OA17841A

OA17841A - System and method for managing the power output of a photovoltaic cell

Info

Publication number: OA17841A
Application number: OA1201600321
Authority: OA
Inventors: Robert P. Mcnamara; Douglas M. Raymond
Original assignee: Solarlytics, Inc.
Priority date: 2014-02-21
Filing date: 2015-02-21
Publication date: 2018-01-22

Abstract

A solar cell management system for increasing the efficiency and power output of a solar cell and methods for making and using the same. The management system provides an electric field across an individual solar cell, an array of solar cells configured as a panel, or a group of solar panels. The imposed electric field exerts a force on both the electrons and holes created by light incident on the solar cell and accelerates the electron-hole pairs towards the electrodes of the solar cell. Compared to conventional solar cells, these accelerated electron-hole pairs travel a shorter distance from creation and spend less time within the solar cell material, therefore the electron-hole pairs have a lower liketihood of recombining within the cells' semiconductor's material. This reduction in the electron-hole recombination rate results in an overall increase in the solar cells' efficiency and greater power output.

Description

SYSTEM AND METHOD FOR MANAGING THE POWER OUTPUT OF A PHOTOVOLTAIC

CELL

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/943,127, filed February 21, 2014; U.S. Provisional Application No. 61/943,134, filed February 21, 2014; U.S. Provisional Application No. 61/947,326, filed March 3, 2014; and U.S. Provisional Application

No. 62/022,087, filed July 8, 2014, the disclosures of which are hereby incorporated by reference in their entirety and for ail purposes.

FIELD

The présent disclosure relates generally to photovoltaic devices and more specifically, but not exclusively, to Systems and methods for maximizing the power or energy generated and the overall efficiency of one or more solar cells, for example, by applying and adjusting an external electric field across the solar cells.

BACKGROUND

A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by a process known as “the photovoltaic effect.” When exposed to light, the solar cell can generate and support an electric current without being attached to any external voltage source.

The most common solar cell consists of a p-n junction 110 fabricated from semiconductor materials (e.g., silicon), such as in a solar cell 100 shown in Fig. 1. For example, the p-n junction 110 includes a thin wafer consisting of an ultra-thin layer of n-type silicon on top of a thicker layer of p-type silicon. Where these two layers are in contact, an electrical field (not shown) is created near the top surface ofthe solar cell 100, and a diffusion of électrons occurs from the région of high électron concentration (the n-type side of the p-n junction 110) into the région of low électron concentration (the p-type side of the p-n junction 110).

The p-n junction 110 is encapsulated between two conductive électrodes 101a, 101b. The top electrode 101a is either transparent to incident (solar) radiation or does not entirely cover the top ofthe solar cell 100. The électrodes 101a, 101b can serve as ohmic metal-semiconductor contacts that are connected to an external load 30 that is coupled in sériés. Although shown as résistive only, the load 30 can also include both résistive and reactive components.

Typically, multiple solar cells 100 can be coupled (in sériés and/or parallel) together to form a solar panel 10 (shown in Fig. 2). With reference to Fig. 2, a typical installation configuration using at least one solar panel 10 is shown. The solar panels 10 can be connected either in parallel as shown in Fig. 2, sériés, or a combination thereof, and attached to a load, such as an inverter 31. The inverter 31 can include both résistive and reactive components.

Returning to Fig. 1, when a photon hits the solar cell 100, the photon either: passes straight through the solar cell material—which generally happens for lower energy photons; reflects off the surface ofthe solar cell; or preferably is absorbed by the solar cell material—ifthe photon energy is higher than the silicon band gap—generating an electron-hole pair.

lf the photon is absorbed, its energy is given to an électron in the solar cell material. Usually this électron is in the valence band and is tightly bound in covalent bonds between neighboring atoms, and hence unable to move far. The energy given to the électron by the photon “excites” the électron into the conduction band, where it is free to move around within the solar cell 100. The covalent bond that the électron was previously a part of now has one fewer électron—this is known as a hole. The presence of a missing covalent bond allows the bonded électrons of neighboring atoms to move into the hole, leaving another hole behind. In this way, a hole also can move effectively through the solar cell 100. Thus, photons absorbed in the solar cell 100 create mobile electron-hole pairs.

The mobile electron-hole pair diffuses or drifts toward the électrodes 101a, 101b. Typically, the électron diffuses/drifts towards the négative electrode, and the hole diffuses/drifts towards the positive electrode. Diffusion of carriers (e.g., électrons) is due to random thermal motion until the carrier is captured by electrical fields. Drifting of carriers is driven by electric fields established across an active field ofthe solar cell 100. in thin film solar cells, the dominant mode of charge carrier séparation is drifting, driven by the electrostatic field of the p-n junction 110 extending throughout the thickness of the thin film solar cell. However, for thicker solar cells having virtually no electric field in the active région, the dominant mode of charge carrier séparation is diffusion. The diffusion length of minor carriers (i.e., the length that photogenerated carriers can travel before they recombine) must be large in thicker solar cells. Ultimately, électrons that are created on the n-type side of the p-n junction 110, “collected” by the p-n junction 110, and swept onto the n-type side can provide power to the external load 30 (via the electrode 101a) and return to the p-type side (via the electrode 101b) ofthe solar cell 100. Once returning to the p-type side, the électron can recombine with a hole that was either created as an electron-hole pair on the p-type side or swept across the p-n junction 110 from the n-type side.

As shown in Fig. 1, the electron-hole pairtravels a circuitous route from the point the electronhole pair is created to the point where the electron-hole pair is collected at the électrodes 101a, 101b. Since the path traveled by the electron-hole pair is long, ample opportunity exists for the électron or hole to recombine with another hole or électron, which recombination results in a loss of current to any external load 30. Stated in another way, when an electron-hole pair is created, one ofthe carriers may reach the p-n junction 110 (a collected carrier) and contribute to the current produced by the solar cell 100. Altematively, the carrier can recombine with no net contribution to cell current. Charge recombination causes a drop in quantum efficiency (i.e., the —

percentage of photons that are converted to electric current when the solar cell 100), and, therefore, the overall efficiency of the solar cell 100.

The cost of the solar cell 100 or the solar panel 10 is typically given in units of dollars per watts of peak electrical power that can be generated under normalized conditions. High-efficiency soiar cells decrease the cost of solar energy. Many of the costs of a solar power system or plant are proportional to the number of solar panels required as well as the (land) area required to mount the panels. A higher efficiency solar cell will allow for a réduction in the number of solar panels required for a given energy output and the required area to deploy the system.

This réduction in the number of panels and space used might reduce the total plant cost, even if the cells themselves are more costly.

The ultimate goal is to make the cost of solar power génération comparable to, or less than, conventional electrical power plants that utilize natural gas, coal, and/or fuel oil to generate electricity. Unlike most conventional means of generating electric power that require large centralized power plants, solar power Systems can be deployed at large centralized locations by electric utilities, on commercial buildings to help offset the cost of electric power, and even on a résidence by résidence basis.

Recent attempts to reduce the cost and increase the efficiency of solar cells include testing various materials and different fabrication techniques used for the solar cells. Another approach attempts to enhance the déplétion région formed around the p-n junction 110 for enhancing the movement of charge carriers through the solar cell 100. For example, see U.S. Patent No. 5,215,599, to Hingorani, et al. (“Hingorani”), filed on May 3, 1991, and U.S. Patent 8,466,582, to Fornage (“Fornage”), filed on December 2, 2011, claiming priority to a December 3, 2010 filing date, the disclosures of which are hereby incorporated by reference in their entireties and for ail purposes.

However, these conventional approaches for enhancing the movement of charge carriers through the solar cell 100 require a modification of the fundamental structure of the solar cell 100. Hingorani and Fornage, for example, disclose applying an external electric field to the solar cell using a modified solar cell structure. The application of the external electric field requires a voltage to be applied between électrodes inducing the electric field (described in further detail with reference to équation 2, below). Without modifying the fundamental structure of the solar cell 100, applying the voltage to the existing électrodes 101a, 101b of the solar cell 100 shorts the applied voltage through the external load 30. Stated in another way, applying voltage to the électrodes 101a, 101b of the solar 100 is ineffective for creating an external electric field and enhancing the movement of charge carriers. Accordingly, conventional approaches—such as disclosed in Hingoriani and Fornage—necessarily modify the fundamental structure of the solar cell 100, such as by inserting an external (and electrically isolated) set of électrodes on the base of the solar cell 100. There are several disadvantages with this approach.

For example, the external électrodes must be placed on the solar cell 100 during the fabrication process—it is virtually impossible to retrofit the external électrodes to an existing solar cell or panel. This modification to the fabrication process significantly increases the cost of manufacturing and decreases the manufacturing yield. Additionally, placement ofthe external électrodes over the front, or incident side, of the solar cell 100 reduces the optical energy which reaches the solar cell 100, thereby yielding a lower power output.

As a furtherdisadvantage, to yield significant improvements in poweroutput ofthe solar cell 100, sizeable voltages must be applied to the external électrodes ofthe solar cell 100. For example, Fornage discloses that voltages on the order of “1,000’s” of volts must be placed on the external électrodes for the applied electric field to be effective and increase the power outputofthe solar cell 100. The magnitude ofthis voltage requires spécial training forservicing as well as additional high voltage equipment and wiring that does not presently exist in existing or new solar panel deployments. As an example, an insulation layer between the external électrodes and the solar cell 100 must be sufficient to withstand the high applied voltage. In the event of a failure of the insulation layer, there is a significant risk of damage to not only the solar cell 100, but also ail solar panels 10 connected in sériés or parallel to the failed solar cell as well as the external load 30 (or the inverter 31).

As a further disadvantage, varying illumination conditions (e.g., due to cloud coverage ofthe sun and/or normal weather fluctuations) can cause instability in the power output of conventional solar cells and solar panels. For example, with reference to Fig. 2, the inverter 31 typically requires a static, non-varying voltage and current input. As shown in Fig. 2, the solar panels 10 provide the input voltage and current to the inverter 31. However, time-varying illumination conditions can cause the output from solar panels 10 to fluctuate (e.g., on the order of seconds or less). The fluctuation of the voltage and current supplied to the inverter 31 compromises the quality of the power output by the inverter 31, for example, in terms of frequency, voltage, and harmonie content. Conventional efforts to combat varying illumination conditions include placing batteries or capacitors at the input ofthe inverter 31 and, unfortunately, only minimize these variations.

In view ofthe foregoing, a need exists for an improved solar cell system and method for increased efficiency and power output, such as with increased mobility of electron-hole pairs, in an effort to overcome the aforementioned obstacles and deficiencies of conventional solar cell Systems.

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SUMMARY

The présent disclosure relates to a system for optimizing a power output of a photovoltaic device and methods for using and making the same. In accordance with a first aspect disclosed herein, there is set forth a method of managing a photovoltaic device, the method comprising: applying a first component of a voltage signal to the photovoltaic device, the first component representing an on state for generating an external electric field across the photovoltaic device; and applying a second component ofthe voltage signal to the photovoltaic device, the second component representing an off cycle.

In some embodiments of the disclosed method, applying the first component comprises applying a high voltage of a time-varying voltage puise from a voltage puiser circuit, and applying the second component comprises shutting off the voltage puiser circuit.

In some embodiments of the disclosed method, applying the first component comprises connecting a voltage source and the photovoltaic device in a first position of a switch disposed between the voltage source and the photovoltaic device, and wherein said applying the second component comprises disconnecting the voltage source and the photovoltaic device in a second position ofthe switch.

In some embodiments ofthe disclosed method, the method further comprises monitoring an output voltage of the photovoltaic device via a voltage probe coupled across the photovoltaic device and monitoring an output current ofthe photovoltaic device via a current sensor coupled in sériés between the photovoltaic device and a load driven by the photovoltaic device.

In some embodiments ofthe disclosed method, the method further comprises adjusting, via a control circuit coupled to the voltage source, at least one of a magnitude, a duration, and a frequency of the first component to maximize a power output based on said monitoring.

In accordance with a another aspect disclosed herein, there is set forth a method of managing a photovoltaic device, comprising:

enabling a voltage source to be coupled to the photovoltaic device; and applying a voltage signal generated by the voltage source to the photovoltaic device, the voltage signal having a first state for generating an external electric field across the photovoltaic device and a second state representing an off cycle.

In some embodiments ofthe disclosed method, enabling the voltage source comprises enabling at least one of:

a voltage puiser circuit to be coupled to the photovoltaic device for providing a time varying voltage puise across the photovoltaic device, the time varying voltage puise providing the first state and the second state; and a switch to be coupled between the voltage source and the photovoltaic device, the switch connecting the voltage source and the photovoltaic device in a first position for generating the

-517841 first state and disconnecting the voltage source and the photovoltaic device in a second position for generating the second state.

In some embodiments of the disclosed method, applying the voltage signal comprises impressing an output of a high voltage source of the voltage puiser circuit onto the photovoltaic device when a switching transistor of the voltage puiser circuit is in an on position for generating the first state, and continuing said impressing the output of the high voltage source until a puise generator of the voltage puiser circuit turns the switching transistor to an off position for generating the second state.

In some embodiments of the disclosed method, the method further comprises enabling a control circuit to be coupled to at least one of the switch and the voltage puiser circuit.

In some embodiments of the disclosed method, the method further comprises enabling a voltage probe to be coupled across the photovoltaic device to monitor an output voltage of the photovoltaic device and a current sensor to be coupled in sériés between the photovoltaic device and a load of the photovoltaic device to monitor a current output of the photovoltaic device.

In some embodiments of the disclosed method, the method further comprises monitoring the output voltage and the output current and adjusting via the control circuit a magnitude of the first state to maximize a power output based on said monitoring.

In some embodiments of the disclosed method, applying the voltage signal comprises generating the external electric field with at least one of a first direction and a second direction, the first direction and a polarity of internai électrodes of the photovoltaic device being in a same direction for increasing a power output of the photovoltaic device, and the second direction being in an opposite direction of the polarity of the internai électrodes for decreasing the power output.

In some embodiments of the disclosed method, enabling the voltage source comprises enabling the voltage source to be coupled to at least one of a solar cell, an array of solar cells, a solar panel, and an array of solar panels.

In accordance with a another aspect disclosed herein, there is setforth a method of managing a photovoltaic device, comprising:

enabling a voltage puiser to be coupled to the photovoltaic device; and applying a voltage signal generated by the voltage puiser to the photovoltaic device, the voltage signal having a first state for generating an external electric field across the photovoltaic device and a second state representing an off cycle.

In some embodiments of the disclosed method, applying the voltage signal comprises applying an adjustable voltage to the photovoltaic device.

In some embodiments of the disclosed method, the method further comprises enabling one or more sériés inductors to be coupled between the voltage puiser and a load of the photovoltaic

617841 device for blocking frequencies of the voltage signal to the load that are greater than a predetermined frequency.

In some embodiments ofthe disclosed method, the method further comprises controlling at least one of a frequency and a duration of the first state and the second state via a control circuit coupled to the voltage puiser.

enabling a first port of a switch to be coupled to the photovoltaic device;

enabling a second port ofthe switch to be coupled to a load driven bythe photovoltaic device; enabling a third port ofthe switch to be coupled to a voltage source, wherein the switch can operate in a first position for providing a current path between the photovoltaic device and the voltage source and a second position for providing the current path between the photovoltaic device and the load; and applying a voltage signal generated by the voltage source to the photovoltaic device when the switch is in a first position, the voltage signal having a first state for generating an external electric field across the photovoltaic device when the switch is in the first position, and a second state to provide electrical isolation between the voltage source and the load when the switch is in the second position.

In some embodiments ofthe disclosed method, enabling thefirst port ofthe switch comprises enabling a first port of a double throw switch to be coupled to the photovoltaic device.

In some embodiments ofthe disclosed method, the method further comprises controlling at least one of a frequency and a duration of switching between the first position and the second position via a switch controller coupled to the double throw switch.

In some embodiments ofthe disclosed method, the method further comprises enabling a device for mitigating any voltage drop-out of the first component to be coupled between the load and the photovoltaic device.

In some embodiments ofthe disclosed method, the method further comprises controlling at leastone ofa frequency, a magnitude, and a duration ofthe first state and the second state via a control circuit coupled to the voltage source and the switch based on an output current of the photovoltaic device measured by a current sensor coupled in sériés between the photovoltaic device and the load and an output voltage ofthe photovoltaic device measured by a voltage probe coupled across the photovoltaic device.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an exemplary top-level cross-sectional diagram illustrating an embodiment of a solar cell of the prior art.

717841

Fig. 2 is an exemplary top-level block diagram illustrating one embodiment of a solar panel array of the prior art using the solar cells of Fig. 1.

Fig. 3 is an exemplary top-level block diagram illustrating an embodiment of a solar cell management system.

Fig. 4 is an exemplary block diagram illustrating an alternative embodiment ofthe solar cell management system of Fig. 3, wherein a solar panel array is coupled to a voltage source through a switch.

Figs. 5A-D are exemplary waveforms illustrating the applied voltage as a function oftime ofthe inputs and outputs ofthe switch used with the solar panel array of Fig. 4.

Fig. 6 is an exemplary block diagram illustrating anotheralternative embodiment ofthe solar cell management system of Fig. 3, wherein a solar panel array is coupled to a voltage puiser circuit. Fig. 7 is an exemplary waveform illustrating the applied voltage as a function of time used with the solar panel array of Fig. 6.

Fig. 8 is an exemplary block diagram illustrating one embodiment ofthe voltage puiser circuit of Fig. 6.

Fig. 9A is an exemplary block diagram illustrating an alternative embodiment ofthe solar cell management system of Fig. 4, wherein the solar cell management system includes a control circuit.

Fig. 9B is an exemplary flow-chart illustrating a state diagram for the control circuit shown in Fig. 9A.

Fig. 10A is an exemplary block diagram illustrating an alternative embodiment ofthe solar cell management system of Fig. 6, wherein the solar cell management system includes a control circuit.

Fig. 10B is an exemplary flow-chart illustrating a state diagram for the control circuit shown in Fig. 10A.

Figs. 11A-Care exemplary waveforms illustrating an embodimentofthe relationship between applied voltage, puise frequency, and puise width to the improved current output of the photovoltaic device of Fig. 3.

It should be noted that the figures are not drawn to scale and that éléments of similar structures or functions are generally represented by like reference numérale for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the preferred embodiments. The figures do not illustrate every aspect of the described embodiments and do not limitthe scope ofthe présent disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Since currently-available solar cell Systems fail to maximize the power output of a photovoltaic cell, a solar cell system that increases the mobility of electron-hole pairs and reduces the recombination current in a semiconductor material can prove désirable and provide a basis for a wide range of solar cell Systems, such as to increase the efficiency and power output of solar cells configured as a solar panel. This resuit can be achieved, according to one embodiment disclosed herein, by a solar cell management system 300 as illustrated in Fig. 3.

Turning to Figure 3, the solar cell management system 300 is suitable for use with a wide range of photovoltaic devices. In one embodiment, the solar cell management system 300 can be suitable for use with the solar cell 100 shown in Fig. 1. For example, the solar cell 100 can represent any suitable génération of solar cells such as wafer-based cells of crystalline silicon (first génération), thin film solar cells including amorphous silicon cells (second génération), and/or third génération cells. The solar cell management system 300 advantageously can be used with any génération of solar cell 100 without structural modification—and the associated drawbacks.

In another embodiment, the solar cell management system 300 can be suitable for use with multiple solar cells 100, such as the solar panels 10 shown in Fig. 2. As previously discussed, multiple solar cells 100 can be coupled (in sériés and/or parallel) together to form a solar panel 10. The solar panels 10 can be mounted on a supporting structure (not shown) via ground mounting, roof mounting, solar tracking Systems, fixed racks, and so on and can be utilized for both terrestrial and space borne applications. Similarly, the solar cell management system 300 advantageously can be used with any génération of solar panel 10 without structural modification—and the associated drawbacks—of the solar panel 10.

As shown in Fig. 3, the photovoltaic device 200 coopérâtes with an electric field 250. In some embodiments, the polarity of the electric field 250 can be applied in either the same direction or the reverse direction as the polarity ofthe électrodes 101a, 101b (shown in Fig. 1) in the photovoltaic device 200. For example, if applying the electric field 250 in the same direction as the polarity of the électrodes 101a, 101 b in the photovoltaic device 200, the electric field 250 acts on the electron-hole pairs in the photovoltaic device 200 to impose a force—e'E or h⁺E on the électron or hole, respectively—thereby accelerating the mobility of the électron and hole towards respective électrodes. Alternatively, if the polarity ofthe electric field 250 is reversed, the mobility of the electron-hole pairs in the photovoltaic device 200 decreases, thereby increasing the recombination current within the photovoltaic device 200. Accordingly, the efficiency of the photovoltaic device 200 can be diminished as desired, such as for managing the power output of the photovoltaic device 200.

Furthermore, the electric field 250 applied to the photovoltaic device 200 can be static or time varying as desired. In the case where the electric field 250 is time varying, the electric field 250 has a time averaged magnitude that is non-zero. Stated in anotherway, the netforce on the électrons and holes is non-zero to provide increased mobility in the electron-hole pairs of the photovoltaic device 200.

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If applied to the conventional solar cell 100 of Fig. 1, in the absence of an external load 30 (shown in Fig. 1), an external voltage can be applied across the électrodes 101a, 101b ofthe solar cell 100 to create the electric field 250. In one embodiment, the electric field 250 (e.g., between the électrodes 101a, 101b) is defined by Equation 1:

_r fapp - Kr) t (Equation 7)

In Equation 1, E represents the electric field 250, V_App is the voltage applied externally to the photovoltaic device 200, V_P is the voltage output ofthe photovoltaic device 200 (e.g., ~ 30 volts), and fis the thickness ofthe semiconductor material in the photovoltaic device 200 from electrode 101a to 101b. For example, assuming V_App — V_P = 200 Volts (nominally) and a thickness t of about 0.02 cm, the electric field 250 is about 10K Volts/cm. It can be seen from Equation 1 that as the thickness t ofthe photovoltaic device 200 decreases (e.g., less than 0.01 cm), higher electric fields 250 can be generated using the same or lower voltages.

As discussed above, the photovoltaic device 200 typically drives an external load, such as the load 30 ofthe solar cell 100. With reference to Equation 1, if applying an external voltage V_Appdirectly to the photovoltaic device 200 that drives the external load 30, the external load 30 can include résistive components thatdraw currentfrom the source ofthe applied voltage V_App. Stated in another way, applying the external voltage V_Appto the photovoltaic device 200 can effectively deliver power to the overall circuit represented by Equation 2:

Power

Input (Equation 2)

In Equation 2, R_L represents the impédance of the external load 30. In some cases, the input power can be substantially greater than the power output of the photovoltaic device 200. Accordingly, the solar cell management system 300 is configured to apply the electric field 250 across the photovoltaic device 200 without injecting more energy than the photovoltaic device 200 is capable of producing or more energy than would be gained by applying the electric field across the photovoltaic device 200.

The solar cell management system 300 can apply the external voltage V%,pto the photovoltaic device 200 using any suitable means described herein, including using a switch 55 as shown in Fig. 4. Turning to Fig. 4, the photovoltaic device 200 can represent any number of photovoltaic devices such as the solar cell 100 and/or the solar panels 10 as illustrated. The solar panels 10 are connected to the switch 55, such as a single pôle, double throw (or three-way) switch as shown. In one embodiment, the switch 55 is also coupled to a voltage source 50 and an external load R_L (e.g., shown as the inverter 31). The inverter 31 can convert a DC voltage and current into an AC voltage and current, which is typically compatible in voltage and frequency with conventional AC power grids. The output frequency of the inverter 31 and the amplitude of the AC current/voltage can be based upon country, location, and local grid requirements. The voltage source 50 can include any suitable means for maintaining a constant voltage, including idéal voltage sources, controlled voltage sources, and so on. However, in some embodiments—such as the embodiment shown below with reference to Fig. 9A—the voltage source 50 can hâve a variable, adjustable output (e.g., time varying voltage). A switch control (or controller) 45 is coupled to the switch 55 to control the duration of connection and/or the frequency of switching, such as between the voltage source 50 and the inverter 31 to the solar panels 10. The switch controller 45 can be preset to operate at a fixed switching duration D and switching frequency f (shown in Figs. 5A-C). The voltage applied in the first position of the switch 55 can be fixed and based on the voltage source 50. In some embodiments, the magnitude of the voltage applied by voltage source 50, the duration D of connection, and/or the frequency f of switching can be preset and/or vary based on load conditions.

For example, the switch 55 connects the solar panels 10 with the voltage source 50 in a first position (as shown with the arrow in the switch 55 of Fig. 4). When connected in the first position, the voltage source 50 applies a voltage V_APP across the électrodes 101a, 101b (shown in Fig. 1) of the solar panels 10 and induces the electric field 250 (shown in Fig. 3) across each solar panel 10. Once the electric field 250 has been established across the solar panels 10, the switch 55 switches to connect the solar panels 10 to the inverter 31 (i.e., the load R_L) in a second position. Accordingly, the voltage source 50 can provide the electric field 250 without being connected to the solar panels 10 and the inverter 31 at the same time. Therefore, with reference again to Equation 2, applying the external voltage V_APP does not allow the load R_L(e.g., the inverter 31) to draw current directly from the voltage source 50.

Application of the electric field 250 to the solar panels 10 can increase the current and power output of the solar panels 10 by a predetermined amount when the solar panels 10 subsequently are connected to the inverter 31 in the second position. The predetermined amount is dépendent upon an intensity of light incident on the solar panels 10, the voltage applied V_APP to the solar panels 10 by the voltage source 50, the thickness of the solar panels 10, the frequency f that the voltage source 50 is connected to the solar panels 10, and the duty cycle of the switching process between the first position and the second position-with the duty cycle being defined as the amount of time that the solar panels 10 are connected to the voltage source 50 divided by 1 ifthe switching time (i.e., multiplied by the frequency for divided by the total period of the signal). It should be noted that the switch duration time D, the switching frequency f, and the duty cycle are ail interrelated quantities such that quantifying any two of the quantifies allows for détermination of the third quantity. For example, specifying the switching frequency and the duty cycle allows for détermination of the switch duration time D. For

-11 17841 example, under high intensity light conditions, the improvement in power output can be on the order of 20%; under low light conditions, 50+%.

The embodiment shown in Fig. 4 advantageously provides the electric field 250 to the photovoltaic device 200 without the need to modify the solar panels 10 and/or solar cells 100 to include additional, external électrodes.

In some embodiments, an energy storage device—such as a capacitor 41, an inductor 42, and/or a battery 43—can be placed before the inverter 31 to mitigate any voltage drop-out being seen by the inverter 31 while the switch 55 is in the first position. Accordingly, while the inverter 31 (i.e., load) is disconnected from the solar panels 10 when the switch 55 is in the first position and the electric field 250 is being established across the solar panels 10 (i.e., switching time D shown in Figs. 5A-D), the energy storage device supplies energy to the inverter 31 to keep current flowing during this switched period. Stated in another way, the energy storage device can discharge while the solar panels 10 are disconnected from the inverter 31.

Therefore, a constant voltage from the voltage source 50-which in turn créâtes the electric field 250—need not be applied continuously to see an improvement in the power output of the solar panels 10. For example, with duration switching times D of nominally 10-2000ns, V_App’s of nominally 100-500+ Volts, and a switching frequency f of 20μ seconds, the duty cycle of nominally 0.1-10% can be used. The inductor 42, the capacitor 41, and/or the battery 43 are chosen to be of sufficient size to provide enough discharge while the solar panels 10 are disconnected while the electric field 250 is being placed across the solar panels 10 so as not to cause a drop out on the output of the inverter 31.

For example, the size ofthe capacitor 41 that is placed across the load (e.g., the inverter 31) is determined by the acceptable voltage droop that the inverter 31 can tolerate during the switching time D. For example, if the voltage droop during the switching time D is not to be less than 90% maximum voltage generated by the photovoltaic device 200, the capacitor needs to be sized such according to Equation 3:

-D ⁴¹ R_L]n(MctxV') (Equation 3)

In Equation 3, D is the duration the switch is connected to the voltage source 50 and MaxV is the percentage of the maximum voltage required (e.g., 90% in the example above). In a similar manner, the inductance and/or the battery can be calculated.

Fig. 5A illustrâtes control voltage as a function of time from the switch controller 45 to activate and control the switch 55 using the solar cell management system 300 of Fig. 4. In this example, the solar panels 10 are disconnected from the inverter 31 and connected to the voltage source 50 in the first position of the switch 55 for the duration D, which is repeated every Vf seconds. Fig. 5B illustrâtes the voltage as a function of time from the voltage source provided to the switch 55 at the first position. Fig. 5C illustrâtes the output voltage of the

-1217841 switch 55 from the solar panels 10 (when wired in parallel) as a function of time at the output of the switch 55 that couples to the inverter 31 in the second position. Similarly, Fig. 5D illustrâtes the voltage as a function of time at the output of the switch 55 that couples to the inverter 31 having a capacitor 41 coupled there between.

The drop in voltage seen by the inverter 31 shown in Fig. 5D at the end of the switching duration D is designated the voltage droop discussed above. The voltage droop is dépendent on the size of the capacitor 41, the inductor 42, and/or the battery 43. In one example of the system 300 that does not include the capacitor 41, the inductor 42, or the battery 43, the voltage applied across the input ofthe inverter31 appears as the outputvoltage illustrated in Fig. 5C. Fig. 6 illustrâtes an alternative embodimentofthe solarcell management system 300 of Fig. 3. Turning to Fig. 6, the photovoltaic device 200 can represent any number of photovoltaic devices such as the solar cell 100 and/or the solar panels 10 as illustrated. As shown, the solar panels 10 are wired in parallel, but can also be wired in sériés and any combination thereof.

A voltage puiser 60, such as a high voltage puise generator, can apply a time varying voltage puise 71 (shown in Fig. 7) across one or more of the solar panels 10. In one embodiment, a duration Dp ofthe voltage puise 71 can be short—nominally 10-2000 ns—and a magnitude can be high—nominally 100-500+ Volts. In the embodiment shown in Figure 6, the voltages applied, the puise width, and the puise répétition rate are fixed at a predetermined level to provide optimum performance under selected operating conditions. For example, with reference to Figs. 6 and 7, the voltage puise 71 has the duration D_P of about 1000 ns, which voltage puise 71 is repeated with a period of 1/f. The duration D_P ofthe voltage puise 71 and thefrequency fofthe voltage puise 71 are chosen such thatthe reactance of inductors in the voltage inverter 31 présent a high impédance to the voltage puiser 60, which high impédance allows a high voltage to be developed across the électrodes 101a, 101b (shown in Fig. 1) ofthe solar panels 10 and not be shorted out by the inverter 31.

Additionally, sériés inductors (not shown) can be placed atthe input ofthe inverter 31, which sériés inductors are capable of handling the current input to the inverter 31 and act as an RF choke such that the voltage puises 71 are not attenuated (or effectively shorted) by the résistive componentofthe inverter 31. The duty cycle (time the puise is on/time the puise is off) can be nominally 0.1-10%.

The strength ofthe electricfield 250 imposed on the photovoltaic device 200 is a function ofthe construction of the photovoltaic device 200, such as the thickness of the photovoltaic device 200, the material and dielectric constant ofthe photovoltaic device 200, the maximum breakdown voltage ofthe photovoltaic device 200, and so on.

For the voltage puise 71 shown in Fig. 7, a Fourier analysis of this waveform results in a sériés of puises with frequencies ω = ηω₀ where ω₀ = 2πί and the strength of the puises is given by Equation 4:

-1317841 _x V sinmtr

7(ω) = 2πτν_Αρρ n=—co (Equation 4)

In Equation 4, n is a sériés of integers from -°° to +°°. Accordingly, the Oth order puise (i.e., n=0) has a DC component that is shorted through the résistive load R_L. The first order of the voltage puise 71 applied across the solar panels 10 is V_App (1 - D_PIf), where D_P/fis the duty cycle ofthe puise, D_P is the puise duration, and fis the répétition rate ofthe puise. Since the inductance of the inverter 31 acts as a high impédance Z to the voltage puise 71 generated by the embodiment of Fig. 6, a high voltage puise 71 is developed across each ofthe solar panels 10, which, in turn, créâtes a high electric field 250 across the solar panels 10.

As shown in Fig. 6, the voltage inverter 31 represents the external load R_L. However, the external load R_L can include purely résistive components such that a set of inductors can be placed in sériés with the load R_L to act as the RF choke so that the voltage puise 71 (and the electric field 250) is applied across the solar panels 10.

Any number of circuits can be used in the voltage puiser 60 to apply the voltage puise 71 as desired. One such exemplary circuit used in the voltage puiser 60 is shown in Fig. 8. As illustrated, the voltage puiser 60 includes a puise generator 61 (not shown), a high voltage source 69 (not shown), and a switching transistor 68 for impressing the high voltage puise 71 on the solar panels 10 (e.g., byswitching the output ofthe high voltage source 69 to the solar panels 10) shown in Fig. 6. The voltage puiser 60 of Fig. 8 contains a device that transfers electrical signais between two, electrically isolated, circuits using light, such as an opto-isolator 62 to isolate the puise generator 61 from the high voltage switching transistor 68.

Advantageously, the opto-isolator 62 prevents a high voltage (e.g., from the high voltage source 69) from affecting the puise signal 71. The opto-isolator circuit 62 is illustrated with pins 1-8 and is shown as part ofthe input circuitto the voltage puiser 60.

A bias voltage supply 63 (not shown) provides voltage (e.g., 15 VDC) to the opto-isolator 62 to supply the required bias for the opto-isolator 62. A capacitor 64 isolâtes the bias voltage supply 63, creating an AC path for any signal from distorting the bias supply to the opto-isolator 62. Pins 6 and 7 of the opto-isolator 62 are the switching signal output of the opto-isolator 62 used to drive the high voltage switching transistor 68. A diode 66—such as a Zener diode—is used to hold the switching threshold ofthe switching transistor 68 to above the set pointofthe diode 66, eliminating any noise from inadvertently triggering the switching transistor 68. Resistor 67 sets the bias point for the gâte G and emitter E of the switching transistor 68. When the voltage applied across pins 6 and 7 of the opto-isolator 62 exceeds the threshold set by the resistor 67, the switching transistor 68 is turned “on” and current flows between the collecter C and the emitter E ofthe high voltage switching transistor 68. Accordingly, the high voltage switching

-1417841 transistor 68 présents an Injected High Voltage source to the solar panels 10 until the Control Puise IN from the puise generator 61 drops below the set threshold on the G ofthe high voltage switching transistor 68, which stops the current flow across C-G shutting the switching transistor 68 “off.”

As in the previous embodiments described above, application ofthe electric field 250 to the solar panels 10 can increase the currentand poweroutput ofthe solar panels 10 when subsequently connected to the inverter 31 by a predetermined amount (e.g., dépendent upon the intensity of light incident on solar panels 10, the voltage applied V_APP to the solar panels 10 bythe voltage source 50, the thickness ofthe solar panels 10, the puise width D_P, and the frequency fthat the voltage puise 71 is applied to the solar panels 10, and so on). Similarly, under high intensity light conditions, the improvement in power output of the solar panels 10 can be on the order of 20%; and under low light conditions can be 50+%.

The improvement in the performance of the photovoltaic device 200 cooperating with the electric field 250 can be measured as an increase in the short circuit current ofthe solar cell, l_SCJas shown in Equation 5:

l_Sc= /Base [1 + c(V(t, f),t, ε) *(p_max- p)](Equation 5) where l_BaSe is the short circuit current when no external electric field 250 is applied and p_max is the maximum optical power whereby any additional power does not create any additional electron-hole pairs. As the improvement in the current output of the solar cell is driven by the electric field 250, the form of c(V(t, f),t,s) can be described by Equation 6:

c(V(t, f), t, ε) = m(t, e)V_App*(1-exp(T/To ))*exp(-f_decay//) (Equation 6)

In Equation 6, m(t, ε) is dépendent on the photovoltaic device 200. The improvement in the short circuit current l_sc due to the electric field 250 can be linear with respect to the applied voltage V_App. The improvement observed with respect to the puise répétition rate has a characteristic decay rate of (1/fdecay) and to behave exponentially with respect to the puise rate f. The improvement observed with respect to the puise width τ can also behave exponentially and describe how quickly the applied voltage V_App, reaches full magnitude. The improvement observed with respect to the puise width τ is dépendent upon the details ofthe voltage puiser 60. The increase in the short circuit current l_sc, as a function of applied voltage V_App, the puise répétition rate f, and the puise width t, are shown in Figs. 11A-C, respectively.

Fig. 11A shows the expected improvement in the short circuit current l_sc, for the solar panel 10 (shown in Fig. 2) as a function ofthe magnitude ofthe applied voltage puise V_APP. As shown, the puise width and the puise répétition rate are fixed and the magnitude ofthe puise voltage is varied from 50 to 250 volts. The improvement in the short circuit current AI_Sc increases from nominally 0.1 to 2 Amps. The change in the short circuit current Al_scas a function ofthe

-1517841 applied voltage puise V_APP is, to first order, approximately linear. Fig. 11B shows the change in the improvement of the short circuit current Al_sc as a function of the puise répétition rate for a fixed puise width and a fixed voltage puise. As shown in Fig. 11B, the improvement in the short circuit current Al_sc decreases from approximately 1.7 amps to about 0.45 amps as the puise répétition rate increases from 10 to 100 in arbitrary time units. This behavior is approximately exponential. Fig. 11C shows the change in the improvement ofthe short circuit current Al_sc as a function ofthe puise width for a fixed puise répétition rate and a fixed voltage puise. For this example, the improvement ofthe short circuit current, Al_sc increases from 0 to 1.2amperes as the puise width increases from 0 to 2000 over time.

In each ofthe described embodiments, increasing the strength ofthe electricfield 250 across the électrodes 101a, 101b of the solar cell 100 or solar panel 10 increases the efficiency of the solar cell 100 or panel 10, for example, up to a maximum electric field strength of E_max. Stated anotherway, once the strength ofthe electricfield 250 reaches a maximum strength, the electron-hole recombination rate has been minimized. Accordingly, it can be advantageous to configure the control circuit ofthe photovoltaic device 200 to maximize the output current and voltage under varying operating conditions.

For example, turning to Fig. 9A, a current sensor 33 and a voltage probe 32 are shown coupled to the solar cell management system 300 of Fig. 4. As illustrated, the current sensor 33 is coupled in sériés between the solar panel 10 and the inverter 31. The current sensor 33 can monitorthe current output ofthe solar panel 10. Similarly, the voltage probe 32 is connected across the solar panels 10 and the inverter 31 to monitor the output voltage of the solar panel 10.

A control circuit 35 is coupled to both ofthe current sensor 33 via control leads 33a and the voltage probe 32 via control leads 32a. The current sensor 33 can be an inline or inductive measuring unit and measures the currentoutput ofthe solar panels 10. Similarly, the voltage sensor 32 is used to measure the voltage outputofthe solar panels 10. The product ofthe current measured from the current sensor 33 and the voltage measured from the voltage probe 32 is the power output from the solar panels 10 to the inverter 31.

In some embodiments, the voltage probe 32 may also serve as a power source for the control circuit 35 and is active only as long as the solar panels 10 are illuminated and provide sufficient power to activate control circuit 35. The control circuit 35 further is coupled to the switch 55 to détermine switching times and frequency discussed with reference to Fig. 4. The duration of the switching times and the frequency can be controlled to apply the voltage V_App across the solar panels 10 such that both the current generated within the solar cell 100 and measured by the current sensor 33 and voltage probe 32 are maximized under various operating conditions, such as under differing or variable lighting conditions.

-1617841

In one embodiment for applying the electric field 250, the solar panel 10 initially does not generate power, for example, during the night or heavy cloud coverage. As the solar panels 10 are illuminated (for example, during the morning), voltage and current are generated by the solar panels 10, and the leads 32a begin to deliver both current and voltage to the control circuit

35. The control circuit 35 contains a low voltage logic power supply (not shown) to drive control logic within the control circuit 35. The control circuit 35 also includes the power source 50 for providing a high voltage power supply. The voltage source 50 has a variable output which can be adjusted by the control circuit 35 and is responsible for placing V_App on a lead 38. The high voltage output V/_ppfrom the control circuit 35 drives the lead 38 and is connected to the switch 55. The lead 38 is used to apply voltage V_App through the switch 55 to the solar panels 10. In this example, the control circuit 35 is configured not to apply any voltage V_App to the solar panels 10 until enough power is generated by the solar panels 10 to activate both the low voltage logic power supply and the high voltage power supply.

In an alternative embodiment, the control circuit 35 can be configured to apply the electric field 250 and maximize the power output as the illumination in the day increases and decreases. The control circuit 35 can provide the electric field 250 and stabilize the power output of the solar panels 10 according to any method described above, including process 9000 shown in Fig. 9B.

Turning to Fig. 9B, the process 9000 includes initializing power, at step 900. Enough power must be présentfrom the output ofthe solar panels 10 to activate both the low voltage logic power supply, which opérâtes the control logic in control circuit 35, and the high voltage power supply necessary to place a high voltage on the lead 38 and through the switch 55. Alternatively, the control circuit 35 can be powered from an external source (not shown)-for example, a battery, a large capacitor, an external AC power supply-which allows the low voltage logic power supply to operate and the control circuit 35 to monitor the power output of the solar panels 10 until the solar panels 10 generate enough power output to warrant applying the electric field 250 on the solar panels 10 to augment their power output. Since the control circuit 35 is starting up, ail ofthe parameters (e.g., the applied high voltage V_App, the switch duration time D, and the switching frequency f) are initialized. In one embodiment, the applied high voltage V_App is set to zéro while the switching duration D and the switching frequency f are set to nominal values of D=r₀ and f = f₀. Ail of the control indices, n, /, and j are initialized to zéro.

The control circuit 35 then détermines, at step 901, whether the voltage as measured on the voltage probe 32 is above or below a predetermined minimum v_mÎn and whether the current as measured on the current sensor 33 is above a predetermined minimum, i_min. The combination of v_minand i_min hâve been chosen such that the solar panels 10 are determined to be illuminated and generating some nominal percentage, for example, 5%, of their average rated power and that there is enough power being generated to supply the power source 50 within the control circuit 35 to augment the output of the solar panels 10. If the control circuit 35 détermines that both the measured current and voltage are above the respective predetermined minimums, the control circuit 35 is now operational and process 9000 moves to step 903; otherwise, the process 9000 goes into a wait state, at step 902, and returns to step 900.

In step 903, the control circuit 35 measures the current flowing into the inverter 31 via the current sensor 33, the voltage across the inverter 31 via the voltage sensor 32, and calculâtes the power (nominally, current x voltage) flowing through the inverter 31. A control index n is incremented to n +1.

In step 904, the control circuit 35 compares V_App with V_max. V_max can be a preset value and represents the maximum voltage that can be placed on the solar panels 10 without damaging either the solar panels 10 or the inverter 31. Depending upon the type of the solar panel 10, V_max is typically between 600 V and 1,000 V. If V_App is less than V_max, then process 9000 proceeds to step 906; otherwise, process 9000 waits in step 905.

In step 906, the control circuit 35 incréments the applied high voltage V_App by an amount nAV, and activâtes the switch 55. Activating the switch 55 disconnects the solar panels 10 from the inverter 31 and connects the solar panels 10 to V_App from the control circuit 35 on leads 38. For this example, AV can be a fixed voltage step of 25 Volts although larger or smaller voltage steps can be used. The voltage V_App imposes the electric field 250 on the solar panels 10 such that the strength ofthe electricfield 250 is proportional to the applied voltage V_App. The duration of the connection ofthe solar panels 10 to V_App within the control circuit 35 is chosen to not interrupt operation of the inverter 31. For this example, the duty cycle is chosen to be 5% (the solar panels 10 are connected 5% ofthe time to V_App within the control circuit 35) and the default duration ofthe switching time is chosen to be nominally 1000ns. Alternative switching times can be used as desired. The control circuit 35 again receives the measurement ofthe currentflowing into the inverter31 via the currentsensor 33, receives the measurement ofthe voltage across the inverter 31 via the voltage sensor 32, and recalculâtes the power flowing through the inverter 31.

In step 908, the control circuit 35 compares the poweroutput ofthe solar panels 10 before V_Appwas placed on the solar panel 10 to the most recent measurement. If the power has increased, the process 9000 returns to step 901 and is repeated. The voltage applied on the lead 38 is increased by AV until either the applied high voltage V_App is greater than V_maxor until the increase in the applied high voltage V_App does not yield an increase in output power ofthe solar panels 10. V_maxis defined here as the maximum voltage that can be placed on a solar panel without causing it any damage. Depending upon the type ofthe solar panel 10, V_maxis typically approximately 600 to 1,000 V. In both cases, process 9000 waits in step 905. The duration of the wait state could be from seconds to minutes.

— 18

After the wait step 905, process 9000 continues to step 907. If the power, as measured through the leads 32a and 33a, has not changed, the index n is decremented (n=n-1), the applied voltage V_App on the leads 38 to the solar panel(s) 10 is decreased by the amount AV, and the control circuit 35 activâtes the switch 55. Process 9000 continues in step 909 where the power output is measured by the current sensor 33 and voltage probe 32. If the power output shows a drop, process 9000 continues to step 910. If the power output has increased, the process 9000 returns to step 907 and the applied voltage V_App continues to décrément until the power output ofthe solar panels 10 ceases to diminish. The process 9000 proceeds to step 910.

In step 910, the control circuit 35 increases the duration that the switch 55 is connected to the solar panels 10 on the lead 38 in the first position discussed above. The amount of time that the switch 55 is connected to the voltage source 50 is increased by an amount ϊΔτ₀. The switch 55 is activated and the power output ofthe solar panels 10 is again monitored by the current sensor 33 and the voltage probe 34. The process 9000 proceeds to state 912 to détermine whetherthe power output ofthe solar panels 10 increases. If so, process 9000 moves to step 910 and the duration that the solar panels 10 are connected to the voltage source 50 is increased again. The switching duration will increase until the output power ofthe solar panels 10 reaches a maximum (or until a fixed duration limit - for example, 3-5 pseconds is reached) at which point the switch duration changes driven by the control circuit 35 stops. However, if at step 912, the control circuit 35 détermines that increasing the switch duration D causes a decrease in the power output as measured by the current sensor 33 and the voltage probe 32, process 9000 continues to step 911 and the switch duration D is decreased by iterating between steps 911 and 913 until the power output ofthe solar panels 10 is maximized again. After the control circuit 35 has determined that the switching duration has been optimized for maximum output power of solar panels 10 by repeating step 910 to step 913, process 9000 continues to step 914.

In step 914, the control circuit 35 begins to increase the frequency of connection fat which the switch 55 is connected to the control circuit 35. The frequency f that the switch 55 is connected to the voltage source 50 is increased by jAf from the original switching frequency f₀ such that f = f_o + JAf. In step 914, the switch 55 is connected between the lead 38 and the solar panels 10 at a newfrequency, f, and the poweroutput ofthe solar panels 10 is again monitored by the current sensor 33 and the voltage probe 34. The process 9000 continues to step 916. If the poweroutput ofthe solar panels 10 has increased, the process 9000 moves backto step 914 and the rate at which the solar panels 10 are connected to the voltage source 50 is increased again. The rate of connection will increase until the output power ofthe solar panels 10 reaches a maximum or until a maximum frequency f_max, at which point the process 9000 moves to step 915. In step 914, the frequency the switch 55 connects to the high voltage 50 on the lead 38 is now decremented by an amount jAf and the switch 55 is activated again and the power output of the solar panels 10 is again monitored by the current sensor 33 and the voltage probe 32. At that point, the control circuit 35 décidés whether the decrease in the rate of connection increases the power output of solar panels 10 in step 917. If so, the process 9000 returns to step 915. Alternatively, if the frequency of switching reaches some minimum frequency f_min, the process 9000 moves to step 918 to wait.

In step 918, once the power output of the solar panels 10 has been maximized, the control circuit 35 goes into a wait state for a period of time. The period of wait time can be seconds or minutes. After waiting in step 918, the process 9000 moves to step 901 where process 9000 again begins to vary the voltage, the switch connection time and the switching rate from the previous optimized values to validate the solar panels 10 are still operating at their maximum output levels. The applied voltage 50 from the control circuit 35, the switching duration, and the switching rate are ali varied over the course of operation during a day to be sure that the solar panels 10 are operating under with maximum output power under the operational conditions of that particular day.

If at step 901, the voltage as measured on voltage sensor 32 drops below the predetermined minimum v_min, and the current as measured on current sensor 33 drops below a predetermined minimum i_mln, the control circuit 35 will remove any voltage on lines 38, and the control circuit 35 will move to step 902 to wait before returning to step 900 (where the system will reinitialize ail of the parameters and indices). Process 9000 will alternate from step 900 to 901 to 902 to 900 until both the voltage as measured on the voltage probe 32 and the current as measured on the current sensor 33 are both above v_min and i_min respectively, at which point the process 9000 will move from step 901 to step 903.

Different state machines within control circuit 35 can be implemented to yield similar results and are covered by this disclosure. However, the process 9000 described above advantageously minimizes the magnitude of the applied voltage V_App to the lowest value possible such that the product of the current measured by the current probe 33 and the voltage measured by the voltage probe 32 are maximized. The applied voltage V_App is dithered - that is changed by small amounts both up and down - over the course of operation in a day to accountfor changes the incident optical power, p, on the solar cell 100, the solar panel 10, or the plurality of solar panels 10 over the course of a day so that the maximum power output can always be maintained.

Most of the steps described in process 9000 above were designed to address adiabatic changes in illumination that occur slowly over periods of multiple minutes or hours. In an alternative embodiment, if the illumination variances were to occur at a higher rate of change, the process 9000 can be adapted to minimize the high frequency variations in DC power output to the inverter by attempting to hold the DC output power from varying at too high a rate of change, hence making the quality of the inverter higher.

In another example, turning to Fig. 10A, the current sensor 33 and the voltage probe 32 are shown coupled to the solar cell management system 300 of Fig. 6. As illustrated, the current sensor 33 is coupled in sériés between the solar panel 10 and the inverter 31. The current sensor 33 can monitorthe current output ofthe solar panel 10. Similarly, the voltage probe 32 is connected across the solar panels 10 and the inverter 31 to monitorthe output voltage ofthe solar panel 10.

A control circuit 36 is coupled to both the current sensor 33 via control leads 33a and the voltage probe 32 via control leads 32a. The current sensor 33 can be an inline or inductive measuring unit and measures the currentoutput ofthe solar panels 10. Similarly, the voltage sensor 32 is used to measure the voltage output ofthe solar panels 10. The product ofthe current measured from the current sensor 33 and the voltage measured from the voltage probe 32 allow for a calculation of the power output from the solar panels 10 to the inverter 31.

In some embodiments, the voltage probe 32 may also serve as a power source for the control circuit 36 and is active only as long as the solar panels 10 are illuminated and provide sufficient power to activate control circuit 36. The control circuit 36 further is coupled to voltage puiser 60 to control the amplitude ofthe voltage puise V_App, the puise duration D_P and the puise frequency f discussed with reference to Fig. 6. The puise duration D_P, the puise frequency f, and the puise voltage V_App applied across the solar panels 10 can be controlled and adjusted such that both the current generated within the solar panel 10 and measured by the current sensor 33 and voltage probe 32 are maximized under various operating conditions, such as under differing or variable lighting conditions.

In one embodiment for applying the electric field 250, the solar panel 10 initially does not generate power, for example, during the night or heavy cloud coverage. As the solar panels are illuminated (for example, during the morning), voltage and current are generated by the solar panels 10, and the leads 32a begin to deliver both current and voltage to the control circuit 36. The control circuit 36 contains a low voltage logic power supply (not shown) to drive control logic within the control circuit 36. The puiser circuit 60 contains both a low voltage and high voltage power supply (not shown). The high voltage power supply in voltage puiser 60 has a variable output which can be adjusted by control circuit 36 and is responsible for placing V_App on solar panels 10. In this example, the control circuit 36 is configured not to apply any voltage to the solar panels 10 until enough power is being generated by the solar panels 10 to activate both the low voltage logic power supply and the high voltage power supply in puiser 60.

In an alternative embodiment, the control circuit 36 is configured to control the electric field 250 and maximize the power output as the illumination in the day increases and decreases. The control circuit 36 can control the electric field 250 applied by voltage puiser 60 and stabilize the power output ofthe solar panels 10 according to any method described above, including process 10000 shown in Fig. 10B.

Turning to Fig. 10B, the process 10000 includes initializing power, at step 1000. Enough power must be présent from the output ofthe solar panels 10 to activate both the low voltage logic power supply, which opérâtes the control logic in control circuit 36, and the low and high voltage power supply in voltage puiser 60. Altematively, the control circuit 36 can be powered from an external source (not shown)-for example, a battery, a large capacitor, an external AC power supply-which allows the low voltage logic power supply to operate and the control circuit 36 to monitor the power output of the solar panels 10 until they hâve enough power output to warrant applying the electric field 250 on the solar panels 10 to augment their power output. Since the control circuit 36 is starting up, ail ofthe parameters (e.g., applied high voltage V_App, the puise duration D_P, and the puise répétition frequency, f) are initialized. In one embodiment, the applied high voltage V_App is setto zéro while the puise duration D_P and puise répétition rate fare set to nominal values of D_p=t₀ and f-f₀. Ail ofthe control indices, n, i, and J are initialized to zéro.

The control circuit 36 then détermines in step 1001 whether the voltage as measured on the voltage probe 32 is above or below a predetermined minimum v_mj_n and whether the current as measured on the current sensor 33 is above a predetermined minimum, i_mîn. The combination of v_miriand i_min hâve been chosen such that the solar panels 10 are determined to be illuminated and generating some nominal percentage, for example, 5%, of their average rated power and that there is enough power being generated to supply the high voltage power supply to augment the output ofthe solar panels 10. Ifthe control circuit 36 détermines that both the measured current and voltage are above the respective predetermined minimums, then process 10000 is now operational and moves to step 1003; if not, process 10000 goes into a wait state 1002 and returns to step 1000.

In step 1003, the control circuit 36 measures the current flowing into the inverter 31 via the current sensor 33, the voltage across the inverter 31 via the voltage sensor 32, and calculâtes the power flowing through the inverter 31 (nominally, I x V). A control index n is incremented to n +1.

In step 1004, process 10000 compares V_App with V_max. V_max is a preset value and represents the maximum voltage that can be placed on the panels without damaging either the panels 10 or the inverter 31. If V_App is less than V_max, then process 10000 proceeds to step 1006; otherwise, process 10000 waits in step 1005.

In step 1006, the control circuit 36 signais the voltage puiser 60 to incrément the applied high voltage V_App by an amount nAV, and signais the voltage puiser 60 to apply the voltage puise to the solar panels 10. For this example, AV can be a fixed voltage step of 25 Volts, although larger or smaller voltage steps can be used. The voltage V_App imposes the electric field 250 on the solar panels 10 and the strength ofthe electricfield 250 is proportional to the applied voltage V_App. For this example, the puise width D_P is chosen to be 1000ns and the puise — 22 — répétition rate is chosen to be 20 pseconds. Other puise widths and puise répétition rates could also be chosen. The control circuit 36 again receives the measurement of the current flowing into the inverter31 via the current sensor 33, receives the measurement ofthe voltage across the inverter 31 via the voltage sensor 32, and recalculâtes the power flowing through the inverter 31.

In step 1008, the control circuit 36 compares the power output of the solar panels 10 before V_Appwas placed on the solar panel 10 to the most recent measurement If the power has increased, process 10000 returns to step 1001 and is repeated. The applied voltage V_App is increased by AV until either the applied high voltage V_App is greater than V_maxor until the increase in the applied high voltage V_App does not yield an increase in output power ofthe solar panels 10. Again, V_maxis defined here as the maximum voltage that can be placed on a solar panel 10 without causing it any damage and depending upon solar panel type, it would typically be approximately 600 to 1,000 V. In both cases, process 10000 waits in step 1005. The duration of the wait state could be from seconds to minutes.

After the wait step 1005, process 10000 enters step 1007. If the power, as measured through the leads 32a and 33a, has not changed, index n is decremented (n=n-1), the applied voltage puise V_App is decreased by the amount AV, and the control circuit 36 activâtes the puiser 60. Process 10000 continues in step 1009 where the power output as measured by the current sensor 33 and voltage probe 32. If the power output shows a drop, process 10000 continues to step 1010. If the power output has increased, process 10000 returns to step 1007 and the applied voltage V_App continues to décrément until the power output ofthe solar panels 10 ceases to diminish. The process 10000 proceeds to step 1010.

In step 1010, the control circuit 36 begins to increase the duration D_P ofthe voltage puise. The voltage puise duration D_P is increased by an amount ϊΔτ₀. The voltage puiser 60 is activated and the power output ofthe solar panels 10 is again monitored bythe current sensor 33 and the voltage probe 34. The process 10000 proceeds to state 1012 to détermine whether the power output of the solar panels 10 increases. If so, process 10000 moves to step 1010 and the duration D_P ofthe voltage puise 71 is increased again. The puise duration D_Pwill increase until the output power ofthe solar panels 10 reaches a maximum or until afixed duration limit-for example, a puise duration of 5pseconds is reached - at which point the puise width changes driven by the control circuit 36 stops. However, if at step 1012, it is found that the increasing the puise width causes a decrease in the power output as measured by the current sensor 33 and the voltage probe 32, process 10000 continues to step 1011. The puise width is decreased by iterating between steps 1011 and 1013 until the power output ofthe solar panels 10 is maximized again. After the control circuit 36 has determined that the puise duration has been optimized for maximum output power of solar panels 10 by going through step 1010 to step 1013, the process continues to step 1014.

In step 1014, the control circuit 36 increases the frequency ofthe voltage puises. The frequency ofthe voltage puises is increased byjâffrom the original switching frequency f₀ such that f= f₀ + jAf. In step 1014, voltage puises are applied by the voltage puiser 60 to the solar panels 10 at a new frequency f, and the power output ofthe solar panels 10 is again monitored by the current sensor 33 and the voltage probe 34. The process 10000 then moves to step 1016.

Ifthe power output ofthe solar panels 10 has increased, the process 10000 moves back to step 1014 and the rate at which voltage puises are applied to the solar panels 10 is increased again. The increase in the rate of voltage puises will increase until the output power ofthe solar panels 10 reaches a maximum or until a maximum frequency f_max, at which point the process 10000 moves to step 1015. In step 1014, the frequency ofthe voltage puises is now decremented by an amountjAf and the voltage puiser60 switch is activated again and the power output ofthe solar panels 10 is again monitored by the current sensor 33 and the voltage probe 32. At that point, the control circuit 36 détermines whether the decrease in the rate of voltage puises increases the power output of solar panels 10 in step 1017. If so, the process 10000 returns to step 1015. Alternatively, if the frequency of switching reaches some minimum frequency f_min, the process 10000 moves to step 1018, which is a wait state.

In step 1018, once the power output ofthe solar panels 10 has been maximized, process 10000 goes into a wait state for a period of time. The period of wait time can be seconds or minutes. After waiting in step 1018, the process 10000 moves to step 1001 where the control circuit 36 again begins to vary the puise voltage, the puise duration, and the puise répétition rate from the previous optimized values to validate the solar panels 10 are still operating at their maximum output levels. The puise amplitude V_App, the puise duration, and the puise répétition rate are ail varied over the course of operation during a day to be sure that the solar panels 10 are operating under with maximum output power under the operational conditions of that particular day.

If at step 1001, the voltage as measured on the voltage sensor 32 drops below the predetermined minimum v_min, and the current as measured on current sensor 33 drops below a predetermined minimum i_min, the control circuit 36 will stop the voltage puiser 60 and the process 10000 will move to step 1002 wait state and then to step 1000 where the system will reinitialize ail of the parameters and indices. The process 10000 will move from step 1000 to 1001 to 1002 to 1000 until both the voltage as measured on the voltage probe 32 and the current as measured on the current sensor 33 are both above v_mj_n and i_min respectively, at which point process 10000 will move from step 1001 to step 1003.

Different state machines within the control circuit 36 can be implemented to yield similar results and are covered by this disclosure. However, the process 10000 described above advantageously minimizes the magnitude ofthe applied voltage puise V_Appto the lowestvalue possible such that the product of the current measured by the current probe 33 and the voltage measured by the voltage probe 32 are maximized. The applied voltage puise V_App is dithered that is changed by small amounts both up and down - over the course of operation in a day to account for changes the incident optical power, p, on the solar cell 100, the solar panel 10, or the plurality of solar panels 10 over the course of a day so that the maximum power output can always be maintained.

The steps described in process 10000 can address adiabatic changes in illumination that occur slowly over periods of multiple minutes or hours. In an alternative embodiment, if the illumination variances were to occur at a higher rate of change, the process 10000 can be adapted to minimize the high frequency variations in DC power output to the inverter by attempting to hold the DC output power from varying at too high a rate of change, hence making the quality of the inverter higher.

The described embodiments are susceptible to various modifications and alternative forms, and spécifie examples thereof hâve been shown by way of example in the drawings and are herein 15 described in detail. It should be understood, however, that the described embodiments are not to be limited to the particular forms or methods disclosed, butto the contrary, the présent disclosure is to cover ail modifications, équivalents, and alternatives.

Claims

What is claimed is:

1. A method of managing a photovoltaic device, comprising:

applying a first component of a voltage signal to the photovoltaic device, the first component representing an on state for generating an external electric field across the photovoltaic device; and applying a second component ofthe voltage signal to the photovoltaic device, the second component representing an off cycle.
2. The method of claim 1, wherein said applying the first component comprises applying a high voltage of a time-varying voltage puise from a voltage puiser circuit, and wherein said applying the second component comprises shutting off the voltage puiser circuit.
3. The method of claim 1 or claim 2, wherein said applying the first component comprises connecting a voltage source and the photovoltaic device in a first position of a switch disposed between the voltage source and the photovoltaic device, and wherein said applying the second component comprises disconnecting the voltage source and the photovoltaic device in a second position of the switch to optionally provide electrical isolation between the voltage source and a load driven by the photovoltaic device when the switch is in the second position.
4. The method of any one of the above claims, wherein said applying the first component comprises impressing an output of a high voltage source ofthe voltage puiser circuit onto the photovoltaic device when a switching transistor ofthe voltage puiser circuit is in an on position for generating the first state, and optionally continuing said impressing the output ofthe high voltage source until a puise generator ofthe voltage puiser circuit turns the switching transistor to an off position for generating the second state.
5. The method of any one ofthe above claims, wherein said applying the first component comprises generating the external electric field with a first direction or a second direction, the first direction and a polarity of internai électrodes of the photovoltaic device being in a same direction for increasing a power output ofthe photovoltaic device, and the second direction being in an opposite direction ofthe polarity ofthe internai électrodes for decreasing the power output.
6. The method of any one of the above claims, further comprising monitoring an output voltage of the photovoltaic device, wherein said monitoring the output voltage optionally is performed via a voltage probe coupled across the photovoltaic device, or monitoring an output currentofthe photovoltaic device, wherein said monitoring the output current optionally is performed via a current sensor coupled in sériés between the photovoltaic device and a load driven by the photovoltaic device.
7. The method of claim 6, further comprising adjusting, wherein said adjusting optionally is performed via a control circuit coupled to the voltage source, at least one of a magnitude, a duration, and a frequency ofthe first componentto maximize a power output of the photovoltaic device based on said monitoring.
8. The method of any one of the above claims, wherein said applying the first component comprises generating the external electric field across at least one of a solar cell, an array of solar cells, a solar panel, and an array of solar panels.
9. A method of managing a photovoltaic device, comprising:

enabling a voltage puiser to be coupled to the photovoltaic device; and applying a voltage signal generated by the voltage puiser to the photovoltaic device, the voltage signal having a first state for generating an external electric field across the photovoltaic device and a second state representing an off cycle.
10. The method of claim 9, wherein said applying the voltage signal comprises applying an adjustable voltage to the photovoltaic device, and optionally impressing an output of a high voltage source ofthe voltage puiser onto the photovoltaic device when a switching transistor ofthe voltage puiser is in an on position for generating the firststate, and optionally continuing said impressing the output ofthe high voltage source until a puise generator of the voltage puiser turns the switching transistor to an off position for generating the second state.
11. The method of claim 9 or claim 10, further comprising enabling one or more sériés inductors to be coupled between the voltage puiser and a load of the photovoltaic device for blocking frequencies of the voltage signal to the load that are greater than a predetermined frequency.
12. The method of any one of claims 9-11, further comprising controlling at least one of a frequency and a duration of the first state and the second state via a control circuit coupled to the voltage puiser.

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13. A method of managing a photovoltaic device, comprising: enabling a first port of a switch to be coupled to the photovoltaic device;

enabling a second port of the switch to be coupled to a load driven by the photovoltaic device;

enabling a third port ofthe switch to be coupled to a voltage source, wherein the switch can operate in a first position for providing a current path between the photovoltaic device and the voltage source and a second position for providing the current path between the photovoltaic device and the load; and applying a voltage signal generated by the voltage source to the photovoltaic device when the switch is in a first position, the voltage signal having a first state for generating an external electric field across the photovoltaic device when the switch is in the first position, and a second state to provide electrical isolation between the voltage source and the load when the switch is in the second position.
14. The method of claim 13, wherein said enabling the first port ofthe switch comprises enabling a first port of a double throw switch to be coupled to the photovoltaic device.
15. The method of claim 13 or claim 14, further comprising controlling at least one of a frequency and a duration of switching between the first position and the second position via a switch controller coupled to the double throw switch.
16. The method of any one of claims 13-15, further comprising enabling a device for mitigating any voltage drop-out of the first component to be coupled between the load and the photovoltaic device.
17. The method any one of claims 13-16, wherein said applying the voltage signal comprises applying an adjustable voltage to the photovoltaic device.
18. The method of any one of claims 13-17, further comprising controlling at least one of a frequency, a magnitude, and a duration ofthe first state and the second state, wherein said controlling optionally is performed via a control circuit coupled to at least one ofthe voltage source and the switch based on an output current of the photovoltaic device optionally measured by a current sensor coupled in sériés between the photovoltaic device and the load and an output voltage ofthe photovoltaic device optionally measured by a voltage probe coupled across the photovoltaic device.