Patent Description:
A typical spaceflight-capable solar cell panel assembly involves building solar cell arrays comprised of long strings of solar cells connected in series. These strings are variable in length, i.e., number of solar cells, and can be very long.

Conventional solar cell arrays are built with a fixed number of solar cells to produce a required output voltage. For example, a string of <NUM> solar cells connected in series may produce an output voltage of 100V. A failure of one or more of the solar cells in the string can greatly compromise the power delivered by all <NUM> solar cells.

This results in extensive efforts to test, validate, and qualify materials and processes to ensure a maximum lifetime and success of solar cell arrays. However, such efforts result in increased costs and decreased innovation. Moreover, the risks of some missions are too high and are avoided altogether.

What is needed, then, is a means for accommodating failures in the solar cell array's operation or where the expected output voltage is otherwise not being delivered during its lifespan.

Document <CIT>, according to its abstract, relates to a reconfigurable solar panel system having a plurality of solar cells arranged in a predefined pattern on a printed circuit board has a predefined pattern of interconnection paths to form at least one solar cell module. The solar panel being made of at least one solar cell module has the capability to be configured and reconfigured by programming at least one integrated circuit that communicates with each and every solar cell on the solar module.

Document <CIT>, according to its abstract, relates to a photovoltaic module with a back side conductive substrate and a plurality of PV-cells having back contacts and being arranged in an array on a top surface of the back side conductive substrate. A circuit of series and/or parallel connected PV-cells is formed by connections between the back contacts and the back side conductive substrate. A plurality of by-pass diodes are present having back contacts in electrical contact with the circuit of series and/or parallel connected PV-cells, wherein the by-pass diodes are positioned on empty parts of the top surface of the back side conductive substrate. Each by-pass diode is a wafer based diode and is connected in parallel with one or more PV-cells.

Document <CIT>, according to its abstract, relates to systems and methods for efficiently allowing current to bypass a group of solar cells having one or more malfunctioning or shaded solar cells without overwhelming a bypass diode. This can be done using a switch (e.g., a MOSFET) connected in parallel with the bypass diode. By turning the switch on and off, a majority of the bypass current can be routed through the switch, which is configured to handle larger currents than the bypass diode is designed for, leaving only a minority of the current to pass through the bypass diode.

According to the present disclosure, a solar cell array, a method of operating a solar cell array, and a method for fabricating a solar cell array as defined in the independent claims are provided. Further embodiments of the invention are defined in the dependent claims. Although the invention is only defined by the claims, the below embodiments, examples, and aspects are present for aiding in understanding the background and advantages of the invention.

An example of the present disclosure describes a solar cell array, method and device, comprising: one or more solar cells attached to a substrate, wherein: the substrate includes one or more electrical connections to the solar cells; and the substrate includes one or more switches for bypassing one or more of the electrical connections to one or more of the solar cells.

An area of the substrate remains exposed when at least one of the solar cells having one or more cropped corners is attached to the substrate; and the area of the substrate that remains exposed includes at least one of the switches. The at least one of the solar cells are attached to the substrate such that a corner region defined by the cropped corners of adjacent ones of the at least one of the solar cells are aligned, thereby exposing the area of the substrate. At least one of the switches is located in the corner region defined by the cropped corners adjacent to the at least one of the solar cells.

The solar cells, one or more bypass diodes, and the switches are electrically connected in parallel. Moreover, the switches are controlled by one or more control signals.

The switches bypass current around the one or more of the solar cells. Specifically, the switches, when closed, connect front and back contacts of the one or more of the solar cells, so that current bypasses the one or more of the solar cells.

There are also switches for adding or removing one or more of the solar cells to or from a string of the solar cells, wherein the string's length is altered to change a voltage produced by the string.

In the following description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific example in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural changes may be made without departing from the scope of the present disclosure.

A new approach to the design of solar cell arrays, such as those used for spaceflight power applications, is based on electrical connections among the solar cells in the array.

This new approach rearranges the components of a solar cell and the arrangements of the solar cells in the array. Instead of having solar cells connected into long linear strings and then assembled onto a substrate, the solar cells are attached individually to a substrate, such that corner regions of adjacent cells are aligned on the substrate, thereby exposing an area of the substrate. Electrical connections between cells are made by corner conductors formed on or in the substrate in these corner regions. Consequently, this approach presents a solar cell array design based on individual cells.

Thus, a single laydown process and layout can be used in the fabrication of solar cell arrays. Current flow between solar cells will be assisted with conductors embedded in the substrate. These electrical connections define the specific characteristics of the solar cell array, such as its dimensions, stayout zones, and circuit terminations. This approach simplifies manufacturing, enables automation, and reduces costs and delivery times.

<FIG> and <FIG> illustrate conventional structures for solar cell panels <NUM>, which include a substrate <NUM>, a plurality of solar cells <NUM> arranged in an array, and electrical connectors <NUM> between the solar cells <NUM>. Half size solar cells <NUM> are shown in <FIG> and full size solar cells <NUM> are shown in <FIG>. Space solar cells <NUM> are derived from a round Germanium (Ge) substrate starting material, which is later fabricated into semi-rectangular shapes to improve dense packing onto the solar cell panel <NUM>. This wafer is often diced into one or two solar cells <NUM> herein described as half size or full size solar cells <NUM>. The electrical connectors <NUM> providing electrical connections between solar cells <NUM> are made along the long parallel edge between solar cells <NUM>. These series connections (cell-to-cell) are completed off-substrate, as strings of connected solar cells <NUM> are built having lengths of any number of solar cells <NUM>. The completed strings of solar cells <NUM> are then applied and attached to the substrate <NUM>.

In <FIG>, wiring <NUM> is attached at the end of a string of solar cells <NUM> to electrically connect the string to other strings, or to terminate the resulting circuit and bring the current off of the array of solar cells <NUM>. String-to-string and circuit termination connections are typically done on the substrate <NUM>, and typically using wiring <NUM>. However, some solar cell panels <NUM> use a printed circuit board (PCB)-type material with embedded conductors.

Adjacent strings of connected solar cells <NUM> can run parallel or anti-parallel. In addition, strings of connected solar cells <NUM> can be aligned or misaligned. There are many competing influences to the solar cell <NUM> layout resulting in regions where solar cells <NUM> are parallel or anti-parallel, aligned or misaligned.

<FIG> illustrate improved devices and structures for a solar cell panel 10a, according to one example, wherein <FIG> is an enlarged view of the details in the dashed circle in <FIG>. The various components of the solar cell panel 10a are shown and described in greater detail in <FIG>.

The solar cell panel 10a includes a substrate <NUM> for solar cells <NUM> having one or more corner conductors <NUM> thereon. In one example, the substrate <NUM> is a multi-layer substrate <NUM> comprised of one or more Kapton® (polyimide) layers separating one or more patterned metal layers. The substrate <NUM> may be mounted on a large rigid panel 10a similar to conventional assembles. Alternatively, the substrate <NUM> can be mounted to a lighter, more sparse frame or panel 10a for mounting or deployment.

A plurality of solar cells <NUM> are attached to the substrate <NUM> in a two-dimensional (<NUM>-D) grid of an array <NUM>. In this example, the array <NUM> is comprised of ninety-six (<NUM>) solar cells <NUM> arranged in four (<NUM>) rows by twenty-four (<NUM>) columns, but it is recognized that any number of solar cells <NUM> may be used in different implementations.

The solar cells <NUM> have cropped corners <NUM> that define corner regions <NUM>, as indicated by the dashed circle. The solar cells <NUM> are attached to the substrate <NUM>, such that corner regions <NUM> of adjacent ones of the solar cells <NUM> are aligned, thereby exposing an area <NUM> of the substrate <NUM>. The area <NUM> of the substrate <NUM> that is exposed includes one or more of the corner conductors <NUM>, and one or more electrical connections between the solar cells <NUM> and the corner conductors <NUM> are made in the corner regions <NUM> resulting from the cropped corners <NUM> of the solar cells <NUM>.

In this example, the corner conductors <NUM> are conductive paths attached to, printed on, buried in, or deposited on the substrate <NUM>, before and/or after the solar cells <NUM> are attached to the substrate <NUM>, which facilitate connections between adjacent solar cells <NUM>. The connections between the solar cells <NUM> and the corner conductors <NUM> are made after the solar cells <NUM> have been attached to the substrate <NUM>.

In one example, four adjacent solar cells <NUM> are aligned on the substrate <NUM>, such that four cropped corners <NUM>, one from each solar cell <NUM>, are brought together at the corner regions <NUM>. The solar cells <NUM> are then individually attached to the substrate <NUM>, wherein the solar cells <NUM> are placed on top of the corner conductors <NUM> to make the electrical connection between the solar cells <NUM> and the corner conductors <NUM>.

The solar cells <NUM> may be applied to the substrate <NUM> as CIC (cell, interconnect and coverglass) units. Alternatively, bare solar cells <NUM> may be assembled on the substrate <NUM>, and then interconnects applied to the solar cells <NUM>, followed by the application of a single solar cell <NUM> coverglass, multiple solar cell <NUM> coverglass, multiple cell polymer coversheet, or spray encapsulation. This assembly protects the solar cells <NUM> from damage that would limit performance.

<FIG> illustrate an alternative structure for the solar cell panel 10a, according to one example, wherein <FIG> is an enlarged view of the details in the dashed circle in <FIG>. In this example, only a few corner conductors <NUM> are printed on or integrated with the substrate <NUM>. Instead, most of the corner conductors <NUM> are contained within a power routing module (PRM) <NUM> that is attached to the substrate <NUM>.

<FIG> illustrates the front side of an exemplary solar cell <NUM> that may be used in the improved solar cell panel 10a of <FIG> and <FIG>. The solar cell <NUM>, which is a CIC unit, is a half-size solar cell <NUM>. (Full-size solar cells <NUM> could also be used.

The solar cell <NUM> is fabricated having at least one cropped corner <NUM> that defines a corner region <NUM>, as indicated by the dashed circle, such that the corner region <NUM> resulting from the cropped corner <NUM> includes at least one contact <NUM>, <NUM> for making an electrical connection to the solar cell <NUM>. In the example of <FIG>, the solar cell <NUM> has two cropped corners <NUM>, each of which has both a front contact <NUM> on the front side of the solar cell <NUM> and a back contact <NUM> on a back side of the solar cell <NUM>, where the contacts <NUM> and <NUM> extend into the corner region <NUM>. (Full-size solar cells <NUM> would have four cropped corners <NUM>, each of which would have a front contact <NUM> and a back contact <NUM>.

The cropped corners <NUM> increase utilization of the round wafer starting materials for the solar cells <NUM>. In conventional panels <NUM>, these cropped corners <NUM> would result in unused space on the panel <NUM> after the solar cells <NUM> are attached to the substrate <NUM>. The new approach described in this disclosure, however, utilizes this unused space. Specifically, metal foil interconnects, comprising the corner conductors <NUM>, front contacts <NUM> and back contacts <NUM>, are moved to the corner regions <NUM>. In contrast, existing CICs have interconnects attached to the solar cell <NUM> front side, and connect to the back side (where connections occur) during stringing.

The current generated by the solar cell <NUM> is collected on the front side of the solar cell <NUM> by a grid <NUM> of thin metal fingers <NUM> and wider metal bus bars <NUM> that are connected to both of the front contacts <NUM>. There is a balance between the addition of metal in grid <NUM>, which reduces the light entering the solar cell <NUM> and its output power, and the reduced resistance of having more metal. The bus bar <NUM> is a low resistance conductor that carries high currents and also provides redundancy should a front contact <NUM> become disconnected. Optimization generally desires a short bus bar <NUM> running directly between the front contacts <NUM>. Having the front contact <NUM> in the cropped corner <NUM> results in moving the bus bar <NUM> away from the perimeter of the solar cell <NUM>. This is achieved while simultaneously minimizing the bus bar <NUM> length and light obscuration. Additionally, the fingers <NUM> are now shorter. This reduces parasitic resistances in the grid <NUM>, because the length of the fingers <NUM> is shorter and the total current carried is less. This produces a design preference where the front contacts <NUM> and connecting bus bar <NUM> is moved to provide shorter narrow fingers <NUM>.

<FIG> illustrates the back side of the exemplary solar cell <NUM> of <FIG>. The back side of the solar cell <NUM> has a metal back layer <NUM> that is connected to both of the back contacts <NUM>.

<FIG> illustrates solar cells <NUM> arranged into the 2D grid of the array <NUM>, according to one example. The array <NUM> comprises a plurality of solar cells <NUM> attached to a substrate <NUM>, such that corner regions <NUM> of adjacent ones of the solar cells <NUM> are aligned, thereby exposing an area <NUM> of the substrate <NUM>. Electrical connections (not shown) between the solar cells <NUM> are made in the exposed area <NUM> of the substrate <NUM> using the front contacts <NUM> and back contacts <NUM> of the solar cells <NUM> and corner conductors <NUM> (not shown) formed on or in the exposed area <NUM> of the substrate <NUM>.

During assembly, the solar cells <NUM> are individually attached to the substrate <NUM>. This assembly can be done directly on a support surface, i.e., the substrate <NUM>, which can be either rigid or flexible. Alternatively, the solar cells <NUM> could be assembled into the 2D grid of the array <NUM> on a temporary support surface and then transferred to a final support surface, i.e., the substrate <NUM>.

<FIG> illustrates an example of the array <NUM> where one or more bypass diodes <NUM> are added to the exposed area <NUM> of the substrate <NUM> in the corner regions <NUM>, for use in one or more of the electrical connections. The bypass diodes <NUM> protect the solar cells <NUM> when the solar cells <NUM> become unable to generate current, which could be due to being partially shadowed, which drives the solar cells <NUM> into reverse bias. In one example, the bypass diodes <NUM> are attached to the substrate <NUM> in the corner regions <NUM> independent of the solar cells <NUM>.

<FIG> illustrates an example where the bypass diode <NUM> is applied to the back side of the solar cell <NUM>, with interconnects or contacts <NUM> for the bypass diode <NUM> connected to the back layer <NUM> and also extending into the corner region <NUM> between the front and back contacts <NUM>, <NUM>.

<FIG> illustrates a front side view of the example of <FIG>, with the interconnect or contact <NUM> for the bypass diode <NUM> (not shown) extending into the corner region <NUM> between the front and back contacts <NUM>, <NUM>.

<FIG> illustrates the solar cells <NUM> of <FIG> and <FIG> arranged into the 2D grid of the array <NUM> and applied to the substrate <NUM>, where the bypass diodes <NUM> (not shown) are applied to the back side of the solar cells <NUM>, with the contacts <NUM> for the bypass diodes <NUM> extending into the corner regions <NUM> of the solar cells <NUM>.

One advantage of this approach is that the layouts illustrated in <FIG>, <FIG> and <FIG> are generalized layouts. Specifically, these layouts can be repeated across any panel 10a dimensions desired by a customer. This greatly simplifies assembly, rework, test, and inspection processes.

The placement of the solar cell <NUM> and bypass diode <NUM> is generic. The electrical connection of the solar cells <NUM> into series connections and string terminations is important customization for the end customer and is done independent of the layout. The front contacts <NUM> and back contacts <NUM> in the corner regions <NUM> of the solar cells <NUM> must be connected. This can be done in many combinations in order to route current through a desired path.

Connections are made between the solar cells <NUM> and the corner conductors <NUM>. Front and back contacts <NUM>, <NUM> of the solar cells <NUM> are present in each corner region <NUM> for attachment to the corner conductors <NUM>. Interconnects for the front and back contacts <NUM>, <NUM> of each of the solar cells <NUM> are welded, soldered, or otherwise bonded onto the corner conductors <NUM> to provide a conductive path <NUM>, <NUM>, <NUM> for routing current out of the solar cells <NUM>.

Using the corner conductors <NUM>, any customization can be made in the electrical connections. Adjacent solar cells <NUM> can be electrically connected to flow current in up/down or left/right directions as desired by the specific design. Current flow can also be routed around stay-out zones as needed. The length or width of the solar cell array <NUM> can be set as desired. Also, the width can vary over the length of the array <NUM>.

In one example, the electrical connections are series connections that determine a flow of current through the plurality of solar cells <NUM>. This may be accomplished by the connection schemes shown in <FIG> and <FIG>, wherein <FIG> shows up/down series connections <NUM> between the solar cells <NUM> of the array <NUM>, and <FIG> shows left/right series connections <NUM> between the solar cells <NUM> of the array <NUM>. In both <FIG> and <FIG>, these series connections <NUM>, <NUM> are electrical connections between the front contacts <NUM> and back contacts <NUM> of the solar cells <NUM>, and the bypass diodes <NUM>, are made using the corner conductors <NUM> formed on or in the exposed areas <NUM> of the substrate <NUM>. These series connections <NUM>, <NUM> determine the current (power) flow, as indicated by the arrows <NUM>, through the solar cells <NUM>.

The corner conductors <NUM> between solar cells <NUM> can be in many forms. They could be accomplished using wires that have electrical connections made on both ends, which could be from soldering, welding, conducting adhesive, or other process. In addition to wires, metal foil connectors, similar to the interconnects could be applied. Metal conductive paths or traces (not shown) can also be integrated with the substrate <NUM>.

In summary, this new approach attaches the solar cells <NUM> individually to a substrate <NUM> such that the corner regions <NUM> of two, three or four adjacent solar cells <NUM> are aligned on the substrate <NUM>. The solar cells <NUM> can be laid out so that the cropped corners <NUM> are aligned and the corner regions <NUM> are adjacent, thereby exposing an area <NUM> of the substrate <NUM>. Electrical connections between solar cells <NUM> are made in these corner regions <NUM> between front contacts <NUM> and back contacts <NUM> on the solar cells <NUM>, bypass diodes <NUM>, and corner conductors <NUM> on or in the exposed area <NUM> of the substrate <NUM>, wherein these conductive paths are used to create a string of solar cells <NUM> in a series connection <NUM>, <NUM> comprising a circuit.

Space-based solar cell arrays <NUM> cannot generally be serviced. Failures are therefore of major concern, and lead to extensive quality programs, as well as avoidance of some missions.

The solar cell arrays <NUM> produce power by stringing together many solar cells <NUM> to produce an output voltage. In one example, a string of <NUM> solar cells <NUM> in series produces an output voltage of 100V. A failure of one or more solar cells <NUM> in the string can greatly compromise the power delivered by all <NUM> solar cells <NUM>.

This disclosure provides a mechanism to bypass a solar cell <NUM>, so that it does not compromise the string. Also, the string length can be changed by add or removing solar cells <NUM>. Together, these capabilities enable the solar cell array <NUM> to continue producing power in the event of solar cell <NUM> failures.

Solar cells <NUM> are generally series-connected in a string. A single triple junction solar cell <NUM> in the string produces approximately 2V. Photocurrent exits the backside (i.e., the p-side) of the solar cell <NUM>, wherein the backside of a first solar cell <NUM> is series-connected to the front side (i.e., the n-side) of a second solar cell <NUM>. The photocurrent again exits the backside of the second solar cell <NUM>. The current is constant through the series-connected solar cells <NUM>, but gains 2V from each additional solar cell <NUM>.

A key design specification is the voltage needed for operation of the system. This is often 100V, but ranges greatly.

Damage to a solar cell <NUM>, bypass diode <NUM>, or their electrical connections, can greatly reduce the power delivered by the string. Because of the series-connected nature of the string, failure of one or more solar cells <NUM> can reduce the power output by <NUM>% or more.

This disclosure describes bypassing a solar cell <NUM>, and its bypass diode <NUM>, from the string, which would result in the solar cell <NUM> being removed from the string, causing a voltage reduction for the string. In order to maintain the output voltage and peak power generation, the string should also change, by adding solar cells <NUM> to the string, after removing solar cells <NUM> from the string. Typically, the string's length would be maintained or increased, in order to provide the 100V output without degradation by the bypassed solar cell <NUM>.

<FIG> shows a circuit diagram of a string comprised of two solar cells <NUM> attached to a substrate <NUM>, wherein the substrate <NUM> includes one or more electrical connections to the solar cells <NUM>, and each solar cell <NUM> has a bypass diode <NUM>. Each solar cell <NUM> also has a set of one or more string length switches 54a to change the string length and a bypass switch 54b to bypass the solar cell <NUM>, thereby altering the electrical connections to the solar cells <NUM>.

The solar cell <NUM> includes a current source, shunt resistance, and diode, which is a common circuit representation. This simplifies consideration of how the solar cell array <NUM> may change. Shadowing or fracturing of the solar cell <NUM> would decrease the current source. Damage to the solar cell <NUM> can reduce the shunt resistance.

Also shown are the interconnects <NUM>, each of which comprise two flange elements with parallel planes connected by a web element, thus appearing similar to the letter H tilted on its side. The interconnects <NUM> are metal foil pieces used to connect the devices (solar cell <NUM>, bypass diode <NUM>, switches <NUM>) to the conductors <NUM>.

The connections <NUM> between the interconnects <NUM>, devices <NUM>, <NUM>, <NUM> and conductors <NUM> are shown as small squares. These connections <NUM> can be soldered or welded connections <NUM>.

The conductors <NUM> could possibly be wires, but the complex network of electrical connections between solar cells <NUM> would be prohibitive, requiring extensive labor and taking up panel 10a area. However, the use of corner conductors <NUM> in the solar cell array <NUM> enables this approach. This solar cell <NUM> layout puts the needed conductors <NUM> all in close proximity (in the corner regions <NUM>) and allows the devices <NUM>, <NUM>, <NUM> also to be in the corner region <NUM>.

Then, the solar cells <NUM> can be assembled on the substrate <NUM>, such as a flex circuit substrate <NUM>, which are readily available with space-approved construction methods. The flex circuit substrate <NUM> has metal traces that can form the wiring patterns of electrical connections shown in the figure. These electrical connections would be virtually impossible in a conventional solar cell array, but become straightforward in the corner connection layout of this disclosure.

<FIG> shows a string with a length of two solar cells <NUM>. This is not very useful in practice, but is useful to demonstrate the functionality of this disclosure. The polarity is such that, when illuminated, photocurrent will flow up in each solar cell <NUM> as shown by the up arrow current source. The resulting voltage will also be greater at the top (VX+ connections) rather than the bottom of the figure. The two string length switches 54a on the right-hand side can control the outputs. The outputs shown include a positive and negative polarity of two outputs V1 and V2. V1- is fixed as the starting point of the solar cell array <NUM>. After the bottom solar cell <NUM>, a set of string length switches 54a can control the output to terminate to V1+. If this is the case, then the top solar cell <NUM> would be connected to V2-. And, the output of the top solar cell <NUM> would then be switch-connected by a set of string length switches 54a to V2+. In this configuration, there would be two outputs with the power of one solar cell <NUM> in each output.

The string length switches 54a could also be set such that, after the bottom solar cell <NUM>, the current continues to the top solar cell <NUM>, albeit through two string length switches 54a. Then, the current continues through the top solar cell <NUM>, where the voltage is boosted. The output is then directed to V1+. V1+ has the same current as before, but now twice the voltage. The circuit lines V2- and V2+ can be connected together to avoid any floating, unconnected conductors.

If a solar cell <NUM> or bypass diode <NUM> is not operating correctly, the bypass switches 54b on the left side can be closed to bypass a solar cell <NUM> and bypass diode <NUM> from the string. When closed, the switch 54b would form a low resistance path bypassing the solar cell <NUM>, the results of which would be a solar cell <NUM> with nearly <NUM> volts across it and little to no current flowing.

This action would remove the solar cell <NUM> from the string resulting in a voltage reduction for the string. In order to maintain the output voltage and peak power generation, the string should also change, which requires another set of switches 54a to add a functioning solar cell <NUM> to the string. Typically, the string length would be maintained or increased so that the string would then provide the 100V output without degradation by the bypassed solar cell <NUM>.

The typical building block for the space-based solar cell array <NUM> is a solar cell <NUM> and bypass diode <NUM>. In this disclosure, the building block now becomes solar cell <NUM>, bypass diode <NUM>, string length switches 54a, and bypass switch 54b. This highly functional building block can be used to build a solar cell array <NUM> with incredible functionality, when combined with a corner connection layout.

The resulting configuration would allow any single solar cell <NUM>, or groups of solar cells <NUM>, to be bypassed. The current would then route through bypass switches 54b around the solar cell <NUM>. The string length could then be expanded as needed to reach the required output voltage. <FIG> shows switch control and bypass control at the level of each individual solar cell <NUM>. It is straightforward to modify the connections so that a group of solar cells <NUM> can be bypassed as s group. This is similar to switching the solar cells <NUM> as group.

The bypass diode <NUM> serves a similar role as the bypass switch 54b. The bypass switch 54b is controlled through an external system that senses operation, determines switch configurations, and transmits the information to the switches. These operations are internal and automatic to the bypass diode <NUM>. If the bypass diode <NUM> has an applied forward bias > <NUM>. 7V, current will automatically flow through the bypass diode <NUM> with a low resistance. With an appropriate sensing and control system, the bypass switch 54b could eliminate the need for the bypass diode <NUM>.

<FIG> shows how a solar cell <NUM> is bypassed by a single bypass switch 54b that connects the front and back contacts <NUM>, <NUM> of the solar cell <NUM> in the corner connection layout. In addition, sets of string length switches 54a are used to adjust the string length.

A corner connection layout is used for the solar cell array <NUM>, which in this example is comprised of four solar cells <NUM>, each having at least one cropped corner <NUM>. The solar cells <NUM> are attached to the substrate <NUM>, i.e., a flex circuit substrate <NUM>, such that corner regions <NUM> of adjacent ones of the solar cells <NUM> resulting from the cropped corners <NUM> are aligned, thereby exposing an area <NUM> of the substrate <NUM>. Front and back contacts <NUM>, <NUM> for the solar cells <NUM> extend into the exposed area <NUM> of the substrate <NUM>. The exposed area <NUM> of the substrate <NUM> also includes corner conductors <NUM> for making one or more electrical connections between the front and back contacts <NUM>, <NUM> of the solar cells <NUM>, as well as bypass diodes <NUM>, string length switches 54a, and bypass switches 54b.

The exposed area <NUM> of the substrate <NUM> also includes one or more bypass switches 54b for bypassing the electrical connections to one or more of the solar cells <NUM>, wherein the switches 54b, when closed, connect front and back contacts <NUM>, <NUM> of the one or more of the solar cells <NUM> to bypass the electrical connections to the one or more of the solar cells <NUM>. The corner connection layout simplifies the use of the bypass switches 54b, because the front and back contacts <NUM>, <NUM> are physically adjacent to each other. In addition, the front and back contacts <NUM>, <NUM> are accessible to the traces on the flex circuit substrate <NUM>.

The corner connection layout also provides another important capability for the bypassing of solar cells <NUM>. Specifically, the flex circuit substrate <NUM> can include traces underneath the solar cells <NUM> that are electrically isolated from the solar cell <NUM>.

In addition, the exposed area <NUM> of the substrate <NUM> also includes one or more sets of switches 54a for altering a string of the solar cells <NUM> by adding and/or removing one or more of the solar cells <NUM> to or from the electrical connections of the string. The string is altered to change a voltage produced by the string.

<FIG> shows a set of three solar cells <NUM> in a vertical column. The bus bar <NUM> is a low resistance metal conductor on the surface of the solar cell <NUM> that carries the current from individual narrow metal fingers <NUM> of the grid <NUM> (not shown) to the front contacts <NUM> of the solar cell <NUM>. Each end of the bus bar <NUM> is connected to a front contact <NUM> that can connect to the traces on the flex sheet substrate <NUM>. The back contact <NUM> is connected to the backside of the solar cell <NUM>.

The dashed lines are traces <NUM>, <NUM> in or on the flex sheet substrate <NUM> underneath the solar cells <NUM> that are electrically isolated from the solar cells <NUM>. These traces <NUM>, <NUM> provide a parallel current path for the front and back contacts <NUM>, <NUM>, respectively, of the solar cell <NUM> between each corner. These traces <NUM>, <NUM> also provide a current path to bypass a solar cell <NUM> and allow for current flow underneath the solar cell <NUM>, when a solar cell <NUM> is bypassed. This is similar to the discussion of stayout zones found in some of the applications cross-referenced above.

The corner regions <NUM> may also include a bypass diode <NUM>, as well as corner conductors <NUM> which support series connection of these solar cells <NUM>. The current will flow from top to bottom through these three solar cells <NUM>.

Bypass switches 54b are shown in the corner regions <NUM> as well. Only a single by-pass switch 54b is necessary in each corner region <NUM>, but a second bypass switch 54b in a corner region <NUM> provides further protection from failure.

Referring again to <FIG>, the switches <NUM> are shown as single-pole single-throw (SPST) switches <NUM>. Such switches <NUM> could be semiconductor-based, for example, Silicon (Si) MOSFETs (metal-oxide-semiconductor field-effect transistors), or Gallium Nitride (GaN) or Silicon Carbide (SiC) FETs (field-effect transistors), and are available from multiple vendors for space applications.

To simplify assembly, however, the functions of the switches <NUM> and bypass diode <NUM> could be combined into a single integrated device. Semiconductor or MEMS (micro-electrical-mechanical system) switches <NUM> could be well integrated with the bypass diode <NUM> on a common semiconductor wafer or through various integration approaches.

A single integrated device <NUM> combining the switch <NUM> functions with a bypass diode <NUM> is shown in <FIG>. The heavy dark lines represent conducting paths <NUM> in the corner region <NUM> and through the integrated device <NUM>. The short parallel lines labeled A through F within the integrated device <NUM> represent switches <NUM>, which can change the resistance in that region from very low to very high. The diode symbol between switches E and C/D <NUM> represents a bypass diode <NUM>. Operation of these switches <NUM> control the operation of the series versus circuit termination and the solar cell <NUM> bypassing performed by the integrated device <NUM>.

The device <NUM> in <FIG> has one more switch <NUM> than the layouts in <FIG> and <FIG>. This extra switch <NUM> enables termination of either solar cell <NUM> connected to the device <NUM>. Another way to understand this is that each solar cell <NUM> in the configuration can terminate at either corner.

Not shown is the control of the integrated device <NUM> and its switches <NUM>. This could be achieved with various communication strategies. A common method would be to serially transmit information including an address to identify the integrated device <NUM> and the switches <NUM> (A-F), and to transmit the open/close state of each switch <NUM>. This serial communication is commonly implemented with a clock signal and an information signal with a power and ground line. These communication lines can be integrated into the flex circuit substrate <NUM>. Since they do not carry much power or current, the size of the conductors can be much smaller than the other traces and can be integrated into the flex circuit substrate <NUM> without difficulty. There are many other ways to communicate information, such as through wireless communication, which could be electromagnetic or optical.

It may be desirable to make the switches <NUM> out of one semiconductor material and the bypass diode <NUM> out of another semiconductor material. For example, Gallium Nitride (GaN) may be preferred for the combined switches <NUM>, while Si is preferred for the bypass diode <NUM>. These functions can be separated into separate devices as shown in <FIG>, wherein the bypass diode <NUM> is shown adjacent and connected to the combined switches <NUM>.

Examples of the disclosure may be described in the context of a method <NUM> of fabricating a solar cell <NUM>, solar cell panel 10a and/or satellite, comprising steps <NUM>-<NUM>, as shown in <FIG>, wherein the resulting satellite <NUM> having a solar cell panel 10a comprised of solar cells <NUM> are shown in <FIG>.

As illustrated in <FIG>, during pre-production, exemplary method <NUM> may include specification and design <NUM> of the solar cell <NUM>, solar cell panel 10a and/or satellite <NUM>, and material procurement <NUM> for same. During production, component and subassembly manufacturing <NUM> and system integration <NUM> of the solar cell <NUM>, solar cell panel 10a and/or satellite <NUM> takes place, which include fabricating the solar cell <NUM>, solar cell panel 10a and/or satellite <NUM>. Thereafter, the solar cell <NUM>, solar cell panel 10a and/or satellite <NUM> may go through certification and delivery <NUM> in order to be placed in service <NUM>. The solar cell <NUM>, solar cell panel 10a and/or satellite <NUM> may also be scheduled for maintenance and service <NUM> (which includes modification, reconfiguration, refurbishment, and so on), before being launched.

For the purposes of this description, a system integrator may include without limitation any number of solar cell, solar cell panel, satellite or spacecraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be a satellite company, military entity, service organization, and so on.

As shown in <FIG>, a satellite <NUM> fabricated by exemplary method <NUM> may include systems <NUM>, a body <NUM>, solar cell panels 10a comprised of solar cells <NUM>, and one or more antennae <NUM>. Examples of the systems <NUM> included with the satellite <NUM> include, but are not limited to, one or more of a propulsion system <NUM>, an electrical system <NUM>, a communications system <NUM>, and a power system <NUM>. Any number of other systems <NUM> also may be included.

<FIG> is an illustration of the solar cell panel 10a in the form of a functional block diagram, according to one example. The solar cell panel 10a is comprised of the solar cell array <NUM>, which is comprised of one or more of the solar cells <NUM> individually attached to the substrate <NUM>. Each of the solar cells <NUM> absorbs light <NUM> from a light source <NUM> and generates an electrical output <NUM> in response thereto.

At least one of the solar cells <NUM> has at least one cropped corner <NUM> that defines a corner region <NUM>, such that an area <NUM> of the substrate <NUM> remains exposed when the solar cell <NUM> is attached to the substrate <NUM>. When a plurality of solar cells <NUM> are attached to the substrate <NUM>, the corner regions <NUM> of adjacent ones of the solar cells <NUM> are aligned, thereby exposing the area <NUM> of the substrate <NUM>.

The area <NUM> of the substrate <NUM> that remains exposed includes one or more corner conductors <NUM> attached to, printed on, or integrated with the substrate <NUM>, and one or more electrical connections between the solar cells <NUM> and the corner conductors <NUM> are made in a corner region <NUM> resulting from the cropped corner <NUM> of the at least one of the solar cells <NUM>.

The corner region <NUM> resulting from the cropped corner <NUM> includes at least one contact, for example, a front contact <NUM> on a front side of the solar cell <NUM> and/or a back contact <NUM> on a back side of the solar cell <NUM>, for making the electrical connections between the corner conductors <NUM> and the solar cell <NUM>. The electrical connections may comprise up/down or left/right series connections that determine a flow of power through the solar cells <NUM>, and may include one or more bypass diodes <NUM>.

The area <NUM> of the substrate <NUM> that remains exposed includes at least one switch <NUM>, located in the corner region <NUM> defined by the cropped corners <NUM> adjacent to the solar cells <NUM>, for changing a current flow path between the solar cells <NUM> and the electrical connections. The substrate <NUM> includes one or more traces connected to the switches <NUM> for making the electrical connections between the solar cells <NUM>.

The switches 54a reconfigure string lengths for the electrical connections between the solar cells <NUM> and the switches 54b bypass solar cells <NUM> in response to a control signal. The switches 54a also reconfigure connections between strings allowing reconfigurability of series connections and outputs between the strings. The switches <NUM> may be single-pole single-throw (SPST) switches, or dual-pole single-throw (DPST) switches, or integrated devices that may be packaged to include functions other than switching functions, such as the functions of the bypass diode <NUM>.

A solar cell array based on the corner conductor design and using a flex circuit substrate was built to demonstrate the reconfiguration of the string length of the array.

<FIG> is an image of a demonstration solar cell array comprised of <NUM> solar cells arranged in three rows with each row having four solar cells. Electrical connections are made in the corner regions to provide either series connections or string terminations. The current flow or conduction paths were selected by welding a metal foil jumper in place. Wire pairs were added at several locations instead of metal jumpers, wherein these wires extended beyond the perimeter of the solar cell array.

<FIG> is an image showing a close-up view of one of the corner regions showing the electrical connections between the front contacts, back contacts, bypass diodes, and solar cells.

<FIG> is a version of <FIG> with the electrical connections between the upper left and the lower left solar cells indicated by the dark lines drawn over the conduction paths. One conduction path connects the back contact of the upper left solar cell to the front contact of the lower left solar cell, so that the current flows downward. Another conduction path connects the back contact of the lower left solar cell through the bypass diode.

The electrical connections between the upper right and the lower right solar cells are rotated <NUM> degrees as compared to the electrical connections between the upper left and the lower left solar cells, so that the current flows from the lower right solar cell to the upper right solar cell.

Jumpers are placed for series connections. By changing the jumper locations, the current flow can be terminated into buried traces.

<FIG> is an image of another corner region where wires have been added in place of jumpers. The wires could be shorted together to function like a jumper, or the wires could be isolated to function like the lack of a jumper.

In this demonstration, through the use of jumpers or wires, the configuration of the solar cell array with <NUM> solar cells can be changed from <NUM> strings with <NUM> solar cells to <NUM> strings with <NUM> solar cells.

<FIG> is a graph of light-current-voltage (LIV) measurements of the solar cell array under AM0 (air mass coefficient for zero atmosphere) illumination, wherein the measurements were made of the configurations of <NUM> strings with <NUM> solar cells and <NUM> strings with <NUM> solar cells. The change in voltage confirms the change in string length.

<FIG> is an image of the demonstration solar cell array of <FIG>, wherein the center <NUM> solar cells are covered to prevent their operation.

<FIG> is a graph of LIV measurements of the solar cell array under AM0 illumination, wherein the measurements were made of the configuration shown in <FIG> with the center <NUM> solar cells covered to prevent their operation. The covering of the solar cells is an experimental way to mimic damage to solar cells where the solar cell has reduced current or voltage output.

In this example, the solar cell array is configured to have <NUM> strings with <NUM> solar cells each. The data is shown for strings <NUM>, <NUM> and <NUM> both covered and uncovered. When uncovered, the <NUM> strings have similar output with a voltage near 11V. When covered, <NUM> strings lose a solar cell and <NUM> string loses <NUM> solar cells. This loss of solar cells is reflected in the loss of voltage. The vertical line for Vload represents a load voltage where current would be collected by the power system. At this selection of load voltage, the load current would fall to near <NUM>.

<FIG> is a graph of LIV measurements of the solar cell array under AM0 illumination, wherein the measurements were made of the configuration shown in <FIG> with the center <NUM> solar cells covered to prevent their operation.

In this example, the solar cell array is configured to have <NUM> strings with <NUM> solar cells each, wherein the <NUM> solar cells increase the power output of the string. With the center <NUM> solar cells covered to prevent their operation, there are <NUM> solar cells that are operating and <NUM> cells that are not operating in each string. Current must flow though the bypass diodes of the solar cells that are not operating, and thus the voltage output of the strings is that of <NUM> operating solar cells minus <NUM> bypass diodes.

The data in <FIG> shows the data for the original string before the center <NUM> solar cells are covered. Then, when the center <NUM> solar cells are covered, the voltage falls to the level indicated by the damaged string.

Reconfiguring to a string length of <NUM> solar cells increases the voltage and power output for resilient strings <NUM> and <NUM>. Like <FIG>, the vertical line for Vload represents a load voltage. For resilient strings <NUM> and <NUM>, the load current is now nearly that of the original string.

The power from the center <NUM> solar cells that are covered is still lost, of course. However, in a conventional solar cell array, damage to <NUM> out of <NUM> solar cells would largely eliminate the current at load delivered to the power system. In this example, by reconfiguring the solar cell array, power from each solar cell is able to be delivered to the power system with nearly optimal collection. Specifically, the original string delivers <NUM> Watts per solar cell at the load voltage, but when the center <NUM> solar cells are covered, the damaged string falls to <NUM> Watts per solar cell. After reconfiguration, the resilient strings <NUM> and <NUM> are able to deliver <NUM> Watts per functioning solar cell.

The addition of another switch to connect the front and back contacts of the solar cells in the array would improve power output. By doing this, the current would bypass the non-functioning solar cells in the array through the switch without power loss. however, this demonstration solar cell array does not provide this functionality, and thus there is power loss into the bypass diodes.

Claim 1:
A solar cell array, comprising:
a plurality of solar cells (<NUM>) attached to a substrate (<NUM>), wherein:
the substrate (<NUM>) includes one or more electrical connections to the solar cells (<NUM>); and
the substrate (<NUM>) includes one or more switches (54b) for bypassing one or more of the electrical connections to one or more of the solar cells (<NUM>),
wherein the solar cells (<NUM>), one or more bypass diodes (<NUM>), and the switches (54b) are electrically in parallel,
wherein an area (<NUM>) of the substrate (<NUM>) remains exposed when at least one of the solar cells (<NUM>) having one or more cropped corners (<NUM>) is attached to the substrate,
wherein the area of the substrate that remains exposed includes at least one of the switches (54b),
wherein the solar cells (<NUM>) are attached to the substrate (<NUM>) such that corner regions (<NUM>) defined by the cropped corners (<NUM>) of adjacent ones of the solar cells (<NUM>) are aligned, thereby exposing the area (<NUM>) of the substrate (<NUM>), and
wherein the at least one of the switches (54b) is located in the corner region (<NUM>) defined by the cropped corners (<NUM>) of adjacent ones of the solar cells (<NUM>).