front side; typical dimensions of the micropyramids are 3.536 micrometer height, 54.74° apex angle, 5 micrometer width). The fraction of radiation energy transmitted by each type of cell (J-trans; i.e. source of radiation for light path II), as obtained from this calculation, is for cells with surface type (frontside-backside)

(12) planar-planar: 11%

(13) pyramid-planar: 2%

(14) pyramid-pyramid: 7%.

(15) For the contribution of light incident from the rear side onto the module (herein modelled as light path IV), a rear side irradiance of 20% of the front side irradiance is set, which is typically obtainable with an albedo of 60 to 70% depending on installation conditions.

(16) Summarizing the contributions from direct front side irradiation (not indicated in FIG. 2) and light paths II, III and IV for modules with structured back sides, and comparing with the corresponding result for the module with unstructured back side, yields the gain resulting from the structuring.

(17) Table 2 shows the gain (average energy collected over the day) obtained for PV modules with structured back side compared to the same module with planar (unstructured) back side for different types of cells.

(18) TABLE-US-00002 TABLE 2 Energy gain (%) relative to module with unstructured back side for various cell types gain for cell type (frontside - backside) Backsheet structuring planar-planar pyramid-planar pyramid-pyramid “V-type” (comparison) 5.5% 1.7% 3.5% “W-Type” (invention) 8.5% 2.3% 5.2%

(19) For each type of cell surface, the present “W-type” structuring leads to an improved energy output of the module.

BRIEF DESCRIPTION OF FIGURES

(20) FIG. 1: General functioning of a photovoltaic module comprising cells connected by a wiring (shown as black line) and embedded in a polymeric material (typically EVA), which are covered on top or on both sides with a protecting sheet (here shown as glass sheets). While larger fractions of the sunlight directly falling on the cells (B) is converted into electricity, light falling into the gap between cells (A), light partially transmitted through the cells (B) and light reflected from the ground towards the module's back side (C) often gets lost.

(21) FIG. 2 shows the cross section of the module with front plate (1, typically glass), PV cells (3), encapsulant (2, e.g. EVA), optional back plate (7, e.g. another glass plate) and a structured layer (9) on the back side. Light may be transmitted by the cell (path II) or strike the gap between cells (paths I and III) or enter the module by its transparent back side (path IV). Suitable structuring (9) may result in a reflection of light coming from the front side back towards the cell either directly (paths I and II) or after a further reflection on the front surface (path III), and may provide efficient entry of light from the rear side (path IV).

(22) FIG. 3 shows a 3-D view of the structured layer with “W” shaped cross section, which is to be applied to the module's back side according to the invention; the period (shown as base length B), denoting the smallest distance between two grooves of depth h2.

(23) FIG. 4 shows a cross section of a PV module of the invention, the optional substrate film (10) carrying the structured layer (9) on the whole back plate surface of the module back side.

(24) FIG. 5 shows a cross section of a PV module of the invention, the optional substrate film (10) carrying the structured layer (9) attached in certain regions of the back plate in order to cover the gap between the PV cells.

(25) FIG. 6 shows a cross section of a PV module of the invention, the optional substrate film (10) carrying the structured layer (9) on the whole surface of the module back side, which is formed by the encapsulant (2).

(26) FIG. 7 shows a schematic cross section of present “W” structured layer indicating lateral faces with small letters, where every 4th lateral face (e.g. a, e, i etc.; b, f, j etc.; c, g, k etc.) is oriented in parallel or about parallel direction, and further indicating peak angle alpha and groove angles beta and gamma at some occurrences. In a specific embodiment, every 2.sup.nd lateral face (e.g. a, c, e, g, i etc.; b, d, f, h, j etc.) stands parallel or about parallel to each other.

Abbreviations

(27) B period of present transparent structured layer (base length, FIG. 3)

(28) EVA poly(ethylene-vinyl acetate)

(29) PET poly(ethylene terephthalate)

(30) PV photovoltaic

(31) AM1.5 air mass 1.5 irradiance conditions

(32) HRI high refractive index

(33) Jsc short circuit current density (of PV module)

(34) TIR total internal reflection

(35) mu micrometer

Numerals

(36) (1) Transparent front sheet (also recalled as front plate) of PV module (2) Encapsulant material embedding the PV cells (3) PV cells (7) Optional Back plate (9) Transparent structured layer (invention or prior art) (10) Optional carrier film for structured layer (9)