High efficiency configuration for solar cell string

Abstract

A high efficiency configuration for a string of solar cells comprises series-connected solar cells arranged in an overlapping shingle pattern. Front and back surface metallization patterns may provide further increases in efficiency.

What is claimed is: 
     
         1 . A solar energy receiver comprising:
 a substrate; and   a series-connected string of two or more solar cells disposed on the substrate with ends of adjacent solar cells overlapping in a shingle pattern;   wherein the linear coefficient of thermal expansion of the solar cells differs from that of the substrate by greater than or equal to about 20×10 −6 .   
     
     
         2 . The solar energy receiver of  claim 1 , wherein the solar cells are silicon solar cells. 
     
     
         3 . The solar energy receiver of  claim 2 , wherein at least some of the silicon solar cells comprise a heterojunction with intrinsic thin layer (HIT) structure. 
     
     
         4 . The solar energy receiver of  claim 2 , wherein at least some of the silicon solar cells are back-contact solar cells. 
     
     
         5 . The solar energy receiver of  claim 4 , wherein at least some of the back-contact solar cells comprise conducting vias that pass through the solar cell to provide in an overlapped portion of a front surface of the solar cell an electrical connection to contacts on the back surface of the solar cell. 
     
     
         6 . The solar energy receiver of  claim 1 , wherein adjacent overlapping pairs of solar cells are electrically connected in series in a region where they overlap by an electrically conducting bond between a front surface of one of the solar cells and a back surface of the other solar cell. 
     
     
         7 . The solar energy receiver of  claim 6 , wherein the electrically conducting bond is formed with an electrically conducting epoxy. 
     
     
         8 . The solar energy receiver of  claim 1 , wherein each solar cell comprises a front surface to be illuminated by light, and the size of the area of the front surface of each solar cell that is not overlapped by an adjacent solar cell varies through the string in a manner that matches the electrical performance of the solar cells. 
     
     
         9 . The solar energy receiver of  claim 1 , wherein:
 each of the solar cells is a silicon solar cell having rectangular or substantially rectangular front and back surfaces with shapes defined by first and second oppositely positioned long sides of the solar cell and two oppositely positioned short sides of the solar cell, the front surface to be illuminated by light;   each solar cell comprises an electrically conducting front surface metallization pattern that is disposed on the front surface and that comprises a plurality of fingers running parallel to the short sides for substantially the length of the short sides and a bus bar or a plurality of contact pads running parallel to and adjacent to the first long side and interconnecting ends of the fingers; and   each solar cell comprise an electrically conducting back surface metallization pattern disposed on the back surface and comprising one or more contact pads running parallel to and adjacent to the second long side.   
     
     
         10 . The solar energy receiver of  claim 1 , positioned for operation in a solar energy collector with the string oriented so that for each solar cell that has a portion of its front surface overlapped by another solar cell, the overlapped front surface portion is closer to the earth's equator than is the uncovered front surface portion, thereby orienting exposed edges of the solar cells away from the earth's equator. 
     
     
         11 . The solar energy receiver of  claim 1 , wherein the substrate is a metal substrate. 
     
     
         12 . The solar energy receiver of  claim 11 , wherein the substrate is an aluminum substrate. 
     
     
         13 . The solar energy receiver of  claim 11 , wherein:
 the metal substrate is linearly elongated;   each of the solar cells is linearly elongated; and   the string of solar cells is arranged in a row along a long axis of the substrate with long axes of the solar cells oriented perpendicular to the long axis of the substrate.   
     
     
         14 . The solar energy receiver of  claim 13 , wherein:
 each of the solar cells is a silicon solar cell having rectangular or substantially rectangular front and back surfaces with shapes defined by first and second oppositely positioned long sides of the solar cell and two oppositely positioned short sides of the solar cell, the front surface to be illuminated by light;   each solar cell comprises an electrically conducting front surface metallization pattern that is disposed on the front surface and that comprises a plurality of fingers running parallel to the short sides for substantially the length of the short sides and a bus bar or a plurality of contact pads running parallel to and adjacent to the first long side and interconnecting ends of the fingers; and   each solar cell comprise an electrically conducting back surface metallization pattern disposed on the back surface and comprising one or more contact pads running parallel to and adjacent to the second long side.   
     
     
         15 . The solar energy receiver of  claim 14 , wherein adjacent overlapping pairs of solar cells are electrically connected in series in a region where they overlap by an electrically conducting bond between the front surface bus bar or contact pads of one solar cell and the one or more back surface contact pads of the other solar cell. 
     
     
         16 . The solar energy receiver of  claim 15 , positioned for operation in a solar energy collector with the string oriented so that for each solar cell that has a portion of its front surface overlapped by another solar cell, the overlapped front surface portion is closer to the earth's equator than is the uncovered front surface portion, thereby orienting exposed edges of the solar cells away from the equator. 
     
     
         17 . The solar energy receiver of  claim 15 , wherein each solar cell comprises a front surface to be illuminated by light, and the size of the area of the front surface of each solar cell that is not overlapped by an adjacent solar cell varies through the string in a manner that matches the electrical performance of the solar cells. 
     
     
         18 . The solar energy receiver of  claim 13 , wherein the series connected string of solar cells is a first string of solar cells;
 comprising a second series-connected string of two or more solar cells disposed on the substrate with ends of adjacent solar cells overlapping in a shingle pattern; and   a mechanically compliant electrical interconnect electrically connecting the first and second strings in series;   wherein the linear coefficient of thermal expansion of solar cells in the second string differs from that of the substrate by greater than or equal to about 20×10 −6 , each of the solar cells in the second string is linearly elongated, and the second string of solar cells is arranged in a row along a long axis of the substrate with long axes of the solar cells oriented perpendicular to the long axis of the substrate, the second string in line with the first string.   
     
     
         19 . The solar energy receiver of  claim 18 , wherein:
 the mechanically compliant electrical interconnect is bonded to a portion of a front surface of a first solar cell located at an end of the first string and bonded to a portion of a back surface of a second solar cell located at an end of the second string, and the second solar cell hides the mechanically compliant electrical interconnect from view from the front surface side of the first solar cell.   
     
     
         20 . The solar energy receiver of  claim 18 , wherein:
 each of the solar cells is a silicon solar cell having rectangular or substantially rectangular front and back surfaces with shapes defined by first and second oppositely positioned long sides of the solar cell and two oppositely positioned short sides of the solar cell, the front surface to be illuminated by light;   each solar cell comprises an electrically conducting front surface metallization pattern that is disposed on the front surface and that comprises a plurality of fingers running parallel to the short sides for substantially the length of the short sides and a bus bar or a plurality of contact pads running parallel to and adjacent to the first long side and interconnecting ends of the fingers; and   each solar cell comprise an electrically conducting back surface metallization pattern disposed on the back surface and comprising one or more contact pads running parallel to and adjacent to the second long side.   
     
     
         21 . The solar energy receiver of  claim 20 , wherein adjacent overlapping pairs of solar cells are electrically connected in series in a region where they overlap by an electrically conducting bond between the front surface bus bar or contact pads of one solar cell and the one or more back surface contact pads of the other solar cell. 
     
     
         22 . The solar energy receiver of  claim 21 , wherein the electrically conducting bond is formed with an electrically conducting silver-filled epoxy. 
     
     
         23 . The solar energy receiver of  claim 21 , positioned for operation in a solar energy collector with the string oriented so that for each solar cell that has a portion of its front surface overlapped by another solar cell, the overlapped front surface portion is closer to the earth's equator than is the uncovered front surface portion, thereby orienting exposed edges of the solar cells away from the earth's equator. 
     
     
         24 . The solar energy receiver of  claim 21 , wherein each solar cell comprises a front surface to be illuminated by light, and the size of the area of the front surface of each solar cell that is not overlapped by an adjacent solar cell varies through the string in a manner that matches the electrical performance of the solar cells. 
     
     
         25 . A concentrating solar energy collector comprising the solar energy receiver of  claim 1  and one or more optical elements arranged to concentrate solar radiation onto the receiver. 
     
     
         26 . A string of solar cells comprising:
 a plurality of series-connected solar cells arranged with ends of adjacent solar cells overlapping in a shingle pattern;   wherein each solar cell comprises a front surface to be illuminated by light, and the size of the area of the front surface of each solar cell that is not overlapped by an adjacent solar cell varies through the string in a manner that matches the electrical performance of the solar cells.   
     
     
         27 . The string of solar cells of  claim 26 , wherein the matched electrical performance is the current generated in each solar cell when all solar cells are equally illuminated. 
     
     
         28 . The string of solar cells of  claim 26 , wherein the solar cells are silicon solar cells. 
     
     
         29 . The string of solar cells of  claim 28 , wherein at least some of the silicon solar cells comprise a heterojunction with intrinsic thin layer (HIT) structure. 
     
     
         30 . The string of solar cells of  claim 28 , wherein at least some of the silicon solar cells are back-contact solar cells. 
     
     
         31 . The string of solar cells of  claim 30 , wherein at least some of the back-contact solar cell comprise conducting vias that pass through the solar cell to provide in an overlapped portion of a front surface of the solar cell an electrical connection to contacts on the back surface of the solar cell. 
     
     
         32 . The string of solar cells of  claim 26 , wherein adjacent overlapping pairs of solar cells are electrically connected in series in a region where they overlap by an electrically conducting bond between a front surface of one of the solar cells and a back surface of the other solar cell. 
     
     
         33 . The string of solar cells of  claim 26 , positioned for operation in a solar energy collector with the string oriented so that for each solar cell that has a portion of its front surface overlapped by another solar cell, the overlapped front surface portion is closer to the earth's equator than is the uncovered front surface portion, thereby orienting exposed edges of the solar cells away from the earth's equator. 
     
     
         34 . A concentrating solar energy collector comprising the string of solar cells of  claim 26  and one or more optical elements arranged to concentrate solar radiation onto the receiver. 
     
     
         35 . A back-contact silicon solar cell comprising:
 a front surface to be illuminated by light;   a back surface;   one or more n-contacts on the back surface that electrically contact an n-conductivity type side of a silicon diode junction;   one or more p-contacts on the back surface that electrically contact a p-conductivity type side of the silicon diode junction; and   one or more electrically conducting vias passing through the solar cell from the back surface to the front surface to provide near an edge of the front surface one or more electrical connections to either the p-contacts or the n-contacts.   
     
     
         36 . The back contact solar cell of  claim 35 , comprising a bus bar or a plurality of contact pads on the front surface electrically interconnecting upper ends of the vias. 
     
     
         37 . The back contact solar cell of  claim 35 , wherein the front and back surfaces have corresponding rectangular or substantially rectangular shapes defined by two oppositely positioned long sides and two oppositely positioned short sides; and upper ends of the vias are arranged along a long side of the front surface. 
     
     
         38 . The back contact solar cell of  claim 37 , wherein:
 the n-contacts comprise a plurality of n-fingers arranged side-by-side and running parallel to the short sides of the back surface;   the p-contacts comprise a plurality of p-fingers arranged side-by-side and running parallel to the short sides of the back surface; and   the n-fingers and the p-fingers are interdigitated.   
     
     
         39 . The back contact solar cell of  claim 38 , comprising a bus bar or a plurality of contact pads on the front surface electrically interconnecting upper ends of the vias. 
     
     
         40 . The back contact solar cell of  claim 37 , wherein:
 the n-contacts comprise a plurality of n-fingers arranged side-by-side and running parallel to each other at an angle to the short sides of the back surface such that opposite ends of each n-finger are offset in a direction parallel to the long sides by a distance equal to a pitch distance between n-fingers;   the p-contacts comprise a plurality of p-fingers arranged side-by-side and running parallel to each other at an angle to the short sides of the back surface such that opposite ends of each p-finger are offset in a direction parallel to the long sides by a distance equal to a pitch distance between p-fingers; and   the n-fingers and the p-fingers are interdigitated.   
     
     
         41 . The back contact solar cell of  claim 40 , comprising a bus bar or a plurality of contact pads on the front surface electrically interconnecting upper ends of the vias. 
     
     
         42 . A concentrating solar energy collector comprising the back-contact solar cell of  claim 35  and one or more optical elements arranged to concentrate solar radiation onto the solar cell. 
     
     
         43 . A string of solar cells comprising:
 a first back-contact silicon solar cell comprising a front surface to be illuminated by light, a back surface, one or more n-contacts on the back surface that electrically contact an n-conductivity type side of a diode junction, one or more p-contacts on the back surface that electrically contact a p-conductivity type side of the diode junction; and   a second back-contact silicon solar cell comprising a front surface to be illuminated by light, a back surface, one or more n-contacts on the back surface that electrically contact an n-conductivity type side of a diode junction, one or more p-contacts on the back surface that electrically contact a p-conductivity type side of the diode junction;   wherein the first and second back-contact silicon solar cells are positioned with an edge of the back surface of the second back-contact silicon solar cell overlapping an edge of the front surface of the first back-contact silicon solar cell and electrically connected in series.   
     
     
         44 . The string of solar cells of  claim 43 , wherein:
 the first back-contact silicon solar cell comprises one or more electrically conducting vias passing through the solar cell from its back surface to its front surface to electrically interconnect either the p-contacts or the n-contacts of the first back-contact silicon solar cell to contacts of opposite polarity on the back surface of the second back-contact silicon solar cell, upper ends of the conducting vias located in a region of the front surface of the first back-contact silicon solar cell that is overlapped by the second back-contact silicon solar cell.   
     
     
         45 . The string of solar cells of  claim 44 , wherein the conducting vias are electrically connected to the contacts on the back surface of the second silicon solar cell by one or more conductive bonds between the front surface of the first back-contact silicon solar cell and the back surface of the second back-contact silicon solar cell. 
     
     
         46 . The string of solar cells of  claim 45 , comprising a bus bar or a plurality of contact pads on the front surface of the first back-contact silicon solar cell electrically interconnecting upper ends of the vias and electrically interconnected to the contacts on the back surface of the second back-contact silicon solar cell by the one or more conductive bonds. 
     
     
         47 . The string of solar cells of  claim 45 , wherein the conductive bonds are formed with a conductive epoxy. 
     
     
         48 . The string of solar cells of  claim 43 , wherein one or more flexible interconnects electrically connect either the p-contacts or the n-contacts on the back surface of the first back-contact silicon solar cell to electrical contacts of opposite polarity on the back surface of the second back-contact silicon solar cell 
     
     
         49 . A concentrating solar energy collector comprising the string of solar cells of  claim 43  and one or more optical elements arranged to concentrate solar radiation onto the solar cell. 
     
     
         50 . A solar energy receiver comprising:
 a substrate;   a thermally conductive encapsulant layer adhering to the substrate;   a string of solar cells disposed on the thermally conductive encapsulant layer;   a clear encapsulant layer disposed on the string of solar cells; and   a clear top sheet disposed on the clear encapsulant layer;   wherein the thermally conductive encapsulant layer comprises pigments.   
     
     
         51 . The solar energy receiver of  claim 50 , wherein the thermally conductive encapsulant layer reflects a substantial portion of solar radiation incident on it. 
     
     
         52 . The solar energy receiver of  claim 51 , wherein at least some of the solar cells are silicon solar cells comprising a heterojunction with intrinsic thin layer (HIT) structure. 
     
     
         53 . The solar energy receiver of  claim 50 , wherein the thermally conductive encapsulant layer absorbs a substantial portion of solar radiation incident on it. 
     
     
         54 . The solar energy receiver of  claim 50 , wherein the thermally conductive encapsulant layer is black. 
     
     
         55 . The solar energy receiver of  claim 50 , wherein the thermally conductive encapsulant layer is white. 
     
     
         56 . The solar energy receiver of  claim 50 , wherein the clear top sheet has a moisture transmission rate of less than or equal to about 0.01 grams per meter-day. 
     
     
         57 . The solar energy receiver of  claim 50 , wherein the string of solar cells comprises a plurality of solar cells arranged with ends of adjacent solar cells overlapping in a shingle pattern. 
     
     
         58 . A method of preparing a string of solar cells comprising:
 arranging a plurality of solar cells with ends of adjacent solar cells overlapping in a shingled manner and with an uncured electrically conductive epoxy disposed between overlapped portions of adjacent solar cells in locations selected to series-connect the solar cells; and   applying a pressure to force overlapping ends of the solar cells against each other while elevating a temperature of the solar cells to cure the electrically conductive epoxy to form electrically conductive bonds between the solar cells.   
     
     
         59 . The method of  claim 58 , comprising:
 after curing the electrically conductive epoxy, disposing the string of solar cells in a stack of layers on a substrate; and   laminating the stack to the substrate.   
     
     
         60 . The method of  claim 58 , comprising:
 prior to curing the electrically conductive epoxy, disposing the string of solar cells in a stack of layers on a substrate; and   laminating the stack to the substrate while curing the electrically conductive epoxy.   
     
     
         61 . A method of laminating solar cells to a substrate, the method comprising:
 arranging a plurality of solar cells to form a series-connected string of solar cells with ends of adjacent solar cells overlapping in a shingle pattern;   disposing the string of solar cells in a stack of layers on the substrate; and   applying a pressure not greater than about 0.6 atmospheres to force the stack of layers and the substrate together.   
     
     
         62 . The method of  claim 61 , wherein the pressure is less than or equal to about 0.4 atmospheres. 
     
     
         63 . The method of  claim 61 , wherein the pressure is between about 0.2 and about 0.6 atmospheres. 
     
     
         64 . The method of  claim 61 , comprising heating the substrate, the stack of layers, or the substrate and the stack of layers to a temperature of between about 130° C. and about 160° C.