WO2022169422A1

WO2022169422A1 - A solar panel, a method of fabricating a solar panel and a method for controlling a solar panel.

Info

Publication number: WO2022169422A1
Application number: PCT/SG2022/050054
Authority: WO
Inventors: Charles Kin Fai HO
Original assignee: Ho Charles Kin Fai
Priority date: 2021-02-05
Filing date: 2022-02-04
Publication date: 2022-08-11

Abstract

A solar panel, a method of fabricating a solar panel and a method for controlling a solar panel. The solar panel comprises a first set of photovoltaic cells including a plurality of first subcells electrically connected together, and provided with a first pair of electrical conductors connecting a cathode and an anode of the first set of photovoltaic cells; and a second set of photovoltaic cells including a plurality of second subcells electrically connected together, and provided with a second pair of electrical conductors connecting a cathode and an anode of the second set of photovoltaic cells; wherein each of the first subcell and the second subcell is arranged to produce maximum power output independently when subjected to irradiation with predetermined light spectrums different from each other; and wherein the first pair of electrical conductors and the second pair of electrical conductors are arranged to form an electrical circuit with an electrical load such that each of the first set of photovoltaic cells and the second set of photovoltaic cells are individually manipulated to achieve an overall maximum power output of the solar panel when subjected to the irradiation.

Description

A SOLAR PANEL, A METHOD OF FABRICATING A SOLAR PANEL AND A METHOD FOR

CONTROLLING A SOLAR PANEL

TECHNICAL FIELD

The invention relates to a solar panel, a method of fabricating a solar panel and a method for controlling a solar panel, and particularly, although not exclusively, to a multi-junction photovoltaic (PV) panel and a multi-source, high-efficiency integrated photovoltaic energy harvester/converter for controlling the PV panel.

BACKGROUND OF THE INVENTION

Solar panels may be applied to the adoption of the optical power transmission technology for remote vehicles such as UAVs, pseudosatellites, satellites, spacecraft to name a few, in which these are highly SWAP (size, weight and power)-limited vehicle, in addition these mobile platforms or remote locations (for example power at lamp/sign posts or mountain top or lunar surface) may have very limited options for power source to choose from and solar or batteries are most common. Scaling up the vehicle only to accommodate more power proves uneconomical in many cases, and this issue may be more severe for airborne and spaceborne platforms.

As capability of electronics and other high-performance payload improves, the specific power consumption or power density for these devices is expected to increase. It follows that the specific power/energy supply should also increase.

SUMMARY OF THE INVENTION In accordance with a first aspect, there is provided a solar panel comprising: a first set of photovoltaic cells including a plurality of first subcells electrically connected together, and provided with a first pair of electrical conductors connecting a cathode and an anode of the first set of photovoltaic cells; and a second set of photovoltaic cells including a plurality of second subcells electrically connected together, and provided with a second pair of electrical conductors connecting a cathode and an anode of the second set of photovoltaic cells; wherein each of the first subcell and the second subcell is arranged to produce maximum power output independently when subjected to irradiation with predetermined light spectrums different from each other; and wherein the first pair of electrical conductors and the second pair of electrical conductors are arranged to form an electrical circuit with an electrical load such that each of the first set of photovoltaic cells and the second set of photovoltaic cells are individually manipulated to achieve an overall maximum power output of the solar panel when subjected to the irradiation.

Preferably, the electrical load includes a plurality of junction boxes each arranged to connect to both conductors of a respective one of the first pair of electrical conductors and the second pair of electrical conductors.

Preferably, the electrical load includes a common junction box arranged to connect to one or both conductors of each of the first pair of electrical conductors and the second pair of electrical conductors.

Preferably, the common junction box is arranged to connect to both the first set and the second set of photovoltaic cells in parallel via the first pair of electrical conductors and the second pair of electrical conductors. Preferably, the first set of photovoltaic cells, the second set of photovoltaic cells, and the common junction box are connected in series.

Preferably, the solar panel further comprises one or more additional photovoltaic cell connected in series with the first set of photovoltaic cells, the second set of photovoltaic cells, and the common junction box.

Preferably, the one or more additional photovoltaic cell includes a monolithic tandem cell, wherein the tandem cell includes a combination of the first subcell and the second subcell connected by a tunneling junction therebetween.

Preferably, the number of subcells in each of the first set and the second set of photovoltaic cells are different.

Preferably, each of the first and the second set of photovoltaic cells further comprises a plurality of interconnecting leads arranged to electrically connect the subcells and the electrical conductors.

Preferably, the plurality of interconnecting leads include a carbon-based light weight conductor material.

Preferably, the irradiation is generated by a narrowband light source, a solar source or an electrical lighting source.

In accordance of a second aspect, there is provided a method of fabricating a solar panel in accordance with the first aspect, comprising the steps of: providing the first set of photovoltaic cells on a substrate; providing an isolation layerto cover the plurality of first subcells; providing the second set of photovoltaic cells on the isolation layer; and packaging or encapsulating the first and the second set of photovoltaic cells.

Preferably, the step of providing the first set of photovoltaic cells on a substrate comprising the steps of providing the plurality of first subcells on the substrate and connecting the plurality of first subcells with the plurality of interconnecting leads.

Preferably, the method further comprises the step of electrically connecting the first set of photovoltaic cells and/or the second set of photovoltaic cells to one or more junction boxes arranged to facilitate an output of electrical power generated by the solar panel when subjected to an irradiation.

Preferably, the isolation layer includes a void or a layer of high-resistive material.

Preferably, the method further comprises the step of forming a monolithic tandem cell including a combination of the first subcell and the second subcell connected by a tunneling junction therebetween.

In accordance with a third aspect, there is provided a method for controlling a solar panel in accordance with the first aspect, comprising the steps of: configuring the solar panel to operate in at least a narrowband energy harvesting mode; and controlling the electrical load of an external circuitry so as to optimize an output power of the first and the second set of photovoltaic cells.

Preferably, the step of controlling the electrical load of the external circuitry comprising the step of individually controlling an electrical current passing through an external circuit in connection to each of the first and the second set of photovoltaic cells so as to extract the maximum power output from each of the first and the second set of photovoltaic cells, such that the overall maximum power output of the solar panel is harvested or stored.

Preferably, the step of controlling the electrical load of the external circuitry comprising the step of controlling an electrical current passing through a common electrical load so as to extract the maximum power output from a selected one of the first and the second set of photovoltaic cells, such that the overall maximum power output of the solar panel is harvested.

Preferably, the solar panel is further arranged to operate in a solar harvesting mode or a broadband energy harvesting mode.

BRIEF DESCRIPTION OF THE DRAWINGS FOR THE INVENTION

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figures 1A to 1C are schematic diagrams of solar panel configurations in accordance with different embodiments of the present invention.

Figures 2A and 2B are circuit diagrams showing equivalent circuits of solar panels each including a multi-junction photovoltaic cell (MJPV) with different terminal configurations, in accordance with different embodiments of the present invention.

Figures 3A and 3B are plots showing simulated J-V behavior of subcells in the solar panels of Figures 2A and 2B.

Figures 4A to 4C are schematic diagrams showing solar panels with a traditional configuration, an independent operation terminal configuration and a series/parallel connected terminal configuration in accordance with embodiments of the present invention.

Figures 5A to 5B are schematic diagrams showing solar panels with an independent operation configuration (4T) and a series/parallel connection configuration (VM) in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The invention designer devised that wireless power or optical wireless power is a flexible and economical way to scale the specific power/energy or power/energy density of power supply (i.e. the Photo Voltaic (PV) cells).

Solar energy available on Earth's surface or even to the many planetary orbits is subjected to unavailability due to shadowing of some kind (by celestial bodies or clouds etc.). It is devised that a solar energy harvester while capable of harnessing solar energy when available, may also be capable to accept other form of supplementary sources of artificial optical energy such as, and without limitations, LEDs, lasers or other optical emitters. However, traditional standard harvesters may have difficulty receiving light of narrow (frequency or wavelength) bandwidth like LEDs or lasers.

Without wishing to be bound by theory, narrowband light or irradiation may either fall outside the sensitivity range of the harvesters or may not be well matched with the spectral response of the harvester, which may limit the output power being harvested from the available solar power.

Referring to Figure 1A, there is shown an example of a more advanced high-efficiency harvester, which may be considered as a 2-terminal multi-junction PV cell 100, each subcell is denoted by its photosensitive "junction" 102 and its respective electrical interface materials 104. This example device comprises multi-junction photovoltaic cells which are serially connected (i.e. internal to the absorber chip), therefore may not be able to convert the narrowband supplement light into useful electrical energy in some occasions.

In one or more embodiments, the invention relates to a novel design of photovoltaic converters that is capable of maximizing the conversion of optical energy from multiple sources in addition to solar energy either by design or for retrofitting.

With reference to Figures IB to 1C, there is shown two example solar panel configurations in accordance with embodiments of the present invention, in which the solar panels 110 comprises: a first set of photovoltaic cells 112 including a plurality of first subcells electrically connected together, and provided with a first pair of electrical conductors 114 connecting a cathode and an anode of the first set of photovoltaic cells 112; and a second set of photovoltaic cells 116 including a plurality of second subcells electrically connected together, and provided with a second pair of electrical conductors 118 connecting a cathode and an anode of the second set of photovoltaic cells; wherein each of the first subcell and the second subcell is arranged to produce maximum power output independently when subjected to irradiation with predetermined light spectrums different from each other; and wherein the first pair of electrical conductors 114 and the second pair of electrical conductors 118 are arranged to form an electrical circuit with an electrical load such that each of the first set of photovoltaic cells and the second set of photovoltaic cells are individually manipulated to achieve an overall maximum power output of the solar panel when subjected to the irradiation.

Figures IB and 1C illustrate two variations of this invention, both are multi-terminal cells. For example, in such a configuration as shown in Figure IB, no subcells are connected on a device level in series but with an external circuitry like a power management module, and the subcells maybe separated by a void between the subcells or a layer of highly-resistive materials. In an alternative example as shown in Figure 1C, some subcells are connected in series but not all. More variations of the present invention will be further described later in this disclosure. In addition junction boxes 120 are included which allows the PV cells to connect to external loads to draw or dissipate the electrical powers generated by the PV cells when the solar panel is subjected to illumination.

It should be understood by a skilled person in the art that the junction box (JB) here refers to a circuitry not necessary a physical item. For example, more than one junction boxes may be provided as "separate JBs" but housed on the same circuit board or housing. Preferably, the separate JBs may facilitate the function of Maximum Power Point Tracking (MPPT) of each of the strings of cell or group of cells in the same circuit. For example, an MPPT controller may be connected to the junction box(es) so as to perform the MPPT function, regardless of the actual configuration of the subcells connecting to the terminals of the junction boxes.

In these example embodiments, different types of photovoltaic subcells may be integrated in a photovoltaic module or a solar panel, but preferably, not in the device level but in a module level, therefore the individual subcells are preferably only electrically connected together with interconnects or external conductors. In this description, the term "multi-junction cell" refers to a physical combination of at least two types of subcell electrically connected together but not necessary forming a "tandem cell" in the device level referring to the illustration in Figure 1A.

It is appreciated that different types of photovoltaic subcells, such as amorphous-Si PV cell, crystalline-Si PV cell, Germanium PV cell, Perovskite-based PV cell, dye-sensitive PV cell, CIGS PV cell, lll-V compound semiconductor-based (e.g. GaAs) cell, OPV cell, etc., are optically and electrically responsive to different optical spectrum, thus a multi-junction cell including at least two different types of subcells (or junctions) is arranged to produce maximum power output when subjected to irradiation of different light spectrums. For simplicity, some embodiments in this disclosure includes a bottom cell (or the first subcell) and a top cell (or the second subcell) only. In some alternative examples, the multi-junction cell in the present invention may comprises more than two types of subcells or photovoltaic junctions so as to further broaden the effective absorption spectrum of the solar panel.

Preferably, the top and bottom cells are vertically stacked, therefore when the stacked top and bottom cell is subjected to any incident light spectrum or combination, being it single source or multi-source, the top and the bottom cells should see the same spectrum, although the subcell may experience difference spectrum due to spectrally selective light absorption or filtering of top subcells and considering different travel path of multiple sources.

In one preferred embodiment, the invention further comprises a power receiver which is capable of optimizing both the harvesting of the solar energy and the narrowband energy delivered from a transmitter facility, synchronously and asynchronously. Preferably, the power receiver may be used to control an operation of the solar panel 110, including configuring the solar panel 110 to operate in at least a narrowband energy harvesting mode; and controlling the electrical load of an external circuitry so as to optimize an output power of the first and the second set of photovoltaic cells 112, 116 of the solar panel 110 in accordance with embodiments of the present invention. In an alternative operation, the solar panel 110 may be configured to operate in a solar harvesting mode or a broadband energy harvesting mode.

For example, in accordance with a preferred embodiment of the present invention, the power receiver enables optimal power reception with multiple optical energy sources (e.g., solar and laser/LED of different colors and power intensities). Under some exemplary scenarios such as spacecraft, drones, autonomous platforms or stationary objects like sensors in operation, they could be powered by ambient light (sunlight or indoor or outdoor light). However, when ambient light is unavailable, directed supplemental light of high-efficiency narrowband character could be delivered using the photovoltaic harvester with minimal increase in weight, size and system complexity.

Advantageously, the invention may also negate the need for 2 separate receivers in some example embodiments. For example, a common junction box may be provided on a solar panel to connect both conductors of each of the first pair of electrical conductors and the second pair of electrical conductors, such as connecting to both sets of PV cells 1 and 2 in parallel, while in each of the first and second sets of PV cells, the subcells are connected in series. In this example, while the cells are able to operate in a vertically stacked (i.e. space efficient manner) configuration, the (MPPT) controller is able to optimally convert energy from changing spectra or multiple sources.

With reference to Figures 2A to 2B, a device with two subcells may be represented by equivalent circuits having a plurality of circuit elements. The circuit 202 as shown in Figure 2A is an equivalent circuit representing a tandem cell 100 as shown in Figure 1A, having a first subcell and a second subcell connected together in series via a tunnelling junction, and has a "two-terminal configuration", whereas the circuits 204 as shown in Figure 2B is an equivalent circuit representing a multi-junction cell 110 having a first subcell and a second subcell each connects to an individual electrical load in a separated circuit, thus the multi-junction cell has a "four-terminal configuration".

In the electrical model of two different embodiments of the multi-junction photovoltaic cell (MJPV) consisting of subcell 1 (i.e. the first subcell or a bottom cell) and subcell 2 (i.e. the second subcell or a top cell) having different frequency spectral range: (i) the traditional two- terminal configuration and (ii) the four-terminal configuration.

To simply illustrate the concept, the non-idealistic effects of series and shunt resistance (R_s and R_Sh) are neglected. Under power generating regime (positive voltage), the reverse-bias breakdown current I t>_r may also be neglected. l_Ph,j refers to electrical current generated by the corresponding subcell, i, when light of certain wavelength or frequency impinges. The electrical power, P, available from a photovoltaic cell is then,

with subcell current being governed by,

Ji ~ Jph.i JD,I

Under illumination, » l_Ph,i, where l_Ph,i scales with the absorbed optical power.

Consider the case when laser beam delivering high intensity power to the MJPV cell. Due to its narrowband characteristics, only subcell 2 is able to convert the laser energy into electrical energy. Without additional broadband background of light (e.g. sunlight or white LED or fluorescence light), l_Ph,i is zero.

In the two-terminal configuration, the subcells are connected in series; hence, the current that flows through the subcells is the same (i.e. the lower of li or h). Therefore,

J = min (J₁J₂, ...J_i) = J_ph,₁ = 0 , as a result PMJPV = 0. In a case where a broadband light is now introduced such that l_P ,2 > l_Ph,i- PMJP = l_Ph,i * V implying any additional laser power absorbed by subcell is not able to contribute to the output power.

In the multi-terminal configuration illustrated in Figures 2B and 3B, the subcells are no longer connected directly, hence P_MjPV

Hence, the advantage of the multi-terminal configuration can be taken as a first approximation to be at least AP = J₂ x V₂ to AP = So/; As such, limited only by the intensity of the laser and launching optics, the power density such PV harvester may achieve a performance that is orders of magnitude beyond existing energy provision (e.g. solar).

Preferably, to extract a maximum output power from the solar panel, the power receiver such as the separate loads individually connected to the subcell 1 and subcell 2 in the four-terminal configuration, the loads may be individually configured to allow an electrical current passing through each of the first and the second set of photovoltaic cells.

For example, the solar panel may comprise a 2-junction cell with a subcell 1 being a gallium arsenide (GaAs)-based cell and subcell 2 being a silicon-based cell. Consider the following situation where the receiver is on one side illuminated by solar irradiance equivalent to 25% of a full sun at ground level (25 mW/cm²) and illuminated at an intensity, baser, of 100 mW/cm² on the other side by a laser having a center wavelength of 985 nm. Taking the following the current contribution of the laser illumination,

where baser is the optical intensity of the laser, X is the central wavelength of the laser, h is the Planck's constant, c is the speed of light and EQE is external quantum efficiency of the photovoltaic cell or subcell at a particular wavelength, and noting that the subcell 1 is not sensitive to the laser frequency,

Jph, 2 ~ Jph.,2(solar) Jph.,2(laser) ■

Assuming the solar spectrum does not change substantially as it weakens, the following figure illustrates the J-V behaviors of the subcells in the 2-terminal (2T) and 4-terminal (4T) configurations.

With reference to Figures 4A and 4B, the maximum output power of the 2 solar panels/receivers is denoted by the shaded area shown (3.84 mW/cm² for the 2T and 47.64 mW/cm² for the 4T). As described above, assuming that the 2T device is initially current- matched and optimally designed for operation under 1 sun, due to current limitation under the current illumination condition, laser power is completely unconverted. On the other hand, the 4T device is free to fully utilize the available power from subcell 1 and subcell 2, since both subcell 1 and subcell 2 may be individually controlled to extract the maximum power from each of the subcells.

In this disclosure, "multiterminal" refers to configuration of multijunction or a combination of n subcells in group within the solar panel, therefore a multi-terminal configuration having m- T where m <= 2n. Where m = 2n, it refers to the fully independent PV operation for all subcells. Where m < 2n, there would be some shared terminals and, abate additional limitation, would be amongst the feasible implementations of the current product. A cell, then, should be an identical unit with a combination of subcells to be repeated to form a module. For example, Areal matching (AM) or voltage matching (VM) should, in general, refer to concepts of wiring the repeated cells in a module.

In an alternative embodiment, the two set of subcells may be connected with a "3-terminal (3T)" configuration. It has also been shown the compromise of the 3T configuration as compared to 4T is negligible. Advantageously, 3T configuration may reduce interconnect wiring but also has other additional advantages (such as reduced optical loss and reduced manufacturing complexity) over 4T implementation with little compromise in performance.

Comparing configurations A and B as shown in Figures 4A and 4B respectively, it may be observable that one drawback with the 4T configuration (i.e. two separate junction boxes 420- 1, 420-2 each being connected to one of the subcells in the solar panel) is that the more conductive interconnecting leads will be required. In one alternative embodiment, such a problem may be improved by the circuit configuration C as shown in Figure 4C. in which only a common junction box 420 is used to connect both the top cells 1 and the bottom cells 2, such as in a parallel manner. Further, lightweight conductor such as carbon-based materials may be used to further reduce the overall weight of the solar panel 410.

In addition, referring to Figure 4C, the number of subcells in each of the first set and the second set of photovoltaic cells are different, such that the output rating of each set of the first and the second set of PV cells may be engineered to fit different applications and/or types of PV cells being integrated in the solar panel 410.

In addition, since now that the top and bottom cell are in parallel configuration, in which voltage of across the either one or a string of serially connected top cells and the voltage of the bottom cell, should preferably be matched or otherwise be limited to lower of the two. Hence, the number of bottom cells (typically operate at lower voltages) may be designed to match the voltage of the top cells. For example, if Vi = 1.1 V and V2 = 0.5 V, then would be optimal to have nearly twice the number of bottom cells as the number of top cells.

The embodiments of the present invention should not restrict the applicability to only individually manipulated sets of subcells as in the example of 3T configurations for 2-junction cells. Therefore, even though some of the embodiments in this disclosure include a common junction box with two terminals, the solar panels in accordance with embodiments of the present invention operate differently when compared to a standard 2T config where subcells are connected in series, in isolation from other cells where the subcells are typically currentlimited, as the subcells 1 and 2 (or the top/bottom cells) in the solar panel are not connected in series therefore each of the subcells 1 and 2 may be individually manipulated by the controller via the junction boxes.

In the configurations which include only a common junction box 420, to harvest an overall maximum power output of the solar panel, the controller may be controlled (e.g. by variating the resistance/impedance of the load in parallel connection with both the top and bottom cells) so as to extract the maximum power output from a selected one of the first and the second set of photovoltaic cells. In this operation, only one of the first and the second set of photovoltaic cells may be optimized since the electrical load is common to both set of PV cells.

Preferably, the controller is arranged to control each terminal of the solar panel array. This terminal arrangement may be determined by a specific design or implementation of the solar panel and may include each string, cell, or combination of cells over various layers (again using appropriate terms). These examples may include a 2T, 3T, 4T, AM or VM arrangement, or other examples as deemed appropriate by the specific solar panel or photovoltaic cell arrangement.

In general, the abovementioned multi-terminal photovoltaic subcell configurations are known to be less sensitive to changing solar spectrum or the illumination sources, therefore it is more preferable to employ multi-terminal PV systems for high-efficiency dynamic light harvesting. Advantageously, with MPPT controlled optimized for different multi-terminal PV solar panels the solar panels may operate with their maximum power conversion efficient in any one of the narrowband, broadband and combined sources effectively.

With reference to 5A to 5B, there is shown two example embodiments of the solar panel 510 which includes different power scaling achieve by stringing up multiple cells together to form a series of subcells electrically connected together. The solar panel 510 may be fabricated by: providing the first set of photovoltaic cells 512 on a substrate 502; providing an isolation layer to cover the plurality of first subcells 512; providing the second set of photovoltaic cells 516 on the isolation layer; and packaging or encapsulating the first and the second set of photovoltaic cells, e.g. using glass with ARC (anti reflective coating) 506. The encapsulation or the covering glass may preferably have functions, such as but not limited to, mechanical superstrate, mechanical protection, filter of charged particles, protection from oxygen or moisture or heat, radiative heat dissipation etc., and the substrate may be included to provide mechanical support (can be in a form of rigid and flexible materials), housing for interconnections and thermal dissipation.

Referring to Figures 5A and 5B, the solar panel 510 includes a lamination 504, which may comprise a layer of high-resistive material, more preferably a layer of material which is electrically insulative yet optically transparent, such as silicon dioxide or silicon nitride, for physically and electrically separating the bottom cells 512 from the top cells 516, such that the two set of PV cells may operate individually. Alternatively or additionally, a lamination layer 504 may be provided on top of the bottom substrate 502 if an electrical isolation between the substrate and the bottom cells are necessary. Alternatively, the first sets of cells and second set of cells may be separated by voids, or simply spatially offset from each other. In addition, a layer of thermally conductive or insulative (depending on optimal thermal management), or radiatively dissipative material may be included to redirect the heat generated or absorbed during an operation of the solar panel.

Preferably, the fabrication process may involve a combination of existing solar cell/panel manufacturing, and two additional manufacturing steps may be required. For example, a new step to make additional leads using semiconductor microfabrication technique as known by a person skilled in the art may be needed, and another one may be mechanically stacking the component cells in a way that is appropriate to the operating environment.

Prior to depositing the top cells 516, interconnects 508 may be deposited to connect the bottom cells 512 together using electrical conductors, such as metal (in forms of thin-film, nanoparticle composites or otherwise), transparent conducting oxides and/or carbon-based conducting materials. For example, the bottom cells 512 may be connected in series with reference to Figure 5A and 5B, in which the cathode of one cell is connected to an anode of another cell adjacent to it.

After the top cells 516 are fabricated, the first set of photovoltaic cells and the second set of photovoltaic cells may be connected to one or more junction boxes 520 arranged to facilitate an output of electrical power generated by the solar panel 510 when subjected to an irradiation. For example, a common junction box 520 may be used to connect both the top cells and the bottom cells in a parallel. Alternatively, each of the first and the second set of PV cells may be connected to individual junction boxes 510-1, 510-2 so as to separate the operations in each of the two sets of PV cells.

In an alternative embodiment, the solar panel further comprises an additional photovoltaic cell, which may include a tandem cell (not shown), connected in series with the first set of photovoltaic cells 512, the second set of photovoltaic cells 516, and the common junction box 520. In this example, the cell includes a combination of the first subcell and the second subcell monolithically fabricated prior to the final encapsulation process. In examples where the cell is a tandem cell, the first subcell and the second subcell may be connected by a tunneling junction therebetween.

Preferably, the junction box may form a string that terminates at the junction box. The purpose of the junction box is to regulate the maximum power point, voltage conversion and switch between live load and energy storage.

It should be appreciated by a skilled person in the art that, the abovementioned embodiments are only possible layered structures of solar panels which may be separately controlled by the MPPT controller of the present invention, therefore other configurations and/or other method of fabricating the solar panel may also be suitable. For example, monolithically integrating the subcells with or without a tunnelling junction depending on the relative polarity of the subcells, in which the different components of the solar panels may be fabricated by film deposition techniques of semiconductor epitaxy, wafer bonding and other such as sputtering and vapour deposition, therefore is not restricted to mechanically stacking subcells, integrating the subcells with a interleaved layer of conductive contact either fabricated by methods of wafer bonding, metal fusion, soldering or adhesives/laminates (as described above).

These embodiments may be advantageous in that the invention may be used in a board scope of applications, including but not limiting to, power supply for mobile and remote devices. For example, the solar panel in accordance with embodiments of the present invention allows a remote platform or location that is under normal operation receiving solar energy to have an option to receive an alternate source and form of optical energy when either sunlight is either not available or inadequate with minimal cost on additional weight, size and system complexity. In addition, example embodiments of the invention may also enable high efficiency optical to electrical energy conversion using multiple energy sources.

Advantageously, multi-terminal configuration may enable optimization in both solar and narrowband mode with little compromise. In solar harvesting mode, the solar panel of the present invention may operate to exceed the efficiency of traditional high-performance (triplejunction) solar cell based on a germanium bottom cell. The solar panel may also be less sensitive to charged particle exposure in service, hence design margin is kept at a minimal.

In narrowband energy mode, an energy conversion efficiency of doubling the one of traditional high-performance cells may be achieved by the solar panel of the present invention hence power density of a power solution including the solar panel in accordance with the abovementioned embodiments is increased significantly, simply matching the wavelength of the laser beam to only one of the top cell(s) or the bottom cell(s) operates to deliver a maximized power efficiency.

Alternatively, the solar panel may also operate in both solar and narrowband energy mode simultaneously, for example with each of the top cells and the bottom cells are individually loaded via separate junction boxes. For example, when both solar power as well as external laser illumination may be available in the environment, which may both be harvested by the solar panel.

Moreover, the multi-junction solar panels with a common junction box may also enable retrofitting on compatible panels, in which the electrical loading module may be relatively easy to be re-programmed.

Although not required, the embodiments described with reference to the Figures can be implemented as an application programming interface (API) or as a series of libraries for use by a developer or can be included within another software application, such as a terminal or personal computer operating system or a portable computing device operating system. Generally, as program modules include routines, programs, objects, components and data files assisting in the performance of particular functions, the skilled person will understand that the functionality of the software application may be distributed across a number of routines, objects or components to achieve the same functionality desired herein.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

Claims

1. A solar panel comprising: a first set of photovoltaic cells including a plurality of first subcells electrically connected together, and provided with a first pair of electrical conductors connecting a cathode and an anode of the first set of photovoltaic cells; and a second set of photovoltaic cells including a plurality of second subcells electrically connected together, and provided with a second pair of electrical conductors connecting a cathode and an anode of the second set of photovoltaic cells; wherein each of the first subcell and the second subcell is arranged to produce maximum power output independently when subjected to irradiation with predetermined light spectrums different from each other; and wherein the first pair of electrical conductors and the second pair of electrical conductors are arranged to form an electrical circuit with an electrical load such that each of the first set of photovoltaic cells and the second set of photovoltaic cells are individually manipulated to achieve an overall maximum power output of the solar panel when subjected to the irradiation.

2. A solar panel in accordance with claim 1, wherein the electrical load includes a plurality of junction boxes each arranged to connect to both conductors of a respective one of the first pair of electrical conductors and the second pair of electrical conductors.

3. A solar panel in accordance with claim 1, wherein the electrical load includes a common junction box arranged to connect to one or both conductors of each of the first pair of electrical conductors and the second pair of electrical conductors.

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4. A solar panel in accordance with claim 3, wherein the common junction box is arranged to connect to both the first set and the second set of photovoltaic cells in parallel via the first pair of electrical conductors and the second pair of electrical conductors.

5. A solar panel in accordance with claim 3, wherein the first set of photovoltaic cells, the second set of photovoltaic cells, and the common junction box are connected in series.

6. A solar panel in accordance with claim 5, further comprising one or more additional photovoltaic cell connected in series with the first set of photovoltaic cells, the second set of photovoltaic cells, and the common junction box.

7. A solar panel in accordance with claim 6, wherein the one or more additional photovoltaic cell includes a monolithic tandem cell, wherein the tandem cell includes a combination of the first subcell and the second subcell connected by a tunneling junction therebetween.

8. A solar panel in accordance with claim 1, wherein the number of subcells in each of the first set and the second set of photovoltaic cells are different.

9. A solar panel in accordance with claim 1, wherein each of the first and the second set of photovoltaic cells further comprises a plurality of interconnecting leads arranged to electrically connect the subcells and the electrical conductors. A solar panel in accordance with claim 9, wherein the plurality of interconnecting leads includes a carbon-based light weight conductor material. A solar panel in accordance with claim 1, wherein the irradiation is generated by a narrowband light source, a solar source or an electrical lighting source. A method of fabricating a solar panel in accordance with claim 9, comprising the steps of: providing the first set of photovoltaic cells on a substrate; providing an isolation layer to cover the plurality of first subcells; providing the second set of photovoltaic cells on the isolation layer; and packaging or encapsulating the first and the second set of photovoltaic cells. A method in accordance with claim 12, wherein the step of providing the first set of photovoltaic cells on a substrate comprising the steps of providing the plurality of first subcells on the substrate and connecting the plurality of first subcells with the plurality of interconnecting leads. A method in accordance with claim 13, further comprising the step of electrically connecting the first set of photovoltaic cells and/or the second set of photovoltaic cells to one or more junction boxes arranged to facilitate an output of electrical power generated by the solar panel when subjected to an irradiation. A method in accordance with claim 12, wherein the isolation layer includes a void, a layer of high-resistive material, a layer of electrically insulative and optically transparent material.

16. A method in accordance with claim 12, further comprising the step of forming a monolithic tandem cell including a combination of the first subcell and the second subcell connected by a tunnelling junction therebetween.

17. A method for controlling a solar panel in accordance with claim 1, comprising the steps of: configuring the solar panel to operate in at least a narrowband energy harvesting mode; and controlling the electrical load of an external circuitry so as to optimize an output power of the first and the second set of photovoltaic cells.

18. A method for controlling a solar panel in accordance with claim 17, wherein the step of controlling the electrical load of the external circuitry comprising the step of individually controlling an electrical current passing through an external circuit in connection to each of the first and the second set of photovoltaic cells so as to extract the maximum power output from each of the first and the second set of photovoltaic cells, such that the overall maximum power output of the solar panel is harvested.

19. A method for controlling a solar panel in accordance with claim 17, wherein the step of controlling the electrical load of the external circuitry comprising the step of controlling an electrical current passing through a common electrical load so as to extract the maximum power output from a selected one of the first and the second set of photovoltaic cells, such that the overall maximum power output of the solar panel is harvested or stored.

25 A method for controlling a solar panel in accordance with claim 17, wherein the solar panel is further arranged to operate in a solar harvesting mode or a broadband energy harvesting mode.