Photovoltaic module

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.