Photovoltaic power generation passive cooling method
By using a passive cooling method that generates an upward airflow through coolant evaporation and solar heating, the problem of energy consumption in photovoltaic power generation system cooling devices is solved, achieving efficient and stable photovoltaic panel cooling.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHONGQING UNIV
- Filing Date
- 2023-05-23
- Publication Date
- 2026-05-15
AI Technical Summary
Existing photovoltaic power generation systems require additional electrical energy for cooling devices, leading to reduced efficiency and increased costs.
The system uses coolant evaporation to remove heat from the photovoltaic panels and utilizes solar energy to heat the airflow at the duct inlet, creating an upward airflow. It achieves passive cooling by relying on the chimney effect, and combines circulating flow and phase change heat transfer. The system also optimizes duct installation by taking advantage of the terrain or installation method.
It achieves highly efficient cooling without the need for additional electricity, improving the cooling efficiency and stability of photovoltaic panels and reducing operating costs.
Smart Images
Figure CN116545373B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photovoltaic power generation technology, and more specifically to a passive cooling method for photovoltaic power generation. Background Technology
[0002] China's photovoltaic (PV) power generation industry started in the 1970s and entered a period of steady development in the mid-1990s. The output of solar cells and modules increased steadily year by year. After more than 30 years of effort, it has entered a new stage of rapid development. Driven by national projects such as the "Bright Future Project" and the "Power to the Countryside" project, as well as the strong impetus from the global PV market, my country's PV power generation industry has developed rapidly.
[0003] As is well known, the conversion efficiency of photovoltaic cells is closely related to their operating temperature; the higher the temperature, the lower the efficiency. Research data shows that for every 1°C increase in cell temperature, the photoelectric conversion efficiency of crystalline silicon cells decreases by approximately 0.4%, while that of amorphous silicon cells decreases by about 0.1%. Furthermore, after reaching their upper operating temperature limit, the aging rate of crystalline silicon cells doubles for every 10°C increase in temperature. Currently, photovoltaic power generation is primarily achieved through overhead air cooling. In actual operation, especially during the hot season in Northwest China, the temperature of photovoltaic panels can reach over 100°C. If the average temperature of photovoltaic panels could be reduced by 40°C during power generation, the annual power generation per panel could increase by 40 x 0.4% = 16%, resulting in significant economic benefits. Therefore, it is necessary to install cooling devices in photovoltaic power generation systems.
[0004] CN202222067115.5 disclosed a solar photovoltaic power generation energy-saving and efficiency-enhancing cooling tower, the structure of which includes: a tower body, the tower body having an upper ventilation cavity, an evaporation cavity communicating with the upper ventilation cavity, and an air inlet cavity located below the evaporation cavity, wherein the upper ventilation cavity is connected to the outside; water-spraying packing, located inside the evaporation cavity; and a water distribution pipe, located inside the evaporation cavity, the water distribution pipe being mounted above the water-spraying packing, and having multiple nozzles installed on the water distribution pipe; in this patent, solar panels are installed on the outer wall of the cylinder to power the motor, so that after the motor starts, it can guide the fan blades to rotate, increasing the air exchange rate inside the tower and preventing the air in the corners inside the tower from not being replaced in time.
[0005] CN201020689851.9 previously disclosed a solar-powered motorized cooling tower, comprising a photovoltaic power generation device for solar power generation and a cooling device. The power output of the photovoltaic power generation device is connected to the power unit of the cooling device via a grid-connected inverter, and the photovoltaic modules of the photovoltaic power generation device are mounted on the cooling tower platform of the cooling device. This utility model utilizes a photovoltaic power generation device connected to an external power grid for grid connection to the cooling device, thereby reducing the primary energy consumption of the cooling tower and making the cooling tower more efficient in summer.
[0006] The existing cooling equipment for solar power generators all require electrical energy as power. Therefore, designing a passive cooling method that does not require additional electrical energy consumption is a problem that needs to be considered and solved by those skilled in the art. Summary of the Invention
[0007] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a passive cooling method for photovoltaic power generation that does not require additional electrical energy.
[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0009] A passive cooling method for photovoltaic power generation is characterized by using the evaporation of coolant to carry the heat from the photovoltaic panel to the inlet below the duct, and then collecting and using solar energy to heat the area above the inlet of the duct to create an upward airflow inside the duct. The upward airflow carries away the heat from the photovoltaic panel that has been sent to the inlet of the duct, thereby cooling the photovoltaic panel.
[0010] In this way, the evaporation of the coolant can quickly remove the heat from the photovoltaic panels. The heat is then delivered to the inlet at the bottom of the duct. Solar energy collection heats the area above the inlet, creating a temperature difference that generates evaporation and an upward airflow. This creates a chimney effect, causing the air inside the duct to rise rapidly and further absorb and remove heat from the coolant. Therefore, no additional electricity is required, achieving passive cooling of the photovoltaic panels with high efficiency, stability, and reliability.
[0011] Furthermore, a coolant with a relatively low boiling point is used to carry the heat from the photovoltaic panel to the inlet below the duct; a heat exchanger with a relatively high boiling point is used to collect solar energy and heat the area above the duct inlet.
[0012] This makes the temperature above the air duct inlet higher than at the inlet itself, thus creating a better upward airflow to carry away the heat.
[0013] Furthermore, the coolant evaporates and vaporizes at the photovoltaic panel and is sent to the inlet below the air duct. It is then liquefied by air and released heat at the air duct inlet before being sent back to the photovoltaic panel, thus achieving circulation.
[0014] This enables cyclic processing, relying on the circulating flow of coolant and phase change heat transfer to achieve more efficient and continuous cooling of photovoltaic panels.
[0015] Furthermore, this method relies on a photovoltaic generator cooling system, which includes a photovoltaic panel cooling device with a pipe heat exchange structure, a solar thermal device, and a vertically arranged duct located above the photovoltaic panel cooling device and the solar thermal device. A vertically downward-opening air intake is connected to the lower inlet of the air intake. A first heat exchanger for heat exchange with the photovoltaic panel cooling device is arranged near the lower inlet of the air intake. A heat exchange air intake device is also arranged inside the air intake, which includes a second heat exchanger spaced above the first heat exchanger. The two interfaces of the photovoltaic panel cooling device and the first heat exchanger are connected and circulated, as are the two interfaces of the solar thermal device and the second heat exchanger.
[0016] In this system, during operation, the photovoltaic panels are cooled and heat is carried away by the evaporation of coolant in the photovoltaic cooling device. The heat is carried by the evaporated coolant to the exhaust duct, where it is released and condenses. The hot air inside the exhaust duct rises and enters the ductwork, creating a chimney effect that draws in outside air from the lower end of the exhaust duct, resulting in a wind-cooling effect. The second heat exchanger, connected to the solar thermal collector, releases the solar heat collected by the solar thermal collector at the upper end of the exhaust duct, further heating the air and enhancing the evaporation effect, increasing suction, airflow speed, and overall cooling efficiency. Therefore, it effectively achieves passive cooling of the photovoltaic generator set.
[0017] Furthermore, the ductwork is installed and fixed on a hillside near the photovoltaic generator set. This utilizes the terrain to achieve the desired height difference for ductwork installation, enabling the chimney effect and further reducing costs. Alternatively, if a hillside is unavailable, mounting frames can be used to vertically fix the ductwork.
[0018] Furthermore, rain caps are installed at intervals on the upper end of the duct. This prevents rainwater from entering.
[0019] Furthermore, the first heat exchanger is a coil-type heat exchanger. It features a simple structure and high heat exchange efficiency.
[0020] Furthermore, the photovoltaic panel cooling device includes cooling pipes arranged in parallel or in a spiral pattern and fixed to the lower surface of each photovoltaic panel. The cooling pipes are filled with coolant. The upper end of each cooling pipe is connected to a coolant vapor pipe, and the lower end is connected to a coolant return pipe, so that the cooling pipes are connected in parallel to form a cooling pipe group. The coolant vapor pipe is connected to the interface at the upper end of the first heat exchanger, and the upper end of the coolant return pipe is connected to the interface at the lower end of the first heat exchanger to form a circulation connection.
[0021] In this way, during operation, the coolant in the cooling pipes absorbs heat from the photovoltaic panels and evaporates to form coolant vapor, which carries away the heat from the photovoltaic panels. The coolant vapor then enters the first heat exchanger at the bottom of the exhaust duct through the coolant vapor pipe, where it releases heat and condenses. The liquefied coolant, under its own weight, flows back through the coolant return pipe to the cooling pipes on the lower surface of each photovoltaic panel, forming a circulation. Therefore, it can quickly and efficiently cool the photovoltaic panels.
[0022] Furthermore, the evaporation temperature of the coolant is 45℃-55℃ (preferably 50℃). This temperature allows for better cooling of the photovoltaic panel through evaporation and maintains the stability of the photovoltaic panel temperature. Methanol is preferably used as the coolant, facilitating pressure control and adjustment of the evaporation temperature.
[0023] As one method of installing cooling pipes, the cooling pipes are directly attached and fixed to the lower surface of the photovoltaic panel. This structure is simple and has low implementation cost.
[0024] As another installation method for cooling pipes, a layer of silicone oil is encapsulated on the lower surface of the photovoltaic panel, and the cooling pipes are installed inside the silicone oil layer. This allows the silicone oil layer to better absorb the heat from the photovoltaic panel, thus cooling it, and also enables better heat transfer to the interior of the cooling pipes.
[0025] Furthermore, the photovoltaic panel cooling device also includes a liquid level holding tank, which is filled with coolant and connected to the cooling pipe assembly. The height of the coolant in the liquid level holding tank is the same as the highest point of the cooling pipe on the lower surface of each photovoltaic panel.
[0026] In this way, the liquid level holding tank can effectively ensure that the coolant in the cooling pipes on the lower surface of each photovoltaic panel is in a liquefied state, thus better guaranteeing the cooling effect on the photovoltaic panel.
[0027] As one approach, the level holding tank and the cooling pipe assembly are connected in parallel. This makes maintenance more convenient.
[0028] As another method, a level holding tank is connected in series with the coolant return pipe. This allows the level holding tank to collect and consolidate the returned coolant, resulting in a more stable level holding effect.
[0029] Furthermore, the photovoltaic panel cooling device also includes a pressure tank, inside which an elastic membrane is horizontally arranged. The space below the elastic membrane is filled with coolant and connected to the cooling pipe assembly, while the space above the elastic membrane is filled with pressure regulating gas. An air injection port is also provided at the top of the pressure tank.
[0030] In this way, pressure-regulating gas can be injected or released into the upper space of the pressure tank through the injection port, thereby regulating the internal pressure of the pressure tank. This pressure can then be applied to the entire photovoltaic panel cooling system through the elastic diaphragm, achieving regulation of the cooling fluid pressure. This pressure change, in turn, controls and regulates the evaporation temperature of the coolant, thus enabling control over the cooling temperature and cooling effect of the photovoltaic panels. Nitrogen gas is used for pressure regulation during implementation, resulting in more stable and reliable performance.
[0031] As a structural design, the second heat exchanger is a coil-type heat exchanger. It features a simple structure and high heat exchange efficiency.
[0032] Furthermore, the solar thermal collection device includes a heat collection tank filled with a heat exchange fluid. Multiple solar heat pipes are connected side-by-side on one side of the heat collection tank to form a solar heat collection tube group. The evaporation end of the solar heat pipes extends outward and the condensation end is inserted into the heat collection tank and located in the heat exchange fluid. A heat exchange fluid steam pipe is connected to the upper end of the heat collection tank and connected to an interface above the second heat exchanger. A heat exchange fluid return pipe is connected to the middle of the side wall of the heat collection tank and connected to an interface below the second heat exchanger to form a circulating connection.
[0033] In this way, solar heat pipes collect solar energy and heat the heat exchange fluid to vaporize it. The high-temperature heat exchange fluid vapor enters the second heat exchanger through the heat exchange fluid vapor pipe, where it exchanges heat, cools down, condenses, and flows back to the heat collection tank through the heat exchange fluid return pipe. This heats the second heat exchanger, improves the evaporation effect inside the draft duct, and increases the suction force for the air intake below.
[0034] Furthermore, the evaporation temperature of the heat exchange fluid is higher than that of the coolant (e.g., 60°C). This allows for better heating of the second heat exchanger, increases evaporation, and improves the air-cooling effect on the first heat exchanger.
[0035] As another structural approach, the second heat exchanger includes a heat exchange chamber separated by two partitions inside the air duct. Several air pipes are vertically arranged inside the heat exchange chamber. The upper and lower ends of the air pipes are sealed and fixed through the two partitions. An interface for the inflow of heat exchange liquid is provided on the side wall in the middle of the heat exchange chamber, and an interface for the outflow of heat exchange liquid is provided on the lower end of the heat exchange chamber.
[0036] This structure is simple and easy to implement. During operation, the high-temperature heat exchange fluid enters the heat exchange chamber from the upper interface, surrounding and heating the air inside the air duct. This rapidly heats the air inside the air duct and causes it to flow upwards, creating a downward suction effect. Therefore, it has the advantages of higher heat exchange efficiency and a better upward suction effect.
[0037] Furthermore, the heat exchange chamber has multiple sets of interfaces for the inflow and outflow of heat exchange fluid, evenly arranged circumferentially. This facilitates connection to solar thermal devices.
[0038] Furthermore, the solar thermal collection device includes a frustoconical base fixed to the outer periphery of the second heat exchanger. A mounting groove is provided on the upper surface of the base. A heat exchange fluid jacket (which can be a circumferentially connected layered structure or a pipe structure corresponding only to the heat-receiving pipes) is provided inside the bottom of the mounting groove. Above the heat exchange fluid jacket, the upper surface of the mounting groove also has multiple heat-receiving pipes evenly distributed circumferentially. The upper end of the heat exchange fluid jacket is connected to the interface at the lower end of the second heat exchanger, and the lower end of the heat exchange fluid jacket is connected to the lower end of the heat-receiving pipes. The upper end of the heat-receiving pipes is connected to the interface at the upper end of the second heat exchanger. At the upper opening of the mounting groove, a fan-shaped threaded lens is positioned directly above each heat-receiving pipe. The threaded lens has an arc-shaped protrusion in the center facing the heat-receiving pipe, and threaded portions on both sides of the arc-shaped protrusion, with the threaded portions gradually converging upwards to form a fan shape.
[0039] In this way, the solar thermal collection device is directly installed outside the exhaust duct, avoiding heat loss over long distances. The device structure incorporates solar energy collection features around the exhaust duct, ensuring efficient solar energy collection to heat the second heat exchanger regardless of the sun's position in the morning or afternoon. During operation, a threaded lens concentrates the solar energy hitting the base onto the heating pipes, heating the heat exchange fluid inside. This causes the fluid to either vaporize (when the heat exchange fluid uses a phase-change heat transfer medium) or undergo significant thermal expansion (when the heat exchange fluid uses a pure liquid medium with a high expansion coefficient, such as silicone oil). The heated fluid then flows upwards into the second heat exchanger, heating the air inside the exhaust duct. The cooled (or condensed) heat exchange fluid returns to the heat exchange fluid jacket, thus achieving circulation. The threaded lens used, also known as a Fresnel lens, has a flat lower surface and an upper surface with an arc-shaped protrusion in the middle and threaded serrations on both sides. Both the arc-shaped protrusion and the threaded serrations refract and converge the incident light onto the heated tube. Its basic structure and principle are mature existing technologies. In this application, its structural shape has been adaptively adjusted to form a fan shape, cleverly converging sunlight to heat the circumferentially arranged heated tubes. Therefore, this device structure can effectively collect sunlight, causing the heat exchange fluid inside the heated tube to vaporize or expand due to heat and flow upwards into the second heat exchanger, achieving the circulation of the heat exchange fluid to heat the second heat exchanger. It features a simple structure and high and stable heat exchange efficiency.
[0040] Furthermore, a heat-absorbing coating is applied to the upper surface of the heating tube, allowing for better absorption of solar energy.
[0041] Furthermore, glass cover plates are spaced apart on the upper surface of the threaded lens. This better protects the lens and ensures its reliable and stable light-gathering effect.
[0042] Furthermore, the heat exchange fluid jacket is a pipe-type structure corresponding to the heat-receiving tube.
[0043] This not only simplifies the structure and makes installation easier, but also, when the heat exchange fluid is silicone oil, the greater pipe resistance better prevents the silicone oil that expands due to heat from flowing downwards inside the heated pipe.
[0044] Furthermore, an inner cylinder is also provided at intervals inside the heat exchange chamber, and all the air pipes are located inside the inner cylinder. An opening is provided between the upper end of the inner cylinder and the upper partition plate, and an outlet is provided at the lower end of the inner cylinder directly opposite the interface for the heat exchange liquid to flow out.
[0045] This design addresses the issue of uneven heat exchanger temperatures at the interfaces due to the different directions of sunlight in the morning and afternoon. The inner cylinder structure allows the heat exchanger entering from each direction to first converge and homogenize within the inner cylinder and the inner wall of the heat exchange chamber before entering the interior and the air in the air passage pipe from the top of the inner cylinder for heat exchange. This results in more even heating of the air passage pipe, more uniform upward airflow, and a more balanced and stable cooling effect on the first heat exchanger. Especially when using silicone oil as the heat exchanger, its lower fluidity compared to gas-phase heat exchangers further enhances the uniformity of the airflow.
[0046] Furthermore, a top plate is installed at the upper end of the inner cylinder, through which the air duct passes. The top plate has evenly distributed perforations. This allows the high-temperature heat exchange fluid to enter the inner cylinder more evenly, achieving uniform heating and ensuring uniform airflow.
[0047] Furthermore, the top plate is a downward-facing cone shape. This not only facilitates the heat exchange fluid flowing here to pass through the perforations on the top plate and enter the interior, but also better avoids the defect of uneven entry of high-temperature heat exchange fluid caused by different distances of the perforations from the edge, thus improving the uniformity of internal heating.
[0048] In summary, this invention fully utilizes the evaporation effect generated by solar energy to achieve air cooling of the photovoltaic generator set, thereby realizing passive cooling of the photovoltaic generator set. It features high solar energy utilization efficiency and excellent cooling effect. Attached Figure Description
[0049] Figure 1 This is a schematic diagram of a photovoltaic generator cooling system used in this invention. The arrows in the diagram indicate the flow direction.
[0050] Figure 2 for Figure 1 A schematic diagram of the structure of a solar thermal heating device.
[0051] Figure 3 This is a schematic diagram of another photovoltaic generator cooling system used in this invention.
[0052] Figure 4 for Figure 3 Schematic diagram of the installation structure of the intermediate cooling pipes.
[0053] Figure 5 for Figure 3 A top view of the individual base section of the structure.
[0054] Figure 6 for Figure 3 A schematic diagram of the cross-sectional structure of a single heated tube and the threaded lens above it.
[0055] Figure 7 for Figure 6 A top view of a single threaded lens.
[0056] Figure 8 for Figure 3 A schematic diagram of the structure of the second heat exchanger. Detailed Implementation
[0057] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0058] Implementation method: A passive cooling method for photovoltaic power generation. This method uses the evaporation of coolant to carry away the heat of the photovoltaic panel to the inlet below the wind tunnel. Then, solar energy is collected and used to heat the area above the inlet of the wind tunnel, so that an upward airflow is formed inside the wind tunnel. The upward airflow carries away the heat of the photovoltaic panel sent to the inlet of the wind tunnel, thereby cooling the photovoltaic panel.
[0059] In this way, the evaporation of the coolant can quickly remove the heat from the photovoltaic panels. The heat is then delivered to the inlet at the bottom of the duct. Solar energy collection heats the area above the inlet, creating a temperature difference that generates evaporation and an upward airflow. This creates a chimney effect, causing the air inside the duct to rise rapidly and further absorb and remove heat from the coolant. Therefore, no additional electricity is required, achieving passive cooling of the photovoltaic panels with high efficiency, stability, and reliability.
[0060] During implementation, a coolant with a relatively low boiling point is used to carry the heat from the photovoltaic panels to the inlet below the duct; a heat exchanger with a relatively high boiling point is used to collect solar energy and heat the area above the duct inlet.
[0061] This makes the temperature above the air duct inlet higher than at the inlet itself, thus creating a better upward airflow to carry away the heat.
[0062] During implementation, the coolant evaporates and vaporizes at the photovoltaic panel and is then sent to the inlet below the air duct. At the air duct inlet, it is liquefied by air and releases heat before being sent back to the photovoltaic panel, thus achieving circulation.
[0063] This enables cyclic processing, relying on the circulating flow of coolant and phase change heat transfer to achieve more efficient and continuous cooling of photovoltaic panels.
[0064] Specifically, Figure 1-2 A photovoltaic generator cooling system for implementing this method is disclosed. The photovoltaic generator cooling system includes a photovoltaic panel cooling device with a pipe heat exchange structure, a solar thermal device, and a duct 1 that is vertically arranged and located above the photovoltaic panel cooling device. A vertically downward-opening air intake duct 2 is connected to the lower inlet of the duct 1. A first heat exchanger 3 for heat exchange with the photovoltaic panel cooling device is arranged near the lower inlet of the air intake duct 2. A heat exchange air intake device is also arranged inside the air intake duct, which includes a second heat exchanger 4 arranged at intervals above the first heat exchanger 3. The two interfaces of the photovoltaic panel cooling device and the first heat exchanger 3 are connected and circulated, and the two interfaces of the solar thermal device and the second heat exchanger 4 are connected and circulated.
[0065] In this system, during operation, the photovoltaic panels are cooled and heat is carried away by the evaporation of coolant in the photovoltaic cooling device. The heat is carried by the evaporated coolant to the exhaust duct, where it is released and condenses. The hot air inside the exhaust duct rises and enters the ductwork, creating a chimney effect that draws in outside air from the lower end of the exhaust duct, resulting in a wind-cooling effect. The second heat exchanger, connected to the solar thermal collector, releases the solar heat collected by the solar thermal collector at the upper end of the exhaust duct, further heating the air and enhancing the evaporation effect, increasing suction, airflow speed, and overall cooling efficiency. Therefore, it effectively achieves passive cooling of the photovoltaic generator set.
[0066] The ventilation duct 1 is installed and fixed on a hillside near the photovoltaic generator set. This utilizes the terrain to achieve the desired height difference for duct installation, enabling the chimney effect and saving costs. In practice, if a hillside is unavailable, a mounting frame can be used to vertically fix the duct.
[0067] Rain caps 5 are provided at intervals on the upper end of the duct 1. This prevents rainwater from entering.
[0068] The first heat exchanger 3 is a coil-type heat exchanger. It features a simple structure and high heat exchange efficiency.
[0069] The photovoltaic panel cooling device includes cooling pipes arranged in parallel or in a spiral pattern and fixed to the lower surface of each photovoltaic panel 6. The cooling pipes are filled with coolant. The upper end of each cooling pipe is connected to a coolant vapor pipe 7, and the lower end is connected to a coolant return pipe 8, so that the cooling pipes are connected in parallel to form a cooling pipe group. The coolant vapor pipe is connected to the interface at the upper end of the first heat exchanger 3, and the upper end of the coolant return pipe 8 is connected to the interface at the lower end of the first heat exchanger 3 to form a circulation connection.
[0070] In this way, during operation, the coolant in the cooling pipes absorbs heat from the photovoltaic panels and evaporates to form coolant vapor, which carries away the heat from the photovoltaic panels. The coolant vapor then enters the first heat exchanger at the bottom of the exhaust duct through the coolant vapor pipe, where it releases heat and condenses. The liquefied coolant, under its own weight, flows back through the coolant return pipe to the cooling pipes on the lower surface of each photovoltaic panel, forming a circulation. Therefore, it can quickly and efficiently cool the photovoltaic panels.
[0071] The evaporation temperature of the coolant is 45℃-55℃ (preferably 50℃). This temperature allows for better cooling of the photovoltaic panel through evaporation and maintains the stability of the photovoltaic panel temperature. Methanol is preferably used as the coolant, facilitating pressure control and adjustment of the evaporation temperature.
[0072] The cooling pipes are directly attached to the lower surface of the photovoltaic panel 6. This structure is simple and inexpensive to implement.
[0073] The photovoltaic panel cooling device also includes a liquid level holding tank 9, which is filled with coolant and connected to the cooling pipe assembly. The height of the coolant in the liquid level holding tank 9 is the same as the height of the highest point of the cooling pipe on the lower surface of each photovoltaic panel.
[0074] In this way, the liquid level holding tank can effectively ensure that the coolant in the cooling pipes on the lower surface of each photovoltaic panel is in a liquefied state, thus better guaranteeing the cooling effect on the photovoltaic panel.
[0075] The liquid level holding tank 8 and the cooling pipe assembly are connected in parallel. This makes maintenance more convenient.
[0076] The second heat exchanger, 4, is a coil-type heat exchanger. It features a simple structure and high heat exchange efficiency.
[0077] The solar thermal collection device includes a heat collection tank 11, which is filled with heat exchange fluid. Multiple solar heat pipes 12 are connected side by side on one side of the heat collection tank 11 to form a solar heat collection tube group. The evaporation end of the solar heat pipe 12 extends outward and the condensation end is inserted into the heat collection tank and located in the heat exchange fluid. The upper end of the heat collection tank 11 is connected to a heat exchange fluid steam pipe 13 and connected to an interface above the second heat exchanger 4. The middle of the side wall of the heat collection tank 11 is connected to a heat exchange fluid return pipe 14 and connected to an interface below the second heat exchanger 4 to form a circulation connection.
[0078] In this way, solar heat pipes collect solar energy and heat the heat exchange fluid to vaporize it. The high-temperature heat exchange fluid vapor enters the second heat exchanger through the heat exchange fluid vapor pipe, where it exchanges heat, cools down, condenses, and flows back to the heat collection tank through the heat exchange fluid return pipe. This heats the second heat exchanger, improves the evaporation effect inside the draft duct, and increases the suction force for the air intake below.
[0079] The evaporation temperature of the heat exchange fluid is higher than that of the coolant (e.g., 60°C). This allows for better heating of the second heat exchanger, increases evaporation, and improves the air-cooling effect on the first heat exchanger.
[0080] Figure 3-8 Another photovoltaic generator cooling system for implementing this method is disclosed, which and Figure 1-2 The systems share some structural similarities but differ in others. Specifically, the photovoltaic generator cooling system includes a photovoltaic panel cooling device with a pipe heat exchange structure, a solar thermal collector, and a vertically arranged duct 1 positioned above both the photovoltaic panel cooling device and the solar thermal collector. A vertically opening downward-facing air intake duct 2 is connected to the lower inlet of the duct 1. A first heat exchanger 3 for heat exchange with the photovoltaic panel cooling device is located near the lower inlet of the air intake duct 2. A heat exchange-type air inlet device is also installed inside the air intake duct, including a second heat exchanger 4 spaced above the first heat exchanger 3. The two interfaces of the photovoltaic panel cooling device and the first heat exchanger 3 are connected and circulated, as are the two interfaces of the solar thermal collector and the second heat exchanger 4.
[0081] In this system, during operation, the photovoltaic panels are cooled and heat is carried away by the evaporation of coolant in the photovoltaic cooling device. The heat is carried by the evaporated coolant to the exhaust duct, where it is released and condenses. The hot air inside the exhaust duct rises and enters the ductwork, creating a chimney effect that draws in outside air from the lower end of the exhaust duct, resulting in a wind-cooling effect. The second heat exchanger, connected to the solar thermal collector, releases the solar heat collected by the solar thermal collector at the upper end of the exhaust duct, further heating the air and enhancing the evaporation effect, increasing suction, airflow speed, and overall cooling efficiency. Therefore, it effectively achieves passive cooling of the photovoltaic generator set.
[0082] The ventilation duct 1 is installed and fixed on a hillside near the photovoltaic generator set. This utilizes the terrain to achieve the desired height difference for duct installation, enabling the chimney effect and saving costs. In practice, if a hillside is unavailable, a mounting frame can be used to vertically fix the duct.
[0083] Rain caps 5 are provided at intervals on the upper end of the duct 1. This prevents rainwater from entering.
[0084] The first heat exchanger 3 is a coil-type heat exchanger. It features a simple structure and high heat exchange efficiency.
[0085] The photovoltaic panel cooling device includes cooling pipes 10 arranged in parallel or in a spiral pattern and fixed to the lower surface of each photovoltaic panel 6. The cooling pipes 10 are filled with coolant. The upper end of each cooling pipe is connected to a coolant vapor pipe 7, and the lower end is connected to a coolant return pipe 8, so that the cooling pipes are connected in parallel to form a cooling pipe group. The coolant vapor pipe is connected to the interface at the upper end of the first heat exchanger 3, and the upper end of the coolant return pipe 8 is connected to the interface at the lower end of the first heat exchanger 3 to form a circulation connection.
[0086] In this way, during operation, the coolant in the cooling pipes absorbs heat from the photovoltaic panels and evaporates to form coolant vapor, which carries away the heat from the photovoltaic panels. The coolant vapor then enters the first heat exchanger at the bottom of the exhaust duct through the coolant vapor pipe, where it releases heat and condenses. The liquefied coolant, under its own weight, flows back through the coolant return pipe to the cooling pipes on the lower surface of each photovoltaic panel, forming a circulation. Therefore, it can quickly and efficiently cool the photovoltaic panels.
[0087] The evaporation temperature of the coolant is 45℃-55℃ (preferably 50℃). This temperature allows for better cooling of the photovoltaic panel through evaporation and maintains the stability of the photovoltaic panel temperature. Methanol is preferably used as the coolant, facilitating pressure control and adjustment of the evaporation temperature.
[0088] The photovoltaic panel 6 has a silicone oil layer 11 encapsulated on its lower surface, and the cooling pipe 10 is installed inside the silicone oil layer 11. This allows the silicone oil layer to better absorb heat from the photovoltaic panel, thus cooling it, and also to better transfer heat to the interior of the cooling pipe.
[0089] The photovoltaic panel cooling device also includes a liquid level holding tank 9, which is filled with coolant and connected to the cooling pipe assembly. The height of the coolant in the liquid level holding tank 9 is the same as the height of the highest point of the cooling pipe on the lower surface of each photovoltaic panel.
[0090] In this way, the liquid level holding tank can effectively ensure that the coolant in the cooling pipes on the lower surface of each photovoltaic panel is in a liquefied state, thus better guaranteeing the cooling effect on the photovoltaic panel.
[0091] The liquid level holding tank 9 is connected in series with the coolant return pipe 8. This allows the liquid level holding tank to collect and consolidate the returned coolant, making the liquid level holding effect more stable.
[0092] The photovoltaic panel cooling device also includes a pressure tank 12. An elastic membrane 13 is horizontally arranged inside the pressure tank 12. The lower space of the elastic membrane 13 is filled with coolant and connected to the cooling pipe assembly. The upper space of the elastic membrane is filled with pressure regulating gas. An air injection port 14 is also provided at the upper end of the pressure tank 12.
[0093] In this way, pressure-regulating gas can be injected or released into the upper space of the pressure tank through the injection port, thereby regulating the internal pressure of the pressure tank. This pressure can then be applied to the entire photovoltaic panel cooling system through the elastic diaphragm, achieving regulation of the cooling fluid pressure. This pressure change, in turn, controls and regulates the evaporation temperature of the coolant, thus enabling control over the cooling temperature and cooling effect of the photovoltaic panels. Nitrogen gas is used for pressure regulation during implementation, resulting in more stable and reliable performance.
[0094] In this system, the second heat exchanger 4 includes a heat exchange chamber 16 separated by two partitions 15 inside the air duct. Several air ducts 17 are vertically arranged inside the heat exchange chamber 16. The upper and lower ends of the air ducts 17 are sealed and fixed to the two partitions 15. An interface for the inflow of heat exchange liquid is provided on the side wall in the middle of the heat exchange chamber, and an interface for the outflow of heat exchange liquid is provided on the lower end of the heat exchange chamber.
[0095] This structure is simple and easy to implement. During operation, the high-temperature heat exchange fluid enters the heat exchange chamber from the upper interface, surrounding and heating the air inside the air duct. This rapidly heats the air inside the air duct and causes it to flow upwards, creating a downward suction effect. Therefore, it has the advantages of higher heat exchange efficiency and a better upward suction effect.
[0096] The heat exchange chamber 16 has multiple sets of ports for the inflow and outflow of heat exchange fluid, evenly arranged circumferentially. This facilitates connection with solar thermal devices.
[0097] The solar thermal device includes a frustoconical base 18 fixed to the outer periphery of the second heat exchanger. A mounting groove 19 is provided on the upper surface of the base 18. A heat exchange fluid jacket 20 is provided inside the bottom of the mounting groove (the heat exchange fluid jacket can be a circumferentially connected layered structure or a pipe structure corresponding only to the heat-receiving pipes). Above the heat exchange fluid jacket, the upper surface of the mounting groove also has multiple heat-receiving pipes 21 evenly distributed circumferentially. The upper end of the heat exchange fluid jacket 20 is connected to the lower end of the second heat exchanger 4, and the lower end of the heat exchange fluid jacket 20 is connected to the lower end of the heat-receiving pipes 21. The upper end of the heat-receiving pipes 21 is connected to the upper interface of the second heat exchanger 4. At the upper opening of the mounting groove 19, a fan-shaped threaded lens 22 is positioned directly above each heat-receiving pipe. The threaded lens 22 has an arc-shaped protrusion in the center facing the heat-receiving pipe, and threaded portions on both sides of the arc-shaped protrusion, with the threaded portions gradually converging upwards to form a fan shape.
[0098] In this way, the solar thermal collection device is directly installed outside the exhaust duct, avoiding heat loss over long distances. The device structure incorporates solar energy collection features around the exhaust duct, ensuring efficient solar energy collection to heat the second heat exchanger regardless of the sun's position in the morning or afternoon. During operation, a threaded lens concentrates the solar energy hitting the base onto the heating pipes, heating the heat exchange fluid inside. This causes the fluid to either vaporize (when the heat exchange fluid uses a phase-change heat transfer medium) or undergo significant thermal expansion (when the heat exchange fluid uses a pure liquid medium with a high expansion coefficient, such as silicone oil). The heated fluid then flows upwards into the second heat exchanger, heating the air inside the exhaust duct. The cooled (or condensed) heat exchange fluid returns to the heat exchange fluid jacket, thus achieving circulation. The threaded lens used, also known as a Fresnel lens, has a flat lower surface and an upper surface with an arc-shaped protrusion in the middle and threaded serrations on both sides. Both the arc-shaped protrusion and the threaded serrations refract and converge the incident light onto the heated tube. Its basic structure and principle are mature existing technologies. In this application, its structural shape has been adaptively adjusted to form a fan shape, cleverly converging sunlight to heat the circumferentially arranged heated tubes. Therefore, this device structure can effectively collect sunlight, causing the heat exchange fluid inside the heated tube to vaporize or expand due to heat and flow upwards into the second heat exchanger, achieving the circulation of the heat exchange fluid to heat the second heat exchanger. It features a simple structure and high and stable heat exchange efficiency.
[0099] The upper surface of the heating tube 21 is provided with a heat-absorbing coating 24, which can better absorb solar energy.
[0100] The upper surface of the threaded lens 22 is also provided with glass cover plates 23 at intervals. This can better protect the lens and ensure its reliable and stable light-gathering effect.
[0101] Among them, the heat exchange fluid jacket 20 is a pipe structure corresponding to the heat receiving pipe 21.
[0102] This not only simplifies the structure and makes installation easier, but also, when the heat exchange fluid is silicone oil, the greater pipe resistance better prevents the silicone oil that expands due to heat from flowing downwards inside the heated pipe.
[0103] The heat exchange chamber is also provided with an inner cylinder 25 at intervals. All the air pipes 17 are located inside the inner cylinder 25. The upper end of the inner cylinder 25 and the upper partition are provided with an opening at intervals. The lower end of the inner cylinder 25 is provided with an outlet facing the interface for the heat exchange liquid to flow out.
[0104] This design addresses the issue of uneven heat exchanger temperatures at the interfaces due to the different directions of sunlight in the morning and afternoon. The inner cylinder structure allows the heat exchanger entering from each direction to first converge and homogenize within the inner cylinder and the inner wall of the heat exchange chamber before entering the interior and the air in the air passage pipe from the top of the inner cylinder for heat exchange. This results in more even heating of the air passage pipe, more uniform upward airflow, and a more balanced and stable cooling effect on the first heat exchanger. Especially when using silicone oil as the heat exchanger, its lower fluidity compared to gas-phase heat exchangers further enhances the uniformity of the airflow.
[0105] The inner cylinder 25 has a top plate 26 at its upper end, through which the air duct passes. The top plate has evenly distributed perforations. This allows the high-temperature heat exchange fluid to enter the inner cylinder more evenly, achieving uniform heating and ensuring uniform airflow.
[0106] The top plate 26 is a downward-facing cone shape. This not only facilitates the heat exchange fluid flowing here to pass through the perforations on the top plate and enter the interior, but also better avoids the defect of uneven entry of high-temperature heat exchange fluid caused by different distances of the perforations from the edge, thus improving the uniformity of internal heating.
Claims
1. A passive cooling method for photovoltaic power generation, characterized in that, The heat from the photovoltaic panels is carried away by the evaporation of the coolant to the inlet below the air duct. The solar energy is then collected and used to heat the area above the air duct inlet, creating an upward airflow inside the air duct. This upward airflow carries away the heat from the photovoltaic panels that have been sent to the air duct inlet, thus cooling the photovoltaic panels. The heat from the photovoltaic panel is carried away to the inlet below the exhaust duct by a coolant with a relatively low boiling point; solar energy is collected by a heat exchange fluid with a relatively high boiling point and the area above the exhaust duct inlet is heated. The coolant evaporates and vaporizes at the photovoltaic panel and is sent to the inlet below the exhaust duct. It is then liquefied by air and released heat at the exhaust duct inlet before being sent back to the photovoltaic panel, thus achieving circulation. This method relies on a photovoltaic generator cooling system, which includes a photovoltaic panel cooling device with a pipe heat exchange structure, a solar thermal device, and a vertically arranged duct located above the photovoltaic panel cooling device and the solar thermal device. A vertically downward-opening air intake is connected to the lower inlet of the air intake. A first heat exchanger for heat exchange with the photovoltaic panel cooling device is arranged near the lower inlet of the air intake. A heat exchange air intake device is also arranged inside the air intake, which includes a second heat exchanger arranged at intervals above the first heat exchanger. The two interfaces of the photovoltaic panel cooling device and the first heat exchanger are connected and circulated, and the two interfaces of the solar thermal device and the second heat exchanger are also connected and circulated.
2. The passive cooling method for photovoltaic power generation according to claim 1, characterized in that, The ventilation ducts are installed and fixed on the hillside near the photovoltaic generator set; Rain caps are installed at intervals on the upper end of the air duct; The first heat exchanger is a coil heat exchanger.
3. The passive cooling method for photovoltaic power generation according to claim 1, characterized in that, The photovoltaic panel cooling device includes cooling pipes arranged in parallel or in a spiral pattern and fixed to the lower surface of each photovoltaic panel. The cooling pipes are filled with coolant. The upper end of each cooling pipe is connected to a coolant vapor pipe, and the lower end is connected to a coolant return pipe, so that the cooling pipes are connected in parallel to form a cooling pipe group. The coolant vapor pipe is connected to the interface at the upper end of the first heat exchanger, and the upper end of the coolant return pipe is connected to the interface at the lower end of the first heat exchanger to form a circulation connection.
4. The passive cooling method for photovoltaic power generation according to claim 3, characterized in that, The cooling pipes are directly attached and fixed to the lower surface of the photovoltaic panel; Alternatively, a layer of silicone oil may be encapsulated on the lower surface of the photovoltaic panel, and the cooling pipe may be installed within the silicone oil layer.
5. The passive cooling method for photovoltaic power generation according to claim 3, characterized in that, The photovoltaic panel cooling device also includes a liquid level holding tank, which is filled with coolant and connected to the cooling pipe assembly. The height of the coolant in the liquid level holding tank is the same as the height of the highest point of the cooling pipe on the lower surface of each photovoltaic panel. The liquid level holding tank and the cooling pipe assembly are connected in parallel; or the liquid level holding tank is connected in series on the coolant return pipe. The photovoltaic panel cooling device also includes a pressure tank. An elastic membrane is horizontally arranged inside the pressure tank. The space below the elastic membrane is filled with coolant and connected to the cooling pipe assembly. The space above the elastic membrane is filled with pressure regulating gas. An air injection port is also provided at the top of the pressure tank.
6. The passive cooling method for photovoltaic power generation according to claim 1, characterized in that, The second heat exchanger is a coil heat exchanger. A solar thermal collection device includes a heat collection tank filled with heat exchange fluid. Multiple solar heat pipes are connected side by side on one side of the heat collection tank to form a solar heat collection tube group. The evaporation end of the solar heat pipes extends outward and the condensation end is inserted into the heat collection tank and located in the heat exchange fluid. A heat exchange fluid steam pipe is connected to the upper end of the heat collection tank and connected to the interface above the second heat exchanger. A heat exchange fluid return pipe is connected to the middle of the side wall of the heat collection tank and connected to the interface below the second heat exchanger to form a circulation connection. The evaporation temperature of the heat exchange fluid is higher than that of the coolant.
7. The passive cooling method for photovoltaic power generation according to claim 1, characterized in that, The second heat exchanger includes a heat exchange chamber separated by two partitions inside the air duct. Several air pipes are vertically arranged inside the heat exchange chamber. The upper and lower ends of the air pipes are sealed and fixed through the two partitions. An interface for the inflow of heat exchange liquid is provided on the side wall in the middle of the heat exchange chamber, and an interface for the outflow of heat exchange liquid is provided on the lower end of the heat exchange chamber.
8. The passive cooling method for photovoltaic power generation according to claim 7, characterized in that, The heat exchange chamber has multiple sets of interfaces for the inflow of heat exchange fluid and interfaces for the outflow of heat exchange fluid, which are evenly arranged circumferentially.
9. The passive cooling method for photovoltaic power generation according to claim 8, characterized in that, The solar thermal collection device includes a frustoconical base fixed to the outer periphery of a second heat exchanger. A mounting groove is provided on the upper surface of the base. A heat exchange fluid jacket is located inside the bottom of the mounting groove. Above the heat exchange fluid jacket, the upper surface of the mounting groove bottom also has multiple heat-receiving pipes evenly distributed circumferentially. The upper end of the heat exchange fluid jacket is connected to the interface at the lower end of the second heat exchanger. The lower end of the heat exchange fluid jacket is connected to the lower end of the heat-receiving pipes. The upper end of the heat-receiving pipes is connected to the interface at the upper end of the second heat exchanger. At the upper opening of the mounting groove, a fan-shaped threaded lens is positioned directly above each heat-receiving pipe. The threaded lens has an arc-shaped protrusion in the center facing the heat-receiving pipe, and threaded portions on both sides of the arc-shaped protrusion, with the threaded portions gradually converging upwards to form a fan shape. The upper surface of the heat-receiving tube is coated with a heat-absorbing coating; The upper surface of the threaded lens is also provided with glass cover plates at intervals.
10. The passive cooling method for photovoltaic power generation according to claim 9, characterized in that, An inner cylinder is also provided at intervals inside the heat exchange chamber. All the air pipes are located inside the inner cylinder. An opening is provided between the upper end of the inner cylinder and the upper partition. An outlet is provided at the lower end of the inner cylinder, which is directly opposite the interface for the heat exchange liquid to flow out. The upper part of the inner cylinder is also equipped with a top plate for the pipes. The air duct passes through the top plate, and there are evenly distributed perforations on the top plate.