FIELD OF THE INVENTION
This invention relates to solar photovoltaic modules used in construction sector. More particularly, the invention relates to a building-integrated photovoltaic module to accommodate solar cells for generating solar power.
BACKGROUND OF THE INVENTION
A photovoltaic module is a container for a plurality of solar cells to provide a mechanical support, high solidity, protection of active materials from weathering, humidity, shocks and mechanical load. Manufacturing cost of photovoltaic modules represents inan average at least 30 to 35% of the final cost.
The design of a module structure is made basically considering the main functions of the solar module within the crystalline solar cells technology, which inter alia constitute:
(i) to provide a mechanical support, wherein a minimal stiffness prevents any strain in the solar cells,
(ii) to fix, isolate and seal the solar cell assembly, for preventing any displacement and any moisture ingress or mechanical shock,
(iii) offer an electrical interface to the user by the means of junction box equipped with electrical connectors.

(iv) to offer a mechanical interface for mounting.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a building-integrated photovoltaic module to accommodate crystalline silicon solar cells for generating solar power.
Another object of the invention is to propose a method of producing photovoltaic module to accommodate crystalline silicon cells.
A still another object of the invention is to propose a building-integrated photovoltaic module to accommodate crystalline silicon solar cells for generating solar power, which is enabled to provide mechanical support to the solar cells including protection from environmental hazards.
SUMMARY OF THE INVENTION
According to the invention, a solution for realiZing a building-integrated solar module using crystalline silicon solar cells as well as a method for fabricating the same is proposed. A thin galvanized steelsheet is used as module mechanical support. For the protection against weather, humidity and any mechanical impact or load a defined stack of films and coatings is used. The final product is a galvanized sheet that is used as a roof and as a solar photovoltaic module.

The inventive method for fabricating the photovoltaic module comprises the steps of:
(i) a hardened glass layer, with a thickness lying between 3.2 and 2.8 mm [2], provide the needed stiffness and is used as a front sheet,
(ii) a set of polymeric materials forms an encapsulation stack, an important number of polymers families can be used with different advantages [3], the choice of materials is to be developed below, the back sheet is usually a stack of polymer materials forming a barrier to the outside [3][4][5], or a second glass layer can be used, edge sealing is realized either by an edge sealant or through the use of a high adhesion encapsultant [6].
(iii) the electrical connection is made at the back side of the module
with a junction box glued and sealed with polymer materials, or is placed at the edge in the case of glass-glass structure,
(iv) a mechanical interface is realized by framing the module with
anodized aluminium in the first module configuration or through the use of clamps in the case of a glass-glass structure.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a conceptual view of a photovoltaic module.
Figure 2 - shows a photovoltaic module according to the invention.
Figure 3(a) - shows a prior art photovoltaic module in particular an anodized-aluminium frame module.
Figure 3(b) - shows another prior art photovoltaic module constituting a glass-glass frameless module.
BRIEF DESCRIPTION OF THE INVENTION
Two standard designs are represented in Figure 3 - Standard Photovoltaic modules designs. On the left, anodized-aluminium framed modules (figure 3a), on the right the glass-glass frameless design, Figure 3(b).
According to the invention, the selection of materials for the inventive photovoltaic module is made with the considerations that the selected material must participate in the loss reductions in solar energy photovoltaic conversion by three means: (i) module fill-factor improvement, (ii) optical losses reduction with clear materials at the front and, (III) module performance ratio increase by evacuating the generated heat in the solar cells1.

The module fill-factor is enhanced by reducing the serial and parallel resistance of the same, that is to say by improving the interconnection design. The use of high quality ribbons is essential, and the contact quality can be improved by a better freezing of the cells in the encapsultant matrix. A high bulk resistivity of back side materials is also needed for reducing leakage currents.
The optical losses reduction occurs by the use of highly clear materials on the front side, highly reflective materials at the back side and by minimizing reflectivity of the stack. The usual material used in front side is glass, but f1uoropolymer films over perform in terms of optical behaviour [5]. Front encapsultant is usually chosen between [3][7:: EVA (Ethylene - Vinylacetate), PVB (Poly Vinyl Butyral), Ionomer (containing Na and Zn ions). Silicone such as PDMS (Polydimethyl Silicone) or thermoplastic polyolefines (TPO) and equivalent polymers. For the back side, the same kinds of polymers are used, through with different formulations for increasing reflectivity.
Heat exchanges must be enhanced in order to evacuate the heat absorbed in the solar cells and reduce their internal temperature. For standard modules, air flow at the backside promotes convection and heat exchange.
ThePhotovoltaic module of the present invention comprises of the following components:
(i) A back layer constituted most preferably by a polymer coating haVing the following properties: high electrical resistivity, good thermal conductivity, high adhesion properties to galvanized steel. Spray coating, roller coating or bar coating are possible deposition processes.

(ii) The coating on steel or galvanized steel is applied as described in the Tata Steel patent WO/2012/048888. The polyetherimide coated back sheet offers properties like high electrical resistivity, good thermal conductivity, high adhesion properties to galvanized steel.
(iii)The photovoltaic module is part of the roofing substrate preferably steel
(iv) Edge sealing with PIS material to avoid ingress of the moisture
(v) Module is encapsulated from front side compared to conventional back side encapsulation.
As shown in figure 2, the inventive module is configured as under:
(i) The mechanical support of the module is selected as a galvanized steel sheet of 0.450 mm thickness. Another function of the module is to be a roof for building-solution, enabling a real and complete building-integrated photovoltaic solution.
(ii) Most preferably glass can be used as a front layer for its protective properties, with the possibility of reducing its thickness compared to the standards values, as stiffness is then shared between glass and steel.
(iii) Most preferably, no glass is used in front layer, but only a polymer protective film, which is laminated, if the state of stress in the solar cells is lower than the maximum allowed value.

(iv) Front encapsulation materials used are the standards materials such as EVA, PVB, and silicone or Ionomer polymers. Depending on the choice of the materials the process is to be adapted. Most preferably standard lamination, of the above mentioned materials, (autoclave or not) is to be performed.
(v) The back layer is constituted most preferably by a polymer coating having the following properties: high electrical resistivity, good thermal conductivity, high adhesion properties to galvanized steel. Spray coating, roller coating or bar coating are possible deposition processes. The coating on steel or galvanized steel is applied as described in the Tata Steel Patent WO/2012/048888. The polyetherimide coated back sheet offers properties like high electrical resistivity, good thermal conductivity, high adhesion properties to galvanized steel.
(vi) Electrical interconnection of solar cells is realized by standard soldering of plated copper strips.
(vii) Cells are most preferably cut in small parts so that the width is the actual wafer width while the length is reduced to between one and three em. Cut solar cells are however all interconnected in series in order to forma solar PV generator.
(Viii) Standard size solar cells can be also assembled in the solar array.

(ix) Edge sealing is realized by the use of a standard commercial butyl rubber, from the family of Poly Isobutylene for preventing moisture ingress from the edge.
(x) A hole in the galvanized sheet is made for a backside junction box. Sealing is realized with the standard process.
(xi) The module area is smaller than the galvanized sheet area allowing to using the uncovered area of the same for its roofing function. The side of the sheet must be corrugated for allowing overlapping and cladding with neighbouring galvanized corrugated steel roofing sheets.
Although galvanized is described with steel substrate but is not limited to steel substrate only. The invention is compatible with mild steel, galvanized steel, galfan, Ni-coated sheet, Tin coated Steel, C-coated steel.
The advantage of the present invention is that it is using coated substrate which has very good properties of adhesion, corrosion resistance, and thermal barriers. Another advantage of the invention is that module is an integrated part of the roofing steel/substrate. Another advantage of the invention is doing away with the heed of mounting structure and hence further reducing the costs. Still another advantage of the invention is transferring the module stiffening function from a 2.8 to 3.2mm thick glass layer to a roofing galvanized steel sheet. The applied coating on the back sheet is not expensive compared to conventional encapsultants. Also, through a back-side junction box and full building-integrated photovoltaic concept, all electrical equipments are already located inside the house.

REFERENCES
[1] ISA-NMCC, "Study on Solar Photovoltaic Industry"" Bangalore, 2008.
[2] PV Group - SEMI, "Internaiional Technology Roadmap for Photovoltaics (ITRPV)," 2011.
[3] M. Kempe, "Overview of Scientific Issues Involved in Selection of Polymers For PV Applications," in 37th IEEE Photovoltaic Specialists Conference (PVSC 37), Seattle,Washington, June 19-24, 2011.
[4] G Jorgensen, K. Terwiliiger, S. Glick and T. McMahon, "Materials Testing for PV Module Encapsulation," National Center for Photovoltaic, 1617 Cole Blvd., Golden, CO 80401 USA, 2003.
[5] M. DeBergalis, "Fluoropolymer Films in the Photovoltaic Industry"" Journal of Fluorine Chemistry. Vol. 125, pp. 1255-1257, 2004.
[6] M. Kempe, A.A. Dameron, T. J. Moricone and M. O. Reese, "Evaluation and Modelling of Edge-Seal Materials for Photovoltaic Applications," National ' Renewable Energy Laboratory, Golden, USA, 2011.
[7] M. Osborne, "Trends and developments in the Lamination Process of PV Modules (Part 1)," Photovoltaics Internationa,, vol. 5th Edition, pp.160-164.

WE CLAIM:
1. A building integrated photovoltaic module accommodating multiple solar cells for generating solar power, comprising :-
- a plurality of solar cells electrically interconnected in series by soldering of plated copper strips to form a solar photovoltaic (PV) generator;
- a front layer made of either glass on a polymer protective film duly laminated;
- a back layer constituting a polymer coating;
- a mechanical support integrated to the roof of the building and formed of a metal sheet such as a galvanized sheet;
- a front encapsulation provided through lamination of one of EVA, PVB, Silicon or Ionomer polymers;
- an edge sealing realized by using a standard commercial butyl rubber to prevent ingress of moisture; and
- a junction box provided at backside connected to the module via a hole configured on the mechanical support.