Systems and methods for solar array communications

Abstract

To provide a system and method for communication using solar cells as a communication device.SOLUTION: A bidirectional circuit 100 for a solar cell array emitting a communication message from the solar cell array by reverse-biasing the solar cell array to cause at least a portion of the solar cell array to emit a detectable amount of radiation corresponding to the communication message includes: a solar cell string 105, 110 comprising a plurality of solar cells coupled together; a charge storage device (battery 190) coupled to a power bus 195; and a two-quadrant bidirectional boost-buck converter 170 having first and second paired MOSFETs 173, 174 connected in series between positive and negative rails of the power bus with an inductor 171 coupled from between the first and second paired MOSFETs to a charging output of the solar cell string.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 62 / 893,756, filed Aug. 29, 2019 by Nader Lotfy et al. and entitled "SYSTEM AND METHOD FOR SOLAR ARRAY COMMUNICATION," which are hereby incorporated by reference in their entireties; and U.S. Provisional Application No. 62 / 838,937, filed Apr. 25, 2019 by Nader Lotfy and entitled "SYSTEM AND METHOD FOR SOLAR ARRAY DIAGNOSIS," which are hereby incorporated by reference in their entireties. [Background technology]

[0002]

[0001] In certain situations, it may not be possible, practical, or desirable to communicate using conventional communication systems. In some cases, conventional communication is not possible, for example, due to equipment failure. In other instances, it may not be desirable, for example, to allow conventional communications to be intercepted. In still other situations, the use of conventional communications may make the sender detectable.

[0003] What is needed are systems and methods that can be used in these and other situations. Summary of the Invention

[0004]

[0003] In one possible implementation, a method for a solar cell array is provided that includes emitting a communication message from the solar cell array by reverse biasing the solar cell array so as to cause at least a portion of the solar cells to emit a detectable amount of radiation corresponding to the communication message.

[0005]

[0004] In one possible embodiment, a solar cell array circuit is provided that includes a solar cell string having a plurality of solar cells coupled together, a charge storage device coupled to a power bus, and a bidirectional boost-buck converter having a first pair and a second pair of MOSFETs connected in series between positive and negative rails of the power bus, with an inductor coupled between the first and second pairs of MOSFETs to the charging output of the solar cell string.

[0006] In one possible implementation, a method is provided for communicating a message to a solar array on a high altitude, long endurance aircraft. This particular embodiment includes displaying a message on a solar array of the high altitude, long endurance aircraft, detecting the message using a satellite, and relaying the detected message from the satellite to a platform below the high altitude, long endurance aircraft. [Brief description of the drawings]

[0007] [Figure 1]

[0006] A simplified schematic diagram of a bidirectional circuit for a solar array is shown. [Figure 2A]

[0007] FIG. 1 is a timing diagram illustrating the operation of a bidirectional circuit in both charging modes. [Figure 2B]

[0008] FIG. 4 is a timing diagram showing the operation of the bidirectional circuit in a display mode. [Diagram 3]

[0009] 1 is a simplified diagram of a circuit having a solar cell. [Figure 4]

[0010] 1 is a simplified diagram of an improved circuit for a solar cell. [Diagram 5]

[0011] 1 is a simplified diagram of an improved circuit for a solar cell. [Figure 6]

[0012] 1 is a simplified diagram of a string circuit. [Figure 7]

[0013] 1 is a simplified diagram of an improved solar cell string circuit. [Figure 8]

[0014] 1 is a plot illustrating an exemplary VI curve of voltage versus current for a typical solar cell system. [Figure 9]

[0015] 1 is a plot illustrating an exemplary VI curve of voltage versus current of a solar cell system for a high performance solar cell utilized in implementing high altitude, long endurance aircraft. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008]

[0016] In one possible implementation of the present invention, it is useful to communicate using solar cells as communication devices. To achieve this, instead of its normal function of absorbing sunlight and converting it to electricity, selected parts or all of the solar cells can be made to emit radiation. Thus, according to an embodiment of the present invention, it is possible to bias the solar cells to cause them to emit radiation when they are not absorbing sunlight and to cause them to emit radiation for communication purposes.

[0009]

[0017] In some implementations, the emitted radiation may be in one or more of the visible, infrared, or other spectrums, depending on the characteristics of the solar cell device. Thus, the solar cell is selected to perform both conventional solar energy conversion and its desired communication spectrum. It is further envisioned that the solar cell can be tuned to emit specific frequencies for such communication purposes when not being utilized for solar collection purposes.

[0010]

[0018] Typically, solar cells are used in arrays to absorb radiation and generate power from the radiation for use in a system or for storage for later use. The use of solar power is becoming more and more widespread. Implementations according to the present invention provide a novel use of solar cells as communication devices. This can be applied to traditional fixed terrestrial applications as well as other uses of solar cells.

[0011]

[0019] In certain implementations, solar cells are utilized in unmanned aerial vehicles (UAVs), aircraft that may fly autonomously or may be remotely piloted and have no pilot on board. In high altitude, long endurance aircraft, solar arrays may be used as power sources for batteries, engines, and other aircraft systems.

[0012]

[0020] For example, in high altitude long endurance aircraft, the solar arrays are typically positioned on the top surface of the aircraft, such as the top surface of the wings or the top surface of the fuselage, or both. High altitude long endurance aircraft are typically light aircraft with large wingspans, sometimes over 100 meters in length. Additionally, high altitude long endurance aircraft may have high lift wings and may be configured to fly relatively slowly. The large wingspan of a high altitude long endurance aircraft covered with solar cells provides a large surface area for visual display during communication. The advantage of using solar cells for communication is that since the arrays are on the top surface of the wings, the communication is directed upwards and is not visible to aircraft on the ground or below. However, the communication can be seen by satellite detectors, such as optical, infrared, or other frequencies. Thus, solar cells may be utilized for directional communication.

[0013]

[0021] In other applications, the solar cells can be portable or even wearable. The solar cells or panels can be made relatively flexible so that they can be attached to textiles such as clothing and other wearable products. The wearable solar panels are then used to charge a portable battery or a battery-equipped / powered appliance or device that is part of the garment or accessory. In such applications, the solar cells are further utilized for short-range or long-range communication.

[0014]

[0022] Solar cells can be configured to operate to emit in a display mode for communication in near-visible, visible, or other detectable spectrums to communicate a message. For example, in a wearable garment, the wearer can cause the garment to emit a message in visible light to communicate a line-of-sight message. Similarly, in a solar-assisted / powered automobile, solar cells or arrays can be used to indicate a position, communicate the driver's intent (as a pointer or other indicator / communication light), or flash a message.

[0015]

[0023] In the case of an aircraft, the direction of communication may be adjusted by adjusting the orientation of the aircraft, thereby changing the orientation of the solar cells. Similarly, the orientation of a satellite or an operational terrestrial solar panel may be adjusted to change the direction of communication. In the case of a portable device that includes a wearable solar cell, the orientation of the portable or wearable device may be adjusted to communicate directly.

[0016]

[0024] FIG. 1 shows a simplified schematic diagram of a bidirectional circuit 100 for a solar array. The solar cells may be arranged in a solar cell string 110 with multiple solar cells 105 coupled together. In this embodiment, the solar cell string 110 is coupled to a power bus 195 through a two-quadrant bidirectional boost-buck converter 170. The solar cell string 110 is thus coupled to the power bus 195 between a MOSFET 173 and a MOSFET 174 through an inductor 171, for example, about 300 to 600 microhenries. The MOSFET 173 and the MOSFET 174 are connected in series between the positive and negative rails of the power bus 195. The control input gates of the MOSFETs 173 and 174 are connected to a microcontroller for modulating the control inputs to the converter 170 to source current from the solar cell string 110 to the bus 195 in a charging mode or to draw current from the bus 195 to drive the solar cell string 110 to emit radiation in a display mode. In the charging configuration, MOSFET 174 is modulated, such as pulse width modulated, while MOSFET 173 is modulated or simply used as a diode to provide power to bus 195 for charging. In the display configuration, MOSFET 173 is modulated while MOSFET 174 is open or modulated.

[0017]

[0025] The solar string 110 may include multiple solar panels in close proximity that may be linear, square, rectangular, or other geometric configurations of solar panels. Alternatively, the solar panels in the string may be spaced apart to allow for indicia such as patterns, characters, letters, numbers, symbols, images, machine-readable linear or matrix bar coding, etc., to allow communication by either direct, coded, or aesthetic communication. The indicia may be a time-variable or coded message, such as an emission duration coded or frequency coded message, or intensity coded or other known coding methods.

[0018]

[0026] In one simplified example, the solar cells can emit messages by optical Morse code. Or, in another simplified example, a barcode or text message can be statically displayed or dynamically scrolled across the wingspan of a high altitude, long endurance unmanned aerial vehicle. In one possible scenario, the displayed message can be a response to a received message when the aircraft is unable to transmit via normal communication channels, i.e., when the aircraft's transmitter is not functioning or when general open transmission of messages is undesirable.

[0019]

[0027] In other possible applications, such as wearable, other mobile or fixed ground applications, the solar cell can be selected to emit only infrared spectrum signals that can be detected only by infrared detection means such as infrared / night vision devices, portable infrared detectors such as binoculars or other handheld infrared detection devices, and / or forward or side facing infrared detectors on aircraft.

[0020]

[0028] In yet another useful application, a person who is stranded, lost or unable to move from their location can utilize the display mode of the solar cell device to send an SOS, another signal or message, or simply illuminate with visual or IR spectrum for nighttime identification or rescue using optical or IR detection means, i.e., IR imaging devices such as binoculars or IR goggles. Thus, for use in communication, the display emits a detectable amount of radiation, such that the radiation can be observed without direct assistance, or with the aid of electronic detectors that can detect in the displayed spectrum and convert to directly observable radiation, or by converting the radiation into information, i.e., by nighttime or periodic visual collection and / or amplification, conversion from one or more spectra to another, detection and conversion for informational displays such as handheld device displays, projection displays, display monitors, readable or text displays, location identification displays, mapping displays, and the like.

[0021]

[0029] Some embodiments may display information generated by the aircraft whose inputs are detected by on-board sensors. The display may be tailored to display vehicle conditions, such as vehicle speed.

[0022]

[0030] 2A and 2B are timing diagrams 200a and 200b illustrating the operation of the bidirectional buck-boost converter in both charging and display modes. MOSFET 173 and MOSFET 174 are operated by adjusting the duty cycle and pulse width of MOSFET 173 and 174 in a complementary manner to provide the charging and display modes. In the charging mode, the duty cycle of MOSFET 174 is increased relative to MOSFET 173. In the display mode, the duty cycle of MOSFET 173 is increased relative to MOSFET 174.

[0023]

[0031] Timing diagrams 200a and 200b show example timing plots 200a and 200b illustrating the pulse width modulation of MOSFET 173 and MOSFET 174, respectively, to generate a positive or negative current I from the solar cell string 110 during charging or in the solar cell string 110 from the power bus 195 during display mode. L Timing plot 200a illustrates how a positive voltage V applied to the battery 190 side of inductor 171 with respect to ground L How does the pulse train 270p generate a positive current I L while the other plot 200b produces a negative current I L For each plot 200a and 200b, the resulting current I L On plots 273 and 274, the voltage V L There are pulse trains 270p and 270n. The MOSFETs 173 and 174 are connected to the L A square wave pulse 270p or 270n is connected to a positive 273 or negative 274 sawtooth current I L The wider voltage pulse 270p generates a positive current I L while the narrower pulse 270n contributes a negative current I L This allows either a charging operation of the solar cell string 105 in a normal charging mode or a display operation of the solar cell string 105 in a display mode.

[0024]

[0032] FIG. 3 is a simplified diagram of a circuit 300 with solar cells. Typically, multiple independent solar cells or strings 310a, 310b, and 310c are connected in parallel to form a channel 320. In an embodiment, the strings may have, for example, multiple replaceable solar panels. Each of the strings 310a, 310b, and 310c includes a blocking diode 315a, 315b, and 315c connected in parallel. The blocking diodes 315a, 315b, and 315c prevent one of the strings 310a, 310b, or 310c from causing a short circuit or other failure in the other non-shorted strings 310a, 310b, or 310c in the event that one of the strings 310a, 310b, and 310c is shorted. The blocking diodes add losses to the system, but are needed to reduce failure of the associated solar cells in the array or other components in the system.

[0025]

[0033] The blocking diode is typically located in the power tracker 380, which includes a boost stage 385 DC / DC converter. The boost stage 385 disconnects the supplied voltage and current from a high voltage power bus 395, i.e., 270V-400V, which is connected to the battery 390 and is configured to provide a suitable voltage to the high voltage power bus regardless of the voltage and current provided by the solar cell. In one embodiment, the power tracker is a maximum power point tracker or MPPT controller configured to boost the voltage from the solar cell to the output and adjust the boost ratio to obtain maximum power from the solar cell. Examples of MPPT controllers include Outback® FLEXmax 60 / 80 MPPT, Xantrex® MPPT solar charge controller, Blue Sky® solar charge controller. In general, the MPPT controller is configured to maximize the available power going into the battery from the solar cell. This is important in a variety of high altitude, long endurance aircraft applications where maximum voltage is a function of solar cell temperature and illumination, both of which can vary throughout the day.

[0026]

[0034] However, in the circuit of Figure 3, the diodes 315a, 315b and 315c prevent reverse biasing of the solar cell strings 310a, 310b or 310c, so the display mode is not possible. The embodiment of Figure 4 and Figure 5 described below allows the solar cell 105 to be reverse biased, so the display mode is permitted.

[0027]

[0035] Figure 4 is a simplified diagram of an improved circuit 400 for solar cells. In this embodiment, a solar cell string control MOSFET 415 is used in channel 410 instead of blocking diode 315a, 315b or 315c (Figure 3). This configuration is more efficient than the circuit of Figure 3 because it eliminates the voltage drop loss across diode 315a, 315b or 316c when solar cell string control MOSFET 415 is turned on. However, this embodiment does not inherently provide isolation between solar cell strings connected in parallel in the event that there is a short circuit in solar cell string 410 when solar cell string control MOSFET 415 is turned on.

[0028]

[0036] Thus, in this embodiment, the voltage drop across the solar cell string control MOSFET 415 is detected and monitored to determine the magnitude and direction of the current in the solar cell string 410 and to determine whether another solar cell string (not shown) has been shorted. If it is determined based on monitoring multiple parallel connected strings that one of the solar cell strings has been shorted, the solar cell string control MOSFET is opened in line with the shorted solar cell string to avoid damaging the other parallel connected solar cell strings. In the open state, the solar cell string control MOSFET 415 acts as a diode as in FIG. 3 to block the current through the shorted solar cell string.

[0029]

[0037] 4 provides a more efficient power transfer, but requires monitoring of the current in the solar cell string 410 to determine if a short circuit has occurred in the solar cell string 410 or any of the associated strings. Typically, monitoring and control of the solar cell string control MOSFET 415 is performed by a power tracker or other associated electronics. The power tracker includes the solar cell string control MOSFET 415 and a boost stage 485 that provides power to a power bus 495.

[0030]

[0038] FIG. 5 is a simplified diagram of an improved circuit 500 for a solar cell. In this embodiment, MOSFET switches 515a, 515b, and 515c with back-to-back MOSFET devices 515a1 and 515a2 are utilized instead of blocking diodes 315a, 315b, and 315c (FIG. 3). Although the output of multiple strings enters a single power stage, such as a boost stage 585 DC / DC converter that provides current to a power bus 595 to charge a battery 590, the MOSFET switches allow each string 510a, 510b, or 510c of a channel 520 to be completely disabled or opened individually. The boost converter 585 controls the MOSFET switches 510a, 510b, or 510c and utilizes the detected string voltage to determine the state of the string 510a, 510b, or 510c along with all other strings (not shown) and channels (not shown) across the solar cell. The advantage of this is that the system can target each string 510a, 510b or 510c and perform many in-flight diagnostics such as short circuit current, open circuit voltage etc. for each string.

[0031]

[0039] Replacing the protection diodes with MOSFET switches is not desirable in terrestrial solar systems as it increases the cost of the system. However, using MOSFET switches is highly desirable in high altitude, long endurance aircraft where extracting maximum energy from the solar cells is important and critical. MOSFET switches can be selected to have lower power losses across the switch compared to protection diodes. Thus, MOSFET switches improve the efficiency of the charging system and allow failures to be predicted and detected (through trend analysis) much easier. Imminent failures can be predicted and action can be taken before the failure becomes critical. This is important in high altitude, long endurance aircraft to be able to avoid critical failures that could lead to power off or even crash on landing. Strings can be tested individually, providing more "visibility" into the function and status of the solar cells in flight.

[0032]

[0040] Additionally, each string can be tested in flight to determine the optimum power output of each string individually according to its VI and power output characteristics. Thus, string characteristics can be tested over time to determine the condition of the strings. This is especially important during long endurance and high altitude flights so that the need for maintenance and / or remedial actions, such as replacing solar panels, can be predicted and performed at a convenient time.

[0033]

[0041] In one embodiment, each string includes multiple solar panels grouped generally spanwise along the aircraft wing, for example, four, five or six small solar panels grouped per string. The solar panels are grouped in this manner so that the solar panels within a string experience similar environmental and operating conditions together. For example, the solar panels near the trailing edge of the wing may be grouped together in a string, while the solar panels at the leading edge of the wing may be grouped together, perhaps with one or more strings extending spanwise or laterally along the span of the wing between the leading edge string and the trailing edge string.

[0034]

[0042] Grouping solar panels into strings is important for high altitude applications because temperatures can vary significantly from the leading edge to the trailing edge of the wing. Additionally, the orientation of the aircraft relative to the sun in elevation, azimuth, rotation, etc., as well as having a greater curvature from the leading edge to the trailing edge of the wing, can further exaggerate the temperature differences. In a high altitude long endurance solar powered aircraft, temperatures can vary across the wing from -60°C at the leading edge to +60°C at the trailing edge. Thus, grouping solar panels into strings, combined with the ability to individually switch individual strings on or off based on the string's performance, allows for more efficient solar power generation.

[0035]

[0043] Referring to Figure 6, a simplified diagram of a string circuit 600 is shown. In Figure 6, the string 600 typically includes a bypass diode 645 in parallel with two or more solar cells 605a and 605b. The bypass diode 645 allows other solar cells 605m to provide current around the solar cells 305a and 605b when one or more of the solar cells fails or becomes open circuit, such as by being cracked or broken.

[0036]

[0044] Referring to FIG. 6, in a further embodiment, the bypass diode 615 is replaced by a bypass MOSFET switch 760 as shown in the simplified diagram of the solar cell string circuit 700 in FIG. 7. Such an embodiment allows for greater efficiency of the diode when a solar cell 605a, 605b, ... or 605m (FIG. 6) fails due to lower power losses associated with the MOSFET switch 760 compared to the bypass diode 645. Furthermore, it allows for closer monitoring and predictive analysis of individual or small groups of solar cells for better predictive analysis of the string. Since the maximum allowable current of the string 710 is limited by the constraints of the lowest individual solar cell, being able to bypass only one or more individual solar cells 705a and 705b or others can be used to optimize the power output of the string 710.

[0037]

[0045] One advantage of various embodiments over string circuits using blocking diodes is that blocking diodes can contribute approximately 0.7% losses, whereas MOSFET switches can reduce those losses. Although discussed above with respect to MOSFET switches, other equivalent types of switches, i.e., lighter weight, lower loss switches, can be utilized in other embodiments. Additionally, while for purposes of illustration, FIG. 5 shows a case with only three solar cell strings in a channel, embodiments may encompass more than two strings and multiple channels.

[0038]

[0046] Various embodiments enable or extend the ability to perform in-flight diagnostics. In high altitude, long endurance solar powered aircraft, factors such as turbulence, frequent and extreme heat, motor vibrations, etc. can increase the likelihood of failure. Various embodiments can provide performance tracking over time with trend analysis and enable superior fault detection, more flexible scheduling of service / routine maintenance, and avoidance of lack of airborne network capability / coverage or surveillance capability / coverage in coverage areas. This is particularly important when high altitude, long endurance aircraft are used as cellular repeaters or other network communications in areas with no coverage when the platform is missing from the network.

[0039]

[0047] 8 is a plot 800 showing an exemplary VI curve 810 of voltage versus current for a typical solar cell system. A power curve 820 for the solar cell system is superimposed on the plot 800. It is desirable to extract maximum power from the solar cell system. Therefore, it is desirable to operate along the VI curve 810 where the power of the system is at its peak.

[0040]

[0048] FIG. 9 is a plot 900 showing an example VI curve 210 of the voltage vs. current of a solar cell system for a high performance solar cell utilized in a high altitude long endurance aircraft implementation. In various high performance solar cell implementations that may be utilized in a high altitude long endurance aircraft, the VI curve 910 and the power curve (not shown) have a very steep slope as they approach maximum current. Thus, the optimal operating point of the system is in a narrow operating range. If the current is even slightly too high, the voltage will go to zero or short out very easily. For example, the difference between optimal power output and a short circuit can be as low as 100 mA of current per channel 120 (FIG. 1). Depending on the solar cell and channel configuration, this can be even lower in some embodiments, such as 75 mA, 50 mA, 25 mA or less. To avoid this while achieving the highest power output, a voltage loop is used to determine the peak power operating point while monitoring the voltage, as well as the current and power. This is because the change in voltage is much larger than either the power or the current near this point.

[0041]

[0049] Therefore, the current is adjusted while monitoring the voltage and power to find the optimum operating point of the system. The commanded current is changed by a power point tracker circuit while monitoring the power. Additionally, since the rate of change of voltage is greater than the rate of change of power near the maximum power output operating point, the voltage is monitored to determine when the power output is maximum.

[0042]

[0050] To achieve the most efficiency in some embodiments, voltage is monitored at a faster rate than current and power. In some embodiments, voltage can be monitored 10 times faster than current or power. For example, current and / or power can be monitored 10 times per second, while voltage is monitored 100 times per second.

[0043]

[0051] This allows various embodiments to extract the maximum amount of solar power from the solar panels in high altitude, long endurance aircraft applications without drawing excessive current and causing the voltage to go to zero, thereby shorting out the solar cells.

[0044]

[0052] It is important to note that factors such as the temperature of the solar panels and the amount of exposure to the sun can shift the maximum power operating point. These factors are more important in high altitude, long endurance solar powered aircraft because the temperature range across the solar cells is more extreme and shading or shadowing typically occurs more frequently and to a greater extent, as described further below. Thus, monitoring and adjusting the operating point is particularly important in high altitude, long endurance solar powered aircraft. FIG. 9 shows example VI curves for high 910 and low 911 temperatures for higher solar intensity or bright solar exposure 910 and lower solar intensity or shaded solar exposure 912.

[0045]

[0053] It is worth noting that references to "one embodiment" or "an embodiment" mean that, where appropriate, a particular feature, structure, or characteristic described in connection with an embodiment may be included in the embodiment. The appearances of the phrase "in one embodiment" in various places in this specification are not necessarily all referring to the same embodiment.

[0046]

[0054] The figures and examples provided herein are for illustrative purposes and are not intended to limit the scope of the appended claims. The present disclosure should be considered as an exemplification of the principles of the invention and are not intended to limit the spirit and scope of the invention and / or the claims of the illustrated embodiments.

[0047]

[0055] Those skilled in the art will make modifications to the invention for their particular applications.

[0048]

[0056] The discussion contained in this patent is intended to serve as a basic description. The reader should be aware that the specific discussion does not explicitly describe all possible embodiments, and alternatives are implicit. Also, the discussion may not fully describe the general nature of the invention, and may not explicitly show how each feature or element may actually be a representative or equivalent element. Again, these are implicitly included in this disclosure. When the invention is described in device-oriented terms, each element of the device implicitly performs a function. It should also be understood that various modifications can be made without departing from the essence of the invention. Such modifications are also implicitly included in the description. These modifications are still within the scope of the invention.

[0049]

[0057] Moreover, each of the various elements of the invention and claims may be accomplished in various ways. The present disclosure should be understood to encompass each such variation, whether it is a variation of any apparatus embodiment, a variation of a method embodiment, or merely a variation of any of these elements. In particular, since the present disclosure is directed to elements of the invention, it should be understood that the words of each element may be expressed in equivalent apparatus terms, even if only the function or result is the same. Such equivalent, broader, or more general terms should be considered to be encompassed in the description of each element or action. Such terms may be substituted where necessary to make clear the implicitly broad scope to which the invention is entitled. It should be understood that every action may be expressed as a means for taking that action or as an element that causes that action. Similarly, each physical element disclosed should be understood to encompass a disclosure of the action that the physical element facilitates. Such modifications and alternative terms should be understood to be expressly included in the description.

[0050]

[0058] While the present invention has been described in connection with a number of embodiments, modifications will no doubt suggest themselves to those skilled in the art. The exemplary embodiments herein are not intended to be limiting, as various configurations and combinations of features are possible. Accordingly, the present invention is not limited to the disclosed embodiments, except as required by the appended claims.

Claims

1. 1. A method for a solar array, comprising: emitting a communication message from the solar array by reverse biasing the solar array to cause at least a portion of the solar cells to emit a detectable amount of radiation corresponding to the communication message; The method further includes reverse biasing selective solar cell strings to emit a message from the solar cell array comprising at least one of a pattern, a letter, a character, a number, a symbol, an image, or a combination thereof.

2. The method of claim 1 , wherein issuing a communication message comprises issuing at least one of a direct, coded, or aesthetic message.

3. The method of claim 1 , wherein issuing the communication message comprises issuing at least one of a time-variable or intensity-variable coded message.

4. The method of claim 3 , wherein issuing the communication message comprises issuing at least one of a duration-coded, a frequency-coded, or an intensity-coded message.

5. The method of claim 1 , wherein emitting the communication message includes emitting at least one of: (1) a visible light message; or (2) an infrared light message.

6. The method of claim 1 , wherein issuing the communication message comprises displaying a visual display message on the solar array.

7. A solar cell array circuit for use in the method of claim 1, comprising: a) a solar cell string comprising a plurality of solar cells coupled together; b) a charge storage device coupled to the power bus; c) a bidirectional boost-buck converter, (i) first and second paired MOSFETs connected in series between positive and negative rails of the power bus; (ii) an inductor coupled between the first and second paired MOSFETs to a charging output of the solar cell string.

8. 8. The circuit of claim 7, further comprising a MOSFET device connected in series between the inductor and the charging output of the solar cell string.

9. 8. The circuit of claim 7, further comprising a MOSFET switch connected in series between the inductor and the charging output of the solar cell string.

10. 10. The circuit of claim 9, wherein the MOSFET switches comprise back-to-back complementary MOSFET devices.

11. 8. The circuit of claim 7, further comprising a plurality of the solar cell strings configured to emit at least one of: (1) a pattern; (2) a letter; (3) a character; (4) a number; (5) a symbol; (6) an image; or (7) a combination thereof.

12. 1. A method for communicating messages by a solar array of a high altitude, long endurance aircraft, comprising: a) displaying a message on a solar array of the high altitude, long endurance aircraft; b) detecting said message using a satellite; and and c) relaying the detected message from the satellite to a platform below the high altitude, long endurance aircraft.

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