Photovoltaic panel, photovoltaic system and evaporation system for photovoltaic system

Abstract

The present invention discloses a photovoltaic (PV) panel comprising: a PV module (102, 202) having a front side (102a, 202a) for exposure to sunlight and absorption of solar energy to convert into electrical energy and a back side opposite the front side; and an evaporator (104, 204, 312) engaged with the back side of the PV module, an upper end (106, 206) of the evaporator being in close proximity to or in contact with a water source to absorb water by capillary action, the evaporator having a structure allowing the water to move therethrough, and the PV module being in a heat transfer relationship with the water moving through the evaporator.

Description

[0001] This application claims priority to U.S. Patent Application No. 63 / 508,481 filed on June 15, 2023 and priority to U.S. Patent Application No. 18 / 667,109 filed on May 17, 2024, the contents of which are incorporated herein by reference in their entirety as if fully set forth herein. Technical Field

[0002] The present invention relates to photovoltaic (PV) panels, PV systems having such PV panels and evaporation systems for PV systems. Background Art

[0003] Given that solar energy is abundant and freely available, it is essential to achieving global energy sustainability. Photovoltaics (PV) hold great promise in harnessing solar energy, as they can convert irradiance into usable electricity with zero carbon emissions. Efficiency improvements and cost reductions in recent decades have enabled the commercialization of crystalline silicon (c-Si) PV technology. The cumulative capacity of PV installations is expected to increase from 700GW in 2020 to 22TW by the end of 2050.

[0004] Despite their promise, c-Si PVs can only utilize a limited portion of the incident solar spectrum (<25.6%), with the remainder wasted as heat. The resulting high temperatures shorten the lifespan and reduce the power conversion efficiency of such panels, and can even cause fires. Typical c-Si panels lose about 5.0% efficiency, and their aging rate doubles with every 10°C increase in operating temperature. As c-Si technology approaches its theoretical limits and next-generation technologies (e.g., perovskites) are far from commercially mature, improving light-to-electricity efficiency through material advances is becoming increasingly difficult. Now is the time to use thermal management techniques to regulate PV temperature, thereby improving efficiency and reliability. Ideal PV thermal management would reliably produce the maximum cooling effect at the lowest cost. Existing PV thermal management technologies are divided into active (mechanically driven) and passive (naturally driven) technologies based on energy requirements.

[0005] Active technologies typically involve forced circulation of a fluid (e.g., air or water) that requires fan and pump power. For example, forced ventilation on a hot PV surface or back radiator can dissipate heat through airflow. However, this solution has not been popularized due to low cooling efficiency, high fan power, and additional air duct structure. In comparison, water has a large heat capacity and thermal conductivity, and can absorb a large amount of heat during evaporation. These characteristics enable advanced water spray, water curtain, and back direct contact water cooling systems to achieve high heat dissipation efficiency. However, due to the fluidity of water and inefficient heat transfer design, these processes may consume a large amount of water. With complex system configuration and a large amount of pump power, the overall cost-effectiveness is still low.

[0006] On the other hand, passive technologies that rely on spontaneous processes offer an attractive solution to this problem. Fin structures are a typical example of enhancing thermal convection at the expense of system compactness, and their heat removal efficiency depends on wind speed. Radiative cooling (RC) is another method for PV cooling that directly discharges waste heat to the universe through an atmospheric transparent window of 8 to 13 μm. However, commercial PV glass is already a high-radiance surface that limits the efficiency of RC cooling. Recent outdoor experiments have shown that RC only contributes to a temperature reduction of 3.6°C in existing mainstream c-Si cells. In addition, phase change materials (PCMs) that can maintain a stable temperature during phase change can be attached to the back of PV for heat removal. Although well-developed PV-PCM systems can achieve a temperature reduction of 7-21°C, low thermal conductivity, inconsistent melting, and cyclic degradation are long-standing problems. Recently, passive evaporative cooling using a back evaporator under PV has attracted great research interest. For example, a burlap-based evaporative cooler with gravity-assisted water supply is able to achieve a temperature drop of 15-20°C. A biomimetic cooler based on bamboo bundles and filled with hydrogels has recently been proposed. In a laboratory-scale proof-of-concept prototype, water for evaporation is supplied to the evaporator via capillary action and transpiration, where the temperature is reduced by about 26°C. Hygroscopic adsorbents (e.g., hygroscopic hydrogels and metal-organic frameworks) are another passive solution option. Without the use of an additional water supply, the technology provides evaporative cooling through an adsorption-evaporation cycle that removes waste heat by evaporation in the sun and recycles water at night. When a hygroscopically saturated adsorbent layer is used, these reported pilot cooling prototypes show impressive temperature reductions (6-15°C). However, due to slow adsorption kinetics and degradation of the cycle, such systems are prone to dehydration in real environments.

[0007] In summary, active thermal management has high cooling efficiency, but due to the large parasitic power and water consumption, it will introduce complex system design and bring additional operating costs. Although various passive cooling methods do not have these problems, they are limited by low cooling power or reliability issues. Therefore, existing cooling technologies still have huge room for improvement in improving cooling performance, optimizing operating strategies, reducing energy / water consumption, and strengthening climate adaptability.

[0008] It is therefore an object of the present invention to provide a photovoltaic (PV) panel, a PV system and an evaporation system for a PV system in which at least one of the above-mentioned disadvantages is alleviated or at least provides a useful alternative for business and the public. Summary of the invention

[0009] According to a first aspect of the present invention, there is provided a photovoltaic (PV) panel comprising: a PV module having a front side for being exposed to sunlight and absorbing solar energy for conversion into electrical energy and a back side opposite to the front side; and an evaporator coupled to the back side of the PV module, wherein a first end of the evaporator is adapted to be in close proximity to or contact with a source of a cooling medium to absorb the cooling medium by capillary action, wherein the evaporator has a structure allowing the cooling medium to move through, and wherein the PV module is adapted to be in a heat transferable relationship with the cooling medium moving through the evaporator.

[0010] In one embodiment, the second end of the evaporator is adapted to be in close proximity or contact with a lower container for collecting the cooling medium exiting the evaporator from the second end.

[0011] According to a second aspect of the present invention, there is provided a photovoltaic (PV) system comprising a PV panel, the PV panel comprising: a PV module having a front side for being exposed to sunlight and absorbing solar energy for conversion into electrical energy and a back side opposite to the front side; and an evaporator coupled to the back side of the PV module; wherein a first end of the evaporator is adapted to be in close proximity to or contact with a source of a cooling medium to absorb the cooling medium by capillary action, wherein the evaporator has a structure allowing the cooling medium to move through, and wherein the PV module is adapted to be in a heat transferable relationship with the cooling medium moving through the evaporator.

[0012] In one embodiment, the second end of the evaporator is adapted to be in close proximity or contact with a lower container for collecting the cooling medium exiting the evaporator from the second end.

[0013] According to a third aspect of the present invention, there is provided an evaporation system for a photovoltaic (PV) system, comprising an evaporator engageable with the back side of a PV module, and an upper container for a cooling medium, wherein a first end of the evaporator extends in close proximity to or at least partially into the upper container and is adapted to absorb the cooling medium in the upper container by capillary action, wherein the evaporator has a structure allowing the cooling medium to move through, and wherein when the evaporator is engaged with the PV panel, the PV module is adapted to be in a heat transferable relationship with the cooling medium moving through the evaporator.

[0014] In one embodiment, the evaporation system further comprises a lower container for a cooling medium, an irradiance sensor, a liquid level sensor, and a control system.

[0015] In a further embodiment, the second end of the evaporator is adapted to be in close proximity or contact with a lower container for collecting the cooling medium exiting the evaporator from the second end.

[0016] In an additional embodiment, the control system is adapted to: stop the operation of the pump when the solar irradiance on the PV panel measured by the irradiance sensor is lower than a threshold level; activate the operation of the pump for a first predetermined time period to pump the cooling medium to the upper container when the solar irradiance on the PV panel measured by the irradiance sensor is higher than the threshold level; and activate the operation of the pump for a second predetermined time period to pump the cooling medium to the upper container when the solar irradiance on the PV panel measured by the irradiance sensor is higher than the threshold level and the cooling medium in the upper container sensed by the liquid level sensor is lower than a preset level. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0018] Figure 1a shows a schematic diagram of a first embodiment of a photovoltaic (PV) system according to the present invention;

[0019] Figure 1b Shown in Figure 1a An enlarged cross-sectional view of an evaporator used in a PV system and the formation of a siphon channel;

[0020] Figure 1c Schematically shows a PV panel having Figure 1a The cooling mechanism of the evaporator shown;

[0021] Figure 1d to Figure 1f Shows Figure 1a Different operating modes of PV systems;

[0022] Figure 1g shows a schematic diagram of a second embodiment of a photovoltaic (PV) system according to the present invention;

[0023] Figure 2a shows an exploded view of a PV panel and an evaporator according to an embodiment of the present invention;

[0024] Figure 2b Scanning electron microscope (SEM) image showing the microporous structure of the evaporator;

[0025] Figure 2c The wetting performance of the evaporator is shown;

[0026] Figure 2dA schematic diagram showing a hardware implementation of an operating strategy for a portion of a PV system according to the present invention;

[0027] Figure 2e shows a control platform for a PV system according to the present invention;

[0028] Figure 2f An embedded control strategy for a PV system according to the present invention is shown;

[0029] Figure 3a shows an in-laboratory test setup for a PV system according to the invention;

[0030] Figure 3b shows the corresponding temperature response of a PV system with an evaporation system according to the invention (PVS-I) and a PV system with the same specifications but without an evaporation system according to the invention (PVS-C), both with a tilt angle of 10° under 1-sun illumination;

[0031] Figure 3c The corresponding power-voltage (PV) curves of PVS-I and PVS-C when thermal steady state is reached are shown;

[0032] Figure 3d The corresponding unit weight loss due to evaporation of PVS-I with a tilt angle of 10° under 1-sun, 0.8-sun, and 0.6-sun illuminations is shown;

[0033] Figure 3e The corresponding steady-state temperature reduction and maximum power point (MPP) improvement of PVS-I as a function of tilt angle are shown;

[0034] Figure 3f The corresponding evaporation rate of PVS-I as a function of the tilt angle is shown;

[0035] Figure 4a Schematic diagram showing the experimental setup of a portion of PVS-I;

[0036] Figure 4b shows the air temperature and relative humidity at the City University of Hong Kong campus (the “experimental site”) in Kowloon Tong, Kowloon, Hong Kong, China on December 21, 2022 (“Day 1”);

[0037] Figure 4c The solar irradiance and wind speed at the experimental site on December 21, 2022 are shown;

[0038] Figure 4d Shows the sky conditions at the experiment site on December 21, 2022;

[0039] Figure 4eThe air temperature and relative humidity at the experimental site on December 22, 2022 ("Day 2") are shown;

[0040] Figure 4f The solar irradiance and wind speed at the experimental site on December 22, 2022 are shown;

[0041] Figure 4g Shows the sky conditions at the experiment site on December 22, 2022;

[0042] Figure 5a The corresponding temperature changes of PVS-I and PVS-C at the experimental site on day 1 are shown;

[0043] Figure 5b The corresponding temperature drops of PVS-I and PVS-C at the experimental site on day 1 are shown;

[0044] Figure 5c Infrared (IR) images of PVS-I and PVS-C at the experimental site during the start-up phase on day 1 are shown;

[0045] Figure 5d shows infrared (IR) images of PVS-I and PVS-C at the experimental site during the stabilization phase on day 1;

[0046] Figure 5e The corresponding PV curves of PVS-I and PVS-C at the experimental site on day 1 are shown;

[0047] Figure 5f The corresponding hourly average maximum power outputs of PVS-I and PVS-C at the experimental site on day 1 are shown;

[0048] Figure 5g The corresponding power conversion efficiencies of PVS-I and PVS-C at the experimental site on day 1 are shown;

[0049] Figure 6a The corresponding temperature changes of PVS-I and PVS-C at the experimental site on day 2 are shown;

[0050] Figure 6b The corresponding temperature drops of PVS-I and PVS-C at the experimental site on day 2 are shown;

[0051] Figure 6c Infrared (IR) images of PVS-I and PVS-C at the experimental site during the start-up phase on day 2 are shown;

[0052] Figure 6d shows infrared (IR) images of PVS-I and PVS-C at the experimental site during the stabilization phase on day 2;

[0053] Figure 6e The corresponding PV curves of PVS-I and PVS-C at the experimental site on day 2 are shown;

[0054] Figure 6f The corresponding hourly average maximum power outputs of PVS-I and PVS-C at the experimental site on day 2 are shown;

[0055] Figure 6g The corresponding power conversion efficiencies of PVS-I and PVS-C at the experimental site on day 2 are shown;

[0056] Figure 7a The relative humidity at the experimental site during the test period from October 18, 2023 to October 25, 2023 (the "Test Period") is shown;

[0057] Figure 7b The solar irradiance, panel temperature and open circuit voltage (V OC )’s temporal evolution;

[0058] Figure 7c shows the daily water consumption per unit PV module area of ​​PVS-I during the test period; and

[0059] Figure 7d The daily power consumption of the controller and water pump per unit PV module area of ​​the PVS-I during the test period is shown. DETAILED DESCRIPTION

[0060] According to the present invention, a smart wick evaporator (SWE) is provided by co-designing capillary action, interface evaporation, siphoning, electronic hardware and climate adaptive control algorithms to provide solutions to these problems. This interdisciplinary design can use interface evaporation to dissipate PV waste heat with near zero energy input and low water consumption. The capillary action triggered siphon flow within the evaporator passively maintains the interface evaporation. In addition, a robust algorithm is embedded in a compact and low-cost electronic hardware platform, achieving climate adaptive operation.

[0061] Figure 1a Components of a photovoltaic (PV) system (referred to herein as "PVS-I"), generally designated 100, according to a first embodiment of the present invention are shown. PVS-I 100 consists of two parts: a PV module 102 having a thin film hydrophilic wick evaporator 104 and an adaptive control platform.

[0062] The PV module 102 has a front side 102a for being exposed to sunlight and absorbing solar energy to be converted into electric energy, and a back side opposite to the front side 102a. The evaporator 104 is directly or indirectly bonded to the back side of the PV module 102, and may be made of a water-absorbing material (such as cotton fabric) having a porous structure. The upper end 106 of the evaporator 104 extends into or is in close proximity to the upper case 108 (such as being immersed in the upper case 108). When the upper case 108 contains a certain level of water (which is used as a cooling medium), the upper end 106 of the evaporator 104 will contact or be in close proximity to the water in the upper case 108, so that the capillary (wicking) effect will overcome the gravity of the water in the upper case 108 to penetrate upward along the upper end 106 of the evaporator 104. Once the water is above the top point of the evaporator 104, gravity becomes a driving force for transporting the water to the lower end 110 in the lower case 112, which is lower than the upper end 106. Some of the water absorbed by the evaporator 104 exits the evaporator 104 from the lower end 110 after moving from the upper end 106 and through the body of the evaporator 104 .

[0063] The evaporator 104 is pre-dried, and its porous structure is filled with air A (such as Figure 1b (I)). Under the capillary action, the porous structure gradually absorbs water, and the water flowing downward (the direction of water flow is Figure 1b (Indicated by the arrow in (II)) gradually exhausts the air initially in the evaporator 104 and eventually leads to the siphon channel ( Figure 1c ). Because the PV modules are always mounted at a certain tilt angle θ relative to the horizontal plane, the thin water film confined within the evaporator 104 spreads downward through the evaporator 104 under the action of gravity.

[0064] In sunlight, waste heat in the PV module 102 is conducted to the evaporator 104 through the thermal interface layer (TIM) 114, resulting in localized water heating and steam release ( Figure 1c ). The thermal interface layer 114 may be made of a thermally conductive double-sided tape, such as 467MP thermally conductive double-sided tape produced by 3M Company in the United States. With such an arrangement, the evaporator 104 may be fixedly coupled to the PV module 102 via the thermal interface layer 114. As the water absorbed by the evaporator 104 moves through the evaporator 104, it is in a heat transferable relationship with the thermal interface layer 114 and thus with the PV module 102. While absorbing heat from the PV module 102, some of the water absorbed by the upper end 106 and moved through the evaporator 104 will evaporate from the face 104a of the evaporator 104 that faces away from the front face 102a of the PV module 102 and evaporate from the evaporator 104 into the environment through the face 104a, thereby helping to cool the PV module 102.

[0065] After leaving the evaporator 104 through the lower end 110 of the evaporator 104, the unevaporated water is collected by the lower box 112 and returned to the liquid pump 118 (such as a water pump) via the hose 116, and then pumped back to the upper box 108 by the liquid pump 118. Since the thin film evaporator 104 and the boxes 108, 112 are hidden below the PV module 102, the compact system can provide cooling without interfering with the incident irradiance. Compared with traditional water-based cooling methods (e.g., spray, channel, mist, water curtain, etc.), the passive siphon effect and high evaporation efficiency enable this method to at least reduce pump power and water waste, thereby achieving water conservation effects similar to drip irrigation used in agriculture. When the unevaporated water is heated by the waste heat generated by the PV module 102 during its movement through the evaporator 104, the unevaporated water also helps to dissipate heat from the PV module 102 (and thus cool it), even if this water is not evaporated into the environment.

[0066] Ensuring that this passive process continues is critical to removing heat from the PV module 102 so that the evaporator 104 can continue to cool the PV module 102, thereby ensuring improved power. In addition, thermal management requirements change as the weather changes, so climate adaptive operation is required. An intelligent control system with three operating modes (i.e., Mode 1, Mode 2, Mode 3) is provided to simultaneously meet these requirements. In Mode 1 (e.g., Figure 1d ), when the PVS-I 100 is operating in a low / no irradiance period (e.g., when the solar irradiance on the PV module 102 measured by the irradiance sensor is below a first threshold level), the PV module 102 generates very low power and has no / little thermal management requirements. The PVS-I 100 is therefore in a standby state to conserve energy. Once the weather is irradiant (e.g., when the solar irradiance on the PV module 102 measured by the irradiance sensor is above a threshold level, which may be the same as or different from the first threshold level described above), the PVS-I 100 enters Mode 2 (e.g., when the solar irradiance on the PV module 102 measured by the irradiance sensor is above a threshold level, which may be the same as or different from the first threshold level described above). Figure 1e ), and the above process is triggered by operating pump 118 for a first predetermined period of time to pump water into upper tank 108. During this period of intense irradiance, PVS-I 100 contributes most of the daytime power generation, and cooling can significantly increase power generation. When the solar irradiance on PV modules 102 measured by the irradiance sensor is still above the threshold level and there is not enough water in upper tank 108 (for example, when the water level in upper tank 108 sensed by a level sensor (such as a water level sensor) drops below a preset level), PVS-I 100 enters Mode 3 (as shown in FIG. 1 ). Figure 1f), wherein the pump 118 operates for a second predetermined period of time (which may be the same as or different from the first predetermined period of time) to pump water to the upper tank 108. The lower tank 112 is located below the lower end 110 of the evaporator 104 and is in close proximity to or contact with the lower end to receive water leaving the lower end 110 to further save water. This enables the developed passive method to exhibit good climate adaptability and reliability, and is therefore superior to existing passive technologies.

[0067] A photovoltaic (PV) system according to a second embodiment of the present invention (referred to herein as "PVS-I") is Figure 1g , generally designated as 200. Similar to the PVS-I 100 discussed above, the PVS-I 200 also includes a PV module 202 having a front side 202a for being exposed to sunlight and absorbing solar energy for conversion into electrical energy and a back side opposite to the front side 202a, and an evaporator 204 (which may be made of a water-absorbing material having a porous structure (such as cotton fabric)), the evaporator being bonded to the back side of the PV module 202 directly or indirectly (such as via a thermal interface layer, for example, 467MP thermally conductive double-sided tape produced by 3M Company).

[0068] The upper end 206 of the evaporator 204 extends into or in close proximity to the upper case 208 so as to be in contact with or in close proximity to a cooling medium (e.g., water) contained in the upper case 208 to absorb the cooling medium in the upper case 208 by capillary (wicking) action. The cooling medium then moves through the porous structure of the evaporator 204 and is heated by the waste heat generated by the PV module 202. The cooling medium (e.g., water) moving through the evaporator 204 is in a heat transferable relationship with the PV module 202 and absorbs the waste heat generated by the PV module 202. Having been heated in this way, some of such cooling medium evaporates from the face 204a of the evaporator 204 facing away from the front face 202a of the PV module 202 and passes through the face 204a, thereby helping to cool the PV module 202.

[0069] After moving through the evaporator 204, the unevaporated cooling medium leaves the evaporator 204 through the lower end 210 of the evaporator 204 (which is lower than the upper end 206 of the evaporator 204) to be collected by the lower tank 212. The cooling medium may then be poured into the pump tank 220 so that when the liquid pump 218 (e.g., a water pump) is operated, the cooling medium may be pumped to the upper tank 208 through the pipe 216 to be absorbed by the evaporator 204 again.

[0070] like Figure 2a As shown in more detail in FIG. 1 , a PV panel 300 according to the present invention is arranged from top to bottom (in Figure 2aThe evaporator layer 312 (also called "wicking layer") made of a cooling medium absorbing material having a porous structure) includes a glass layer 302, an upper encapsulation layer 304a, a PV module 306, a lower encapsulation layer 304b, a back sheet 308, a waterproof thermal interface layer (TIM) 310 and an evaporator layer 312 (also called "wicking layer") made of a cooling medium absorbing material having a porous structure.

[0071] The evaporator layer 312 is attached to the back sheet 308 of the PV module 306. The two components are bonded to each other via a waterproof thermal interface layer (TIM) 310 (such as 467MP thermal conductive double-sided tape produced by 3M Company) for heat conduction and moisture barrier. Cotton fabric with a thickness of 3 mm is used as the evaporator layer 312 because of its rich hydrophilic porous structure (such as Figure 2b ) enables fast water transport dynamics (see Figure 2c ) and local heating. The thermal interface layer 310 is made of a thermally conductive double-sided tape.

[0072] Figure 2d A schematic diagram of an adaptive control circuit 400 for use in a PVS-I 100, 200 is shown. The circuit 400 uses an Arduino Nano board as a microcontroller unit (MCU) 402 to control a water pump 404 via a relay 406 based on solar irradiance and water level. With carefully designed circuits and code, the MCU 402 can make a climate adaptive response based on signals from a light dependent resistor (LDR) 408 and a water level sensor in the form of a distance sensor 410. Figure 2e The finished control platform is shown with high compactness. Figure 2f An embedded control strategy with a daily distribution of patterns is shown. The daily distribution can be customized to meet local needs by setting one or more threshold irradiances.

[0073] The improvements made to the PVS-I100 and 200 have been demonstrated through performance comparisons of PV system prototypes operating under controlled laboratory conditions. Figure 3a As shown, a solar simulator 502 is used to provide simulated sunlight, an electronic balance 504, a thermocouple 506 connecting the PV system prototype to a data acquisition (DAQ) module 508, and a digital source meter (SMU) 510 are used to measure the evaporation rate, temperature change, and current and power-voltage (IV&P-V) curves. The prototypes (including a PV system with an evaporation system according to the present invention (PVS-I) and a PV system without an evaporation system (PVS-C), thus serving as a control) were tested at three irradiance levels (1-sun, 0.8-sun, and 0.6-sun) at different tilt angles (0°, 10°, 20°, 30°, 40°) for 3 hours. The light intensity "1-sun" corresponds to 1 kW / m 2The scheme comprehensively evaluates the technologies in different regions, since the optimal tilt angle always depends on the local latitude. Limited by the scale of the prototype, the cooling performance and control circuits were verified separately.

[0074] The results of a prototype PV system with a 10° angle under 1-sun irradiance are selected as representative ( Figure 3b to Figure 3d ). Temperature curves of two PV system prototypes ( Figure 3b ) reaches thermal stability in about 20 minutes. The steady-state temperature of PVS-I is 42.5±0.5°C, while PVS-C reaches ~57.5±0.5°C. Interfacial cooling provides a constant temperature drop of 14.7-15.4°C. It has been observed that capillary action drives water in the upper box into the upper tail of the evaporator, which then triggers a siphon flow within 4 minutes. This slow and passive flow maintains interfacial evaporation. The effective heat transfer capacity of the thin wicking layer facilitates the cooling effect to achieve performance improvements, while the lower box recycles excess water that is not evaporated to save water.

[0075] PV curve measurement( Figure 3c ) confirms the benefit of lowering the temperature. The shapes of the two PV curves are similar, that is, when the voltage increases, the power first rises to the maximum power point (MPP), and then when the voltage reaches the open circuit voltage (V OC ) drops sharply to zero. PVS-I improves MPP by 10.22W / m 2 And V OC The improvement was 26.43 mV. Therefore, the absolute photoelectric conversion efficiency (η) was improved by 1.02% (absolute value). For the 0.8-sun and 0.6-sun cases, PVS-I provided a temperature reduction of 12.6°C and 9.4°C, respectively. The MPP was improved by 8.54 W / m 2 and 3.28W / m 2 , providing absolute efficiency gains of 0.79% and 0.54%, respectively. The specific weight loss of water (as measured by electronic balance 504) as a function of time is shown in Figure 3d The mass change rate increases at the beginning and then reaches a constant value. The stable evaporation rates at 1-sun, 0.8-sun and 0.6-sun are 711.77 mL / (m 2 ·h)、555.03mL / (m 2 h) and 476.8 mL / (m 2 h).

[0076] Because the IV curves are measured several times within an hour, these metrics are averaged hourly in the following analysis to facilitate comparison. The detailed definitions are as follows:

[0077] (a) Short-circuit current I SC :

[0078]

[0079] where n represents the total number of IV curves in a particular hour, and is i th Short-circuit current of IV curve;

[0080] (b) Open circuit voltage V oc :

[0081]

[0082] in is i th Open circuit voltage of IV curve;

[0083] (c) Maximum power output P max :

[0084]

[0085] in is i th Maximum power of the IV curve; and

[0086] (d) Power conversion efficiency η:

[0087]

[0088] Among them G i It is measuring th The IV curve is the irradiance on the module plane, and A m is the area of ​​the PV modules of the PV system.

[0089] It has been found that the overall trends of temperature response, electrical performance improvement, and weight loss are largely consistent in PVS-I and PVS-C with different tilt angles. The steady-state temperature reduction and MPP improvement at different tilt angles are summarized in Figure 3e Under 1-sun irradiance, the temperature of PVS-I can be reduced by 15.1-17.3℃ compared with that of PVS-C, and the corresponding MPP is improved by 9.16-10.38W / m 2 Under 0.8-sun irradiance, the temperature of PVS-I can be reduced by 12.6-13.6℃ compared with that of PVS-C, and the corresponding MPP is improved by 6.13-8.31W / m 2 Under 0.6-sun, the temperature of PVS-I can be reduced by 9.2-10.1℃ compared with that of PVS-C, and the corresponding MPP is improved by 2.87-3.60W / m 2These results confirm that thermal management can yield higher benefits during high irradiance hours. The evaporation rates at 1-sun, 0.8-sun, and 0.6-sun irradiances ( Figure 3f The results are shown in Table 1. 2 ·h)、555.03-632.72mL / (m 2 h) and 476.8-534.96 mL / (m 2 ·h). In general, the evaporation rate shows that irradiance is the main factor determining water consumption. In theory, a larger tilt angle contributes to a larger height difference between the two ends of the evaporator. However, due to the rich and tortuous pore structure of the evaporator material, the flow velocity is relatively slow, that is, the sensible heat removal of the siphon flow is limited, and the interfacial evaporation dominates the heat dissipation.

[0090] Considering the above laboratory results and the changing environmental conditions in practice, it is believed that the benefits of cooling can be maximized by integrating effective operation strategies. 2 The control circuit is developed as a threshold for high irradiance and sunny weather. The LDR 408 measures the irradiance on the panel prototype and returns a value between 0-1023 to the controller 402 depending on the irradiance level. The LDR 408 provides a 0-1200W / m 2 The irradiance series has a stable return value. When the irradiance is higher than 600W / m 2 When the water reaches the preset level, the voltage between the relays 406 returns to 0V, allowing the PVS-I to move from mode 1 to mode 3, and the water pump 404 operates to fill the tank with water. Once the water reaches the preset level, the voltage between the relays 406 returns to 0V, allowing the PVS-I to move to mode 2.

[0091] PSV-I was then applied to a commercial PV system and its performance was compared to that of the same PV system operating alone (i.e., without the evaporation system). The comparative tests were conducted from 10:00 on December 21, 2022 ("Day 1") to 24:00 on December 22, 2022 ("Day 2") on the rooftop of the City University of Hong Kong campus in Kowloon Tong, Kowloon, Hong Kong, China (22°15′N, 114°15′E). Figure 4a The test setup is schematically shown. Two PV systems are provided for comparative testing, one is PVS-I (i.e., a PV system with an evaporation system according to the present invention) 602a, and the other is PVS-C (i.e., a PV system without an evaporation system according to the present invention, used as a control) 602b. The PV modules of PVS-I and PVS-C face south and are fixed on the frame at a tilt angle of 30°.

[0092] Meteorological sensors (including irradiance sensor 604, wind speed sensor 606, and temperature and humidity sensor 608) are provided for sensing relevant weather conditions and inputting corresponding data into DAQ module 610 for subsequent input into computer 612. Thermocouples are attached to two points (P1, P2) of each of PVS-I 602a and PVS-C 602b for obtaining relevant data and inputting them into DAQ module 610 for subsequent input into computer 612. Each of PVS-I 602a and PVS-C 602b is connected with a corresponding IV analyzer 614a, 614b for providing current and voltage data of the corresponding PVS-I 602a and PVS-C 602b to the IV analyzer 614a, 614b for subsequent input into computer 612. An infrared (IR) camera 616 is also provided to obtain IR images of the PV modules of the corresponding PVS-I 602a and PVS-C 602b, and again input into the computer 612.

[0093] Figure 4b to Figure 4d The weather conditions at the experimental site on December 21, 2022 (Day 1) are shown. The air temperature during the sunshine hours was 23.5-28.8°C and dropped to 16.3-18.5°C at night. The relative humidity (RH) was 25.09-40.67%, which is already dry weather locally. The maximum solar irradiance reached 895.37W / m 2 , and the solar irradiance exceeds 800W / m 2 Almost 3 hours. The average wind speed was 0.61 m / s and the sky was clear all day. These characteristics show a typical sunny day in the transition season in the subtropical region, which is also a typical PV working condition.

[0094] Figure 4e to Figure 4g The weather conditions at the experimental site on December 22, 2022 (Day 2) are shown. The daytime temperature is 13.7-31.1°C, with an average of 19.2°C. The RH is 15.73-35.50%, and the average is only 30.19%. It is foreseeable that this dry climate will be conducive to evaporation. The maximum solar irradiance reaches 992W / m 2 , and the solar irradiance is higher than 940W / m within 2.5 hours 2 There will still be light winds most of the time, with an average wind speed of 0.86m / s. According to the sky conditions (see Figure 4g ), dense clouds blocked the sun before 10:10. Then, the weather became very clear and open until the sun set behind the building. Therefore, the solar irradiance increased rapidly at 09:56 and suddenly dropped at 16:50. This rapidly changing condition exerted a dynamic influence on the device and provided relatively harsh conditions for testing the present invention.

[0095] Figure 5a and Figure 5b The temperature changes and corresponding temperature drops of the PV modules of the corresponding PVS-I 602a and PVS-C 602b are shown respectively. The temperature field during the experiment is shown in Figure 5c and Figure 5d According to the temperature change characteristics, the entire process of the first day can be divided into three areas: blue area, purple area and orange area.

[0096] In the blue area, the solar irradiance is higher than 600W / m 2 , so PVS-I 602a directly switches to Mode 3. As the siphon water flow moves downward through the evaporator, the temperatures at two selected points (P1@PVS-I, P2@PVS-I) in PVS-I 602a decrease sequentially within 14 minutes, indicating a cooling effect. Figure 5c The IR image in shows this process: the movement of the water flow causes a cooling front to appear in the temperature field; as the front moves downward, the entire PV module is eventually cooled. Due to the presence of other components and edge effects, the adjacent areas are not cooled as uniformly as the downstream areas. Therefore, the temperature at P1@PVS-I is always slightly higher than the temperature at P2@PVS-I. PVS-I 602a enters a stable state in the purple area with a stable siphon flow in the evaporator, resulting in a significant cooling effect. During three high irradiance hours (solar irradiance > 800 W / m 2 ), the temperature of the PV module of PVS-C 602b fluctuates around 53.5°C, and the maximum temperature is 56.3°C. In comparison, the temperature of the PV module of PVS-I 602a is suppressed to around 37.5°C, and the maximum temperature drop reaches 20.0°C. These differences can be seen in Figure 5d Finally, due to the irradiance lower than 600W / m 2 , so PSV-I 602a enters Mode 1 in the orange area. Although no water is supplied to PVS-I 602a, the cooling effect lasts for nearly 2 hours after entering Mode 1 due to the remaining water in the evaporator. The benefits from thermal management ultimately translate into electrical performance gains. Figure 5e As shown, due to the improved V OC , cooling leads to a PV curve with a higher maximum power. In addition, the results are consistent with those of in-laboratory tests, i.e., the effect of temperature on the short-circuit current I SC The influence of V OC Can be significantly increased. Figure 5fAs shown, the power output of PVS-I 602a is much higher than that of PVS-C 602b, especially during the high irradiance hours (11:00-14:00), where cooling results in an increase of 5.63-7.06 W. Figure 5g The power conversion efficiency shown is increased by 1.62-3.17%. This also means that the PVS-I 602a generates 27.57% more power than the conventional PVS-C 602b.

[0097] Similarly, the temperature evolution on the second day can be divided into three stages (e.g. Figure 6a and Figure 6b As shown in Figure 2, the experiment lasted all day, so there were orange areas in the morning and at night. In the orange area in the morning, the solar irradiance was less than 600 W / m 2 , so PVS-I 602a is in Mode 1 to save energy. The temperature of the PV modules of PVS-I 602a and PVS-C 602b is therefore Figure 6a The same pattern is shown in Figure 2. In the blue region, when the irradiance increases from 155.13 W / m 2 Soared to 830.5W / m 2 , PVS-I 602a immediately wakes up and moves to Mode 3 to generate interface cooling. Therefore, the rising trend of temperature in PVS-I 602a is quickly suppressed, while the rising trend of temperature in PVS-C 602b continues to increase. Figure 6c A similar cooling front propagation process can be found in .

[0098] After entering the purple region, there is a sustainable cooling effect in PVS-I 602a. 2 ), the temperature of PVS-C 602b varies between 47.7°C and 53.1°C, while PVS-I 602a fluctuates only between 27.8°C and 40.2°C, with the maximum temperature drop reaching 17.7°C. Figure 6d Finally, in the orange region at night, when the solar irradiance is below 600 W / m 2 , PVS-I 602a returns to Mode 1. Similarly, due to the remaining water in the evaporator in PVS-I 602a, cooling continued for nearly 2.5 hours after entering Mode 1.

[0099] Since the daytime irradiance on the second day is slightly higher than that on the first day, the electrical performance of the two modules of PVS-I 602a and PVS-C602b on the second day is slightly better than that on the first day, but the overall trend is consistent. Figure 6eThe PV curves at four selected moments on day 2 are shown. Similarly, it is found that the improved MPP comes from the enhanced V OC , while I SC Not affected by cooling. Figure 6f As shown, after the interface cooling is fully developed, the power output in PVS-I 602a is significantly improved. As shown in the figure, PVS-I 602a can significantly improve the power output, especially during the high irradiance period. For example, the power output increased by 7.42W from 12:00 to 13:00. The daily power generation increased by 27.67%. Figure 6g As shown, the respective efficiencies of PVS-C 602b and PVS-I 602a are 9.77-12.75% and 11.16-15.10%. This means that PVS-I 602a provides an absolute improvement of 0.3-3.58% over PVS-C 602b.

[0100] In addition to high cooling performance, reliability is critical for real-world PV thermal management applications. In order to systematically evaluate the reliability of the PVS-I according to the present invention, continuous control tests were performed using the same experimental setup. The 8-day period (18 / 10 / 2023 to 25 / 10 / 2023) ("test period") (from 09:00 to 17:00 each day) included rainy, overcast, cloudy and sunny conditions.

[0101] like Figure 7a As shown, during the test period, complex weather conditions caused complex and unstable solar irradiance. Figure 7a The relative humidity and air temperature at the experimental site during the test period are shown. Their temporal dynamic patterns of air temperature and relative humidity are roughly consistent with the irradiance changes. Figure 7b The middle panel of FIG. 60 shows the temperature changes of PVS-I 602a and PVS-C 602b. As shown, PVS-I 602a accurately identifies whether the PV system needs thermal management and strongly suppresses the trend of increasing temperature when necessary. 2 ), PVS-I 602a can produce a temperature drop of 8.2-18.8°C during the time period of . The temperature drop is always rapid and is not affected by continuous rainy weather or rapidly changing irradiance. Figure 7b The bottom graph shows the open circuit voltage (V OC ) changes. During the period without cooling, the PV modules of both PVS-I 602a and PVS-C 602b show the same trend. However, once the cooling system of PVS-I 602a is activated, PVS-I 602a shows a higher V OCIn areas with strong solar irradiance (irradiance > 600W / m 2 ) period, PVS-I 602a will V OC Improved by 0.76-1.47V.

[0102] Figure 7c The daily water consumption per unit PV module area of ​​the PVS-I 602a is shown. Since there was no thermal management load during the first three days of the test period, the daily water consumption mainly came from evaporation to the environment and measurement errors. In the following days, depending on weather conditions, the water consumption ranged from 858-3461 mL / m 2 The maximum water consumption per hour is 433mL / (m 2 h). Figure 7d The daily power consumption per unit PV module area of ​​PVS-I 602a is shown. As shown in the figure, the daily power consumption is 3.5×10 -4 kWh. Due to the low water consumption, the pump only needs to work for a few seconds to meet several hours of cooling. Therefore, there is no significant difference in the daily power consumption of these days. Such low power consumption also means that PVS-I 602a will not consume more than 1kWh of electricity even in a year. Generally speaking, the above long-term experimental results under various weather conditions show that PVS-I 602a can adjust the PV temperature to an effective range.

[0103] It should be understood that the foregoing merely illustrates examples in which the present invention may be implemented, and that various modifications and / or changes may be made thereto without departing from the spirit of the present invention.

[0104] It should also be understood that certain features of the invention described in the context of separate embodiments for clarity may be provided in combination in a single embodiment. Conversely, for brevity, the various features of the invention described in the context of a single embodiment may also be provided individually or in any suitable sub-combination.

Claims

1. A photovoltaic (PV) panel comprising: A PV module having a front side for exposure to sunlight and absorbing solar energy for conversion into electrical energy and a back side opposite to the front side, and an evaporator coupled to the back side of the PV module, wherein the first end of the evaporator is adapted to be in close proximity or contact with a source of cooling medium to absorb the cooling medium by capillary action, wherein the evaporator has a structure that allows the cooling medium to move through, and Wherein the PV module is adapted to be in heat transferable relationship with the cooling medium moving through the evaporator.

2. The PV panel of claim 1, wherein the evaporator is made of at least a cooling medium absorbing material.

3. The PV panel of claim 2, wherein the evaporator is coupled to the back side of the PV module via a thermally conductive layer.

4. The PV panel of claim 3, wherein the thermally conductive layer is made of at least a viscous thermally conductive material.

5. The PV panel of claim 1, wherein the evaporator has a porous structure that allows the cooling medium absorbed by the evaporator to evaporate into the environment or move from the first end of the evaporator to an opposite second end of the evaporator.

6. The PV panel of claim 5, wherein the second end of the evaporator is adapted to be in close proximity or contact with a lower container for collecting the cooling medium exiting the evaporator from the second end.

7. A photovoltaic (PV) system comprising the PV panel according to claim 1.

8. The PV system of claim 7, wherein the PV modules are tilted relative to a horizontal plane, and The evaporator has a porous structure that allows at least a portion of the cooling medium absorbed by the evaporator to move from the first end to an opposite second end lower than the first end under the action of gravity to leave the evaporator.

9. The PV system of claim 7 or 8, wherein the evaporator comprises a face facing away from the front face of the PV module, the face allowing at least a portion of the cooling medium absorbed by the evaporator to evaporate into the environment.

10. The PV system of claim 7, wherein the evaporator is coupled to the back side of the PV module via a thermally conductive layer.

11. The PV system of claim 10, wherein the thermally conductive layer is made of at least a viscous thermally conductive material.

12. The PV system of claim 7, further comprising a pump operable to pump the cooling medium to an upper container to be absorbed by the evaporator.

13. The PV system of claim 12, further comprising: Irradiance sensor, Liquid level sensors, and Control systems, The control system is adapted to: when the solar irradiance on the PV panel measured by the irradiance sensor is below a threshold level, stopping operation of the pump, activating operation of the pump for a first predetermined period of time to pump the cooling medium to the upper container when the solar irradiance on the PV panel measured by the irradiance sensor is above the threshold level, and When the solar irradiance on the PV panel measured by the irradiance sensor is above the threshold level and the cooling medium in the upper container sensed by the liquid level sensor is below a preset level, the operation of the pump is activated for a second predetermined period of time to pump the cooling medium to the upper container.

14. The PV system of claim 8, further comprising a path that allows the cooling medium exiting the evaporator from the second end of the evaporator to move to a pump.

15. The PV system of claim 14, wherein the second end of the evaporator is in close proximity to or in contact with a lower container for collecting the cooling medium exiting the evaporator from the second end.

16. An evaporation system for a photovoltaic (PV) system, comprising: an evaporator capable of engaging with the back side of the PV module, and Upper container for cooling medium, wherein the first end of the evaporator extends in close proximity to the upper container or at least partially into the upper container and is adapted to absorb the cooling medium in the upper container by capillary action, wherein the evaporator has a structure that allows the cooling medium to move through, and Wherein the PV module is adapted to be in heat transferable relationship with the cooling medium moving through the evaporator when the evaporator is engaged with the PV panel.

17. The evaporation system of claim 16, wherein the evaporator is made of at least a cooling medium absorbing material.

18. The evaporation system of claim 16, wherein the evaporator has a porous structure that allows at least a portion of the cooling medium absorbed by the evaporator to move from the first end to an opposite second end lower than the first end under gravity to leave the evaporator.

19. The evaporation system of claim 18, wherein the second end of the evaporator is in close proximity to or in contact with a lower container for collecting the cooling medium exiting the evaporator from the second end.

20. The evaporation system of claim 16 or 17, wherein the evaporator comprises a face facing away from the front face of the PV module, the face allowing at least a portion of the cooling medium absorbed by the evaporator to evaporate into the environment.

21. The evaporation system of claim 16, wherein the evaporator is engageable with the back side of the PV module via a thermally conductive layer.

22. The evaporation system of claim 21, wherein the thermally conductive layer is made of at least a viscous thermally conductive material.

23. The evaporative system of claim 16, further comprising a pump operable to pump the cooling medium to the upper container to be absorbed by the cooling member.

24. The evaporation system of claim 23, further comprising: Irradiance sensor, Liquid level sensors, and Control systems, The control system is adapted to: stopping operation of the pump when the solar irradiance on the PV panel measured by the irradiance sensor is below a threshold level; activating operation of the pump for a first predetermined period of time to pump the cooling medium to the upper container when the solar irradiance on the PV panel measured by the irradiance sensor is above the threshold level; as well as When the solar irradiance on the PV panel measured by the irradiance sensor is above the threshold level and the cooling medium in the upper container sensed by the liquid level sensor is below a preset level, the operation of the pump is activated for a second predetermined period of time to pump the cooling medium to the upper container.

25. The evaporative system of claim 19, further comprising a path that allows the cooling medium exiting the evaporator from the second end of the evaporator to return to a pump.

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