Claims:WE CLAIM:

1. A solar photovoltaic system comprising of :
- a horizontal single axis tracker for tracking the sun from east to west through the day,
- a bifacial solar photovoltaic absorption module with potential to absorb additional sunlight on bottom surface, is mounted on the tracker, wherein direct solar radiation is absorbed on top surface of PV module, and
- a reflector module comprising of a pair of identical mirrors disposed on either side of module and along the outer contour of the PV module and at the level of tracking axis, thereby reflecting the direct normal solar irradiation (DNI) from the periphery of the module onto its bottom surface of the PV module which is mounted above the said mirrors.
characterized in that the bifacial PV module is mounted at a height above the axis of rotation of the tracker and the said two mirrors are flat mirrors and spaced away from each other with open space therein between.
2. The solar photovoltaic system as claimed in claim 1 wherein the reflector module is mounted below the solar module and at a height above the axis of rotation of the tracker.
3. The solar photovoltaic system as claimed in claim 1 wherein the reflector module is mounted below the solar module and at a height below the axis of rotation of the tracker.
4. The solar photovoltaic system as claimed in claim 1 wherein the PV module is mounted on the system along a horizontal plane parallel to the earth surface.
5. The solar photovoltaic system as claimed in claim 1 wherein the PV module is mounted on the system such that only top surface is facing the sun to receive direct normal solar irradiation on its top surface.
6. The solar photovoltaic system as claimed in claim 1 wherein the tracker is adapted to track from morning to evening of a day for angle + 45° to - 45° on a horizontal surface.
7. The solar photovoltaic system as claimed in claim 1 wherein the flat mirror is disposed at an angle with respect to PV module surface.
8. The solar photovoltaic system as claimed in claim 5 with respect to PV module surface wherein the flat mirrors are disposed below the PV module and at an angle which is either 13° or 26° with respect to PV module surface.
9. The solar photovoltaic system as claimed in claim 1 wherein the length of each of the two mirrors shall be same as that of length of the module.
10. The solar photovoltaic system as claimed in claim 1 wherein each mirror is adapted to reflect radiation onto a specific portion of the module width surface reflector.
11. The solar photovoltaic system as claimed in claim 8 wherein each mirror is adapted to reflect radiation atleast onto one half of the module width bottom surface reflector. , Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules 2003

COMPLETE SPECIFICATION
(SECTION 10 and Rule 13)

TITLE

“A TRACKING BIFACIAL SOLAR MODULES WITH MIRROR REFLECTORS”

A P P L I C A N T

We, LARSEN & TOUBRO LIMITED, an Indian Company incorporated under the Companies Act 1956, having its Principal place of business at Mount Poonamalle Road, Manapakkam, Post Box No.979, Chennai – 600 089, State of Tamil Nadu, India.

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION

A system with tracking bifacial solar modules and optical reflectors.

OBJECT OF INVENTION

The main objective of the system here is to a develop a configuration to enhance the rear surface generation of a bifacial module by using intentional reflection of solar radiation by optical reflectors along with the usage of diffused, ground reflected, sky diffused etc. components of the available solar radiation. The proposed system assimilates the benefits of horizontal single axis tracking, specular/non-specular reflectors and structural arrangement favoring optical geometry for enhancing the diffused radiation collection thus reducing the loss of generation and increasing the efficiency of bifacial module system in a single design.

PRIOR ART

Few prior art documents are discussed herein:-

D1 - CN103199745 A: Focus efficiency-increasing double-side solar photovoltaic power generation device

The document refers to a double-sided power generation device with two photovoltaic plates attached back-to-back, where the back side is illuminated with a single mirror that reflects light to the double sided PV arrangement.

Sr.No Feature Article Proposed System
1. Module Double-sided PV device with back-to-back PV panels

Usage of two PV panels

– one facing top and one facing bottom Bifacial PV modules
2. Structure arrangement Fixed system with reflective mirrors Horizontal single axis tracker with optical reflectors, which may be diffused or specular in nature
3. Reflector area Higher than module area (inferred from the drawing attached) Total width of optically reflecting surface (mirrors) in EW direction is proportional to total width of all modules in this direction. It can range from 50% - 100% of total width of all modules placed in EW direction.
Collective length of optically reflecting surface will be 0.5m to 1 m longer on southern end than length of all solar PV modules organized in NS direction.
4. Type of reflector Curved mirror Flat mirror
5. Concentration >1 times Structural arrangement and optical geometry does not permit concentration of light
6. Module to mirror
distance Not mentioned ~ 1 meter
7. Ground to module distance Not mentioned ~ 2 meters

D2- Research article ID 465837: Characterization of a bifacial photovoltaic panel integrated with external diffuse and semi-mirror type reflectors

An experimental set up for bifacial PV module characterization with a single external diffuse or semi-mirror reflector is discussed in this paper. The experiment aims to find the effect of using a semi-mirror reflector and a diffuse reflector to reflect light at the rear side of a bifacial module. The height of module mounting and angle of reflector/module mounting for the best performance were also empirically determined.

Sr.No Feature Article Proposed System
1. Module 4 cell bifacial PV module (experimental set-up from Hitachi) Usage of commercially available bifacial PV modules
2. Structure arrangement Fixed system Horizontal single axis tracker
3. Reflector area Equal to the module area Total width of optically reflecting surface (mirrors) in EW direction is proportional to total width of all modules in this direction. It can range from 50% - 100% of total width of all modules placed in EW direction.
Collective length of optically reflecting surface will be 0.5m to 1 m longer on southern end than length of all solar PV modules organized in NS direction.
4. Type of reflector Flat semi-mirror and diffuse reflectors mounted parallel to the module Flat mirror
5. Concentration ~ 1 times Structural arrangement and optical geometry does not permit concentration of light
6. Module to mirror distance To be determined experimentally ~ 1 meter
7. Ground to module distance To be determined experimentally ~ 2 meters

D3- Bifacial dye-sensitized solar cells: A strategy to enhance overall efficiency based on transparent polyaniline electrode

This publication discusses on the development of dye-sensitized bifacial solar cells with the use of transparent polyaniline electrode and using mirrors to reflect radiation to the back face of such cells.

Sr.No Feature Article Proposed System
1. Purpose To enhance efficiency by incorporating transparent polyaniline back electrode in the module To enhance the efficiency of a bifacial module by developing a concept to increase the rear surface generation
2. Module Dye-sensitized bifacial solar cells with polyaniline transparent back electrode Commercially available bifacial PV modules
3. Structure arrangement Fixed system Horizontal single axis tracker
4. Reflector area Not mentioned Total width of optically reflecting surface (mirrors) in EW direction is proportional to total width of all modules in this direction. It can range from 50% - 100% of total width of all modules placed in EW direction.
Collective length of optically reflecting surface will be 0.5m to 1 m longer on southern end than length of all solar PV modules organized in NS direction.
5. Type of reflector Mirror Flat mirror
6. Concentration ~ 1 times Structural arrangement and optical geometry does not permit concentration of light
7. Module to mirror distance Not mentioned ~ 1 meter
8. Ground to module distance Not mentioned ~ 2 meters

D4 - Photo-voltaic Trackers:

This article discusses tracker technologies for PV application including a tracker system for bifacial PV modules from Poulek Solar. In this system, bifacial modules are mounted on a polar axis tracker with 2X reflectors fixed along the tracking axis to illuminate lower surface of the bifacial module and compensate for the loss of diffuse radiation at the rear surface.

Sr.No Feature Article Proposed System
1. Module Commercially available bifacial modules Commercially available bifacial PV modules
2. Structure arrangement Polar axis tracker with reflecting mirrors Horizontal single axis tracker
3. Reflector area Greater than the module area Total width of optically reflecting surface (mirrors) in EW direction is proportional to total width of all modules in this direction. It can range from 50% - 100% of total width of all modules placed in EW direction.
Collective length of optically reflecting surface will be 0.5m to 1 m longer on southern end than length of all solar PV modules organized in NS direction.
4. Type of reflector Flat mirrors arranged to form a parabolic reflecting surface Flat mirror
5. Concentration > 1 times Structural arrangement and optical geometry does not permit concentration of light.
6. Module to mirror distance No data available ~ 1 meter
7. Ground to module distance No data available ~ 2 meters

SUMMARY OF INVENTION

Sr.No Salient Feature Parameter Remarks
1. Purpose To enhance the efficiency of a bifacial module by developing a concept to increase the rear surface generation
2. Module Commercially available bifacial solar PV modules
3. Structure arrangement Horizontal single axis tracker with mirror reflector To maximizes the energy collection by the module by diverting solar radiation available between two rows of trackers via reflection on the rear surface of the PV modules with help of specular / diffuse reflector affixed on the tracker. structure.
4. Concentration Maximum 1 times To limit the operating
parameters of the module within its certified limits. Structural design and optical geometry does not permit any concentration.

5. Type of reflector Flat mirrors Designed to keep the concentration below 1 X (times) by reflection using flat mirror (no concentration)
6. Reflector area Lower than module area Total width of optically reflecting surface (mirrors) in EW direction is proportional to total width of all modules in this direction. It can range from 50% - 100% of total width of all modules placed in EW direction.
Collective length of optically reflecting surface will be 0.5m to 1 m longer on southern end than length of all solar PV modules organized in NS direction.
7. Module to mirror distance ~ 1 meter To optimize the mirror length for optimum collection of total solar radiation available between two rows of tracker while avoiding shading due to structural elements to maximum possible extent.
8. Ground to module distance
~ 2 meters Provision to accommodate more diffused and ground reflected radiation incident on the rear surface of the module and also to compensate for the deficiency
generated due to reduced mirror area and mirror efficiency

DESCRIPTION OF INVENTION

Solar photovoltaic module, are used to generate electricity from sunlight by using technologies based on crystalline silicon and thin film semiconductors. These technologies have only one surface to absorb sunlight and convert it to electricity. With the improvement in solar photovoltaic module technology, the solar modules are able to generate electricity from both the surfaces known bifacial solar module. This module comprises of photovoltaic cells, which can generate electricity from both top and bottom surface. These cells are connected in series to provide the output power based on the cell efficiency.

Purpose:

The proposed system aims to increase the generation of electricity by diverting available solar radiation available between rows of modules with the help of optical reflectors which are optimally sized and positioned and connected with module stracture. The arrangement thereby increases the amount of radiation absorbed by the bottom surface of a bifacial solar photovoltaic module , which otherwise depends on nature for unintentional feeble radiation reflected from the ground to generate electricity. With this arrangement the electricity generated will be significantly higher compared to a system without the mirror reflectors.

Uniqueness:

The system uses bifacial modules mounted on a horizontal single axis tracker which tracks the sun from east to west through the day. To increase the light incident on the back surface of the bifacial module, two identical optical reflectors are mounted symmetrically along the outer contour of the module at the level of the tracking axis, which reflect DNI from the periphery of the module to its back surface. The tracking system and reflectors together enhance the collection of direct normal incidence at both surfaces of the module.

Total width of optically reflecting surface (mirrors) in EW direction is proportional to total width of all modules in this direction. It can range from 50% - 100% of total width of all modules placed in EW direction.

Collective length of optically reflecting surface will be 0.5m to 1 m longer on southern end than length of all solar PV modules organized in NS direction. Further, they are designed to limit the concentration less than 1Xand its reflectivity coefficient considered as 0.9. Thus only about 80% of the DNI can be made available at the back surface with respect to the front surface, where the incoming solar radiation is directly incident. To compensate for this drop in the DNI availability and to increase the collection of diffused radiation at the back side, the bifacial module is mounted at a height of around 1m from the axis of tracking. Space between the two mirrors is intentionally left vacant to increase the collection of ground reflected radiation and to reduce the wind load on the structure. Convergence of all the above features makes this system unique and improves the overall techno-commercial performance of a bifacial PV module over any existing system.

System:

The module is to be mounted on horizontal plane parallel to the earth surface. At any point of time only one surface of the module can be kept facing the sun. To utilize the capability of the bifacial module to generate from both the surface, the system uses a set of flat mirrors with reflective surface that will facilitate in directing the solar radiation to the back surface of the module. To maximize the power generated in a day the structure will track the sun over the day from east to west direction on the horizontal plane of the earth surface. The bifacial module will receive the solar radiation directly from the sun on the front surface and reflected radiation on the back surface from the flat mirror reflector. Individual components like the module, flat mirror reflectors and structural members will be fixed but structure as a whole will be tracking from morning to evening for angle +45o to -45o on the horizontal surface.

Arrangements:

In one aspect of the invention, the bifacial photovoltaic module will be mounted on a horizontal single axis tracker. These modules will be mounted at around 1 meter height from the axis of rotation of the tracker. The flat mirror reflectors will be mounted at an angle of 13o with the module’s surface. The space beneath the bifacial module will be open without any mirror reflectors. The reflective mirrors will be mounted at the exterior area of the structure corresponding to the outer periphery of the bifacial module. The mirror reflectors will be around 450 millimeter in width and the length will be same as that of the module length. The flat mirrors reflectors will be mounted on both the sides of the structure at the level of the tracking axis. Each flat mirror reflector will reflect the radiation to half of the module width. This arrangement will provide the requisite symmetry & stability for the structure.

This arrangement is best suited for landscope mode.

In another aspect the bifacial photovoltaic module will be mounted on a horizontal single axis tracker. These modules will be mounted at around at a certain height which is above the axis of rotation of the tracker.

The flat mirror reflector will be mounted at an angle of 13° or 26° with the tracker. The reflectors can have width in the range of 1m to 1.5m and its length will be same as that of module length. This arrangement is suited for landscape and portrait mode.

The two aspects differ in the arrangement that in the first aspect the solar module is above the axis of rotation of the tracker and so also the reflector positioned above the axis of rotation of the tracker. However in the second aspect the solar module is above the axis of rotation of the tracker but the reflector is positioned below the level of the axis of the rotation of the tracker.

In both aspects however the solar module is essentially above the axis of the rotation of tracker and variance is limited to alternatively arranging the reflector either above or below the axis of rotation of the tracker. Further the ground to module distance in first aspect is around 1 m whereas the ground to module in second aspect is around 2.3 m to 2.5m. In the second aspect the account of error in reflected ray angle in between -5° to +5°. Moreover the CG balancing of the system is improved in the arrangement as per second aspect. This illustrated in Fig II.

The description and embodiments have been provided merely for the purpose of understanding and these shall not limit the scope of the invention. All variations and modifications that can be thought of by the skilled person is well within the scope of this invention.