Patent Application
20090025778
1. Field of Invention
This invention relates to photovoltaic (PV) cells, in particular, protecting a PV cell and/or PV module against overheating caused by shading or other light obstruction to a PV cell when used as one of a plurality of series-connected PV cells in a PV module.
2. Description of Related Art
A typical PV cell comprises semiconductor material with at least one p-n junction and front and back side surfaces equipped with current collecting electrodes. When illuminated, the cell generates a voltage of approximately 0.6-0.62 V and an electric current of about 34 mA/cm2. A plurality of PV cells may be electrically connected in series and/or in parallel arrays to form PV modules that produce higher voltages and/or higher currents. A PV module only performs at optimal efficiency when all the series-connected PV cells are illuminated with approximately similar light intensity. However, if even one PV cell within the module is shaded, while all other cells are illuminated, the overall efficiency of the entire PV module is strongly affected, resulting in a substantial decrease in power output from the PV module.
It was demonstrated in “Numerical Simulation of Photovoltaic Generators with Shaded Cells,” V. Quaschning and R. Hanitsch, 30th Universities Power Engineering Conference, Greenwich, Sep. 5-7, 1995, p.p. 583-586 that PV modules comprised of 36 PV cells can lose up to about 70% of their potential power when as little as 75% of one PV cell of the module is shaded. In addition, the module may be permanently damaged as a result of cell shading.
When a PV cell in a module of series-connected PV cells is shaded, the shaded cell acts as a resistor rather than as a power source. Heating of the shaded cell due to current flow through the resistance of the shaded cell may result in the cell reaching temperatures of 160° C. or higher. These high temperatures may eventually damage the shaded PV cell and destroy the entire PV module.
In order to reduce the problems that can result from shading, practically all conventional PV modules employ bypass diodes that allow current from neighbouring strings to bypass strings containing shaded cells. While power generated by the non-shaded cells in the bypassed string is completely lost, the use of bypass diodes allows the rest of the module to continue producing power and reduces heating of the shaded cell. It is also known to bypass individual cells rather than strings of cells. While bypassing individual cells has been known for many years, and several patents have been issued, several economical and technical problems have impeded the introduction of a practical industrial solution. Generally most solutions employ similar principles in that generally a bypass diode is connected to a PV cell in the opposing direction to the solar cell it protects so that when the solar cell is reverse-biased, the associated bypass diode begins to conduct. This interconnection may employ electrical conductors which connect the diode terminals to the cell terminals or the bypass diode may be directly integrated with the PV cell during fabrication using microelectronics techniques and equipment. Generally, to date, the primary focus of research in this area appears to be to minimize the thickness and area of the bypass diode in order to minimize PV cell breakage during PV module lamination.
U.S. Pat. No. 6,184,458 B1, entitled Photovoltaic Element and Production Method Therefor, to Murakami et al. describes a PV element formed by depositing a photovoltaic element and a thin film bypass diode on the same substrate whereby the bypass diode does not reduce the effective area of the PV element because it is formed under a screen printed current collecting electrode. The production of such cells is complicated and requires precision alignment between the screen printed current collecting electrode and the bypass diode portion. Furthermore the techniques disclosed would not be practical for modern high efficient crystalline silicon PV cells because thin film bypass diodes can not withstand high currents such as about 8.5 A which is a typical current value in a high efficiency 6 inch cell. Furthermore, there appears to be no regard for dissipation of heat that is generated in the bypass diode which could cause overheating and eventually cause the diode to fail and may possibly lead to the destruction of the PV cell and the PV module.
U.S. Pat. No. 5,616,185, 1997, entitled Solar Cell with Integrated Bypass Diode and Method to Kukulka describes an integrated solar cell bypass diode assembly that involves forming at least one recess in a back (non-illuminated) side of a solar cell and placing discrete low-profile bypass diodes in respective recesses so that each bypass diode is approximately coplanar with the back side of the solar cell. The production methods described are complicated and require precision grooves to be cut in the solar cell. The grooves can make the solar cell fragile, increasing cell breakage and yield losses. Again, the techniques described in this reference would not be practical for modern high efficient crystalline silicon PV cells because thin film bypass diodes generally can not withstand the high currents typically found with such cells, or the resultant heating caused by such high currents.
U.S. Pat. No. 6,384,313 B2, 2002, entitled Solar Cell Module and Method of Producing the Same to Nakagawa, et al. describes a method of forming a light-receiving portion of a solar cell element and a bypass diode on the same side of the substrate on which the solar cell is formed. A solar cell with these features allows for series connection of a plurality of solar cell units from only one side of the substrate.
U.S. Pat. No. 5,223,044 1993 entitled Solar Cell Having a By-Pass Diode, to Masahito Asai provides a solar cell having only two terminals and an integrated bypass diode formed on a common semiconductor substrate on which the solar cell is formed. Again, the techniques described in the above two patents require complicated and costly microelectronic technological approaches not easily incorporated into a production line and the bypass diodes created would likely not be able to withstand the high current and resulting heat that can occur when the bypass diode is required to conduct current.
U.S. Pat. No. 6,784,358 B2, 2004, entitled Solar Cell Structure Utilizing and Amorphous Silicon Discrete By-Pass Diode, to Kukulka describes a solar cell structure with protection against reverse-bias damage. The protection employs a discrete amorphous silicon bypass diode with a thickness that does not exceed 2-3 microns so that it protrudes from a surface of the solar cell by only a small distance and does not protrude from the sides of the solar cell. The terminals of the amorphous semiconductor bypass diode are electrically connected by soldering, to corresponding sides of an active semiconductor structure. The soldering of such extremely thin and fragile diodes to the active semiconductor substrate requires extreme accuracy in order to avoid diode breakage. In addition, the amorphous semiconductor bypass diode cannot withstand the high currents and resulting temperatures that can occur in crystalline silicon solar cell systems.
U.S. Pat. No. 5,330,583 entitled Solar Battery Module to Asai, et al. describes a solar battery module that includes interconnectors for series-connecting a plurality of solar battery cells, and one or more bypass diodes which allow output currents of the cells to be bypassed with respect to one or more cells. Each diode is a chip-shaped thin diode and is attached on an electrode of a cell or between interconnectors. More particularly, the chip-shaped bypass diodes are either connected to a front surface of the solar battery or are positioned to the side of a solar battery or are connected to rear surface of a solar battery to protect a string of solar batteries. When the bypass diodes are connected to the front surface, they are soldered directly to one of two parallel conductors which appear to be bus bars, on the front surface of the solar cell. Generally in solar cell design it is an objective to keep the front face of the solar cell clear to keep shading of the front surface to a minimum. Current collecting fingers and bus bars connected to the fingers to gather current from the solar cell are usually the only things acceptable to occlude the front surface, due to their necessity. Generally, fingers and bus bars have width and length dimensions that keep the area they occupy on the front surface to a minimum. Therefore bus bars typically have a narrow width and as a result, the bypass diodes of Asai are necessarily small in width. Although bypass diodes with such a small width and length may be able to carry relatively large currents, due to their small area they tend to heat up due to current flow and impose a localized extreme heat source on the solar cell to which they are mounted.
In accordance with one aspect of the invention, there is provided a shading protected solar cell apparatus for use in a solar cell system. The apparatus includes a solar cell having a front side current collector and a back side current collector. The apparatus also includes a bypass diode closely adjacent the back side current collector, the bypass diode having a front side current collector and a back side current collector. The apparatus further includes a first electrical coupling for electrically coupling the front side current collector of the bypass diode to the back side current collector of the solar cell. The apparatus also includes a second electrical coupling for electrically coupling the back side current collector of the bypass diode to the front side current collector of the solar cell, the first and second electrical couplings cooperating to enable a current generated by non-shaded solar cells in the system to be shunted through the bypass diode when the solar cell is shaded. The apparatus further includes a thermal coupling thermally coupling the bypass diode to a back side of the solar cell such that heat generated in the bypass diode due to current shunted through the bypass diode is dissipated by the solar cell sufficiently to avoid burning the solar cell or the bypass diode when the solar cell is shaded.
The bypass diode may include a silicon wafer fragment, the front and back sides of the bypass diode being on opposite sides of the silicon wafer fragment.
The front side current collector of the bypass diode may be generally planar.
The silicon wafer fragment may be formed from the same crystal as the solar cell.
The solar cell may include a surface area and the bypass diode may include a surface area between about 5% to about 25% of the surface area of the solar cell.
The bypass diode may include a surface area of about 10% of the surface area of the solar cell.
The first electrical coupling may include a first electrically insulating film that may have first and second adjacent portions each having a first adhesive coating thereon, the first electrical coupling further including a first plurality of wires having first and second portions secured to the first and second portions respectively of the electrically insulating film by the first adhesive coating, and the first adhesive coating adhesively secures the first portion of the first electrically insulating film to the front side current collector of the bypass diode and the first portion of the first plurality of wires is soldered to the front side current collector of the bypass diode.
The apparatus may further include a first bus bar having first and second oppositely facing surfaces, and the second portion of the first electrically insulating film may be secured to the first surface of the first bus bar by the first adhesive coating and the second portion of the plurality of wires may be soldered to the first surface of the first bus bar.
The first surface of the first bus bar generally faces a back side of the solar cell.
The second oppositely facing surface of the first bus bar generally faces away from the solar cell and the first electrical coupling may further include a second electrically insulating film having first and second adjacent portions each having a second adhesive coating thereon and a second plurality of wires having first and second portions secured to the first and second portions respectively of the second electrically insulating film by the second adhesive coating, and the second adhesive coating adhesively secures the first portion of the second electrically insulating film to the second surface of the first bus bar and the first portion of the second plurality of wires may be soldered to the second surface of the first bus bar.
The second portion of the second electrically insulating film may be secured by the second adhesive coating to the back side current collector of the solar cell and the second portion of the second plurality of wires may be soldered to the back side current collector of the solar cell.
The first electrically insulating film may have first and second oppositely facing surfaces, the first adhesive coating being on the first surface and the thermal coupling may include a thermal adhesive between the second surface of the first electrically insulating film and the back side current collector on the back side of the solar cell to secure the bypass diode to the solar cell while providing for heat transfer therebetween.
The second electrical coupling may include a third electrically insulating film having first and second adjacent portions each having a third adhesive coating thereon and a third plurality of wires having first and second portions secured to the first and second portions respectively of the third electrically insulating film by the third adhesive coating, and the third adhesive coating adhesively secures the first portion of the third electrically insulating film to the back side current collector of the bypass diode and the first portion of the third plurality of wires may be soldered to the back side current collector of the bypass diode.
The apparatus may further include a second bus bar having first and second oppositely facing surfaces, the second portion of the third electrically insulating film being adhesively secured to the first surface of the second bus bar by the third adhesive coating and the second portion of the third plurality of wires being soldered to the first surface of the second bus bar.
The apparatus may further include a fourth transparent electrically insulating film having first and second adjacent portions each having a fourth adhesive coating thereon and a fourth plurality of wires having first and second portions secured to the first and second portions respectively of the fourth transparent electrically insulating film by the fourth adhesive coating, and the fourth adhesive coating adhesively secures the first portion of the fourth transparent electrically insulating film to the second surface of the second bus bar and the first portion of the fourth plurality of wires may be soldered to the second surface of the second bus bar.
The second portion of the fourth transparent electrically insulating film may be adhesively secured to the front side current collector of the solar cell and the second portion of the wires of the fourth plurality of wires may be soldered to the front side current collector of the solar cell.
The second plurality of wires may include a third portion soldered to a bus bar of an adjacent apparatus.
The system may include a plurality of apparatuses.
The solar cell, the bypass diode, the first and second electrical couplings and the thermal coupling may be configured to act as a modular self-protected solar cell apparatus.
At least one of a length and a width of the bypass diode is approximately the same as a corresponding one of a length and a width of the solar cell.
In accordance with another aspect of the invention, there is provided a method for protecting a solar cell against effects caused by shading, in a solar cell system. The method involves electrically coupling a back side current collector of a bypass diode to a front side of the solar cell and electrically coupling a front side current collector of the bypass diode to a back side current collector of the solar cell to enable a current generated by non-shaded solar cells in the solar cell system to be shunted through the bypass diode when the solar cell is shaded. The method also involves disposing the bypass diode closely adjacent the back side current collector of the solar cell and thermally coupling the bypass diode to the back side current collector of the solar cell such that heat generated in the bypass diode due to current shunted through the bypass diode is dissipated by the solar cell sufficiently to avoid burning the solar cell or the bypass diode when the solar cell is shaded.
Electrically coupling may involve causing a first adhesive coating on a first electrically insulating film to adhesively secure a first portion of the first electrically insulating film to the front side current collector of the bypass diode and soldering a first portion of a first plurality of wires embedded in the first adhesive coating to the front side current collector of the bypass diode.
The method may involve causing the first adhesive coating to secure a second portion of the first electrically insulating film to a first surface of a first bus bar and soldering a second portion of the first plurality of wires to the first surface of the first bus bar.
The method may involve causing the first surface of the first bus bar to generally face toward a back side of the solar cell.
The method may involve causing a second oppositely facing surface of the first bus bar to generally face away from the back side of the solar cell.
The method may involve causing a second adhesive coating on a second electrically insulating film to adhesively secure a first portion of the second electrically insulating film to a second surface of the first bus bar and soldering the first portion of the second plurality of wires to the second surface of the first bus bar.
The method may involve causing the second adhesive coating to adhesively secure a second portion of the second electrically insulating film to the back side current collector of the solar cell and soldering a second portion of the second plurality of wires to the back side current collector of the solar cell. Thermally coupling may involve applying a thermal adhesive between a surface of the first electrically insulating film and a back side of the solar cell to secure the bypass diode to the solar cell while providing for heat transfer there between.
The method may involve causing a third adhesive coating to mechanically secure a first portion of a third electrically insulating film to the front side surface of the bypass diode and soldering a first portion of the third plurality of wires to the front side current collector of the bypass diode.
The method may involve causing the third adhesive coating to adhesively secure a second portion of the third electrically insulating film to a first surface of a second bus bar and soldering a second portion of the third plurality of wires to the first surface of the second bus bar.
The method may involve causing a fourth adhesive coating to adhesively secure a first portion of a fourth transparent electrically insulating film to a second surface of the second bus bar and soldering a first portion of a fourth plurality of wires on the fourth transparent electrically insulating film to the second surface of the second bus bar.
The method may involve causing the fourth adhesive coating to adhesively secure a second portion of the fourth plurality of wires to the front side current collector of the solar cell and soldering a second portion of the wires of the fourth plurality of wires to the front side current collector of the solar cell.
The method may involve soldering a third portion of the second plurality of wires to a second bus bar of an adjacent apparatus.
In accordance with another aspect of the invention, there is provided a use of at least a portion of a first solar cell as a bypass diode for a second solar cell, where the second solar cell is series connected to other solar cells a system of solar cells, by electrically coupling a back side current collector of the at least a portion of the first solar cell to a front side current collector of the second solar cell and electrically coupling a front side current collector of the at least a portion of the first solar cell to a back side current collector of the second solar cell to enable a current generated by non-shaded solar cells in the system to be shunted through the at least a portion of the first solar cell when the second solar cell is shaded. There is also provided a use for disposing the bypass diode closely adjacent the back side current collector and thermally coupling the at least a portion of the first solar cell to the back side of the second solar cell such that heat generated in the at least a portion of the first solar cell due to current shunted through the at least a portion of the first solar cell is dissipated by the second solar cell sufficiently to avoid burning the at least a portion of the first solar cell or the second solar cell when the second solar cell is shaded.
In accordance with another aspect of the invention, there is provided a method of protecting a solar cell against shading in a system of series-connected solar cells exposed to light. The method involves electrically coupling a back side current collector of at least a portion of a first solar cell configured to act as a bypass diode to a front side current collector of a second solar cell configured to convert light energy into electrical energy, wherein the second solar cell is series connected to other solar cells in the system, where the other solar cells are configured to convert light energy into electrical energy. The method also involves electrically coupling a front side current collector of the at least a portion of the first solar cell to a back side current collector of the second solar cell such that a current generated by non-shaded solar cells in the system is shunted through the at least a portion of the first solar cell when the second solar cell is shaded. The method further involves disposing the bypass diode closely adjacent the back side current collector of the solar cell. The method also involves thermally coupling the at least a portion of the first solar cell to the back side of the second solar cell such that heat generated in the at least a portion of the first solar cell due to current shunted through the at least a portion of the first solar cell is dissipated by the second solar cell sufficiently to avoid burning the at least a portion of the first solar cell or the second solar cell when the second solar cell is shaded.
In accordance with another aspect of the invention, there is provided a method of generating electric current from light energy. The method involves connecting in series, a plurality of photovoltaic (PV) cell apparatuses to form a PV module. Each PV cell apparatus includes a solar cell having a front side current collector and a back side current collector. Each PV cell apparatus also includes a bypass diode closely adjacent the back side current collector, the bypass diode having a front side current collector and a back side current collector. Each PV cell apparatus further includes a first electrical coupling for electrically coupling the front side current collector of the bypass diode to the back side current collector of the solar cell. Each PV cell apparatus also includes a second electrical coupling for electrically coupling the back side current collector of the bypass diode to the front side current collector of the solar cell, the first and second electrical couplings cooperating to enable a current generated by non-shaded solar cells in the system to be shunted through the bypass diode when the solar cell is shaded. Each PV cell apparatus also includes a thermal coupling thermally coupling the bypass diode to the back side of the solar cell such that heat generated in the bypass diode due to current shunted through the bypass diode is dissipated by the solar cell sufficiently to avoid burning the solar cell or the bypass diode when the solar cell is shaded.
In accordance with another aspect of the invention, there is provided an apparatus for generating electric current from light energy. The apparatus includes a photovoltaic (PV) module comprising a plurality of series-connected PV cell apparatuses. Each PV cell apparatus includes a solar cell having a front side current collector and a back side current collector and a bypass diode closely adjacent the back side current collector, the bypass diode having a front side current collector and a back side current collector. Each PV cell apparatus also includes a first electrical coupling for electrically coupling the front side current collector of the bypass diode to the back side current collector of the solar cell. Each PV cell apparatus further includes a second electrical coupling for electrically coupling the back side current collector of the bypass diode to the front side current collector of the solar cell, the first and second electrical couplings cooperating to enable a current generated by non-shaded solar cells in the system to be shunted through the bypass diode when the solar cell is shaded. Each PV cell apparatus further includes a thermal coupling thermally coupling the bypass diode to the back side of the solar cell such that heat generated in the bypass diode due to current shunted through the bypass diode is dissipated by the solar cell sufficiently to avoid burning the solar cell or the bypass diode when the solar cell is shaded.
The solar cell, the bypass diode, the first and second electrical couplings and the thermal coupling may be configured to act as a modular self-protected solar cell apparatus.
At least one of a length and a width of the bypass diode may be approximately the same as a corresponding one of a length and a width of the solar cell.
In accordance with another aspect of the invention, there is provided a method of generating electric current from light energy. The method involves connecting in series, a plurality of photovoltaic (PV) cell apparatuses to form a PV module. Each PV cell apparatus includes a solar cell having a front side current collector and a back side current collector and a bypass diode closely adjacent the back side current collector, the bypass diode having a front side current collector and a back side current collector. Each PV cell apparatus also includes a first electrical coupling for electrically coupling the front side current collector of the bypass diode to the back side current collector of the solar cell. Each PV cell apparatus further includes a second electrical coupling for electrically coupling the back side current collector of the bypass diode to the front side current collector of the solar cell, the first and second electrical couplings cooperating to enable a current generated by non-shaded solar cells in the system to be shunted through the bypass diode when the solar cell is shaded. Each PV cell apparatus also includes a thermal coupling thermally coupling the bypass diode to the back side of the solar cell such that heat generated in the bypass diode due to current shunted through the bypass diode is dissipated by the solar cell sufficiently to avoid burning the solar cell or the bypass diode when the solar cell is shaded. Each PV cell apparatus further includes grouping the PV cell apparatuses into a plurality of series connected groups each comprised of N series connected PV cell apparatuses and connecting a respective group bypass diode to first and last PV cell apparatuses of each group such that when 0.5 N+1 solar cells in a group are shaded, the bypass diode associated with the group conducts current produced by the remaining groups to bypass the group having shaded solar cells.
The method may involve connecting the bypass diodes associated with respective groups to a heatsink.
The method may involve placing the PV apparatuses into a PV module mount for holding the PV apparatuses.
Connecting the bypass diodes to a heatsink may involve connecting the bypass diodes associated with respective groups to an exterior surface of the PV module mount
In accordance with another aspect of the invention, there is provided an apparatus for generating electric current from light energy. The apparatus includes a photovoltaic (PV) module comprising a plurality of series-connected PV cell apparatuses. Each PV cell apparatus includes a solar cell having a front side current collector and a back side current collector and a bypass diode closely adjacent the back side current collector, the bypass diode having a front side current collector and a back side current collector. Each PV cell apparatus also includes a first electrical coupling for electrically coupling the front side current collector of the bypass diode to the back side current collector of the solar cell. Each PV cell apparatus further includes a second electrical coupling for electrically coupling the back side current collector of the bypass diode to the front side current collector of the solar cell, the first and second electrical couplings cooperating to enable a current generated by non-shaded solar cells in the system to be shunted through the bypass diode when the solar cell is shaded. Each PV cell apparatus also includes a thermal coupling thermally coupling the bypass diode to the back side of the solar cell such that heat generated in the bypass diode due to current shunted through the bypass diode is dissipated by the solar cell sufficiently to avoid burning the solar cell or the bypass diode when the solar cell is shaded. The apparatus also includes the PV cell apparatuses being arranged into a plurality of series connected groups each comprised of N series connected PV cell apparatuses. The apparatus also includes respective group bypass diodes electrically connected to first and last PV cell apparatuses of each group such that when 0.5 N+1 solar cells in a group are shaded, the bypass diode associated with the group conducts current produced by the remaining groups to bypass the group having shaded solar cells.
The bypass diodes associated with respective groups may be connected to a heatsink.
The apparatus may further include a PV module mount for holding the PV apparatuses.
The heatsink may include the PV module mount.
The solar cell, the bypass diode, the first and second electrical couplings and the thermal coupling may be configured to act as a modular self-protected solar cell apparatus
At least one of a length and a width of the bypass diode may be approximately the same as a corresponding one of a length and a width of the solar cell.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
In drawings which illustrate embodiments of the invention,
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The apparatus 10 further includes a bypass diode shown generally at 18 disposed closely adjacent the back side current collector 16 and in thermal contact therewith as will be described below. The bypass diode 18 has a front side current collector 20 and a back side current collector 22. The front side current collector 20 may include a screen printed metallization pattern and since the bypass diode will not and need not receive light, the metallization pattern on the front side need not be concerned with the admission of light to the front side surface of the bypass diode. The back side current collector 22 may be formed using any of the methods described above in connection with the back side current collector of the solar cell 12. In this embodiment, the bypass diode 18 is formed from the same material as the solar cell 12 and may be formed from a fragment of the same wafer from which the solar cell is produced. Thus both the solar cell 12 and bypass diode 18 may have similar electrical properties.
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A first plurality of parallel, spaced apart wires, one of which is shown at 34, is secured to the first electrically insulating film 26 by the first adhesive coating 32 such that portions of the wires are embedded in the first adhesive coating while other portions of the wires are not embedded in the first adhesive to provide for contacting the wires to conductive surfaces. The wires extend from the first portion 28 to the second portion 30. An exemplary film having the above described adhesive coating and wires embedded therein is described in published PCT application No. PCT/CA03/01278 published Nov. 3, 2004 under Publication Number WO/2004/021455 which is incorporated herein by reference. Film with the adhesive and plurality of wires embedded therein, as described in the above mentioned PCT publication can be pre-ordered from Day4 Energy Inc. of Burnaby, B.C., Canada and used in assembling the shading protected solar cell apparatus described herein.
The first adhesive coating 32 adhesively secures the first portion 28 of the first electrically insulating film 26 to the front side current collector 20 of the bypass diode 18 and a first portion of the first plurality of wires 34 is soldered to the front side current collector of the bypass diode. Soldering of the first plurality of wires 34 to the front side current collector 20 of the bypass diode 18 may be accomplished simultaneously with causing the first adhesive coating to adhere to the front side current collector by heating and pressing the first portion 28 of the first electrically insulating film 26 onto the front side current collector 20.
Heating may involve heating the first electrically insulating film, adhesive and pre-coated wires 34 to a temperature of about 125° C. to about 160° C. Pressing may involve pressing the first electrically insulating film 26 and wires 34 onto the front side current collector 20 with a pressure of up to about 15 psi.
Thus, the first plurality of wires 34 is in electrical contact with the front side current collector 20 of the bypass diode 18 and is secured thereto by solder and in addition, the first electrically insulating film 26 is secured to the front side current collector by the first adhesive coating 32 such that the second portion 30 of the first electrically insulating film extends beyond the outer extremity of the bypass diode 18.
The first electrical coupling 24 further comprises a first bus bar 36 which may be comprised of a copper conductor, for example, having first and second oppositely facing surfaces 38 and 40 respectively and cross-sectional dimensions of about H 0.05-0.2 mm×about W 2-8 mm, for example. The first and second oppositely facing surfaces 38 and 40 may be flat planar surfaces, for example. The first surface 38 of the first bus bar 36 generally faces a back side 132 of the solar cell 12. The second portion 30 of the first electrically insulating film 26 is secured to the first surface 38 of the first bus bar 36 by the first adhesive coating 32 and a second portion of the first plurality of wires 34 is secured to the first surface of the first bus bar by soldering the wires thereto. Soldering and causing the adhesive to adhere to the first surface 38 of the first bus bar 36 may be accomplished by heating and pressing at the same time the first electrically insulating film 26 is secured to the front side current collector 20 of the bypass diode 18, or at an earlier or later time.
The first electrical coupling 24 further includes a second electrically insulating film 42 same as the first electrically insulating film 26. The second electrically insulating film 42 has first and second adjacent portions 44 and 46 respectively and a second adhesive coating 48 on each of the first and second adjacent portions 44 and 46. A second plurality of wires 50 having first and second portions 52 and 54 is secured to the first and second portions 44 and 46 respectively of the second electrically insulating film 42 by the second adhesive coating 48. The second adhesive coating 48 adhesively secures the first portion 44 of the second electrically insulating film 42 to the second surface 40 of the first bus bar 36 and the first portion 52 of the second plurality of wires 50 is soldered to the second surface of the first bus bar. Soldering and causing the second adhesive coating 48 to adhere to the second surface may be accomplished by heating and pressing as described above, for example.
The second portion 46 of the second electrically insulating film 42 is secured by the second adhesive coating 48 to the back side current collector 16 of the solar cell 12 and the second portion 54 of the second plurality of wires 50 is soldered to the back side current collector 16 of the solar cell 12, in the same manner as described above. Thus, there is an electrical connection between the front side current collector 20 of the bypass diode 18 through the first plurality of wires 34 to the first bus bar 36 and then to the second plurality of wires 50 to the back side current collector 16 of the solar cell 12.
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The second electrical coupling 60 further includes a second bus bar shown generally at 80 having first and second oppositely facing surfaces 82 and 84. The second portion 66 of the third electrically insulating film 62 is adhesively secured to the first surface 82 of the second bus bar 80 by the third adhesive coating 68 and the second portion 74 of the third plurality of wires 70 is soldered to the first surface 82 of the second bus bar 80. The back side current collector 22 of the bypass diode 18 is thus in electrical contact with the second bus bar 80 through the third plurality of wires 70.
The second electrical coupling 60 further includes a fourth electrically insulating film 90 same as the first electrically insulating film 26 described above having first and second adjacent portions 92 and 94 respectively, with the exception that at least the second portion 94 must be transparent to light. Each of these portions has a fourth adhesive coating 96 thereon and a fourth plurality of wires 98 having first and second portions 100 and 102 is secured to the first and second portions 92 and 94 of the fourth electrically insulating film 90 by the fourth adhesive coating 96. The fourth adhesive coating 96 adhesively secures the first portion 92 of the fourth electrically insulating film 90 to the second surface 84 of the second bus bar 80 and the first portion 100 of the fourth plurality of wires 98 is soldered to the second surface 84 of the second bus bar.
The second portion 94 of the fourth electrically insulating film 90 is adhesively secured to the front side current collector 14 of the solar cell 12 and the second portion 102 of the fourth plurality of wires 98 is soldered to the front side current collector 14 of the solar cell. Thus, the second bus bar 80 is in electrical contact with the front side current collector 14 of the solar cell 12 through the fourth plurality of wires 98. At least the second portion 94 of the fourth electrical insulating film 90 must be transparent to permit light to pass through to reach the solar cell 12. All other electrically insulating films described herein, including the first, second, and third electrically insulating films 26, 42, and 62 can be transparent but need not be.
In effect, the first and second electrical couplings 24 and 60 act to connect the front side current collector 20 of the bypass diode 18 to the back side current collector 16 of the solar cell 12 and to connect the back side current collector 22 of the bypass diode to the front side current collector 14 of the solar cell. Thus, the solar cell 12 and bypass diode 18 are connected in opposing arrangements as shown in
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The second side 144 is also coated with a second layer 148 of adhesive which may also be formed from ethylene vinyl acetate and also having a thickness of between about 25 μm to about 50 micrometers. Desirably, the total thickness of the thermally conductive polymeric film 140 and the first and second adhesive layers 146 and 148 will be about 100 μm to provide for sufficient adhesion while providing for a low impedance to thermal conduction between the first electrically insulating film 26 and the back side current collector 16 of the solar cell 12.
Desirably, regardless of which thermal coupling is used, i.e., that shown in
In addition, since the bypass diode 18 is disposed closely adjacent the back side current collector 16 it does not shade the front side 133 of the solar cell 12 and provides no blocking whatsoever to light impinging upon the front side of the solar cell. Furthermore, disposing the bypass diode 18 closely adjacent the back side current collector 16 of the solar cell 12 facilitates thermally coupling the bypass diode to the solar cell as described. The use of the first, second, third and fourth electrically insulating films 26, 42, 62 and 90 facilitates easy connection of the bypass diode 18 to the solar cell 12 it protects and as will be seen below, to other solar cells in the system. The solar cell 12, bypass diode 18, electrically insulating films 26, 42, 62, and 90 and bus bars 36 and 80 form a unitary device that may be regarded as a modular, self protected PV cell unit.
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Referring to
Referring to
In this embodiment, the PV cell apparatuses 186 to 204 are arranged into a plurality of series-connected groups, each comprised of six series connected PV cell apparatuses. For example, a first group 206 is comprised of PV cell apparatuses 182 to 192 and a second group 208 is comprised of PV cell apparatuses 194 to 204. Each respective group 206 and 208 has a group bypass diode 210 and 212 respectively which are connected to first and last PV cell apparatuses of each group. For example, an anode of the first group bypass diode 210 is connected to the first PV apparatus 182 of the first group 206 and the cathode 216 of the first group bypass diode 210 is connected to the last PV cell apparatus 92 of the first group 206. Similarly, an anode 218 of the second group bypass diode 212 is connected to the first PV apparatus 194 of the second group 208 and a cathode 220 of the second group bypass diode 212 is connected to the last PV apparatus 204 of the second group 208.
Effectively, when 0.5N+1 solar cells in a group (206 or 208) are shaded, the group bypass diode (210 or 212) associated with that group conducts current produced by the remaining group(s) to bypass the group having shaded solar cells. For example, referring to
Referring back to
It was discovered that by grouping the solar cells into groups and connecting separate bypass diodes as shown in
The above described embodiments may provide a practical and inexpensive way of installing bypass diodes on a solar cell, especially since fragments of solar cell wafers can be used as bypass diodes and since no special processing techniques are required other than to adhesively adhere electrically insulating films and solder wires to various surfaces of the various components, which can be done quite easily and efficiently by employing conventional vacuum or hot roll lamination techniques. Since the bypass diodes in the embodiments described are relatively large compared to conventionally used diodes such as those described in the background section of this document, the solar cell is more amenable to vacuum or hot roll lamination since the pressure due to these processes is spread out over the entire large surface of the bypass diode rather than focused on a point such as would be case with some of the prior art bypass diodes. Since the pressure is spread out over a large area, the possibility of breaking the solar cell during vacuum or hot roll lamination is significantly reduced.
The above described embodiments may provide efficient protection of PV modules against shading and reduces the risk of damage to a shaded solar cell due to overheating.
The use of the group diodes as described enables continued collection of electric power from a group of PV cells provided fewer than 0.5 N+1 solar cells are shaded. This enables power to be generated by a group even though a few solar cells of the group are shaded, which enables the total generated kWa per year to be substantially higher than with conventional systems.
While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.
