Centralized photovoltaic dc line water cooling system

Abstract

This application relates to a centralized photovoltaic DC line water-cooling system for cooling negative and positive photovoltaic cables. One end of the negative photovoltaic cable is connected to the negative terminal of the photovoltaic module, and the other end is connected to a string inverter or combiner box. One end of the positive photovoltaic cable is connected to the positive terminal of the photovoltaic module, and the other end is connected to the string inverter or combiner box. The water-cooling system includes cooling pipes filled with a cooling medium to form a cooling loop. The cooling pipes have a first port, a second port, and a third port. The negative photovoltaic cable is laid between the first and third ports of the cooling pipes, and the positive photovoltaic cable is laid between the second and third ports of the cooling pipes. The cooling medium cools the negative and positive photovoltaic cables by flowing through the cooling pipes. This achieves uniform cooling of the positive and negative photovoltaic cables throughout the entire process, limiting the increase in resistance of the cable conductors due to high temperatures and improving the overall power generation efficiency of the photovoltaic power station.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a centralized photovoltaic DC line water cooling system. Background Technology

[0002] Centralized photovoltaic (PV) power generation systems are the mainstream form of large-scale, centralized, and grid-connected PV power plants. They generate power by connecting numerous PV modules in series to form power strings, which are then combined through combiner boxes or directly connected to string inverters to convert direct current (DC) to alternating current (AC) before being connected to the grid. The positive and negative PV cables connecting the PV modules to the combiner box / inverter are the core power transmission components of the system. These cables are typically exposed to the outdoor air, facing severe environmental and operating conditions.

[0003] On the one hand, the insulation and sheathing materials of photovoltaic cables not only need to meet basic electrical performance requirements, but also need to withstand the aging effects of environmental factors such as outdoor high temperature, sunlight ultraviolet rays, and ozone. Therefore, traditional photovoltaic cables need to use expensive weather-resistant and flame-retardant insulation and sheathing materials, which significantly increases the construction cost of power stations. On the other hand, when the photovoltaic power station generates the maximum power, the line operating current reaches its peak value, and the conductor temperature rise caused by the current and the DC resistance of the cable conductor also reaches its maximum. Moreover, this period is often accompanied by the highest outdoor ambient temperature. High temperature will accelerate the performance degradation of cable insulation materials, reduce the safe operation performance of cables, and in severe cases, easily cause line arcing, short circuits, or even fire accidents.

[0004] Meanwhile, high temperatures significantly increase the DC resistance of cable conductors, drastically increasing power loss in the lines. Taking centralized photovoltaic power stations in plateau regions as an example, the surface temperature of photovoltaic cables laid out in the air can exceed 70°C during the peak power generation period at noon. The DC resistance of a 4-square-millimeter single-core photovoltaic cable will rise from 5.05 Ω / km at 20°C to 6.042 Ω / km at 70°C. For megawatt-level photovoltaic power stations, the increase in total cable resistance over thousands of kilometers will cause a continuous power loss of tens of kilowatts, significantly reducing the power station's power generation efficiency.

[0005] To address the high-temperature issue of photovoltaic cables, existing technologies often mitigate the problem by optimizing cable materials and increasing cable diameter. However, these methods do not fundamentally solve the temperature rise problem and further increase material and construction costs, resulting in limited energy-saving and efficiency-enhancing effects. Some cooling solutions attempt to use air cooling to lower the cable temperature, but this is greatly affected by outdoor wind speed and temperature, leading to unstable cooling effects. These solutions cannot achieve continuous and efficient cooling of the cable, nor can they solve the problem of cable aging due to ultraviolet radiation and ozone. Summary of the Invention

[0006] This application provides a centralized photovoltaic DC line water cooling system to solve the problems of poor cooling effect, rapid cable aging, and high power loss in existing centralized photovoltaic DC lines. This system, through the combination of a dedicated cooling pipe structure and a circulating cooling medium, achieves efficient and uniform cooling of the positive and negative photovoltaic cables, while simultaneously isolating the aging effects of ultraviolet radiation and ozone on the cables, reducing cable material costs, limiting the increase in conductor resistance, reducing line power loss, extending cable lifespan, and improving the overall power generation efficiency and operational safety of centralized photovoltaic power plants.

[0007] This application provides a centralized photovoltaic DC line water cooling system for cooling negative and positive photovoltaic cables. One end of the negative photovoltaic cable is connected to the negative terminal of the photovoltaic module, and the other end is connected to a string inverter or combiner box. One end of the positive photovoltaic cable is connected to the positive terminal of the photovoltaic module, and the other end is connected to a string inverter or combiner box.

[0008] The water cooling system includes a cooling pipe filled with a cooling medium to form a cooling circuit. The cooling pipe has a first port, a second port, and a third port. A negative photovoltaic cable is laid between the first port and the third port of the cooling pipe, and a positive photovoltaic cable is laid between the second port and the third port of the cooling pipe. The cooling medium cools the negative photovoltaic cable and the positive photovoltaic cable by flowing in the cooling pipe.

[0009] In one possible design, the negative photovoltaic cable enters the cooling pipe from the first port and extends out of the cooling pipe from the third port.

[0010] In one possible design, the negative photovoltaic cable has a ring-shaped conductive layer, which is laminated onto the surface of the cooling pipe between the first port and the third port.

[0011] In one possible design, the positive photovoltaic cable enters the cooling pipe from the second port and extends out of the cooling pipe from the third port.

[0012] In one possible design, the cooling medium includes deionized water, which has good insulation and heat exchange properties. This avoids short circuits caused by the conductivity of the cooling medium and can efficiently absorb the heat generated by the cable conductor, achieving rapid cooling.

[0013] In one possible design, the water cooling system also includes a chilled water tank and a heat exchanger. The chilled water tank is used to store deionized water and has an outlet, a first return outlet, and a second return outlet. The outlet and the first return outlet, as well as the outlet and the second return outlet, are connected by cooling pipes to form independent dual-path cooling cycles, which are adapted to the cable cooling needs of multiple sets of photovoltaic power generation strings. The heat exchanger is located in the chilled water tank and is connected to the compressor. The compressor provides cooling power to the heat exchanger, and the heat exchanger continuously cools the deionized water in the chilled water tank through heat exchange to ensure a constant temperature supply of the cooling medium.

[0014] In one possible design, the water cooling system also includes a circulation pump connected to the cooling pipes to provide circulation power for the cooling medium, maintain a stable flow of the cooling medium in the cooling pipes, ensure that fresh low-temperature cooling medium flows through each section of the cooling pipes, and ensure the continuity and uniformity of the cooling effect.

[0015] In one possible design, temperature sensors are respectively installed at the first return water inlet and the second return water inlet of the cooling pipe.

[0016] In one possible design, the water cooling system also includes a microbubble generator, which is installed on the connecting pipe between the circulating pump and the cooling pipe. The microbubble generator is used to introduce inert microbubbles with a diameter of 5-10 μm into the cooling medium. The inert microbubbles are preferably nitrogen microbubbles. After the microbubbles enter the heat dissipation channel with the cooling medium, they form a microbubble turbulent flow in the cooling medium, breaking the thermal boundary layer formed by the cooling medium on the inner wall of the cooling pipe and the outer surface of the photovoltaic cable. This allows the fresh, constant-temperature cooling medium to continuously contact the inner wall of the cooling pipe and the outer surface of the photovoltaic cable, improving the heat exchange efficiency by more than 30%, reducing the temperature rise required for the cooling medium to complete the heat exchange, and further ensuring the uniformity of cooling in each section of the cooling pipe.

[0017] The beneficial effects of this application are as follows: The centralized photovoltaic DC line water cooling system provided in this application directly exchanges heat with the cable through deionized water flowing in the cooling pipe, achieving uniform cooling of the positive and negative photovoltaic cables throughout the entire process. This effectively limits the increase in resistance of the cable conductor caused by high temperature and significantly improves the overall power generation efficiency of the photovoltaic power station.

[0018] When both the negative and positive photovoltaic cables are run inside the cooling pipe, the aging effects of outdoor ultraviolet rays and ozone are completely isolated. Furthermore, the continuous cooling of the cooling medium keeps the cables operating at low temperatures. Therefore, the cables do not need to use expensive weather-resistant and flame-retardant insulation sheath materials; ordinary thermoplastic polyethylene insulation is sufficient to meet the requirements, significantly reducing the cable procurement and construction costs of photovoltaic power plants. For the exposed cable connection parts outside the cooling pipe, only heat-shrink tubing is needed to solve the aging problem, resulting in low protection costs.

[0019] When the negative photovoltaic cable uses a ring-shaped conductive layer, which is laminated on the surface of the cooling pipe between the first and third ports, and the positive photovoltaic cable is run through the cooling pipe, in addition to isolating the positive photovoltaic cable from the environmental aging effects of outdoor ultraviolet rays and ozone, the continuous cooling of the cooling medium keeps the cable working at a low temperature. Furthermore, because the negative photovoltaic cable uses a ring-shaped conductive layer, the conductive heat dissipation area is effectively increased. With the support of the continuous cooling of the cooling medium, the negative photovoltaic cable can always work at a low temperature.

[0020] The dual-outlet design of the cooling water tank enables simultaneous cooling of multiple sets of generator string cables. The cooperation between the circulating pump and the heat exchanger ensures constant temperature and stable circulation of the cooling medium. The overall system structure is highly modular and can be flexibly deployed according to the installed capacity of the centralized photovoltaic power station. It is suitable for photovoltaic power stations in different geographical environments such as plateaus, deserts, and plains, and is especially suitable for photovoltaic power station conditions with high altitude and poor heat dissipation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of a centralized photovoltaic DC line water-cooling system provided in one embodiment of this application; Figure 2 A schematic diagram of the structure of a centralized photovoltaic DC line water-cooling system provided in another embodiment of this application; Figure 3 A schematic diagram of the structure of the cooling pipe located between the first port and the third port of a centralized photovoltaic DC line water cooling system provided in another embodiment of this application; Figure label: 1. Photovoltaic module; 2. Negative photovoltaic cable; 21. Conductive layer; 3. Positive photovoltaic cable; 4. String inverter; 5. Cooling pipe; 501. First port; 502. Second port; 503. Third port; 6. Cooling water tank; 601. Outlet; 602. First return port; 603. Second return port; 7. Heat exchanger; 8. Compressor; 9. Circulating pump; 12. Buffer layer; 13. Microbubble generator; 14. Cooling medium. Detailed Implementation

[0023] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The following is combined Figures 1-3 This describes the centralized photovoltaic DC line water cooling system provided in the embodiments of this application.

[0025] This embodiment provides a centralized photovoltaic DC line water-cooling system applied to a 100 MW-level plateau centralized photovoltaic power station. It is used to cool the negative photovoltaic cable 2 and positive photovoltaic cable 3 between the photovoltaic module 1 and the string inverter 4. One end of the negative photovoltaic cable 2 is connected to the negative terminal of the photovoltaic module 1 via an MC4 or other dedicated connector, and the other end is connected to the negative terminal of the string inverter 4 via an MC4 or other dedicated connector. One end of the positive photovoltaic cable 3 is connected to the positive terminal of the photovoltaic module 1 via an MC4 or other dedicated connector, and the other end is connected to the positive terminal of the string inverter 4 via an MC4 or other dedicated connector. The photovoltaic modules 1 are connected in series to form a power generation string, and every ten power generation strings constitute a cooling unit, which is adapted to one water-cooling system.

[0026] The water cooling system includes a cooling pipe 5, which is made of weather-resistant polyethylene and has a first port 501, a second port 502 and a third port 503.

[0027] Reference Figure 1 As shown, in one embodiment, the negative photovoltaic cable 2 enters the cooling pipe 5 from the first port 501 and exits from the third port 503 to connect with the string inverter 4; the positive photovoltaic cable 3 enters the cooling pipe 5 from the second port 502 and exits from the third port 503 to connect with the string inverter 4. Both the positive and negative photovoltaic cables pass through the cooling pipe 5.

[0028] Because centralized photovoltaic power plants generally use a negative grounding wiring method for their DC side systems, in another embodiment, the positive photovoltaic cable passes through the cooling pipe 5. The outer ring wall of the cooling pipe 5 is fitted with a buffer layer 12, which is a microporous structure layer made of microporous insulation cotton with a thickness of 2cm. This reduces the heat exchange between the deionized water in the heat dissipation channel 508 and the outdoor environment at high altitudes, and also buffers the physical damage to the cooling pipe 5 caused by strong winds and sand and gravel impacts in high-altitude areas.

[0029] The negative electrode photovoltaic cable is designed as a ring-shaped conductive layer. A buffer layer 12 is fitted over the conductive layer; this buffer layer 12 is a microporous structure layer made of microporous insulation cotton. For details, refer to... Figure 3As shown, the conductive layer is laminated onto the surface of the cooling pipe between the first and third ports, resulting in a simple process and low manufacturing cost. Furthermore, the ring-shaped conductive layer in the negative photovoltaic cable effectively increases the conductive heat dissipation area. Crucially, with the continuous cooling of the cooling medium, the negative photovoltaic cable can always operate under low-temperature conditions.

[0030] The water cooling system also includes a chilled water tank 6, a heat exchanger 7, a compressor 8, a circulating pump 9, and a microbubble generator 13. The chilled water tank 6 is made of stainless steel and has a volume of 500L. It is used to store deionized water. The top of the tank has a first return water port 602 and a second return water port 603, and the lower part of the side wall has a water outlet 601. The first return water port 602 and the second return water port 603 are connected to the water outlet 601 through cooling pipes 5, forming a dual-circuit cooling cycle, which provides cooling medium for the cables of the five sets of generator strings. The heat exchanger 7 is a copper tube heat exchanger, which is buried at the bottom of the chilled water tank 6 and connected to the compressor 8 through copper pipes. The compressor 8 is a 3P variable frequency compressor, which provides cooling power to the heat exchanger 7 and controls the temperature of the deionized water in the chilled water tank 6 at 22℃.

[0031] Temperature sensors are installed at the first and second return water inlets of the cooling pipe to monitor the temperature of the deionized water at the first and second return water inlets of the cooling pipe.

[0032] The circulating pump 9 is a micro variable frequency circulating pump, which is installed on the connecting pipe between the outlet 601 of the cooling water tank 6 and the cooling pipe 5. It provides circulation power for the deionized water and controls the flow velocity of the deionized water in the cooling pipe to be 0.8 m / s, ensuring that low-temperature deionized water flows through each section of the cooling pipe 5. The microbubble generator 13 is installed on the connecting pipe between the circulating pump 9 and the cooling pipe 5 and is connected to the cooling pipe. It introduces nitrogen microbubbles with a diameter of 8 μm into the deionized water. After the nitrogen microbubbles enter the cooling pipe with the deionized water, they form a microbubble turbulent flow, breaking the thermal boundary layer formed by the deionized water on the inner wall of the cooling pipe and the outer surface of the photovoltaic cable.

[0033] The working process of the centralized photovoltaic DC line water cooling system in this application is as follows: The compressor 8 starts to provide cooling power to the heat exchanger 7. The heat exchanger 7 performs heat exchange to cool the deionized water in the cooling water tank 6, and stabilizes the temperature of the deionized water at 22°C, providing a constant temperature cooling medium for the cooling cycle. When the circulation pump 9 starts, it delivers the low-temperature deionized water in the cooling water tank 6 from the outlet 601 to the cooling pipe 5. The deionized water flows along the cooling pipe 5 to form a closed cooling cycle. The microbubble generator 13 introduces nitrogen microbubbles into the flowing deionized water. The microbubbles form a turbulent flow inside the cooling pipe, breaking the thermal boundary layer of the deionized water on the inner wall of the cooling pipe and the outer surface of the photovoltaic cable, allowing the low-temperature deionized water to continuously and fully contact the inner wall of the cooling pipe and the outer surface of the photovoltaic cable. When the photovoltaic cable is working, it generates heat, which is transferred to the deionized water in the cooling pipe through the outer surface of the cable. After absorbing heat, the temperature of the deionized water rises slowly and flows back to the cooling water tank 6 along the heat dissipation channel 508 to complete the heat exchange and form a cycle. The buffer layer 12 provides thermal insulation and physical protection for the cooling pipe 5, reducing the impact of the external environment on the cooling system. The heated deionized water returned to the cooling water tank 6 is cooled down to 22°C again by the heat exchanger 7, and then re-enters the cooling pipe 5 under the action of the circulating pump 9, so as to achieve continuous and uniform cooling of the photovoltaic cable.

[0034] In this embodiment, due to poor air heat dissipation conditions at high altitudes, with an outdoor ambient temperature of 38°C, the surface temperature of the photovoltaic cables deployed in the air may exceed 70°C at midday when power generation is at its peak. However, by adopting the water-cooling system of this application, the heat generated by the current in the cables during peak power generation is forcibly cooled by circulating water, and the surface temperature of the photovoltaic cables is stably controlled at 28°C. Therefore, the increase in conductor resistance is limited, and the increase in DC resistance of the cable conductor is limited to within 5%. A single cooling unit can reduce power loss by 15.46kW per day and increase power generation by approximately 140 kWh. The entire 100-megawatt photovoltaic power station can increase power generation by approximately 1400 kWh per day, significantly improving power generation efficiency.

[0035] Taking a 4 square millimeter single-core photovoltaic cable as an example, its typical DC resistance is 5.05 Ω / km at 20℃, 5.355 Ω / km at 35℃, and 6.042 Ω / km at 70℃. For a 100 MW photovoltaic power station, approximately 1000 km of photovoltaic cable is needed. The total line resistance is 5355 Ω at 35℃, but only 6042 Ω at 70℃, an increase of 687 Ω compared to 35℃. Since photovoltaic modules typically operate at currents above 15A, this extra 687 Ω of line resistance results in a power loss of up to 154.6 kW. Therefore, using forced cooling with circulating water can increase daily power generation by approximately 1400 kWh.

[0036] Furthermore, when the current heats the conductor, the forced cooling by the circulating cooling water significantly reduces the conductor's operating temperature compared to when it was exposed to air. Moreover, the conductor is no longer affected by ultraviolet radiation and ozone within the pipes. Therefore, photovoltaic cables operating under these conditions do not require expensive weather-resistant and flame-retardant insulation sheath materials; ordinary thermoplastic polyethylene insulation suffices. Using ordinary thermoplastic polyethylene insulation reduces material costs by over 60% compared to traditional weather-resistant and flame-retardant photovoltaic cables, and extends cable lifespan from the traditional 15 years to over 25 years. As for the exposed wiring section within the pipes, due to conductor heat conduction, the temperature of the exposed short cable will not be significantly higher. Ultraviolet radiation and ozone issues can be addressed by placing a protective sleeve (such as the most common heat-shrink tubing) over the cable.

[0037] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0040] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0041] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A centralized photovoltaic DC line water cooling system, characterized in that, This system is used to cool the negative and positive photovoltaic cables. One end of the negative photovoltaic cable is connected to the negative terminal of the photovoltaic module, and the other end is connected to a string inverter or combiner box. One end of the positive photovoltaic cable is connected to the positive terminal of the photovoltaic module, and the other end is connected to a string inverter or combiner box. The water cooling system includes a cooling pipe filled with a cooling medium to form a cooling circuit. The cooling pipe has a first port, a second port, and a third port. The negative photovoltaic cable is laid between the first port and the third port of the cooling pipe, and the positive photovoltaic cable is laid between the second port and the third port of the cooling pipe. The cooling medium cools the negative and positive photovoltaic cables by flowing in the cooling pipe.

2. The centralized photovoltaic DC line water cooling system according to claim 1, wherein, The negative photovoltaic cable enters the cooling pipe from the first port and extends out of the cooling pipe from the third port.

3. The centralized photovoltaic DC line water cooling system of claim 1, wherein, The negative photovoltaic cable has a ring-shaped conductive layer, which is laminated onto the surface of the cooling pipe between the first port and the third port.

4. The centralized photovoltaic DC line water cooling system according to claim 2 or 3, characterized in that, The positive photovoltaic cable enters the cooling pipe from the second port and extends out of the cooling pipe from the third port.

5. The centralized photovoltaic DC line water cooling system of claim 4, wherein, The cooling medium includes deionized water.

6. The centralized photovoltaic DC line water cooling system of claim 5, wherein, The water cooling system also includes: A cooling water tank for storing deionized water has an outlet, a first return water inlet, and a second return water inlet. The outlet and the first return water inlet, and the outlet and the second return water inlet are respectively connected by cooling pipes. A heat exchanger, located in the cooling water tank and connected to the compressor, is used to cool the deionized water.

7. The centralized photovoltaic DC line water cooling system of claim 6, wherein, It also includes a circulation pump, which is connected to the cooling pipe and is used to maintain the circulation of the cooling medium in the cooling pipe.

8. The centralized photovoltaic DC line water cooling system of claim 7, wherein, Temperature sensors are respectively installed at the first return water inlet and the second return water inlet of the cooling pipe.

9. The centralized photovoltaic DC line water cooling system of claim 8, wherein, It also includes a microbubble generator, which is installed on the connecting pipe between the circulating pump and the cooling pipe, and is used to introduce inert microbubbles with a diameter of 5-10 μm into the cooling medium.

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