Photovoltaic-photothermal system

Abstract

This invention belongs to the field of solar photovoltaic and photothermal technology, and particularly relates to a photovoltaic and photothermal system. The photovoltaic and photothermal system includes: a photovoltaic and photothermal module for converting solar energy into electrical and thermal energy, comprising, from top to bottom, a photovoltaic power generation layer, a heat-conducting cover plate, and a heat dissipation substrate, wherein the heat dissipation substrate integrates heat exchange channels for fluid flow; a ground source heat exchange unit, disposed below the ground surface, comprising vertically buried concrete pipe piles and heat exchange buried pipes inserted into the concrete pipe piles; and a circulation pipeline connecting the heat exchange channels of the heat dissipation substrate with the heat exchange buried pipes of the ground source heat exchange unit to form a closed loop, wherein a circulating working fluid circulates in the closed loop under the action of a driving device, transporting the heat generated by the photovoltaic and photothermal module to the ground source heat exchange unit.

Description

Technical Field

[0001] This invention belongs to the field of solar photovoltaic and photothermal technology, and particularly relates to a photovoltaic and photothermal system. Background Technology

[0002] With the global energy crisis and environmental pollution, solar energy, as a clean, renewable, and green energy source, has become an important part of the energy strategies of various countries. Among solar energy utilization technologies, photovoltaic power generation and solar thermal utilization are the two most important forms. However, traditional photovoltaic modules exhibit a significant "temperature effect" during operation; that is, as the intensity of sunlight increases, the surface temperature of the solar cells rises significantly, typically reaching 60°C or even higher. Studies have shown that for every 1°C increase in the temperature of crystalline silicon cells, their photoelectric conversion efficiency decreases by approximately 0.4% to 0.5%, and long-term high-temperature operation accelerates the aging of cell encapsulation materials, shortening the module's lifespan. To address this issue, photovoltaic-thermal integration (PVT) technology has emerged. This technology aims to remove waste heat from photovoltaic modules through fluids, reducing cell temperature, improving power generation efficiency, and recovering heat energy for domestic hot water or building heating, thus achieving the comprehensive utilization of electrical and thermal energy.

[0003] Despite the broad application prospects of PVT technology, it still faces many technical bottlenecks in practical engineering applications. Firstly, regarding module structure, most existing PVT modules adopt a "tube-sheet" bonding process, simply attaching copper or aluminum tubes to the photovoltaic backsheet using thermally conductive adhesive. Because the photovoltaic backsheet (usually made of TPT or PET composite material) has a low thermal conductivity, and the tubes and backsheet often have line contact with each other, resulting in high contact thermal resistance, heat cannot be dissipated in a timely and uniform manner. Under high-irradiation conditions in summer, this structure struggles to control the cell temperature within the ideal range, easily forming hot spots on the module surface and affecting system reliability. Secondly, regarding heat utilization and dissipation, although ground source heat pump systems are often used as heat sinks or heat sources for PVT systems, traditional ground source heat exchangers typically require drilling deep holes in the open ground around the building to bury U-shaped tubes. This method not only results in extremely high initial investment costs due to the large amount of drilling work (often accounting for 30% to 50% of the total cost of a ground source heat pump system), but also requires a large land area, making construction extremely difficult in urban buildings where land is scarce or in areas with limited land. Furthermore, traditional systems lack an effective thermal buffer mechanism between the buried pipes and the surface equipment, causing the underground heat exchange efficiency to be significantly limited by the soil's thermal conductivity, making it difficult to cope with the explosive heat dissipation demands of photovoltaic modules during midday.

[0004] In summary, the pressing technical challenges in existing technologies lie in improving the internal structure of photovoltaic (PV) thermal modules to overcome the heat conduction bottleneck of traditional backsheet-mounted tube structures and achieve efficient and uniform heat dissipation. Simultaneously, it's crucial to construct a stable and efficient underground heat exchange channel without increasing drilling land use and construction costs, thereby achieving low-cost, integrated, and efficient coupling of the PV system with the building foundation and shallow geothermal energy. Developing a comprehensive energy system that can significantly reduce module operating temperature while fully utilizing the existing building structure for underground heat exchange is a key issue that urgently needs to be addressed in the fields of building-integrated photovoltaics (BIPV) and shallow geothermal energy utilization. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a photovoltaic thermal system.

[0006] A photovoltaic-thermal system, comprising: A photovoltaic thermal module is used to convert solar energy into electrical energy and thermal energy. It includes, from top to bottom, a photovoltaic power generation layer, a heat-conducting cover plate, and a heat dissipation substrate. The heat dissipation substrate has an integrated heat exchange channel for fluid flow. A ground source heat exchange unit is installed below the ground surface and includes vertically buried concrete pipe piles and heat exchange pipes inserted into the concrete pipe piles. The circulation pipeline connects the heat exchange channel of the heat dissipation substrate with the heat exchange buried pipe of the ground source heat exchange unit to form a closed loop. The circulating working fluid circulates in the closed loop under the action of the driving device, and transports the heat generated by the photovoltaic thermal module to the ground source heat exchange unit.

[0007] Furthermore, the heat dissipation substrate is a metal extrusion profile, and an S-shaped serpentine flow channel is provided inside the heat dissipation substrate, which covers the heat exchange area of ​​the heat dissipation substrate; the heat-conducting cover plate is attached between the back of the photovoltaic power generation layer and the upper surface of the heat dissipation substrate; the two ends of the serpentine flow channel are respectively provided with liquid inlet and liquid outlet, and the liquid inlet and liquid outlet are connected to the circulation pipeline through connectors.

[0008] Furthermore, the photovoltaic thermal module also includes a frame and fasteners; the photovoltaic power generation layer, the heat-conducting cover plate, and the heat dissipation substrate are stacked, and the edges of the photovoltaic power generation layer and the heat-conducting cover plate are covered within the frame; the frame and the heat dissipation substrate are fixedly connected by the fasteners, so that the heat-conducting cover plate and the heat dissipation substrate are tightly attached.

[0009] Furthermore, the gap between the backplate of the photovoltaic / thermal module and the heat dissipation substrate, or the cavity of the heat dissipation substrate profile, is filled with a first phase change material; the first phase change material is used to absorb the peak heat of the photovoltaic / thermal module.

[0010] Furthermore, the concrete pipe pile of the ground source heat exchange unit has a hollow inner cavity; the heat exchange buried pipe is a U-shaped pipe, vertically suspended in the inner cavity of the concrete pipe pile; the inner cavity and the surrounding area of ​​the U-shaped pipe are filled with a backfill material layer; the backfill material layer contains a second phase change material, or the outer wall of the U-shaped pipe is wrapped with a second phase change material layer, for storing thermal energy underground.

[0011] Furthermore, the circulation pipeline includes a liquid storage tank, a first circulation pump, a flow regulating component, the photovoltaic thermal component, the ground source heat exchange unit, and a second circulation pump connected in series; the liquid storage tank is used to store the cooling circulation working fluid; the first circulation pump is located between the outlet of the liquid storage tank and the inlet of the photovoltaic thermal component to provide fluid power.

[0012] Furthermore, the flow regulation assembly includes a flow regulation valve and a flow meter disposed on the pipeline; the flow regulation valve is used to control the flow rate of the circulating working fluid entering the heat dissipation substrate; the flow meter is used to monitor the fluid flow rate in the pipeline in real time.

[0013] Furthermore, the second circulation pump is located between the outlet of the ground source heat exchange unit and the inlet of the storage tank; the second circulation pump is used to help overcome the fluid resistance of the ground source heat exchange unit and the return pipeline.

[0014] Furthermore, the photovoltaic thermal system also includes a temperature monitoring and control module; the temperature monitoring and control module includes a temperature sensor for monitoring the temperature of the photovoltaic thermal module, a fluid temperature sensor for monitoring the inlet and outlet water temperatures of the ground source heat exchange unit, and a controller; the controller dynamically adjusts the speed of the first circulating pump and the opening of the flow regulating valve based on the feedback data from the temperature sensor.

[0015] Furthermore, the concrete pipe pile is a prestressed high-strength concrete pipe pile; the heat exchange buried pipe is made of high-density polyethylene; the phase change temperature range of the second phase change material is 10℃~25℃, which is used to match the temperature range of shallow geothermal energy.

[0016] The beneficial effects of this invention are: This invention provides a photovoltaic-thermal system that constructs an integrated heat-conducting structure with extremely low contact thermal resistance by tightly stacking a photovoltaic power generation layer with a heat dissipation substrate and a heat-conducting cover plate that integrates internal heat exchange channels. This structure utilizes the high thermal conductivity of the heat dissipation substrate, combined with the extended fluid path of the serpentine flow channel, to eliminate heat exchange dead zones and significantly improve the temperature uniformity of the heat dissipation substrate surface. This allows the heat accumulated by the photovoltaic module under illumination to be uniformly and rapidly discharged and transferred to the circulating working fluid within the flow channel, thereby significantly reducing the operating temperature of the photovoltaic cells, effectively avoiding power decay of crystalline silicon cells due to high temperatures, and improving photoelectric conversion efficiency. Simultaneously, this invention integrates the ground-source heat exchange unit with the building foundation, using vertically embedded concrete pipe piles as the carrier of the heat exchange channel. Because it directly utilizes the pile foundation structure necessary for building construction, this design eliminates the need for large-scale drilling operations around the building, greatly saving on drilling costs and land occupation for the ground source heat pump system. In addition, thanks to the huge heat capacity of the concrete pipe piles and their excellent thermal coupling characteristics with deep soil, the heat exchange buried pipes can efficiently release the heat absorbed by the photovoltaic modules into the underground soil for cross-seasonal storage. This not only enables the reuse of the building's existing structural functions but also ensures the system's efficient and stable operation throughout the year, significantly improving the overall energy efficiency ratio of the building's energy system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the photovoltaic-thermal system provided by the present invention; Figure 2 This is a three-dimensional assembly diagram of the photovoltaic thermal module provided by the present invention; Figure 3 This is a cross-sectional view of a photovoltaic thermal module provided by the present invention; Figure 4 A cross-sectional view of the heat dissipation substrate provided by the present invention; Figure 5 A cross-sectional view of the ground source heat exchange unit provided by the present invention; Figure 6 This is a partial cross-sectional view of the assembly of the ground source heat exchange unit provided by the present invention.

[0018] Reference numerals: 100, Photovoltaic thermal system; 110, Photovoltaic thermal module; 111, Photovoltaic power generation layer; 1111, Cover glass; 1112, Upper sealing film; 1113, Photovoltaic panel; 1114, Lower sealing film; 1115, Back plate; 112, Thermally conductive cover plate; 113, Heat dissipation substrate; 1131, Heat exchange channel; 114, Frame; 115, Fastener; 120, Ground source heat exchange unit; 121, Concrete pipe pile; 122, Heat exchange buried pipe; 123, Backfill material layer; 124, Second phase change material layer; 130, Circulation pipeline; 131, Liquid storage tank; 132, First circulation pump; 133, Flow regulation component; 1331, Flow regulation valve; 1332, Flow meter; 134, Second circulation pump; 135, Circulating working fluid. Detailed Implementation

[0019] The following detailed description of a photovoltaic thermal system according to the present invention, in conjunction with embodiments, provides further specific details. For the sake of simplicity, this document cannot exhaustively list all alternative technical features and embodiments included in the present invention. Therefore, those skilled in the art should understand that any technical feature and embodiment within this embodiment does not limit the scope of protection of the present invention. The scope of protection includes all alternative technical features and embodiments adopted by those skilled in the art without inventive effort. Specifically, any embodiment obtained by replacing any technical feature in the present invention or by combining any two or more technical features provided by the present invention should be within the scope of protection of the present invention.

[0020] See appendix Figure 1 This embodiment proposes a photovoltaic-thermal system 100, which is a comprehensive energy utilization device integrating solar photovoltaic power generation, solar thermal collection, and shallow geothermal energy storage and extraction. The photovoltaic-thermal system 100 mainly comprises a photovoltaic-thermal module 110 above the ground surface, a ground source heat exchange unit 120 below the ground surface, and a circulation pipeline 130 connecting the two parts. The entire system achieves efficient heat transfer and distribution between the photovoltaic power generation end, the geothermal storage end, and the heat load end through forced convection circulation of the circulating working fluid 135 in a closed loop. This system is particularly suitable for engineering projects using prestressed high-strength concrete pipe piles as building foundations, achieving a perfect integration of building structure and energy system by integrating the ground source heat exchanger inside the pile foundation.

[0021] like Figure 2 and Figure 3As shown, the photovoltaic thermal module 110 adopts a highly integrated stacked encapsulation structure, which aims to minimize the contact thermal resistance between functional layers and ensure that the heat generated by the photovoltaic cells can be quickly dissipated. The photovoltaic thermal module 110 is mainly composed of a photovoltaic power generation layer 111, a thermally conductive cover plate 112, and a heat dissipation substrate 113 tightly bonded together from top to bottom along the thickness direction. Among them, the photovoltaic power generation layer 111 itself is also a multi-layer composite structure, which includes, from the light-facing side to the back-facing side, a cover glass 1111, an upper sealing film 1112, a photovoltaic panel 1113, a lower sealing film 1114, and a back plate 1115.

[0022] The cover glass 1111, serving as the outermost protective material of the module, is made of high-transmittance ultra-clear tempered glass, typically around 3.2 mm thick. Its surface can be coated to increase light transmittance and reduce reflection, ensuring the photovoltaic cells receive maximum solar radiation while possessing sufficient mechanical strength to withstand external environmental loads such as hail and wind pressure. The upper sealing film 1112 and lower sealing film 1114 are usually made of ethylene-vinyl acetate copolymer or polyolefin elastomer. These two films melt and cross-link under high temperatures during lamination, tightly wrapping and bonding the photovoltaic panel 1113 between the cover glass 1111 and the backsheet 1115, providing sealing, insulation, waterproofing, and stress buffering. The photovoltaic panel 1113, composed of several monocrystalline or polycrystalline silicon cells connected in series and parallel via busbars, is the core component of the system for converting solar energy into electrical energy and is also the main heat source for waste heat generation. The backsheet 1115 is located at the bottom of the photovoltaic power generation layer 111. It is made of composite materials with high weather resistance, high insulation and good water vapor barrier properties, such as TPT or KPE structure, to protect the cells from environmental corrosion on the back side.

[0023] To address the poor thermal conductivity of traditional photovoltaic module backsheets, this embodiment includes a thermally conductive cover plate 112 abutting directly beneath the backsheet 1115. The thermally conductive cover plate 112 is made of a high thermal conductivity metal, preferably an aluminum alloy or copper plate, with a thickness controlled between 1.0 mm and 3.0 mm. Aluminum alloy not only possesses excellent thermal conductivity but also exhibits low density, corrosion resistance, and ease of processing. The upper surface of the thermally conductive cover plate 112 is filled with a thermally conductive interfacial material such as thermally conductive silicone grease or thermally conductive double-sided adhesive to eliminate air gaps at the microscopic interface and significantly reduce contact thermal resistance. The function of the thermally conductive cover plate 112 is to homogenize the heat generated by the photovoltaic panel 1113 horizontally, preventing the formation of localized hot spots, and to rapidly transfer heat to the heat dissipation substrate 113 below in the vertical direction.

[0024] The heat dissipation substrate 113 is the core component responsible for fluid heat exchange in the photovoltaic thermal module 110, located below the heat-conducting cover plate 112. The heat dissipation substrate 113 is formed using die casting or machining processes, and is preferably made of aluminum alloy. Figure 2 , 3 As shown in Figure 4, a continuous serpentine heat exchange channel 1131 is provided inside the heat dissipation substrate 113. This heat exchange channel 1131 is arranged in an S-shaped reciprocating bend within the plane of the heat dissipation substrate 113, covering the heat dissipation area of ​​the back plate as much as possible. The serpentine channel design extends the residence time and heat exchange path of the fluid within the plate, effectively avoiding fluid short-circuiting and ensuring uniform heat dissipation. An inlet and outlet are respectively led out from one or both sides of the heat dissipation substrate 113, and connected to an external circulation pipeline 130 via a standard pipe fitting with external threads to realize the entry and exit of the circulating working fluid 135.

[0025] To assemble the photovoltaic power generation layer 111, the heat-conducting cover plate 112, and the heat dissipation substrate 113 into a stable whole, the photovoltaic thermal module 110 is also equipped with a frame 114 and fasteners 115. The frame 114 is typically made of aluminum alloy profile with a C-shaped or L-shaped cross-section, surrounding the perimeter of the module. The edges of the stacked photovoltaic power generation layer 111, heat-conducting cover plate 112, and heat dissipation substrate 113 are all covered within the grooves of the frame 114, which are filled with sealing silicone for waterproofing, dustproofing, and fixation. The fasteners 115 include bolts, nuts, and washers. The bolts pass through the pre-drilled mounting holes on the edge of the heat-conducting cover plate 112 and the corresponding holes on the edge of the heat dissipation substrate 113, or through a specific structure of the frame 114, pressing the aforementioned layers together under mechanical pressure. The pre-tightening force applied by the fasteners 115 causes elastic deformation at the contact surface between the heat-conducting cover plate 112 and the heat dissipation substrate 113, further reducing contact thermal resistance and ensuring efficient heat transfer.

[0026] To enhance the thermal inertia of the photovoltaic module and mitigate drastic temperature fluctuations caused by light irradiance, a first phase change material (PCM) is filled in the tiny gap between the backsheet 1115 and the heat dissipation substrate 113 of the photovoltaic thermal module 110, or more preferably, within the cavity structure of the extruded profile of the heat dissipation substrate 113 itself. The first phase change material is an organic phase change material with a solid-liquid phase change temperature between 35°C and 55°C, such as paraffin wax, fatty acids, or their eutectic mixtures. This temperature range is designed because the optimal operating temperature of crystalline silicon photovoltaic cells is typically around 25°C, but often exceeds 60°C in summer. When the module temperature rises to the melting point of the first phase change material, the phase change material begins to undergo a phase change, absorbing a large amount of latent heat while maintaining a relatively constant temperature. This "clamps" the operating temperature of the photovoltaic cell near the phase change temperature, preventing efficiency degradation and permanent damage caused by overheating. At night or when sunlight is insufficient, the phase change material releases latent heat, which is carried away by the circulating working fluid 135 through the heat exchange channel 1131 or provides insulation and antifreeze for the module. To prevent leakage of liquid phase change materials, they are usually encapsulated in microcapsules or adsorbed into porous matrices (such as expanded graphite) to form shaped phase change composite materials.

[0027] like Figure 5 and Figure 6 As shown, the ground source heat exchange unit 120 does not employ the traditional method of drilling and burying pipes, but cleverly utilizes the building's pile foundation structure. In this embodiment, the ground source heat exchange unit 120 includes concrete pipe piles 121 vertically embedded in the foundation. These concrete pipe piles 121 are prestressed high-strength concrete pipe piles, a widely used deep foundation type in modern construction, possessing advantages such as high bearing capacity, good bending resistance, and fast construction speed. During factory prefabrication, the PHC pipe piles form a through-hole cylindrical hollow cavity in their center. This embodiment utilizes this cavity space to arrange the heat exchange structure, eliminating the need for additional drilling of ground source heat pump wells, thus significantly saving construction costs and land resources.

[0028] One or more sets of heat exchange pipes 122 are vertically suspended within the hollow cavity of the concrete pipe pile 121. The heat exchange pipes 122 are typically made of high-density polyethylene, which possesses excellent corrosion resistance, low-temperature resistance, and long-term chemical stability, enabling them to withstand erosion from groundwater and soil environments. The heat exchange pipes 122 have a U-shaped structure, consisting of a down-flow pipe and an up-flow pipe, connected at the bottom by a U-shaped elbow. The length of the U-shaped pipe is determined by the depth of the pipe pile, typically ranging from 15 to 50 meters. To enhance the heat exchange effect, the position of the U-shaped pipe within the pipe pile can be fixed using positioning brackets, ensuring it is located at the center of the pipe pile or close to the inner wall of the pile.

[0029] Inside the concrete pipe pile 121, the space excluding the heat exchange pipe 122 is filled with a backfill material layer 123. The formula of the backfill material layer 123 is specially designed, which not only serves to fix the heat exchange pipe 122 and prevent it from shaking and being damaged, but more importantly, it serves as a heat transfer medium. The backfill material layer 123 is usually made of fine sand, bentonite, cement, and thermal conductivity enhancers (such as graphite powder, iron sand, etc.) mixed in a certain proportion. After being mixed with water to form a slurry, it is poured into the inner cavity of the pipe pile and solidifies to form a dense substance with high thermal conductivity.

[0030] To achieve efficient storage of shallow geothermal energy, this embodiment also introduces phase change thermal energy storage technology in the ground source heat exchange unit 120. A second phase change material is mixed into the backfill material layer 123, or a layer 124 of the second phase change material is directly wrapped around the outer wall of the heat exchange buried pipe 122. The selection of the second phase change material differs from that of the first phase change material on the ground, and its phase change temperature range is set to 10℃ to 25℃. This temperature range is designed to match the constant temperature layer temperature of the shallow soil (typically around 15℃). Using a second phase change material with a lower phase change temperature allows the soil to release / expose heat during winter heating conditions, even at lower return water temperatures on the ground source side; and during summer cooling or heat storage conditions, the soil around the pipe pile can more effectively absorb heat. The second phase change material is preferably a hydrated salt inorganic phase change material or modified low-temperature paraffin, which has the characteristics of high thermal density, relatively high thermal conductivity, and low cost. By integrating a second phase change material layer 124 inside the pipe pile, the concrete pipe pile 121 is actually a cylindrical thermal battery. By utilizing the high heat capacity of the concrete itself and the high latent heat of the phase change material, heat can be stored across seasons or across days and nights, thus alleviating the problem of soil thermal imbalance.

[0031] A circulation pipe 130 connects the photovoltaic thermal module 110 to the ground source heat exchange unit 120. For example... Figure 1 As shown, the circulation pipeline 130 is a closed-loop pressure system filled with a circulating working fluid 135. The circulating working fluid 135 is typically water or a mixture of water and ethylene glycol to prevent freezing at low winter temperatures. The main components of the circulation pipeline 130 include a storage tank 131, a first circulation pump 132, a flow regulating assembly 133, and a second circulation pump 134, which are connected in series via insulated pipes.

[0032] The storage tank 131 is located at the return water end of the system and is used to store the circulating working fluid 135. It also serves to maintain pressure, replenish water, vent air, and buffer thermal expansion. The storage tank 131 is typically an insulated water tank made of stainless steel, and its capacity is determined based on the total water volume of the system. The first circulation pump 132 is installed on the pipeline between the outlet of the storage tank 131 and the inlet of the photovoltaic thermal module 110. As one of the main driving forces of the system, its main function is to overcome the fluid resistance caused by the narrow flow channels inside the photovoltaic thermal module 110, ensuring that the fluid can flow through the heat dissipation substrate 113 at a sufficient flow rate to remove heat. The first circulation pump 132 is a variable frequency shielded pump, which features low noise, no leakage, and adjustable speed.

[0033] A flow regulation assembly 133 is installed on the pipeline after the first circulating pump 132, including a flow regulation valve 1331 and a flow meter 1332 connected in series. The flow regulation valve 1331 can be an electric proportional-integral regulating valve, used to precisely adjust the flow opening in the pipeline according to control commands. The flow meter 1332 is used to monitor the fluid velocity or instantaneous flow rate in the pipeline in real time and feed the data back to the control system to achieve closed-loop control.

[0034] After the fluid flows out of the photovoltaic thermal module 110, its temperature rises, and it then enters the heat exchange buried pipe 122 of the ground source heat exchange unit 120. To overcome the frictional and local resistance caused by the deep buried pipeline on the ground source side, especially considering the large hydrostatic pressure at the bottom of the U-shaped pipe, this embodiment incorporates a second circulation pump 134 connected in series in the pipeline. The second circulation pump 134 is located between the outlet of the ground source heat exchange unit 120 and the inlet of the storage tank 131 (or it can be located before the inlet of the ground source heat exchange unit, depending on the hydraulic balance design; in this embodiment...). Figure 1 (For reference, located in the reflux section for auxiliary lifting). The dual-pump series design allows the system to flexibly handle different operating conditions: single-pump operation saves energy when resistance is low, while dual-pump operation is used when resistance is high or high-flow flushing is required. The second circulation pump 134 also adopts frequency conversion control.

[0035] The intelligent operation of the entire photovoltaic thermal system 100 relies on a comprehensive temperature monitoring and control module. This module includes sensors distributed at key nodes: temperature sensors that monitor the temperature of the photovoltaic thermal modules 110 (especially the backsheet temperature of the solar panels), fluid temperature sensors that monitor the inlet and outlet water temperatures of the ground source heat exchange unit 120, and sensors that monitor ambient temperature and solar irradiance. All sensor signals are fed into a central controller (such as a PLC or microcontroller). The controller has a pre-set logic algorithm that dynamically adjusts the speed and start / stop status of the first circulation pump 132 and the second circulation pump 134, as well as the opening degree of the flow regulating valve 1331, based on the collected temperature data.

[0036] The working principle and process of the photovoltaic thermal system provided in this embodiment are as follows: The main operating modes of the photovoltaic thermal system 100 are divided into summer heat dissipation / storage mode, winter solar thermal utilization mode, and transition season mode.

[0037] In summer, intense solar radiation causes the photovoltaic power generation layer 111 to generate a large amount of heat while generating electricity, leading to a rapid rise in module temperature. When the module backsheet temperature sensor detects that the temperature exceeds a set threshold (e.g., 45°C), the controller activates the first circulation pump 132 and the second circulation pump 134. Low-temperature circulating working fluid 135 flows from the storage tank 131, is pressurized by the first circulation pump 132, and then enters the heat dissipation substrate 113 of the photovoltaic thermal module 110. Within the heat exchange channel 1131, the circulating working fluid 135 undergoes sufficient heat exchange with the high-temperature pipe wall, absorbing heat from the photovoltaic module and lowering its temperature, thereby maintaining the photovoltaic cells in a high-efficiency temperature range. If the temperature continues to rise and reaches the melting point of the first phase change material (e.g., 45°C), the first phase change material within the heat dissipation substrate 113 undergoes a phase change and absorbs heat, further suppressing temperature spikes and acting as a peak smoothing agent.

[0038] After absorbing heat and heating up, the circulating working fluid 135 leaves the photovoltaic thermal module 110 and enters the underground ground source heat exchange unit 120. As the high-temperature working fluid flows through the heat exchange pipe 122 within the concrete pipe pile 121, it transfers heat to the backfill material layer 123 and the surrounding soil through the pipe wall. At this time, the second phase change material (melting point 10-25℃) inside the pipe pile undergoes a phase change and absorbs heat due to heating by the high-temperature fluid, converting sensible heat into latent heat and storing it inside the pipe pile, while simultaneously accelerating the diffusion of heat to the surrounding deep soil. This process not only cools the photovoltaic module but also stores the abundant and excess solar thermal energy in summer underground as geothermal energy, achieving "summer heat storage in winter." The cooled working fluid flows back to the storage tank 131 via the second circulation pump 134, completing one cycle.

[0039] In winter, when the ambient temperature is low but there is solar radiation, the photovoltaic modules still generate heat, but the temperature is not high. At this time, the system can operate according to heating demand. The circulating working fluid 135 absorbs the latent heat released by the underground soil and the second phase change material in the ground source heat exchange unit 120 (the ground temperature is usually higher than the winter air temperature), thus raising its temperature. The working fluid then flows through the photovoltaic thermal module 110. If the photovoltaic module temperature is higher than the working fluid temperature, the working fluid further absorbs solar heat energy; if the photovoltaic module temperature is extremely low (such as at night), geothermal energy heats the photovoltaic module in reverse, preventing frost or snow accumulation and protecting the module. When heat needs to be extracted to supply the building heat pump unit, this system acts as a stable heat source side of the heat pump, providing a heat source with a higher temperature than the ambient air, thereby improving the COP value of the heat pump unit.

[0040] During the transitional season, the controller, based on feedback from the flow meter 1332 and the temperature sensor, adjusts the flow regulating valve 1331 and the frequency of the variable frequency pump to maintain the thermal balance of the system with minimal energy consumption, preventing excessive accumulation or dissipation of ground temperature.

[0041] In summary, this embodiment organically combines photovoltaic power generation, phase change thermal storage, and pile foundation buried pipe technology, which not only solves the problems of photovoltaic heat dissipation and the difficulty of drilling ground source heat pumps, but also realizes the spatiotemporal transfer of energy through the application of two-stage phase change materials, resulting in significant energy saving and emission reduction benefits.

[0042] For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, but obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this invention.

Claims

1. A photovoltaic-photothermal system, characterized in that, include: A photovoltaic thermal module is used to convert solar energy into electrical energy and thermal energy. It includes, from top to bottom, a photovoltaic power generation layer, a heat-conducting cover plate, and a heat dissipation substrate. The heat dissipation substrate has an integrated heat exchange channel for fluid flow. A ground source heat exchange unit is installed below the ground surface and includes vertically buried concrete pipe piles and heat exchange pipes inserted into the concrete pipe piles. The circulation pipeline connects the heat exchange channel of the heat dissipation substrate with the heat exchange buried pipe of the ground source heat exchange unit to form a closed loop. The circulating working fluid circulates in the closed loop under the action of the driving device, and transports the heat generated by the photovoltaic thermal module to the ground source heat exchange unit.

2. The photovoltaic-thermal system according to claim 1, characterized in that, The heat dissipation substrate is a metal extrusion profile. The heat dissipation substrate has an S-shaped serpentine flow channel inside, which covers the heat exchange area of ​​the heat dissipation substrate. The heat-conducting cover is attached between the back of the photovoltaic power generation layer and the upper surface of the heat dissipation substrate. The two ends of the serpentine flow channel are respectively provided with liquid inlet and liquid outlet, which are connected to the circulation pipeline through connectors.

3. The photovoltaic-thermal system according to claim 2, characterized in that, The photovoltaic thermal module also includes a frame and fasteners; the photovoltaic power generation layer, the heat-conducting cover plate and the heat dissipation substrate are stacked, and the edges of the photovoltaic power generation layer and the heat-conducting cover plate are covered within the frame; the frame and the heat dissipation substrate are fixedly connected by the fasteners, so that the heat-conducting cover plate and the heat dissipation substrate are in close contact.

4. The photovoltaic-thermal system according to claim 1, characterized in that, The gap between the backplate of the photovoltaic / thermal module and the heat dissipation substrate, or the cavity of the heat dissipation substrate profile, is filled with a first phase change material; the first phase change material is used to absorb the peak heat of the photovoltaic / thermal module.

5. The photovoltaic-thermal system according to claim 1, characterized in that, The concrete pipe pile of the ground source heat exchange unit has a hollow inner cavity; the heat exchange buried pipe is a U-shaped pipe, which is vertically suspended in the inner cavity of the concrete pipe pile; the inner cavity and the surrounding area of ​​the U-shaped pipe are filled with a backfill material layer; the backfill material layer contains a second phase change material, or the outer wall of the U-shaped pipe is wrapped with a second phase change material layer, for storing thermal energy underground.

6. The photovoltaic-thermal system according to claim 1, characterized in that, The circulation pipeline includes a liquid storage tank, a first circulation pump, a flow regulating component, the photovoltaic thermal component, the ground source heat exchange unit, and a second circulation pump connected in series; the liquid storage tank is used to store the cooling circulation working fluid; the first circulation pump is located between the outlet of the liquid storage tank and the inlet of the photovoltaic thermal component to provide fluid power.

7. The photovoltaic-thermal system according to claim 6, characterized in that, The flow regulation assembly includes a flow regulation valve and a flow meter disposed on the pipeline; the flow regulation valve is used to control the flow rate of the circulating working fluid entering the heat dissipation substrate; the flow meter is used to monitor the fluid flow rate in the pipeline in real time.

8. The photovoltaic-thermal system according to claim 6, characterized in that, The second circulation pump is located between the outlet of the ground source heat exchange unit and the inlet of the liquid storage tank; the second circulation pump is used to help overcome the fluid resistance of the ground source heat exchange unit and the return pipeline.

9. The photovoltaic-thermal system according to any one of claims 1 to 8, characterized in that, The photovoltaic thermal system also includes a temperature monitoring and control module; the temperature monitoring and control module includes a temperature sensor for monitoring the temperature of the photovoltaic thermal module, a fluid temperature sensor for monitoring the inlet and outlet water temperatures of the ground source heat exchange unit, and a controller; the controller dynamically adjusts the speed of the first circulating pump and the opening of the flow regulating valve based on the feedback data from the temperature sensor.

10. The photovoltaic-thermal system according to claim 5, characterized in that, The concrete pipe pile is a prestressed high-strength concrete pipe pile; the heat exchange buried pipe is made of high-density polyethylene; the phase change temperature range of the second phase change material is 10℃~25℃, which is used to match the temperature range of shallow geothermal energy.

Images