WO2024030076A1 - A photovoltachromic device - Google Patents

Abstract

A photovoltachromic device is provided. The photovoltachromic device may include a photovoltaic cell, and a transparent-reflective switchable device in light communication with the photovoltaic cell. The transparent-reflective switchable device may be operable between a reflective mode in which light falling thereon is reflected to the photovoltaic cell, and a transmission mode in which light falling thereon is directed through the transparent-reflective switchable device.

Description

A PHOTOVOLTACHROMIC DEVICE

CROSS-REFERENCE TO RELATED APPLICATION

[001] This application claims the benefit of priority of Singapore patent application no. 10202250676M, filed 5 August 2022, the contents of which being hereby incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

[002] Various embodiments relate to a photovoltachromic device, such as a photovol tachromic window. The photovoltachromic device may be used for modulating light into a building and/or harvesting light energy.

BACKGROUND

[003] Greenhouses in a tropical climate may trap excessive heat to result in unnecessary loss of moisture from plants and elevated temperatures detrimental to plant growth. Agrivoltaics and dynamic sunlight shading may constitute two key technologies for energy saving in tropical greenhouses and farms.

[004] Agrivoltaics may refer to the use of photovoltaic (PV) panels such as solar panels in agriculture. By installing solar panels, shade may be provided and solar energy may be harnessed at the same time. Disadvantages of this method, however, exist in that fixed PV panels may introduce unnecessary shading.

[005] With a dynamic sunlight shading system, excessive amounts of heat trapped in the interior of a greenhouse during a hot day may be prevented, while during lowlight conditions (or in a cold/cloudy weather), shading may be minimised or removed. In doing so, Photosynthetic Photon Flux Density (PPFD) may be optimised for the plants. At the same time, solar energy harvesting by smart window comprised in a dynamic sunlight shading system may increase the energy efficiency of the greenhouse operation. However, integration of dynamic shading and photovoltaic energy harvesting in large area fenestrations of greenhouses is still challenging.

[006] A mechanical photovoltaic shutter may be able to realize both dynamic solar shading and solar energy harvesting in one window system. However, the mechanical components may increase costs, for example cost for maintenance, which limits its large area application.

[007] Another integration approach is to add solar panels to an electrochromic (EC) window, involving integrating solar panels with EC panels in a parallel configuration with a passive (nonadjustable) solar energy harvesting. Due to the opaque nature of the solar panels, however, light transmission tends to be compromised and dynamic modulation range of the smart window may be reduced.

[008] In light of the above, there exists a need for an improved method of modulating light and/or harvesting light energy that overcomes or at least alleviates one or more of the above problems.

SUMMARY

[009] Various embodiments refer in a first aspect to a photovol tachromic device. The photovol tachromic device may comprise a photovoltaic cell, and a transparent-reflective switchable device in light communication with the photovoltaic cell. The transparent- reflective switchable device may be operable between a reflective mode in which light falling thereon is reflected to the photovoltaic cell, and a transmission mode in which light falling thereon is directed through the transparent-reflective switchable device. [0010] Various embodiments refer in a second aspect to an apparatus comprising the photovol tachromic device according to the first aspect, wherein the apparatus is a window or a door.

[0011] Various embodiments refer in a third aspect to a method of modulating light into a building using the photo vol tachromic device according to the first aspect. The method may comprise positioning the photovol tachromic device at a facade of the building which is adapted to allow light to pass through into the building, and operating the photovol tachromic device to modulate light into the building.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings.

[0013] FIG. 1A is a schematic diagram depicting a two-dimensional front view of a photovol tachromic device 100 according to an embodiment, depicting a reversible electrodeposition mirror/photovoltaic cell (REM/PV) integrated structure for modulation of solar light transmission and energy harvesting. The photovoltachromic device 100 comprises a photovoltaic cell 111 and transparent-reflective switchable device 112, arranged between a top transparent substrate 115 and a bottom transparent substrate 117. The photovoltaic cell 111 may be arranged substantially vertical to a surface of the bottom transparent substrate 117. The transparent-reflective switchable device 112 may be arranged to be in light communication with the photovoltaic cell 111. Incident light (Pi) 151 falls on the photovoltachromic device 100 through the top transparent substrate 115 at angle 0 = 90°, and may be split into 2 modes: transmission mode (PT) and reflection mode (PR). PT refers to transmitted light 1511, while PR refers to reflected light 1513 that is being redirected onto the photovoltaic cell 111. Using the transparent-reflective switchable device 112 to modulate PT/PR values, light transmission and solar energy harvesting of the photovol tachromic device 100 may be adjusted on demand according to requirements. For example, when the transparent-reflective switchable device 112 is in its maximum clear (transparent) state, light transmission through the photovol tachromic device 100 may be maximized and power generation through the photovoltaic cell 111 may be minimized. Conversely, when the transparent-reflective switchable device 112 is in its most reflective state, light transmission through the photovol tachromic device 100 may be minimized and power generation through the photovoltaic cell 111 may be maximized. In other words, by toggling opacity (or reflectivity) of the transparent-reflective switchable device 112, varying portions of the incident light 151 may be transmitted through the transparent-reflective switchable device 112 and bottom transparent substrate 117 as transmitted light 1511, and/or be reflected by the transparent-reflective switchable device 112 as reflected light 1513, to the photovoltaic cell 111. The reflected light 1513 may be harvested by the photovoltaic cell 111 and converted to electrical energy.

[0014] FIG. IB is schematic diagram depicting a two-dimensional front view of a photovol tachromic device according to an embodiment. A reversible electrodeposition mirror/photovoltaic cell (REM/PV) integrated structure as depicted in FIG. 1A is shown, comprising the photovoltaic cell 111 and the transparent-reflective switchable device 112 in light communication with the photovoltaic cell 111. A second electrodeposition mirror/photovoltaic cell (REM/PV) integrated structure, comprising a second photovoltaic cell 113 and a second transparent-reflective switchable device 114 in light communication with the photovoltaic cell 113, is oriented opposite to and arranged as a mirror image to the first integrated structure about the photovoltaic cell 111.

[0015] FIG. 1C is schematic diagram depicting a two-dimensional front view of a photovol tachromic device according to an embodiment. A reversible electrodeposition mirror/photovoltaic cell (REM/PV) integrated structure as depicted in FIG. 1A is shown, comprising the photovoltaic cell 111 and the transparent-reflective switchable device 112 in light communication with the photovoltaic cell 111. A second electrodeposition mirror/photovoltaic cell (REM/PV) integrated structure, comprising a second photovoltaic cell 113 and a second transparent-reflective switchable device 114 in light communication with the photovoltaic cell 113, having the same orientation as the first integrated structure is arranged in series to the first integrated structure.

[0016] FIG. ID is a schematic diagram depicting a three-dimensional perspective view of a photovol tachromic device 100 according to an embodiment, such as a reversible electrodeposition mirror/photovoltaic cell (REM/PV) integrated structure (showing a plurality of units of the photovoltaic cell/transparent-reflective switchable device structure) for modulation of solar light transmission (PT) and energy harvesting (PR). One unit of the photovoltaic cell/transparent-reflective switchable device structure is described herein for illustration purposes. The photovol tachromic device 100 comprises a photovoltaic cell 111, which may be in the form of a double-sided photovoltaic module. The photovoltaic cell 111 may be arranged between a top transparent substrate 115 and a bottom transparent substrate 117, and may be arranged substantially vertical to a surface of the bottom transparent substrate 117. The photovoltachromic device 100 further comprises transparent-reflective switchable devices (112, 114) arranged on either side of the photovoltaic cell 111, and which are in light communication with the photovoltaic cell 111. Incident light 151 falls on the photovoltachromic device 100 through the top transparent substrate 115. By toggling opacity or reflectivity of the transparent-reflective switchable devices (112, 114), varying portions of the incident light 151 may be transmitted through the transparent-reflective switchable device (112, 114) and bottom transparent substrate 117 as transmitted light 1511, and/or be reflected by the transparent-reflective switchable device (112, 114) as reflected light 1513, to the photovoltaic cell 111. The reflected light 1513 may be harvested by the photovoltaic cell 111 and converted to electrical energy.

[0017] FIG. 2A is a graph showing measured transmittance and reflectance spectra of a REM panel at its clear state according to an embodiment.

[0018] FIG. 2B is a graph showing measured transmittance and reflectance spectra of a REM panel at its half mirror (T @650nm about 25%) state, with settings of about 2.5 V, 30 s, according to an embodiment.

[0019] FIG. 2C is a graph showing measured transmittance and reflectance spectra of a REM panel at its full mirror (T @650nm about 1.5%) state, with settings of about 2.5 V, 120 s, according to an embodiment.

[0020] FIG. 3A is a graph showing simulated visible light transmission and lateral reflected to PV portion of a window structure with varied prism angle 0 (light incident angle 0 = 90°, 60°), in clear state (REM optical status of reflectivity R = 10% to 70% were used for simulation). In the graph, 381 denotes downwards transmission (0 = 90°), 382 denotes lateral transmission to PV (0 = 90°), 383 denotes downwards transmission (0 = 60°), and 384 denotes lateral transmission to PV (0 = 60°).

[0021] FIG. 3B is a graph showing simulated visible light transmission and lateral reflected to PV portion of a window structure with varied prism angle 0 (light incident angle 0 = 90°, 60°), in dark state (REM optical status of reflectivity R = 10% to 70% were used for simulation). In the graph, 381 denotes downwards transmission (0 = 90°), 382 denotes lateral transmission to PV (0 = 90°), 383 denotes downwards transmission (0 = 60°), and 384 denotes lateral transmission to PV (0 = 60°).

[0022] FIG. 4A depicts simulation results of the smart window folded at an angle of 0 = 45 ⁰ at incident angle 0 = 90° for the wavelength of 350 nm to 2000 nm in clear state.

[0023] FIG. 4B depicts simulation results of the smart window folded at an angle of 0 = 45 ⁰ at incident angle 0 = 90° for the wavelength of 350 nm to 2000 nm in mirror state.

[0024] FIG. 5A is a schematic diagram of a photovol tachromic device 500 according to an embodiment, such as a REM/PV integrated smart window (showing only 2 units of a photovoltaic cell/transparent-reflective switchable device structure), with incident light 551 at angle 0 = 90°, and with transparent-reflective switchable devices (512, 514) (such as REM panels) in clear state. One unit of the photovoltaic cell/transparent-reflective switchable device structure is described herein for illustration purposes. The photovol tachromic device 500 comprises a photovoltaic cell 511, which may be in the form of a double-sided photovoltaic module, and transparent-reflective switchable devices (512, 514), arranged between a top transparent substrate 515 and a bottom transparent substrate 517. The photovoltaic cell 511 may be arranged substantially vertical to a surface of the bottom transparent substrate 517. The transparent-reflective switchable devices (512, 514) may be arranged on either side of the photovoltaic cell 511, and in light communication with the photovoltaic cell 511. In the depicted clear state, incident light 551 falls on the photovol tachromic device 500 through the top transparent substrate 515. At least substantially all of the incident light 551 may be transmitted through the transparent-reflective switchable device (512, 514) and bottom transparent substrate 517 as transmitted light 5511. The top transparent substrate 515 and the bottom transparent substrate 517 may be spaced apart by distance x. The transparent-reflective switchable devices (512, 514) may be of length y, and be arranged at an angle 0 to the photovoltaic cell 511. The sides of the double-sided photovoltaic module of the photovoltaic cell 511 may be spaced apart by distance z. The 2 units of the photovoltaic cell/transparent-reflective switchable device structure may be spaced apart by distance p. In the experiments carried out, x was 50 mm, y was 70 mm, z was 5 mm, and p was 105 mm.

[0025] FIG. 5B is a schematic diagram of the photovol tachromic device 500 according to the embodiment shown in FIG. 5A, with the transparent-reflective switchable devices (512, 514) (such as REM panels) in half mirror state. In the depicted half mirror state, incident light 551 falls on the photovol tachromic device 500 through the top transparent substrate 515. A portion of the incident light 551 is transmitted through the transparent-reflective switchable device (512, 514) and bottom transparent substrate 517 as transmitted light 5511. A portion of the incident light 551 is reflected by the transparent-reflective switchable device (512, 514) as reflected light 5513, to the photovoltaic cell 511, which may be harvested by the photovoltaic cell 511 and converted to electrical energy.

[0026] FIG. 5C is a schematic diagram of the photovol tachromic device 500 according to the embodiment shown in FIG. 5A, with the transparent-reflective switchable devices (512, 514) (such as REM panels) in full mirror (highly reflective) state. In the depicted full mirror state, incident light 551 falls on the photovol tachromic device 500 through the top transparent substrate 515. At least substantially all of the incident light 551 is reflected by the transparent- reflective switchable device (512, 514) as reflected light 5513, to the photovoltaic cell 511, which may be harvested by the photovoltaic cell 511 and converted to electrical energy.

[0027] FIG. 5D is a photograph of a prototype of a photovol tachromic device 500 according to an embodiment, such as a REM/PV integrated smart window (showing only 2 units of the photovoltaic cell/transparent-reflective switchable device structure), with photovoltaic cell 511, and with transparent-reflective switchable devices (512, 514) (such as REM panels) in clear state. [0028] FIG. 5E is a photograph of a prototype of a photovol tachromic device 500 according to an embodiment, such as a REM/PV integrated smart window (showing only 2 units of the photovoltaic cell/transparent-reflective switchable device structure), with photovoltaic cell 511, and with transparent-reflective switchable devices (512, 514) (such as REM panels) mirror (dark) state.

DESCRIPTION

[0029] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practised. These embodiments are described in sufficient detail to enable those skilled in the art to practise the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0030] Various embodiments refer in a first aspect to a photovol tachromic device. As used herein, the term “photovoltachromic” may refer to a behaviour exhibited or a property conferred by combining photovoltaic and electrochromic behaviours or properties. Accordingly, a photovoltachromic device may refer to a device which is capable of achieving adjustable light transparency and reflectivity through electrochromic behaviour, for use in modulating light and/or for harvesting of light as electrical energy using photovoltaic technology.

[0031] For example, the photovoltachromic device may control light intensity by reducing or increasing light blockage so as to increase or decrease amount of light that reaches an underlying surface. This may be carried out by way of a transparent-reflective switchable device comprised in the photovoltachromic device. The transparent-reflective switchable device may be operable between a reflective mode in which light falling thereon is reflected away from the underlying surface, and a transmission mode in which light falling thereon is directed through the transparent-reflective switchable device to the underlying surface. By modulating or adjusting the transparent-reflective switchable device between the two modes, amount of light that reaches the underlying surface may be varied. In situations whereby at least a portion of incident light is reflected away from the underlying surface, the reflected light may be directed to a photovoltaic cell, so that the light energy may be harvested as electrical energy.

[0032] Advantageously, photovol tachromic devices disclosed herein may be used for modulating light transmission (for both visible light and infrared radiation) and for energy harvesting. This may ensure that the light transmission range is not compromised due to photovoltaic cell integration, and only excess solar energy (for example, more than indoor illumination needs) may be harvested by the photovoltaic cell. Active solar radiance control through both intensity control and infrared control may be achieved, which is particularly important, and may even be essential, for providing optimal temperature and light for plant growth in greenhouse applications. The harvested energy may be used to power the photovol tachromic device. Accordingly, the photovol tachromic device may be a self-powered photovol tachromic device. Photovol tachromic devices disclosed herein, such as structures integrated with light-reflecting reversible electrodeposition mirrors and photovoltaic (REM/PV), may allow more efficient solar heat regulation, as compared to an integrated lightabsorbing photovoltaic-electrochromic structure.

[0033] In various embodiments, the photovol tachromic device comprises a photovoltaic cell, and a transparent-reflective switchable device in light communication with the photovoltaic cell. By the term “light communication”, this may mean that the photovoltaic cell and the transparent-reflective switchable device may be arranged, such that light that is received by the transparent-reflective switchable device may be transferred to the photovoltaic cell. For example, the transparent-reflective switchable device and the photovoltaic cell may be arranged such that light received by the transparent-reflective switchable device may be reflected directly to the photovoltaic cell.

[0034] The term “light” as used herein refers to electromagnetic radiation in any wavelength, such as wavelength in the range from about 350 nm to about 2000 nm, about 350 nm to about 1000 nm, or wavelength in the range from about 380 nm to about 750 nm. In various embodiments, the term “light” may refer to visible light and infrared radiation.

[0035] The term "photovoltaic cell" as used herein may refer to a light absorbing material which absorbs photons and generates electrons via a photoelectric effect. The photovoltaic cell may absorb light in any wavelength, such as wavelength in the range from about 350 nm to about 2000 nm, about 350 nm to about 1000 nm, or wavelength in the range from about 380 nm to about 750 nm. The photovoltaic cell may, for example, be a solar cell.

[0036] The photovoltaic cell may be in the form of a plurality of photovoltaic cells, which may be arranged into arrays or panels. In various embodiments, the photovoltaic cell is in the form of a photovoltaic panel, such as a double-sided photovoltaic module.

[0037] The term “transparent-reflective switchable device” as used herein may refer to an element, material or means that is able to toggle between an optically transparent state and optically reflective state by way of a stimulus or trigger. The stimulus or trigger may be chemical and/or electrical in nature. Upon application of the stimulus or trigger, the transparent-reflective switchable device is able to toggle between an optically transparent hence transmitting state, whereby at least substantially all of the light that is directed to the transparent-reflective switchable device is transmitted therethrough, and an optically reflective state, whereby at least substantially all of the light that is directed to the transparent- reflective switchable device is not transmitted therethrough but is directed or reflected away. Examples of such transparent-reflective switchable devices may include, but are not limited to, reversible electrodeposition mirrors, metal hydrides, cholesteric liquid crystals and microshutters.

[0038] Advantageously, use of the transparent-reflective switchable device allows a photovol tachromic device disclosed herein to realize a wide modulation range for transmittance control and solar power generation, without using any mechanical moving parts nor a solar tracking system.

[0039] In various embodiments, the transparent-reflective switchable device is a reversible electrodeposition device, such as a reversible electrodeposition mirror (REM). As used herein, the term “reversible electrodeposition device” may refer to an element or a means which utilizes appearance and disappearance of a metal layer, such as one which is only a few tens of nanometers thick, via electrochromic behaviour to achieve light and/or heat modulation. When the metal layer is present, both visible light and infrared radiation incident on the reversible electrodeposition device may be reflected away. When the metal layer is absent, both visible light and infrared radiation incident on the reversible electrodeposition device may be transmitted through the reversible electrodeposition device to an underlying surface.

[0040] As mentioned above, the transparent-reflective switchable device may be operable between a reflective mode in which light falling thereon is reflected to the photovoltaic cell, and a transmission mode in which light falling thereon is directed through the transparent- reflective switchable device.

[0041] In its reflective mode, the transparent-reflective switchable device may function like a light-reflector and return a high percentage of light that is directed to it. The transparent- reflective switchable device may function like reflective surfaces such as mirrors or highly polished metallic surfaces, which are able to return at least 50% of incident light, such as at least 60%, at least 70%, or at least 80% of incident light. [0042] In various embodiments, the transparent-reflective switchable device is operable between the reflective mode and the transmission mode by applying a voltage across the transparent-reflective switchable device. The voltage may be 5V or less, such as less than 5V, less than 4V, less than 3V, or be in the range from 3V to 5V, 4V to 5V, 3V to 4V, or about 3V. In some embodiments, voltage is in the range from IV to 5V. Dynamic switching of transmittance with high contrast ratio, such as more than 65%, of the transparent-reflective switchable device may be achieved.

[0043] The photovoltaic cell and the transparent-reflective switchable device may be arranged on a transparent substrate or between a pair of opposing transparent substrates. For example, the photovoltaic cell and the transparent-reflective switchable device may be sandwiched between a pair of opposing transparent substrates. Suitable transparent substrates may include an optically transparent substrate such as glass, or polymer, for example, polyethylene terephthalate, polycarbonate, an acrylic polymer, polyethylene terephthalate glycol (PETG), polypropylene (PP), fluorinated ethylene propylene (FEP), or acrylonitrile butadiene styrene.

[0044] In various embodiments, the photovoltaic cell is arranged substantially vertical to a surface of the transparent substrate, and the transparent-reflective switchable device is arranged inclined at an angle to the photovoltaic cell. By the term “substantially vertical”, this may include a range about a true vertical orientation of 90°, such as a range that is within 10° or ± 10° of the true vertical orientation, of the surface. For example, the photovoltaic cell may be arranged at an angle of 80°, 82°, 84°, 86°, 88°, 90°, 92°, 94°, 96°, 98° or 100°, to a surface of the transparent substrate. In some embodiments, the photovoltaic cell is arranged vertical to a surface of the transparent substrate, for example, at an angle of 90°.

[0045] The transparent-reflective switchable device is arranged inclined at an angle to the photovoltaic cell. The angle may be defined by a surface of the transparent-reflective switchable device and a surface of the photovoltaic cell, and may be in the range from 45° to 55°, such as from 48° to 55°, 50° to 55°, 52° to 55°, 45° to 52°, 45° to 50°, 45° to 47°, or 47° to

52°

[0046] In various embodiments, the photovoltaic cell is one of a double-sided photovoltaic panel or two photovoltaic panels arranged in a back-to-back configuration, and wherein two transparent-reflective switchable devices are present, with each transparent-reflective switchable device arranged on either side of the photovoltaic cell. Arrangement of the photovoltaic cell and the two transparent-reflective switchable devices may be repeated for one or more times in the photovol tachromic device, which may in turn depend on intended use of the photovol tachromic device according to requirements.

[0047] In some embodiments, the photovoltaic cell is two photovoltaic panels arranged in a back-to-back configuration and defining a gap therebetween, the gap being operable as a channel for flow of a heat transfer medium. Advantageously, flow of a heat transfer medium such as water, may be integrated into a photovol tachromic device disclosed herein to take away heat that is absorbed by the photovoltaic cell.

[0048] Various embodiments refer in a second aspect to an apparatus comprising the photovol tachromic device according to the first aspect, wherein the apparatus is a window or a door. Accordingly, the apparatus may be termed a photovol tachromic window or a photovol tachromic door.

[0049] Depending on the size of the apparatus, a plurality of the photovol tachromic devices may be arranged. In so doing, control of light transmission to the underlying surface and/or light energy harvested by the photovol tachromic devices may be achieved.

[0050] Advantageously, power generated by a photovol tachromic device disclosed herein has been shown to be much higher than energy consumed by the photovol tachromic device, in the range of 100 times higher. This means that the apparatus comprising the photovol tachromic device may be self-sufficient as it is able to self-power, with any excess energy used for other purposes such as cooling or lighting. Efficient solar energy power conversion of near 10 % have also been demonstrated.

[0051] Various embodiments refer in a further aspect to a method of modulating light into a building using the photovoltachromic device according to the first aspect.

[0052] The method may comprise positioning the photovoltachromic device at a facade of the building which is adapted to allow light to pass through into the building, and operating the photovoltachromic device to modulate light into the building.

[0053] Such a facade may include, but not limited to, an opening, a window or a door.

[0054] In various embodiments, the building is a greenhouse. Advantageously, a plurality of the photovoltachromic devices may be arranged on a side of a greenhouse to modulate light into the greenhouse and/or to harvest light energy. Other application areas may include modulating light and/or to harvest light energy for indoor farms, shelters, and residential and commercial buildings for indoor comfort.

[0055] In order that the invention may be readily understood and put into practical effect, particular embodiments will now be described by way of the following non-limiting examples.

EXAMPLES

[0056] Various embodiments disclosed here relate to a photovoltachromic approach, involving photovoltaics and electrochromic, in particular, use of reversible electrodeposition mirrors (REM) and photovoltaic (PV) panels.

[0057] Present disclosure may relate to a smart window integrated with transparent-reflective switchable (TRS) panels and photovoltaic (PV) modules for dynamic optical modulation and solar power generation. Reversible electrodeposition mirrors (REMs) may be used as TRS panels, and they may form a wave-shaped structure with specific folding angles (e.g. 45° with respect to the vertical). One or more PV modules may be placed in a vertical position next to a folded REM panel or between two folded REM panels, such as that shown in FIG. 1A to FIG. ID. The incident sunlight (Pi) may be controlled by the REM transmi ssivity/reflectivity so that the light may either be transmitted indoor (PT) or reflected to the PV panels (PR) for energy harvesting. The light transmission and power generation of the window may be adjusted by modulating the transmittance/reflectance of the REM panels. When the REM is in its maximum clear (transparent) state, light transmission indoors may be maximized and PV power generation may be minimized; while the REM is in most reflective state, light transmission indoors may be minimized and PV power generation may be maximized. A smart window disclosed herein is able to realize a wide modulation range for transmittance control and solar power generation, without using any mechanical moving parts nor a solar tracking system.

[0058] A smart window according to embodiments disclosed herein may comprise arrays of REM/PV sets arranged on the plane of a transparent substrate (or between two transparent substrates). Each set (unit) may comprise one double-sided PV panel positioned vertically (perpendicular to the substrate plane), and two REM panels folded with an angle 0 to the PV panel, as shown in FIG. IB. The REM may be switchable between clear (transparent) state and mirror (reflective) state by applying suitable voltages (such as less than 5 V, or less than 4 V, or most preferably less than 3 V). Incident light (Pi) impinging on the REM may be split into 2 modes: transmission mode (PT) and reflection mode (PR) (the absorbed light by REM is not considered here). PT refers to transmitted light, while PR refers to reflected light that is being redirected onto PV panels. The PV component can be a double-sided panel, or a device with two PV panels assembled back-to-back with a gap in between. The gap can serve as a channel for water flow for harvesting IR (heat) from the sunlight (PR) (the visible and near IR part may be harvested by the PV panels). [0059] In this structure, the PV panels may receive light mainly from the REM, thus it may be in a tandem configuration for solar energy harvesting. By modulating the PT/PR values with the REM, light transmission and solar energy harvesting of the window may be adjustable. When the REM is in its maximum clear (transparent) state, light transmission indoors may be maximized and PV power generation may be minimized; while the REM is in its most reflective state, light transmission indoors may be minimized and PV power generation may be maximized.

[0060] The optical performance of the folded REM/PV structure was simulated using ray optics software (Zemax) for different permutations of light incident angles (0), prism angles (0) at both the clear and mirror state. FIG. 3A and FIG. 3B show the simulated visible light transmission and lateral reflected to PV portion of the REM/PV structure (see FIG. ID) with varied prism angle 0, whereby prism angle 0 is as that shown in FIG. IB (and with incident light angles 0 = 90°, 60°) in clear and dark states. The range of 0 = 45 to 55° is able to obtain a well-balanced performance in transmission (to indoor) and lateral reflection (to PV).

[0061] Shown in FIG. 4A and FIG. 4B are simulated spectral performances of the REM/PV structure for 0 = 45° and 0 = 90° across the optical wavelengths of 350 to 2000 nm. In the simulation model, reflectivity r(X) = 10% for the REM in the clear state, and reflectivity r(X) = 70% for the REM in the dark state were used for the different optical wavelength of 350 to 2000 nm. This ideal model allowed determination of the impact of structural dispersion on the performance of the device, as compared to the material dispersion. As shown in FIG. 4A and FIG. 4B, downward transmission may be modulated from around 78% (clear state) to around 48% (dark state), and the lateral transmission to the PV changed from around 5% (clear state) to around 37% (dark state), for the case of ideal REM.

[0062] Based on the simulation results, a prototype was demonstrated with two sets of REM/PV panels and folding angle 0 = 45°. Each PV panel (polycrystalline Si-based) had a size of 50 (h) X 200 (1) X 5 (t) mm. The PV panels were placed vertically and spaced apart with a pitch of 105 mm (FIG. 5D and FIG. 5E). The REM panel has a size of 70 X 200 X 2 mm. FIG. 5A illustrates two REM/PV sets in clear state, with the light transmission maximized and PV light harvesting minimized. FIG. 5B illustrates the REM/PV sets in half mirror state, with partial light transmission and partial light harvesting by PV. FIG. 5C illustrates the REM/PV sets in full mirror state, with the light transmission minimized and PV light harvesting maximized. Curved or flexible REM panels are also suitable to be used for this window structure. The photo images of the prototype are shown here with the REM in clear and mirror states (FIG. 5D and FIG. 5E, respectively).

[0063] TABLE 1 shows the measured photovoltaic performance (short circuit current density Isc, open circuit voltage V_oc, fill factor, maximum point power output Pmax and power conversion efficiency T]_s) of a single PV module used for the prototype. The single PV module used here has an efficiency r|_s of 12.2%.

[0064] TABLE 1: Figures of merit for a single PV module (polycrystalline Si based)

[0065] TABLE 2 shows the performance of a single REM panel developed in the lab.

[0066] TABLE 2: Figures of merit for a single REM panel

[0067] TABLE 3 shows the measured photovoltaic performance of the integrated window with the simulated sunlight (one sun intensity) at an incident angle 0 of 90° (perpendicular to the window plane) and 45°.

[0068] TABLE 3: Measured window performance under one sun with incident angle 0

(prototype size: 25X25 cm²)

* The visible light transmittance T_viS (@ 400 to 750 nm) and SHGC of the window were calculated based on the measured values of the single REM panel by multiplying a factor (0.95 for 0 = 90°, 0.48 for 0 = 45°), which is derived from the opening aperture ratio.

^# Based on 12.2 % efficiency of the single PV modules used

[0069] The visible light transmittance T_vis (@ 400 to 750 nm) and solar heat gain coefficient (SHGC) of the window were calculated based on the measured values of a single REM panel (see TABLE 2) by multiplying a factor (0.95 for 0 = 90°, 0.48 for 0 = 45°), which is derived from the opening aperture ratio. The opening aperture ratio arises from the opaque PV modules and clear REM panels. The results showed that the best modulation performance of the window was achieved when the window was placed perpendicular (0 = 90°) to the sunlight, with the modulation range of T_vis (1 to 66.5%), SHGC (0.03 to 0.54), and power generation (1.53 to 6.35 mW/cm²).

[0070] With current design, power generated by the PV modules was enough to self-power the operation (switching) of the REM panels. The daily energy profile of window under sunny day, with power generation was estimated to be about 240 Wh/m² (for daily 6h sun irradiation, half mirror) which was much higher than the energy consumption for the operation (about 2.4 Wh/m², for daily 4 times switching). As demonstrated, there was remarkable net daily energy gain.

[0071] Higher photovoltaic power generation from the smart window can be obtained if more efficient PV modules are used (e.g. r|_s = 20%). As a result, excess energy can be harvested from the smart window system. If the system is connected to or integrated with an energy storage system, excess harnessed energy can be used for other purposes (e.g. cooling or lighting).

[0072] Technical features in various embodiments may include:

[0073] A method for collecting and harvesting solar energy in a self-powering smart window. The solar energy collection includes visible (for PV electrical power conversion) and IR light (for heat conversion).

[0074] A method for collecting and harvesting solar energy in a self-powering smart window wherein REM panels work in tandem with PV panels.

[0075] A method for collecting and harvesting solar energy in a self-powering smart window wherein the REM panel manipulates solar energy through transmission or redirection.

[0076] A method for collecting and harvesting solar energy in a self-powering smart window wherein the redirected solar energy effectuated by the REM panel is harvested by the PV panel. [0077] A photovoltaic and self-powering switchable window which can modulate both light transmission and energy harvesting (for both visible and IR). The modulation may be realized by controlling the transmittance/reflectance ratio of the switchable REM panels, and the reflected solar energy being redirected for solar energy harvesting by photovoltaic devices.

[0078] A photovoltaic smart window wherein REM panels work in tandem with PV panels.

[0079] Advantages of methods disclosed herein may include: Adjustable light intensity and heat control; dynamic switching of transmittance with high contrast ratio (more than 65%); efficient solar energy power conversion (near 10%).

[0080] Application areas may include: greenhouse for plant growth; indoor farms; commercial buildings for indoor comfort; shelters.

[0081] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0082] By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0083] The inventions illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising”, “including”, “containing”, etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied therein herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

[0084] By “about” in relation to a given numerical value, such as for temperature and period of time, it is meant to include numerical values within 10% of the specified value.

[0085] The invention has been described broadly and generically herein. Each of the narrower species and sub-generic groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0086] Other embodiments are within the following claims and non- limiting examples. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

Claims

1. A photovoltachromic device, comprising a photovoltaic cell, and a transparent-reflective switchable device in light communication with the photovoltaic cell, wherein the transparent-reflective switchable device is operable between a reflective mode in which light falling thereon is reflected to the photovoltaic cell, and a transmission mode in which light falling thereon is directed through the transparent- reflective switchable device.

2. The photovoltachromic device according to claim 1, wherein the transparent-reflective switchable device is a reversible electrodeposition device.

3. The photovoltachromic device according to claim 1 or 2, wherein the photovoltaic cell and the transparent-reflective switchable device are arranged on a transparent substrate or between a pair of opposing transparent substrates.

4. The photovoltachromic device according to claim 3, wherein the photovoltaic cell is arranged substantially vertical to a surface of the transparent substrate, and the transparent- reflective switchable device is arranged inclined at an angle to the photovoltaic cell.

5. The photovoltachromic device according to claim 4, wherein the angle is in the range from 45° to 55°

6. The photovol tachromic device according to claim 4 or 5, wherein the photovoltaic cell is one of a double-sided photovoltaic panel or two photovoltaic panels arranged in a back-to- back configuration, and wherein two transparent-reflective switchable devices are present, with each transparent-reflective switchable device arranged on either side of the photovoltaic cell.

7. The photovol tachromic device according to claim 6, wherein the photovoltaic cell is two photovoltaic panels arranged in a back-to-back configuration and defining a gap therebetween, the gap being operable as a channel for flow of a heat transfer medium.

8. The photovol tachromic device according to claim 6 or 7, wherein arrangement of the photovoltaic cell and the two transparent-reflective switchable devices is repeated for one or more times in the photovol tachromic device.

9. The photovol tachromic device according to any one of claims 1 to 8, wherein the photovoltaic cell is a solar cell.

10. The photovol tachromic device according to any one of claims 1 to 9, wherein the transparent-reflective switchable device is operable between the reflective mode and the transmission mode by applying a voltage across the transparent-reflective switchable device.

11. The photovol tachromic device according to claim 10, wherein voltage is in the range from IV to 5V.

12. The photovol tachromic device according to any one of claims 1 to 11, wherein the photovol tachromic device is a self-powered photovol tachromic device.

13. An apparatus comprising the photovoltachromic device according to any one of claims 1 to 12, wherein the apparatus is a window or a door.

14. A method of modulating light into a building using the photovoltachromic device according to any one of claims 1 to 12, the method comprising positioning the photovoltachromic device at a facade of the building which is adapted to allow light to pass through into the building, and operating the photovoltachromic device to modulate light into the building.

15. The method according to claim 14, wherein the facade of the building is an opening, a window or a door.

16. The method according to claim 14 or 15, wherein the building is a greenhouse.