Patent Description:
A typical spaceflight-capable solar cell panel assembly involves building solar cell arrays comprised of long strings of solar cells. 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. The fixed number of solar cells must be sized under the most difficult conditions, which is the hottest period of operation with the highest dosage of electron and proton radiation. Specifically, existing solutions produce strings sized for worst case environments.

For a 100V operation, this may be ~<NUM> solar cells. At the beginning of the solar cell array's operation, the radiation damage is minimal and the 100V can be achieved with ~<NUM> solar cells. Thus, at the beginning of operation, roughly <NUM>% (<NUM>/<NUM>) of the solar cells are not producing usable power.

This will change with operating temperature and with the accumulated dose of high energy electrons and protons in the space environment. Of primary concern is the changing voltage during the lifespan of the solar cell array.

What is needed, then, is a means for accommodating the changes to the solar cell array's operation during its lifespan.

<CIT> according to its abstract states: A reconfigurable solar panel system having a plurality of solar cells arranged in a predefined pattern on a printed circuit board having 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 and having 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. The present approach is capable of monitoring, controlling, and protecting the solar panel, as well as being reconfigured before, during and after the panel is assembled. With the present approach it is also possible to reconfigure the solar panel after it has been employed in an application, such as a satellite that is in orbit.

<CIT> according to its abstract states: 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.

To overcome the limitations described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present disclosure describes a solar cell array as defined in claim <NUM>. The solar cell array according to the invention comprises a group of 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 configured to split the group of solar cells into two strings and to change a string length by altering a current flow path between the solar cells and one or more of the electrical connections, wherein each string has a voltage output, wherein the switches are configured to change the string length of both strings to allow for reconfigurability of series connections and outputs between the strings. The invention also relates to the method of operating a solar cell array according to claim <NUM> and to a method for fabricating a solar cell array according to claim <NUM>.

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. The 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 switches change the string length for the one or more of the solar cells in response to a control signal, wherein the switches change the string length to allow for reconfigurability of series connections and outputs between multiple strings. The switches are single-pole single-throw (SPST) switches or dual-pole single-throw (DPST) switches.

The substrate includes one or more traces connected to switches for making the electrical connections between the solar cells.

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 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.

A satellite power system requires power produced at a specific voltage which is produced by a plurality of series-connected solar cells <NUM>. The voltage produced by each solar cell <NUM> varies depending primarily on the operating temperature, and electron and proton radiation history. The string is typically of a fixed length of solar cells <NUM> and designed to have enough solar cells <NUM> to reach the required voltage throughout the operation. Over many parts of the mission, the string is producing more voltage than needed. Effectively, one or more solar cells <NUM> are not contributing to power. This disclosure describes a way to reconfigure string lengths during operation so that power can be collected from each solar cell <NUM> throughout the mission. This results in the ability to produce strings operating with a constant total output voltage and produce higher power from the solar cell array <NUM>.

A conventional triple junction solar cell <NUM> generates its maximum power at roughly <NUM>. 2A and <NUM>. This will change with operating temperature and with the accumulated dose of high energy electrons and protons in the space environment.

Of primary concern is the changing voltage. The power system often collects current at a specific voltage known as the load voltage. From the beginning of life (BOL) of the satellite to the end of life (EOL), the voltage may fall from <NUM> to <NUM>. In order to reach the load voltage, which may be 20V to 100V, many solar cells <NUM> are connected in series, so each solar cell <NUM> adds to the voltage of the string.

In one example, <NUM> solar cells <NUM> may be needed to have a maximum power point near 100V at BOL. At EOL, on the other hand, <NUM> solar cells <NUM> may be needed to have a 100V maximum power point. Thus, the additional <NUM> solar cells <NUM> at BOL are not contributing any power.

By implementing switches in the solar cell array <NUM>, the string length can be reconfigured during operation. Specifically, the solar cell array <NUM> is reconfigured to have a string length that produces a maximum power point near the load voltage.

For example, a solar cell array <NUM> with <NUM> solar cells <NUM> can be split up into many strings to deliver power to a 100V power system. In order to deliver power at 100V at EOL, the solar cell array <NUM> will need <NUM> strings, each <NUM> solar cells <NUM> long, having a 100V maximum power point. The power output would be <NUM> x 100V x <NUM>. 2A = 2160W. A conventional solar cell array with a fixed string length would deliver this power at BOL and EOL. There would be some change of current and fill factor with radiation, but that is a secondary factor for this discussion.

Reconfiguration of the string length would deliver much higher power levels at BOL. At BOL, the solar cell array <NUM> could be reconfigured to use <NUM> strings, each with a length of <NUM> solar cells <NUM>, to produce a maximum power point of 100V. The power output would be <NUM> x 100V x <NUM>. 2A = 2640W. This is <NUM>% more power than the previous example. The solar cell array <NUM> can be reconfigured throughout its mission to change the string length from <NUM> to <NUM> solar cells <NUM>. This will keep the voltage at the maximum power point near the load voltage of 100V and deliver optimal power.

A reconfigurable array <NUM> can also be advantageous in interplanetary missions, where radiation and operating temperature change greatly, thereby changing the solar cell <NUM> voltage.

Another application is where the load voltage may change. For example, during its early stages of operation, a satellite may move into its orbital position using electrical propulsion. The electrical propulsion system may prefer a higher load voltage, as compared to operations during other stages of the mission. Reconfigurability could be implemented to change the string length, so that the maximum power point of the string could change to 160V or 200V or 300V for electrical propulsion and then to 100V for other stages of the mission.

Reconfigurability requires several switches to be introduced into the solar cell array <NUM>. To wire these switches into a conventional solar cell array requires the insertion of end tabs between the solar cell and the wiring, and the switches. The switches will also need signal electrical lines to communicate to them the desired state (open or closed). This would require extensive labor, cost, and panel area. Additionally, the extra connections also raise the risk of a problem developing. These costs and risks have outweighed the benefits and prevented reconfigurable arrays from being built.

However, a solar cell array <NUM> using the corner conductor <NUM> layout dramatically changes the cost to implement a reconfigurable array <NUM>.

<FIG> illustrate switches <NUM> used for changing a current flow path between the solar cells <NUM> and the electrical connections. In these figures, the switches <NUM> are single-pole single-throw (SPST) switches <NUM> packaged together in pairs, but other switches <NUM> may be used and the switches <NUM> may be packaged singly, in pairs, or as otherwise desired.

Each of the SPST switches <NUM> in the pair may be controlled independently or together using one or multiple control signals (not shown). <FIG> shows a pair of SPST switches <NUM> that are both open, <FIG> shows a pair of SPST switches <NUM> with the left one open and the right one closed, <FIG> shows a pair of SPST switches <NUM> that are both closed, and <FIG> shows a pair of SPST switches <NUM> with the left one closed and the right one open.

<FIG> shows a layout where the switches <NUM> are positioned in the corner region <NUM>. The pair of SPST switches <NUM> in the top center of the corner region <NUM> connects the back contact <NUM> of the top left solar cell <NUM> to either a string output line <NUM> or a series connection to a bypass diode <NUM> and the next solar cell <NUM> in the lower left. The photocurrent flows from the back contact <NUM> of the top left solar cell <NUM> to the front contact <NUM> of the lower left solar cell <NUM>. The pair of SPST switches <NUM> on the left side of the corner region <NUM> allows the front contact <NUM> of the bottom left solar cell <NUM> to connect to the back contact <NUM> of the top left solar cell <NUM> in a series connection, and connects the front contact <NUM> of the bottom left solar cell <NUM> to the string output line <NUM>.

These switches <NUM> enable the solar cells <NUM> to either have a series connection to another solar cell <NUM>, or to terminate to buried V+ or V- string output lines <NUM>. Moreover, the switches <NUM> enable the solar cells <NUM> to terminate at multiple connection paths. Similarly, the switches <NUM> can also have several connection paths, which all follow the logic laid out here.

The connections among the solar cells <NUM> on the right side of the corner region <NUM> are a <NUM> degree reflection of the connections among the solar cells <NUM> on the left side of the corner region <NUM>. However, the configuration of the SPST switches <NUM> on the left side is reversed. On this side, the current flows from the back contact <NUM> of the lower right solar cell <NUM> to the buried V+ string output line <NUM> for string termination. The front contact <NUM> of the top right solar cell <NUM> is connected to the V- string output line <NUM>.

The electrical connections made in the corner regions <NUM> use a common layout of the solar cells <NUM> regardless of whether they have a series connection or circuit output. No bus bars or wiring is needed, saving labor and panel 10a area. Furthermore, the layout of the electrical connections in the corner region <NUM> takes advantage of the ability to include patterned wiring in the substrate <NUM>. More or less complex substrate <NUM> wiring layouts have no or minimal increase in costs. The additional wiring required by the switches <NUM> is simply built with little additional effort. This combination of traits is ideally suited to a reconfigurable solar cell array <NUM>.

The pairs of SPST switches <NUM> may be operated so that one SPST switch <NUM> is closed when the other SPST switch <NUM> is open, which could be implemented using a dual-pole single-throw (DPST) switch <NUM>. Moreover, the pair of SPST switches <NUM>, or the DPST switch <NUM>, could be implemented with one or more control signals. These SPST or DPST switches <NUM> could be electromechanical relays, or microelectromechanical system (MEMS) relays, where a solid conductor is mechanically flexed to make and break conducting paths. A field effect transistor device is another switch <NUM> that is available built from Silicon (Si), Silicon Carbide (SiC), or Gallium Nitride (GaN).

<FIG> shows a group <NUM> of solar cells <NUM> labeled from <NUM> to <NUM>. This group <NUM> can be split into two strings. There is a series of eight switches <NUM> between the solar cell <NUM> labeled as <NUM> to the solar cell <NUM> labeled as <NUM> that control the length of each of the two strings, and a ninth switch <NUM> coupled between the solar cell <NUM> labeled as <NUM> and the outputs V1+ and V2+. The switches <NUM> can make the length of a first string between <NUM> and <NUM> solar cells <NUM>, and the length of a second string between <NUM> and <NUM> solar cells <NUM>. There are <NUM> fixed output lines, wherein the output of the first string is V1- and V1+, and the output of the second string is V2- and V2+.

V1- always is set from the beginning of the string preceding the solar cell <NUM> labeled as <NUM>. V1+ can be at any point after the solar cell <NUM> labeled as <NUM> to after the solar cell <NUM> labeled as <NUM>, which may be the configuration at the end of life (EOL) when the solar cell <NUM> voltage has fallen. As drawn, V1+ terminates after the solar cell <NUM> labeled as <NUM>, and V2+ always terminates after the solar cell <NUM> labeled as <NUM>. As drawn, V2-terminates before the solar cell <NUM> labeled as <NUM>.

This solar cell array <NUM> can allow the first string to reconfigure to have the needed string length to optimize the operating voltage. The second string would have a lesser voltage output. Multiple copies of the second string, using other groups <NUM>, may need to be connected in series to reach the load voltage.

<FIG> is a layout that demonstrates how to combine the strings for a desired voltage output, and shows <NUM> groups <NUM> of solar cells <NUM>. Each group <NUM> is comprised of the solar cells <NUM> and the switches <NUM> shown in <FIG>. The first string of the solar cells <NUM> in each group <NUM> produces the desired voltage from <NUM>-<NUM> solar cells <NUM>, which is connected to outputs V1, V2,. The second string of the solar cells <NUM> in each group <NUM> produces the desired voltage from <NUM>-<NUM> solar cells <NUM>, which is connected to outputs Va, Vb,.

The layout of <FIG> shows two rows of groups <NUM> with additional switches <NUM> between the rows for connecting the second strings from each of the groups <NUM>. In this example, string output Va- is terminated directly to V15-. Va+ is connected to Vb-through two pairs of switches <NUM>. The same occurs between Vb+ and Vc-, and continues across the groups <NUM>. As shown, the switches <NUM> allow series connection from Va to Vg. In this example, the first string of each group <NUM> is <NUM> solar cells <NUM> long and the second string is <NUM> solar cells <NUM> long. The combination of segments that output Va to Vg is a string <NUM> solar cells <NUM> long. These are combined for output V15, which is <NUM> solar cells <NUM> long and produces sufficient voltage to be utilized by the system.

Between Vg+ and Vh-, the output is terminated at switches 54a. These terminating switches 54a show the change in the state of the switch elements <NUM>. The terminating switches <NUM> terminate Vg+ into V15+ and Vh- into V16-. Then, Vh to Vn are series-connected, producing another string of <NUM> solar cells <NUM>. Vn+ is connected to V16+.

Consequently, <FIG> shows how a group <NUM> of solar cells <NUM> can be reconfigured between a long first string with the desired voltage output and a short second string that is a fraction of the desired voltage, while <FIG> shows how those short second strings can be combined to produce the desired voltage.

The string lengths and layouts can change as needed. This disclosure is focused on the switching topology. To implement this wiring and switching on a conventional solar cell array would require extensive manual effort. The solar cell array <NUM> of this disclosure, where buried traces are patterned in the substrate <NUM>, can accommodate complex wiring with minimal extra effort, making the complexity of the reconfigurable solar cell array <NUM> achievable.

There are many configurations where solar cells <NUM> could be switched to change the string length. <FIG> shows a group <NUM> comprised of <NUM> solar cells <NUM>, where the string length can be changed by single solar cells <NUM>. It may be advantageous to switch certain groups <NUM> of solar cells <NUM>.

<FIG> demonstrates one such combination. <FIG> shows a solar cell array <NUM> with <NUM> solar cells <NUM> arranged in <NUM> rows of <NUM> columns. Solar cells <NUM> are labeled as <NUM>-<NUM>, and are series-connected by line <NUM> along the sides (and tops) of the solar cells <NUM>.

There are also traces <NUM> running left-right in the flex circuit substrate <NUM>. These traces <NUM> are buried beneath, and are electrically isolated from, the solar cells <NUM> and are intended as string termination outputs. The traces <NUM> can be accessible in the corner regions <NUM> between solar cells <NUM>, allowing any solar cell <NUM> to easily access the output lines <NUM>.

Two of the buried traces <NUM> are labeled as A and B. These traces <NUM> could be accessed by the solar cells <NUM> labeled as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. This is a typical configuration described for a solar cell array <NUM> comprised of solar cells <NUM> connected in the corner regions <NUM>. This is valuable for a reconfigurable solar cell array <NUM>.

<FIG> shows how this can be used in a reconfigurable solar cell array <NUM>. Here, the <NUM> solar cells <NUM> are shown smaller to allow more space to diagram the wiring and switching connections. The geometry shown is well suited to the use of electrical connections in corner regions <NUM>. Between the solar cells <NUM> labeled as <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and after the solar cell <NUM> labeled as <NUM>, there are switches <NUM> analogous to those in <FIG>. These switches <NUM> could be implemented in the corner regions <NUM> as in <FIG>, located between the solar cells <NUM> in the same column position. As in <FIG>, there are two string outputs, namely, V1 for the first string and V2 for the second string. V2- and V1+ are accessed by each switch <NUM>. Only single traces <NUM> for V1+ and V2-running under the solar cells <NUM> are needed to enable this switching.

The traces <NUM> are deposited on the surface of the substrate <NUM>, and the traces <NUM> of V1+ and V2- are buried to pass beneath the surface traces <NUM>. The vertical compound lines <NUM> indicate interconnects that connect the switches <NUM> to the buried traces <NUM>, wherein the switches <NUM> are set so that the first string is <NUM> solar cells <NUM> long and the second string is <NUM> solar cells <NUM> long.

The V1 string can have a length of <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> solar cells <NUM>. This is accomplished with the buried trace <NUM> running between the solar cells <NUM> in rows <NUM> and <NUM>. These connections to the output lines could move up a row so that it is between the solar cells in rows <NUM> and <NUM>. This would result in string lengths of <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. These different combinations result from the four-row solar cell array <NUM> with an output line running between two rows. Additional output lines could be added between other rows to enable more switching points and more control of the string length. However, this complexity will lead to crossing in the buried traces <NUM>, requiring additional effort.

This layout is easily manufactured as no traces cross each other on the same layer, i.e., no crossing solid traces or crossing dashed traces. If these traces were to cross, then another metal layer and vias would be needed, which raise concerns about longevity in the space environment. This configuration with the corner connected solar cell array <NUM> having buried traces <NUM> in the substrate <NUM> allows for very simple connection paths.

The configurations of <FIG> and <FIG> were based on a group <NUM> of solar cells <NUM> split into a full voltage first string and a partial voltage second string. Then, the second strings of the groups <NUM> are connected together to build the needed voltage.

A related approach is shown in <FIG> includes multiple groups <NUM> of solar cells <NUM>, each having the same configuration as shown in <FIG> and <FIG>. Each group <NUM> includes first and second strings 68a, 68b, wherein the first strings 68a are full voltage strings and the second strings 68b are partial voltage strings, and multiple partial voltage second strings 68b across multiple groups <NUM> are connected together to provide the needed string length and output voltage.

<FIG> shows each group <NUM> split into two strings 68a, 68b of different lengths, wherein the first and second strings 68a, 68b from each group <NUM> are connected together to provide the needed string length. Specifically, the first string 68a of the first group <NUM> is a full voltage string; the second string 68b of the first group <NUM> is a partial voltage string that is combined with the first string 68a of the second group <NUM> to create a full voltage string; the second string 68b of the second group <NUM> is a partial voltage string that is combined with the first string 68a of the third group <NUM> to create a full voltage string; and the second string 68b of the third group <NUM> is a full voltage string.

Although the examples shown have only two strings 68a, 68b, these groups <NUM> could include a greater or lesser number of strings. Specifically, a group <NUM> could be comprised of <NUM>, <NUM>, <NUM>, <NUM>, etc., full voltage strings and zero, one or possibly multiple partial voltage strings.

<FIG> have focused on reconfiguring by changing string length by a small number of solar cells <NUM> in order to control the output voltage. This is valuable as individual solar cell <NUM> voltages will change during the mission due to space radiation exposure and due to operating temperature changes.

<FIG> and <FIG> apply reconfigurability to larger changes in string length. This could be for an application where the output voltage is desired to have a large change.

For example, during satellite operation, the solar cell array <NUM> is generally charging a set of batteries, where the load voltage may be at 100V or less. However, during mission stages, the satellite may use electric propulsion to change its orbit location, where the load voltage may be at 160V or 200V or 300V or other. It could be desirable for the solar cell array <NUM> to output the desired voltage for the different operations.

Another configuration would be with interplanetary missions, where the solar cell array <NUM> could become very hot or very cold as the distance to the sun changes. Alternatively, the solar cell array <NUM> temperature could change dramatically if the vehicle environment changes, such as if landing on an asteroid, or other object or planet. These changes in temperature will change the voltage produced by the solar cells <NUM> and the needed length of the string, which can be dramatic.

<FIG> shows a layout of solar cells <NUM> comprised of three flex sheet substrates <NUM>, 12b, 12c. Each substrate 12a, 12b, 12c has a grid of <NUM> (horizontal) x <NUM> (vertical) solar cells <NUM>. The lower sections 12d of each substrate 12a, 12b, 12c have <NUM> solar cells <NUM> producing 100V. The upper sections 12e of each substrate 12a, 12b, 12c have <NUM>, <NUM> and <NUM> solar cells <NUM>, respectively, for a total of <NUM> solar cells <NUM>. There are several solar cell <NUM> positions where a solar cell <NUM> is not included, as indicated by the rectangular elements <NUM> with the diagonal fill. The serpentine lines <NUM> show generally how the solar cells <NUM> in each section 12d, 12e of each substrate 12a, 12b, 12c are series-connected in a string. There are eight pairs of SPST switches <NUM> shown as triangles, wherein the switches <NUM> can be reconfigured so that each of the lower sections 12d are single strings and the upper sections 12e of each substrate 12a, 12b, 12c are series-connected together in a single string. In this configuration, every solar cell <NUM> is in a series-connected string having <NUM> solar cells <NUM>. This is a configuration to produce 100V for a typical geosynchronous (GEO) near-earth environment after <NUM> years of radiation caused voltage loss.

<FIG> shows how the layout of <FIG> can be reconfigured using the switches <NUM>. When series-connected, the lower sections 12d and upper sections 12e of each substrate 12a, 12b, 12c comprise strings that are <NUM> (<NUM>+<NUM>), <NUM> (<NUM>+<NUM>) and <NUM> (<NUM>+<NUM>) solar cells <NUM> long, respectively. The strings would produce 132V, 132V and 134V, respectively, under GEO conditions. Or, in a hot environment, the 100V output can be maintained.

In conclusion, this description involves the addition of switches <NUM> and wiring to a solar cell array <NUM> to achieve the reconfigurable functionality. The application of switches and wiring onto a conventional solar cell array would be extremely complicated and expensive. What makes the reconfigurable solar cell array <NUM> now possible is the use of wiring traces in the substrate <NUM> instead of conventional wires. Reconfigurability requires wiring in parallel to many or all the solar cells <NUM>, whereas conventional wires only have a start and end connections. Traces in the substrate <NUM> can have many connections made to them at any point down the length of the trace. Therefore, traces can be routed under the solar cells <NUM> and very easily provide circuit output lines for all the solar cells <NUM>. Furthermore, the front and back contacts <NUM>, <NUM> of the solar cells <NUM> are available in the corner regions <NUM>. Switches <NUM> can be added to achieve reconfigurability without consuming panel 10a area. The figures and descriptions show how reconfigurability can be at the solar cell <NUM> level, changing the number of solar cells <NUM> in a string and its resulting output voltage. Alternatively, reconfigurability can connect strings together building voltage in larger blocks.

In a conventional solar cell array, the addition of switches would require end tabs, wiring, switches, and circuit wiring. These components would need to be between any two solar cells that can be reconfigured. In addition to labor, these components would take considerable panel area, thereby reducing power production.

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 and/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 <NUM> reconfigure string lengths for the electrical connections between the solar cells <NUM> in response to a control signal. The switches <NUM> 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, and may be packaged singly, in pairs, or as otherwise desired.

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.

Claim 1:
A solar cell array, comprising:
a group (<NUM>) of solar cells (<NUM>) attached to a substrate (<NUM>), wherein:
the substrate includes one or more electrical connections (<NUM>) to the solar cells; and
the substrate includes one or more switches (<NUM>) configured to split the group of solar cells (<NUM>) into two strings and to change a string length by altering a current flow path between the solar cells and one or more of the electrical connections, wherein each string has a voltage output (V1-, V1+, V2-, V2+),
wherein the switches are configured to change the string length of both strings to allow for reconfigurability of series connections and outputs between the strings.