Title of invention -
Old Title;Use of Bi-Facial solar ceil with reflection grating for Photovoltaic Application
New Title : Bi-facial Solar Cell Module with reflection gratings
P102
Field of the Invention
This invention relates to a bi-facial solar cell module. Particularly this invention relates to bi-facial
solar cell module wherein reflection gratings are used for redirecting the incident light towards the
back face of the solar cells , thereby improving the overall cell efficiency.
Background of invention -
The average solar cell efficiency at present is around 17 %. This is because of substantial amount
of the incident solar radiation is lost as it passes through the gaps of the active substrate of the
solar cells in the module and substantial amount of the photons remain unutilized. This results in
lesser number of electron - hole pair generation and hence less power generation.
Presently there exists a trade-off between cost of manufacturing of the cells and efficiency. Cost
involved in producing energy using solar cell can be compensated if the efficiency of the solar cell
can be increased.
Presently different methods and different materials have been employed for such purpose.
Nowadays, another attempt is made to increase the incident ray collection efficiency by using
tandem solar cells. Total efficiency of the solar cell module can be improved by using bi-facial
solar cells . To utilize the bifacial cell effectively it is required to allow sun light fall on the both
side of the cell at the same time. Different methods have been employed to achieve this object to
but satisfactory result could not be achieve in production environment.
It is known to use holograms to reflect the light on to backside of the cell. The production of
these holograms is not a very user-friendly process and not satisfactory in making them at mass
production level.
US Patent US5538563 discloses bi-facial cells and the method being used in this invention is to
strike the rays on both side is different .In this patent reflector sheet has been used to reflect the
light to fall on the surface of the bi-facial Solar cell. The reflector sheet are mounted at a angle of
45 degree to the bi-facial cell and are at 90 deg to each other. However, there is further scope of
improvement in this area ,
Object of the Invention.
It is an object of the invention to provide an improved bi-directional solar cell module.
It is another object of the present invention to provide a solar cell module with diffraction gratings.

It Is yet another object of the present invention to a capture a wide spectrum of the incident solar ray.
It is yet further object of the invention to improve the efficiency of the solar cell module.
It Is another object of the invention to reduce the cost of generation of electricity from the solar cell module.
It is yet another object of the invention to provide a feasible and easily replicable solution to improve the efficiency of the solar panels.
Brief Description of the Accompanying Drawings
Fig 1 is a cross sectional view of an exemplary embodiment of the solar cell module containing the blazed reflection grating .
Fig 2 is an exploded view of an exemplary diffraction grating used in the present invention.
Summary of the Invention
Accordingly the present invention provides a solar cell module comprising bi-directional solar
cell array placed between the front transparent glass panel and back panel , said solar cell array
being operatively connected to a refractive grating disposed below the solar cell array to
redirect the residuary solar rays on the back surface of the said solar cell array, to Improve its
efficiency.
Preferably the said refractive grating is placed parallel to the solar cell array.
Said refractive grating may be made of blazed reflective material.
Said refractive grating may also be made of transparent material with metallic coating on its
reflective surface.
The metallic coating may be of Aluminium Oxide.
Preferably said solar cell array is multiple band gap solar cell array.
Said solar cell module is also hermetically sealed.
The refractive grating is capable of reflecting spectrum form infra-red to ultra-vlolet.
The present invention also provides a method of making a solar cell module as claimed in any of
the preceding claims comprising the steps of providing a bi-facial solar cell array;attaching a
suitable refractive grating to the said bi-facial refractive grating by injection molding; placing the
said solar cell array and refractive grating between the transparent front glass panel and suitable
back panel and hermetically sealing the module and providing for suitable electrical connections.

Detailed Description of the Invention
The present invention provides a feasible and easily replicable solution to improve the efficiency of the solar panels. The solar cell module design of the present invention causes the light to fall on both side of the bi-facial cell at the same time and the solar panel can be placed horizontally or at an angle.
The diffraction grating is an optical component used to spatially separate polychromatic light (white light) into its constituent optical frequencies. A typical diffraction grating consists of a substrate, usually of an "optical material", with large number of parallel grooves ruled or replicated in its surface and overcoated with a reflecting material such as aluminum. The quality and spacing of the grooves are crucial to the performance of the grating.
A reflection grating as shown in figure 2 has grooves ruled onto a reflective coating on a surface that may be plane or concave. It produces a spectrum extending from ultraviolet to infrared, since the light does not pass through the grating material.
As shown in figure 2 , light rays A and B, of wavelength A, incident on adjacent grooves at angle I to the grating normal are shown. Consider light at angle D to the grating normal; this light originates from the A and B rays as they strike the grating. The path difference between the Al and Bl rays can be seen to be:
a sin I + a sin D
Summing of the rays Al and Bl results in constructive interference if the path difference is equal to any integer multiple of the wavelength A:
a(sin I + sin D) = mA Where:
m = an integer, and is the order of diffraction a = distance between grating normals I = angle of incidence D = angle of diffraction A = wavelength of the incident beam
This design helps in capturing a wide range of spectrum of solar ray.

The present invention uses diffraction grating to reflect the sunlight onto the back side of the solar cell surface. The diffraction grating can be made of different transparent as well as reflective materials. The transparent material can be made reflective by metal deposition on its surface. The grating can be fabricated to reflect particular band of wavelength towards the back side of the solar cell array.
As shown in figure 1 the incident solar ray or photons , which do not fall on the front face of the solar cell substrate are reflected back on the back face of the solar cell substrate. The selection of photovoltaic material could be fabricated depending upon the wavelength diffracted by the shape of the grating. Thus different spectrum of light efficiently can be used. The bi-facial cells have the efficiency slightly less on back surface, as the light reflected from the grating will become less intense due to optical losses.
To obviate this problem multiple band gap solar cells is used in the present invention. The present invention provides for the combination of bi- facial solar cell with the reflection grating. These blazed gratings are molded through injection molding machines .The bi-faclal solar cell along with the reflection grating are hermetically sealed between the transparent front glass panel and back panel together at a distance so that they could not came into the contact with moisture directly. The sealed structure is used in a full panel and the shape of the panel would be preferably around 1 m x 1.3 meter. These bi- facial cells are normally available cell in the market. The novelty of the invention lies in using the bi-directional solar cell arrays operatively connected to these gratings so that they can be placed at flat surface too.
The optical phenomenon in reflection grating is that , diffraction & reflection both can be utilized and not only of reflection of the incident solar rays as disclosed in the US Patent 5538563. The incident rays are being diffracted in two directions +1 and -1 both from the grating. This is shown in figure 2 of the accompanying drawings. The reflection grating and the bi-facial Solar cell are adapted to be fixed parallel to each other in the present invention.
The inventive solar cell module of the present invention provides for increased efficiency of the solar cells and therefore it has industrial applicability.
The novel concept of the invention is in increasing the collection efficiency of the panel and use of wide spectrum of light. The present invention uses simple optics in order to get maximum collection of incident solar radiation. The efficiency of the system is increased and the cost of the system is reduced.
The instant invention has been described with the help of exemplary embodiments only . Various modifications and alterations can be thought of without departing from of the spirit and scope of the invention as defined in the appended claims.

We claim:
l.A solar cell module comprising bi-directional solar cell array placed between the front transparent glass panel and back panel , said solar cell array being operatively connected to a refractive grating disposed below the solar cell array to redirect the residuary solar rays on the back surface of the said solar cell array, to improve its efficiency.
2. A solar cell module as claimed in claim 1 , wherein the said refractive grating is placed parallel to the solar cell array.
3. A solar cell module as claimed in claim 1 and 2 , wherein said refractive grating is made of blazed reflective material.
4. A solar cell module as claimed in claim 1 and 2, said refractive grating is made of transparent material with metallic coating on its reflective surface.
5. A solar cell module as claimed in claim 4, wherein the metallic coating is of Aluminium Oxide.
6. A solar cell module as claimed in any preceding claim, wherein said solar cell array is multiple band gap solar cell array.
7. A solar cell module as claimed in any preceding claim , wherein the said solar cell module is hermetically sealed.
8 A solar cell module as claimed in any preceding claim , wherein said refractive grating is capable
of reflecting spectrum form infra-red to ultra-violet.
9. A method of making a solar cell module as claimed in any of the preceding claims comprising
the steps of:
— providing a bi-facial solar cell array;

- attaching a suitable refractive grating to the said bi-facial refractive grating by injection
molding;
-- placing the said solar cell array and refractive grating between the transparent front glass panel
and suitable back panel and hermetically sealing the module and providing for suitable electrical
connections.
Dated this the 21st day of February 2008