Photovoltaic photo-thermal generation, storage and supply integrated system and control method

Abstract

The invention relates to the technical field of photovoltaic systems, in particular to a photovoltaic and photo-thermal generation, storage and supply integrated system and a control method, and the system comprises an electric system, a power output end of a photovoltaic panel is connected to a user load distribution box through an inverter, and a redundant electric energy output end of the inverter is connected to a lithium ion battery pack through a bidirectional converter; the output end of the power distribution controller is connected back to the user load power distribution box; according to the heat system, a heat medium outlet of the PVT assembly is connected to an evaporator inlet of an absorption heat pump through a first plate heat exchanger; according to the auxiliary heat source unit, a water outlet of the geothermal well and a water outlet of the air source heat pump are connected in parallel through a first three-way adjusting valve, and the geothermal well and the air source heat pump are jointly connected into a water inlet header pipe of the user heating pipe network. Through the structural design, the energy comprehensive utilization efficiency can be improved, the energy supply stability and reliability can be improved, and the equipment operation and maintenance cost can be reduced.

Description

Technical Field

[0001] This application generally relates to the technical field of photovoltaic systems, and particularly to a photovoltaic-thermal integrated production, storage, and supply system and its control method. Background Art

[0002] Traditional photovoltaic power generation systems only focus on electricity production, without fully exploring the potential of solar full-spectrum utilization, resulting in a large amount of heat loss and an overall energy efficiency of less than 40%. In existing photovoltaic-thermal complementary systems, most adopt a separate design of independent photovoltaic panels and collectors, which have problems such as equipment redundancy and complex thermal management. Moreover, there is a lack of effective control means for the power generation efficiency attenuation caused by the temperature rise of photovoltaic modules. In terms of the coordination of energy storage and power supply, lithium battery energy storage systems often operate independently, with high energy losses during the charging and discharging processes and insufficient real-time matching ability with the power grid and user loads; The heating system generally relies on a single heat source (such as a gas boiler or an air source heat pump), making it difficult to cope with extreme weather or fluctuations in day-night temperature differences. The technology of cross-seasonal waste heat storage is not yet mature, resulting in the inability to efficiently recover and utilize solar waste heat during the non-heating season.

[0003] In addition, the multi-heat source cooperative control strategies for geothermal energy and air source heat pumps in the existing technology are relatively crude, lacking a dynamic regulation mechanism based on temperature-pressure feedback, which easily causes pipe network hydraulic imbalance and energy waste.

[0004] Therefore, there is an urgent need for an integrated system that integrates photovoltaic-thermal production and storage, multi-energy complementary regulation, and cross-seasonal heat storage to break through the bottleneck of single energy utilization and improve the clean energy consumption rate and system operation economy. Summary of the Invention

[0005] To address the problem of low solar full-spectrum utilization rate caused by single electric energy conversion in traditional photovoltaic systems, this application provides a photovoltaic-thermal integrated production, storage, and supply system, which realizes multi-energy complementarity and high-efficiency full-spectrum utilization, dynamic energy storage and precise matching of power supply and demand, cross-seasonal heat storage and intelligent allocation of multiple heat sources.

[0006] According to one aspect of this application, a photovoltaic-thermal integrated production, storage, and supply system is provided. The integrated system includes: Electrical system: The power output end of the photovoltaic panel is connected to the user load distribution box through an inverter, and the redundant power output end of the inverter is connected to the lithium-ion battery pack through a bi-directional converter; The discharge end of the lithium-ion battery pack is connected to the power distribution controller through a DC bus, and the output end of the power distribution controller is connected back to the user load distribution box; Thermal system: The heat medium outlet of the PVT component is connected to the inlet of the evaporator of the absorption heat pump through a first plate heat exchanger, and the outlet of the condenser of the absorption heat pump is connected to the input end of the phase change heat storage tank through a second shell-and-tube heat exchanger; The output end of the phase change heat storage tank is connected to the water inlet main pipe of the user's heating pipe network through a variable frequency circulating pump; Auxiliary heat source unit: The water outlet of the geothermal well is connected in parallel with the water outlet of the air source heat pump through a first three-way regulating valve, and both are jointly connected to the water inlet main pipe of the user's heating pipe network.

[0007] In some embodiments, the phase change heat storage tank is a stratified domestic hot water tank. The outlet of the condenser of the absorption heat pump is connected to the inlet of the spiral coil at the bottom of the stratified domestic hot water tank through a second shell-and-tube heat exchanger. The hot water outlet at the top of the stratified domestic hot water tank is connected to the user's domestic hot water pipe through a thermostatic mixing valve.

[0008] In some embodiments, it further includes an inter-seasonal heat storage unit, and the inter-seasonal heat storage unit includes a geothermal well and a ground source heat pump; The heat medium outlet branch of the PVT assembly is connected to the heat injection port of the geothermal well through a third plate heat exchanger. The input end of the ground source heat pump is connected to the geothermal well through a U-shaped buried pipe. The output end of the ground source heat pump is connected to the water inlet main pipe of the user's heating pipe network through a fourth shell-and-tube heat exchanger. In some embodiments, the electrical system further includes a proton exchange membrane electrolyzer and a hydrogen storage bottle group; The redundant power output end of the bidirectional inverter is connected to the DC input end of the proton exchange membrane electrolyzer through a rectifier. The hydrogen outlet of the proton exchange membrane electrolyzer is connected to the inlet valve of the hydrogen storage bottle group through a high-pressure compressor; The gas outlet end of the hydrogen storage bottle group is connected to the anode inlet of the hydrogen fuel cell through a pressure reducing valve. The power output end of the hydrogen fuel cell is connected to the DC bus of the power distribution controller, and its cooling water outlet is connected in parallel to the input end of the phase change heat storage tank or the water inlet main pipe of the user's heating pipe network through a fifth plate heat exchanger.

[0009] In some embodiments, the cooling water outlet of the hydrogen fuel cell and the heat medium outlet of the PVT assembly converge through a second three-way regulating valve and are jointly connected to the heat injection port of the geothermal well of the inter-seasonal heat storage unit; A temperature compensation valve is provided between the output end of the ground source heat pump and the water inlet main pipe of the user's heating pipe network through a fourth shell-and-tube heat exchanger.

[0010] In some embodiments, the PVT assembly includes: a mounting housing, the mounting housing is a rectangular frame structure, both ends of the mounting housing are open, one end is provided with the photovoltaic panel, and the other end is provided with a sealing cover plate; It further includes: a heating box, which is arranged inside the mounting housing. One side of the heating box is provided with a heat conducting plate, and the heat conducting plate is arranged close to the photovoltaic panel; A plurality of serpentine conduits are arranged inside the heating box, and each serpentine conduit is respectively arranged at each top corner inside the heating box; A high-temperature chamber is also provided inside the heating box. The outer wall of the high-temperature chamber is slidably connected to the inner wall of the heat conduction plate. A hydraulic rod is provided in the sliding direction of the high-temperature chamber. One end of the hydraulic rod is connected to the outer wall of the high-temperature chamber, and the other end is connected to the inner wall of the heating box; One end of each serpentine conduit communicates with the high-temperature chamber through a corrugated pipe, and the other end passes through the outer wall of the heating box and is connected to a water supply pipe; A plurality of water supply pipes are provided. The plurality of water supply pipes are respectively connected to one end of each serpentine conduit away from the high-temperature chamber. Each water supply pipe is respectively arranged in the space between the high-temperature chamber and the heating box, and one end of each water supply pipe away from the serpentine conduit passes through the installation shell; An L-shaped pipe is provided at one end of the high-temperature chamber away from the heat conduction plate. One end of the L-shaped pipe communicates with the inner wall of the high-temperature chamber, and the other end passes through the heating box and the installation shell. The L-shaped pipe is slidably sealed with the heating box and the shell.

[0011] In some embodiments, slide rails are provided on the surface of the heat conduction plate, and a chute is provided on the side of the high-temperature chamber close to the heat conduction plate. The chute is slidably matched with the slide rails; Oil guide pipes are arranged at intervals inside the high-temperature chamber. Both ends of the oil guide pipes communicate with the heating box. The oil guide pipes are arranged parallel to the slide rails, and heat-conducting oil is filled in the heating box; A number of water guide plates are provided inside the high-temperature chamber. Each water guide plate is distributed in an S shape inside the heating box.

[0012] A control method for an integrated system, wherein the power distribution controller switches the charge and discharge modes of the lithium-ion battery pack according to the user load demand, and realizes the grid-connected or off-grid control of photovoltaic power and the power grid through the bidirectional converter; The variable-frequency circulating pump adjusts the flow according to the signal of the heating network pressure sensor, and the first three-way regulating valve switches the water supply ratio of the medium-deep geothermal energy and the air source heat pump according to the signal of the inlet main pipe temperature sensor; In the transitional season, the waste heat of the PVT module and the waste heat of the cooling water of the hydrogen fuel cell are injected into the geothermal well through the third plate heat exchanger. In winter, the heat stored in the geothermal well is extracted by the ground source heat pump and input into the heating network.

[0013] The embodiments of the present application have the following advantages.

[0014] Improved comprehensive energy utilization efficiency: The PVT module generates electricity and heat simultaneously, with a comprehensive efficiency of 80% (the power generation efficiency of traditional photovoltaic panels is only 15-20%). The overall energy utilization rate of the system is increased to more than 85% (the split system ≤ 60%); The heat storage density of the phase change heat storage tank reaches 250 kWh / m³ (the heat storage of a conventional water tank ≤ 60 kWh / m³). Combined with the precise temperature control of the variable-frequency pump (the water temperature fluctuation < ±1°C), the heat supplement energy consumption is reduced by more than 30%; Improve the stability and reliability of energy supply: Electrical system: Three-way power supply of photovoltaic + lithium battery + power grid, seamlessly switches to off-grid mode during power outages (switching time < 100 ms) to ensure the continuous operation of critical loads; Thermal system: PVT heat generation + phase change heat storage + dual heat source assistance, can still maintain the heating water temperature ≥ 45°C under continuous rainy weather (72-hour endurance); The medium-deep geothermal well serves as a cross-seasonal heat storage body (heat loss < 3% / month), and can stably output 55°C hot water in winter, avoiding the efficiency attenuation problem of air source heat pumps at extremely low temperatures; Reduce operation and maintenance costs: The lithium battery has a cycle life ≥ 6000 times (DOD = 80%), a charge and discharge efficiency ≥ 98%, and the full life cycle cost is reduced by 40% compared to lead-acid batteries.

[0015] The combined operation of the geothermal well and the air source heat pump reduces the auxiliary heating energy consumption by 50% (compared with the single electric boiler heat supplement scheme); Carbon emission reduction indicators: The system can annually replace 15 tons of standard coal per 100㎡ of collector area, reducing CO2 emissions by 35 tons (calculated based on photovoltaic replacing coal-fired power generation); The PVT module serves as both a power generation and heat generation unit at the same time. Through the absorption heat pump for temperature increase, it realizes the efficient utilization of low-grade heat energy. Based on the dynamic switching logic of real-time sensor data (such as the threshold control of the first three-way valve and the pressure feedback of the variable frequency pump), it ensures the stability of energy supply. The geothermal well and the phase change heat storage tank form a "short-term - long-term" dual-stage heat storage system to solve the intermittency problem of renewable energy.

[0016] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will become apparent from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the written specification and the accompanying drawings.

[0017] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments. Description of the Drawings

[0018] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the drawings: Figure 1 Shows a schematic structural diagram of an integrated system according to an embodiment of the present application.

[0019] Figure 2 Shows a schematic structural diagram of an electrical system according to an embodiment of the present application.

[0020] Figure 3 Schematic diagram showing the principle of an integrated system according to an embodiment of the present application.

[0021] Figure 4 Schematic diagram showing the installation of a photovoltaic panel according to an embodiment of the present application.

[0022] Figure 5 Schematic diagram showing the installation of a heating box according to an embodiment of the present application.

[0023] Figure 6 Schematic diagram showing the installation of a high-temperature storage bin according to an embodiment of the present application.

[0024] Figure 7 Schematic diagram showing the installation of a water guide plate according to an embodiment of the present application.

[0025] Reference numerals 1 - Photovoltaic panel; 3 - User load distribution box; 4 - Bidirectional inverter; 5 - Lithium-ion battery pack; 6 - Power distribution controller; 7 - PVT module; 8 - First plate heat exchanger; 9 - Absorption heat pump; 10 - Second shell-and-tube heat exchanger; 11 - Phase change heat storage tank; 12 - Variable frequency circulation pump; 13 - User heating pipeline network; 14 - Geothermal well; 15 - First three-way regulating valve; 16 - Air source heat pump; 17 - Third plate heat exchanger; 18 - Ground source heat pump; 19 - U-shaped buried pipe; 20 - Fourth shell-and-tube heat exchanger; 21 - Installation housing; 22 - Sealing cover plate; 23 - Heating box; 24 - Heat conducting plate; 25 - Serpentine conduit; 26 - High-temperature storage bin; 27 - Hydraulic rod; 28 - Bellows; 29 - Water supply pipe; 30 - L-shaped pipe; 31 - Slide rail; 32 - Slide groove; 33 - Oil guide pipe; 34 - Water guide plate. Detailed implementation manners

[0026] In order to make the objectives, solutions and advantages of the technical solutions of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments of the present application. Unless otherwise specified, the terms used herein have the ordinary meanings in the art. The same reference numerals in the drawings represent the same components.

[0027] In the description of the present application, it should be noted that, unless otherwise clearly defined and limited, the terms "installed", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0028] As described above, in a traditional photovoltaic system, due to the instability of solar energy, the cold, heat, and electricity loads of users are unstable.

[0029] To at least partially solve one or more of the above problems and other potential problems, exemplary embodiments of the present application provide a photovoltaic-thermal integrated production, storage, and supply system, which includes: Electrical system: The power output terminal of the photovoltaic panel 1 is connected to the user load distribution box 3 through an inverter, and the redundant power output terminal of the inverter is connected to the lithium-ion battery pack 5 through a bi-directional converter 4; The discharge terminal of the lithium-ion battery pack 5 is connected to the power distribution controller 6 through a DC bus, and the output terminal of the power distribution controller 6 is connected back to the user load distribution box 3; Thermal system: The heat medium outlet of the PVT module 7 is connected to the evaporator inlet of the absorption heat pump 9 through a first plate heat exchanger 8, and the condenser outlet of the absorption heat pump 9 is connected to the input end of the phase change heat storage tank 11 through a second shell-and-tube heat exchanger 10; The output terminal of the phase change heat storage tank 11 is connected to the water inlet main pipe of the user heating pipe network 13 through a variable frequency circulating pump 12; Auxiliary heat source unit: The water outlet of the geothermal well 14 is connected in parallel with the water outlet of the air source heat pump 16 through a first three-way regulating valve 15, and both are connected to the water inlet main pipe of the user heating pipe network 13.

[0030] In the above embodiment, the photovoltaic panel 1 converts solar energy into direct current, which is converted into alternating current through an inverter and preferentially supplied to the user load distribution box 3. When the load demand is less than the photovoltaic power generation, the inverter stores the remaining power in the lithium-ion battery pack 5 in a constant voltage and constant current mode (voltage range: 48 - 60V, maximum charging current ≤ 1C) through the bi-directional converter 4. The power distribution controller 6 monitors the load power in real time (sampling period ≤ 1 second). When the load demand suddenly increases (such as starting a high-power device), the lithium-ion battery pack 5 discharges at a constant power through the DC bus (response time < 100ms) and supplies power together with the photovoltaic power; In the grid-connected mode, the bi-directional converter 4 can feed power to the grid; in the off-grid mode, the lithium battery and the photovoltaic form an independent microgrid (voltage fluctuation ≤ ±5%); After the PVT module 7 absorbs solar radiation, the temperature of its heat medium (such as ethylene glycol solution) rises to 55 - 65°C, and the heat is transferred to the evaporator of the absorption heat pump 9 through the first plate heat exchanger 8 (heat transfer efficiency ≥ 85%). The absorption heat pump 9 boosts the low-temperature heat energy to 75 - 85°C through the evaporation - condensation cycle, and outputs high-temperature hot water to the second shell-and-tube heat exchanger 10 through the condenser. The second shell-and-tube heat exchanger 10 stores the heat in the phase change heat storage tank 11 (the phase change material is paraffin-based composite, melting point 60 ± 2°C, latent heat ≥ 180 kJ / kg). The phase change heat storage tank 11 supplies water to the user heating pipe network 13 through a variable-frequency circulating pump 12 (power adjustment range 10 - 100%), and the pump speed is feedback-controlled by the pipe network pressure sensor (pressure set value 0.2 - 0.5 MPa, control accuracy ± 5 kPa). When the temperature of the heat storage tank is lower than the set value (such as 50°C), the auxiliary heat source is automatically started for heat compensation; The medium-deep geothermal well 14 (constant temperature 55 - 60°C) is connected in parallel with the air source heat pump 16 (output temperature 50 - 60°C, COP ≥ 3.0 when the ambient temperature > -10°C) through the first three-way regulating valve 15; The first three-way valve dynamically adjusts according to the signal of the total water inlet temperature sensor: When the total water temperature ≥ 45°C, the geothermal well 14 is preferentially used for water supply (energy-saving mode); When the water temperature < 45°C or the flow rate of the geothermal well 14 is insufficient, it is switched to the air source heat pump 16 (heat compensation mode); Improvement of comprehensive energy utilization efficiency: The PVT module 7 generates electricity and heat simultaneously, with a comprehensive efficiency of 80% (the traditional photovoltaic panel 1 only has a power generation efficiency of 15 - 20%), and the overall energy utilization rate of the system is increased to more than 85% (the split system ≤ 60%); The heat storage density of the phase change heat storage tank 11 reaches 250 kWh / m³ (the heat storage of the conventional water tank ≤ 60 kWh / m³). Combined with the precise temperature control of the variable-frequency pump (water temperature fluctuation < ± 1°C), the heat compensation energy consumption is reduced by more than 30%; Improvement of energy supply stability and reliability: Electrical system: Three-way power supply of photovoltaic + lithium battery + power grid, seamlessly switching to off-grid mode during power outages (switching time < 100 ms) to ensure the continuous operation of critical loads; Thermal system: PVT heat generation + phase change heat storage + dual heat source assistance, and the heating water temperature can still be maintained ≥ 45°C under continuous rainy weather (72-hour endurance); The medium-deep geothermal well 14 serves as a cross-seasonal heat storage body (heat loss < 3% / month), and can stably output 55°C hot water in winter, avoiding the problem of efficiency decay of the air source heat pump 16 at extremely low temperatures; Reduction of operation and maintenance costs: The lithium battery has a cycle life of ≥ 6000 times (DOD = 80%), a charge-discharge efficiency of ≥ 98%, and the overall life cycle cost is reduced by 40% compared with lead-acid batteries.

[0031] The geothermal well 14 and the air source heat pump 16 operate in combination, reducing the auxiliary heating energy consumption by 50% (compared with the single electric boiler heat supplement scheme); Carbon emission reduction targets: The system can annually replace 15 tons of standard coal per 100㎡ of heat collection area, reducing CO2 emissions by 35 tons (calculated based on photovoltaic replacing coal-fired power generation); The PVT module 7 serves as both a power generation and heat production unit. Through the absorption heat pump 9 for temperature increase, efficient utilization of low-grade heat energy is achieved. Based on the dynamic switching logic of real-time sensor data (such as the threshold control of the first three-way valve and the pressure feedback of the variable frequency pump), the energy supply stability is ensured. The geothermal well 14 and the phase change heat storage tank 11 form a "short-term - long-term" dual-stage heat storage system to solve the intermittency problem of renewable energy.

[0032] Please refer to Figures 1-7 , in some embodiments, the phase change heat storage tank 11 is a stratified domestic hot water tank. The outlet of the condenser of the absorption heat pump 9 is connected to the inlet of the spiral coil at the bottom of the stratified domestic hot water tank through the second shell-and-tube heat exchanger 10. The hot water outlet at the top of the stratified domestic hot water tank is connected to the user's domestic hot water pipeline through a thermostatic mixing valve.

[0033] In the above embodiments, the high-temperature hot water (75 - 85°C) output by the absorption heat pump 9 transfers heat to the spiral coil (coil outer diameter 40mm, material is copper-nickel alloy) through the second shell-and-tube heat exchanger 10. The spiral coil is located at the bottom of the tank and quickly heats the bottom water body through the turbulent flow effect. The cold and hot water form a vertical temperature gradient due to density difference (60 - 70°C at the bottom → 45 - 50°C at the top), realizing natural stratified heat storage; The hot water outlet at the top of the tank is mixed with the cold water pipeline through a thermostatic mixing valve (with a built-in PID controller, temperature setting error ±0.5°C), and the outlet water temperature is adjusted to 45 ± 1°C in real time. When the water temperature at the top is lower than the set value, the mixing valve reduces the cold water mixing ratio (adjustment period < 1 second) to give priority to ensuring the stability of domestic hot water; The bottom of the tank is filled with spherical phase change materials (such as sodium acetate trihydrate, melting point 58°C, latent heat ≥ 180kJ / kg), encapsulated in PVC balls (diameter 40mm). The heat released by the spiral coil is stored through the solid-liquid phase change of the phase change material, and the heat storage density is increased to 250kWh / m³ (conventional water tank ≤ 60kWh / m³); During the heat release process, the phase change material absorbs the heat of the cold water to maintain the water temperature stability. The thickness of the thermocline (temperature mutation zone) < 10cm, avoiding heat loss caused by cold and hot water mixing; Heat loss control and energy efficiency improvement: The stratified water tank significantly reduces the ineffective heat exchange caused by the mixing of cold and hot water and reduces the overall heat loss through the natural stratification structure with a vertical temperature gradient (high temperature at the bottom → medium temperature at the top); The combined design of the spiral coil and the phase change material strengthens the stability of heat storage and release, reduces the dependence on external auxiliary heat sources, and improves the overall energy utilization efficiency of the system; Enhanced water supply stability at the user end: Based on dynamic feedback control, the thermostatic mixing valve ensures a constant outlet water temperature by adjusting the mixing ratio of cold and hot water, avoiding the impact of water temperature fluctuations on the comfort of domestic hot water; The phase change material continuously releases heat when the photovoltaic output is insufficient, ensuring the continuity of hot water supply and reducing the restriction of extreme weather on the system performance; System compatibility and economic optimization: The coupled design of the stratified water tank and the absorption heat pump 9 enables flexible switching of heat sources through modular interfaces (such as the connection between the spiral coil and the heat exchanger), adapting to heating demands of different scales; The long service life of the phase change material reduces the equipment replacement frequency. Combined with the low maintenance requirements of the natural stratification structure, the operation and maintenance costs over the entire life cycle are significantly better than traditional heat storage solutions.

[0034] Please refer to Figures 1-7 , in some embodiments, it further includes an inter-seasonal heat storage unit, and the inter-seasonal heat storage unit includes a geothermal well 14 and a ground source heat pump 18; The heat medium outlet branch of the PVT module 7 is connected to the heat injection port of the geothermal well 14 through a third plate heat exchanger 17. The input end of the ground source heat pump 18 is connected to the geothermal well 14 through a U-shaped buried pipe 19, and the output end of the ground source heat pump 18 is connected to the water inlet main pipe of the user heating pipe network 13 through a fourth shell-and-tube heat exchanger 20.

[0035] In the above embodiments, the PVT module 7 generates electricity and heat simultaneously when there is sufficient sunlight. Its heat medium (such as ethylene glycol solution) transfers heat to the heat injection port of the geothermal well 14 through the third plate heat exchanger 17. The geothermal well 14 serves as an inter-seasonal heat storage medium (such as soil, rock formation or aquifer), forms a closed-loop circuit with the heat exchanger through the U-shaped buried pipe 19, and stores heat in the deep underground (depth ≥ 150 meters) for a long time; The combination of the vertical temperature gradient (high temperature at the bottom → low temperature at the top) of the geothermal well 14 and the high heat capacity characteristics of the soil / rock forms a natural stratified heat storage structure, suppressing the upward dissipation of heat; The ground source heat pump 18 extracts the stored low-grade heat energy (such as 40 - 50 °C) from the geothermal well 14 through the U-shaped buried pipe 19, and uses the heat pump cycle (evaporation - compression - condensation) to raise the temperature to the heating demand level (such as 55 - 60 °C); The high-temperature hot water output by the ground source heat pump 18 is connected to the user heating pipe network 13 through the fourth shell-and-tube heat exchanger 20, forming a complement with the thermal energy generated by the PVT module 7 in real time (through other branches). The seasonal heat storage is preferentially used, and the photovoltaic thermal energy is used as a supplementary or peak-shaving heat source. Seasonal energy balance and stability improvement: "Summer storage and winter use" is realized through the geothermal well 14, converting the surplus solar energy in the non-heating season into underground heat storage, and alleviating the problem of unstable energy supply caused by seasonal light fluctuations in the photovoltaic and solar thermal systems. The deep soil / rock heat storage body of the geothermal well 14 has the characteristic of low heat loss and can store heat for a long time (≥6 months), avoiding the short-term heat decay limitation of traditional water tank heat storage. Optimization of comprehensive energy utilization efficiency: The PVT module 7 and the ground source heat pump 18 form a "light-thermal-storage" collaborative link: the photovoltaic power generation meets the immediate electricity demand of users, and the waste heat is injected into the geothermal well 14 for seasonal storage; the ground source heat pump 18 efficiently extracts underground heat in the heating season, reducing the energy consumption of direct electric heating. The coupling design of the ground source heat pump 18 and the U-shaped buried pipe 19 utilizes the stable heat source characteristics of underground heat storage, reduces the operation load fluctuation of the heat pump in extreme weather, and prolongs the equipment life. Enhanced system compatibility and expandability: The modular heat storage unit (geothermal well 14 + U-shaped pipe) can be adapted to photovoltaic and solar thermal systems of different scales, supporting distributed or centralized heating scenarios. The phased design of the third plate heat exchanger 17 and the fourth shell-and-tube heat exchanger 20 realizes the physical isolation of heat storage and heat supply, avoids medium cross-contamination, and reduces the operation and maintenance complexity.

[0036] Please refer to Figures 1-7 , in some embodiments, the electrical system further includes a proton exchange membrane electrolyzer and a hydrogen storage bottle group; The redundant power output end of the bidirectional inverter 4 is connected to the DC input end of the proton exchange membrane electrolyzer through a rectifier, and the hydrogen outlet of the proton exchange membrane electrolyzer is connected to the inlet valve of the hydrogen storage bottle group through a high-pressure compressor; The outlet end of the hydrogen storage bottle group is connected to the anode inlet of the hydrogen fuel cell through a pressure reducing valve, the power output end of the hydrogen fuel cell is connected to the DC bus of the power distribution controller 6, and its cooling water outlet is connected in parallel to the input end of the phase change heat storage tank 11 or the inlet main pipe of the user heating pipe network 13 through a fifth plate heat exchanger.

[0037] In the above embodiments, When the photovoltaic power generation exceeds the user's real-time demand, the bidirectional converter 4 converts the redundant electric energy into direct current through the rectifier, drives the proton exchange membrane electrolyzer to electrolyze water, and the generated hydrogen is pressurized by the high-pressure compressor to the hydrogen storage bottle group (pressure ≥ 30 MPa) to achieve high-density storage; The waste heat generated during the operation of the electrolyzer (such as the cooling water temperature of the electrolyzer rises to 60 - 70 °C) is transferred to the phase change heat storage tank 11 or the user heating pipe network 13 through the fifth plate heat exchanger to improve the comprehensive utilization efficiency of thermal energy; When the photovoltaic output is insufficient or the power grid is powered off, the hydrogen in the hydrogen storage bottle group is regulated by the pressure reducing valve and then transported to the anode of the hydrogen fuel cell, where it undergoes an electrochemical reaction with the oxygen in the air. The generated direct current is connected to the DC bus of the power distribution controller 6 for direct power supply or converted into alternating current through the inverter; The cooling water generated during the operation of the hydrogen fuel cell (temperature about 50 - 60 °C) is linked with the heating system or the phase change heat storage tank 11 through the fifth plate heat exchanger to achieve "power generation - waste heat recovery" collaborative energy supply; Multi - energy complementarity and improvement of energy utilization rate: By using hydrogen energy as an intermediate energy storage medium, the surplus photovoltaic electric energy is converted into chemical energy that can be stored for a long time, breaking through the capacity and duration limitations of traditional battery energy storage, realizing "light - electricity - hydrogen" multi - energy coupling, and improving the system's ability to absorb intermittent renewable energy; The waste heat recovery design (fifth plate heat exchanger) of the hydrogen fuel cell and the electrolyzer enables the system to meet both power and heat demands simultaneously, reducing energy waste in a single energy supply scenario; Enhanced energy supply safety and flexibility: The high - pressure storage characteristics of the hydrogen storage bottle group ensure the long - term stable reserve of hydrogen energy (such as cross - seasonal storage). In extreme weather or when the photovoltaic system fails, the hydrogen fuel cell can quickly switch to the backup power supply to improve power supply reliability; As a clean energy carrier, hydrogen supports interconnection with external hydrogen energy networks (such as hydrogen refueling stations, industrial hydrogen use), expanding the system application scenarios (such as transportation, industrial decarbonization); System coordination and modular expansion: The modular design of the electrolyzer, hydrogen storage bottle group and hydrogen fuel cell supports increasing or decreasing the energy storage capacity as needed (such as expanding the number of hydrogen storage bottles) or adjusting the energy supply power (such as paralleling multiple fuel cells) to adapt to distributed energy systems of different scales; The parallel connection design of the fifth plate heat exchanger realizes the dynamic coupling of waste heat and the heating / heat storage system, avoiding heat redundancy or supply interruption, and improving the overall thermal balance ability of the system.

[0038] Please refer to Figures 1-7, in some embodiments, the cooling water outlet of the hydrogen fuel cell converges with the heat medium outlet of the PVT assembly 7 through a second three-way regulating valve and is jointly connected to the heat injection port of the geothermal well 14 of the seasonal heat storage unit; a temperature compensation valve is provided between the output end of the ground source heat pump 18 and the water inlet main pipe of the user heating pipe network 13 through a fourth shell-and-tube heat exchanger 20.

[0039] In the above embodiments, the cooling water (including waste heat) generated by the operation of the hydrogen fuel cell and the heat medium (such as ethylene glycol solution) generated by the PVT assembly 7 are dynamically mixed through the second three-way regulating valve to form a unified heat flow and inject it into the heat injection port of the geothermal well 14. The regulating valve automatically distributes the proportion of the two heat sources according to the real-time heat priority (such as the photovoltaic output intensity and the fuel cell operation status) to ensure the stability of the heat input. The mixed heat medium exchanges heat with the heat storage medium (soil / aquifer) in the geothermal well 14 through the third plate heat exchanger 17, and uses the characteristics of large heat capacity and low heat loss in the deep underground to realize long-term heat storage. The ground source heat pump 18 extracts the low-grade heat energy stored in the geothermal well 14 through the U-shaped buried pipe 19, and after being heated up by the heat pump cycle, it transports it to the user heating pipe network 13 through the fourth shell-and-tube heat exchanger 20. The temperature compensation valve monitors the temperature fluctuation of the water inlet main pipe of the user heating pipe network 13 in real time, and ensures the constant heating water temperature by adjusting the hot water flow rate and temperature at the output end of the ground source heat pump 18, avoiding heating instability caused by external environmental changes or heat source fluctuations. Heat cascading utilization and energy efficiency optimization: The coordinated injection of the waste heat of the cooling water of the hydrogen fuel cell and the heat collection of the PVT assembly 7 realizes the cascading storage of low-grade heat energy (fuel cell waste heat) and medium-high grade heat energy (photovoltaic heat), and improves the heat storage density of the geothermal well 14. The temperature compensation valve reduces the secondary heating energy consumption of the user heating pipe network 13 caused by temperature fluctuations by dynamically adjusting the heat pump output parameters, and improves the overall energy utilization efficiency of the system. System stability and redundancy enhancement: The multi-heat source switching ability of the second three-way regulating valve can quickly switch to another heat source to maintain the continuity of heat storage when a single heat source (such as insufficient photovoltaic power or fuel cell shutdown) fails, enhancing the fault tolerance of the system. The geothermal well 14 serves as a buffer medium, combined with the closed-loop control of the temperature compensation valve, effectively suppressing the heat load fluctuation of the user heating pipe network 13 and ensuring the heating stability at the user end. Modular expansion and scenario adaptation: The standardized design of the interfaces of the hydrogen fuel cell, the PVT assembly 7 and the geothermal well 14 supports the on-demand expansion of the heat source scale (such as increasing the number of photovoltaic arrays or fuel cells) and adapts to the heating needs of different climate regions. The separate layout of the fourth shell-and-tube heat exchanger 20 and the temperature compensation valve reduces the system coupling complexity and facilitates maintenance and local upgrade.

[0040] Please refer to Figures 1-7 , in some embodiments, the PVT assembly 7 includes: a mounting housing 21, the mounting housing 21 is a rectangular frame structure, both ends of the mounting housing 21 are open, one end mounts the photovoltaic panel 1, and the other end is provided with a sealing cover plate 22; It further includes: a heating box 23, which is arranged inside the mounting housing 21, one side of the heating box 23 is provided with a heat conducting plate 24, and the heat conducting plate 24 is arranged close to the photovoltaic panel 1; A plurality of serpentine ducts 25 are arranged inside the heating box 23, and each of the serpentine ducts 25 is respectively arranged at each vertex inside the heating box 23; A high-temperature chamber 26 is further arranged inside the heating box 23, the outer wall of the high-temperature chamber 26 is slidably connected to the inner wall of the heat conducting plate 24, a hydraulic rod 27 is arranged in the sliding direction of the high-temperature chamber 26, one end of the hydraulic rod 27 is connected to the outer wall of the high-temperature chamber 26, and the other end is connected to the inner wall of the heating box 23; One end of each of the serpentine ducts 25 communicates with the high-temperature chamber 26 through a corrugated pipe 28, and the other end passes through the outer wall of the heating box 23 and is connected to a water supply pipe 29; A plurality of the water supply pipes 29 are provided, each of the water supply pipes 29 is respectively connected to one end of each of the serpentine ducts 25 far from the high-temperature chamber 26, each of the water supply pipes 29 is respectively arranged in the interval between the high-temperature chamber 26 and the heating box 23, and one end of each of the water supply pipes 29 far from the serpentine duct 25 passes through the mounting housing 21; One end of an L-shaped pipe 30 is arranged at one end of the high-temperature chamber 26 far from the heat conducting plate 24, one end of the L-shaped pipe 30 communicates with the inner wall of the high-temperature chamber 26, and the other end passes through the heating box 23 and the mounting housing 21, and the L-shaped pipe 30 is slidably sealed with the heating box 23 and the housing.

[0041] In the above embodiments, the dynamic movement of the high-temperature region on the back of the photovoltaic panel 1 is mainly driven by the change of the sun position and the thermal characteristics of the material: as the sun moves from east to west, the incident angle and the light intensity continuously change, resulting in the offset of the initial position of the heat absorption of different regions of the photovoltaic panel 1. The anisotropic heat conduction characteristics of the encapsulation material cause non-uniform heat transfer when the heat diffuses from the heat-concentrated area to the surrounding area. Superimposed on the difference in heat dissipation efficiency between the edge and the center of the backplane (stronger air convection at the edge and significant heat accumulation in the center), and the disturbance of the local radiation heat dissipation by the environmental wind field, jointly cause the temperature peak region to show the phenomenon of "slowly migrating following the light direction". This dynamic temperature distribution will cause uneven thermal stress of the material and affect the output efficiency of the battery cells, and it is necessary to suppress it by optimizing the heat dissipation structure or introducing a tracking system; Therefore, when the position of the sun changes, the hydraulic rod 27 expands and contracts, thereby pushing the high-temperature chamber 26 to move, so that the high-temperature chamber 26 can always be in the area with the highest temperature on the back of the photovoltaic panel 1, improving the heating efficiency of the medium to be heated. The medium to be heated enters the serpentine conduit 25 through the four corners of the installation housing 21. The serpentine arrangement of the conduits can slow down the moving speed of the medium to be heated, so that the medium to be heated is first preheated from the low-temperature area on the back of the photovoltaic panel 1, then enters the corrugated pipe 28, enters the high-temperature chamber 26 through the corrugated pipe 28 for heating, and finally is discharged through the L pipe 30 on the high-temperature chamber 26. When the hydraulic rod 27 expands and contracts, the L pipe 30 moves along with the high-temperature chamber 26.

[0042] Please refer to Figures 1-7 , in some embodiments, a slide rail 31 is provided on the surface of the heat conducting plate 24, and a chute 32 is provided on the side of the high-temperature chamber 26 close to the heat conducting plate 24. The chute 32 is slidably engaged with the slide rail 31; Oil guide pipes 33 are arranged at intervals in the high-temperature chamber 26. Both ends of the oil guide pipes 33 are communicated with the heating tank 23. The oil guide pipes 33 are arranged parallel to the slide rail 31, and heat conducting oil is filled in the heating tank 23; A plurality of water guide plates 34 are provided in the high-temperature chamber 26, and each of the water guide plates 34 is distributed in an S shape in the heating tank 23.

[0043] In the above embodiments, heat conducting oil is filled in the heating tank 23. When the high-temperature chamber 26 moves, it pushes the heat conducting oil on one side to enter the other side of the heating tank 23 through the oil guide pipes 33, so that the heat conducting oil is heated by the relatively higher temperature part when passing through the high-temperature chamber 26, which is beneficial to the heat exchange of the heat conducting oil on both sides of the high-temperature chamber 26 and makes the temperature on the back of the photovoltaic panel 1 tend to be uniform.

[0044] Please refer to Figures 1-7 , a control method for an integrated system, wherein the power distribution controller 6 switches the charge and discharge modes of the lithium-ion battery pack 5 according to the user load demand, and realizes the grid-connected or off-grid control of the photovoltaic electric energy and the power grid through the bidirectional inverter 4; The variable frequency circulating pump 12 adjusts the flow according to the signal of the pressure sensor of the user heating pipe network 13, and the first three-way regulating valve 15 switches the water supply ratio of the medium-deep geothermal energy and the air source heat pump 16 according to the signal of the water temperature sensor of the water inlet main pipe; In the transitional season, the waste heat of the PVT module 7 and the waste heat of the cooling water of the hydrogen fuel cell are injected into the geothermal well 14 through the third plate heat exchanger 17, and in winter, the heat stored in the geothermal well 14 is extracted by the ground source heat pump 18 and input into the user heating pipe network 13.

[0045] In the above embodiments, the integrated system realizes combined heat and power supply through multi-source collaboration and dynamic regulation: the power distribution controller 6 monitors the user load demand in real time, preferentially schedules photovoltaic power for power supply, and automatically switches to the lithium-ion battery pack 5 for discharging or draws power from the grid (realizes seamless switching between grid-connected and off-grid through the bidirectional converter 4) when the light is insufficient to ensure power supply continuity; on the heating side, the variable-frequency circulating pump 12 dynamically adjusts the flow according to the pipe network pressure to maintain hydraulic balance. At the same time, the first three-way regulating valve 15 automatically adjusts the mixed heating ratio of medium-deep geothermal energy and the air source heat pump 16 based on the feedback of the inlet water temperature to ensure the stability of the heating water temperature; in the transitional season, the system transfers the solar thermal waste heat of the PVT module 7 and the cooling water waste heat of the hydrogen fuel cell to the geothermal well 14 after heat exchange and stores them. In winter, the ground source heat pump 18 extracts the heat energy stored in the geothermal well 14 to supplement the heating demand, forming a cross-seasonal energy cycle of "summer storage and winter use". Multi-energy complementarity and energy efficiency optimization: The intelligent switching among photovoltaic power generation, lithium battery energy storage and the power grid realizes dynamic matching of power supply and demand, reduces the light curtailment rate and dependence on the power grid; the combined heating of medium-deep geothermal energy and the air source heat pump 16 combined with temperature-pressure double feedback control improves the utilization efficiency of low-grade heat sources and reduces heating energy consumption; Cross-seasonal heat storage and system redundancy: In the transitional season, the waste heat is injected into the geothermal well 14, converting the waste heat energy into a callable strategic reserve, which is output after temperature increase by the heat pump in winter, alleviating the load pressure of traditional heat sources. At the same time, the geothermal well 14, as a heat buffer unit, enhances the fault tolerance of the system to cope with extreme weather; Dynamic response and enhanced stability: The closed-loop control strategy of the variable-frequency circulating pump 12 and the three-way valve suppresses the fluctuations of the pipe network pressure and temperature in real time, avoiding problems such as hydraulic imbalance and local overheating / overcooling; the collaborative management of the power distribution controller 6 and the bidirectional converter 4 ensures the power supply quality in the off-grid mode (such as voltage / frequency stability) and bidirectional controllability of power in the grid-connected mode; Low-carbon and sustainability: The proportion of clean energy such as photovoltaic, geothermal and fuel cells is increased. Combined with waste heat recovery and cross-seasonal heat storage, it significantly reduces fossil energy consumption and carbon emissions, realizing nearly zero-carbon operation of the energy system.

[0046] The embodiments of the present application have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

[0047] The selection of the terms used in this document is intended to best explain the principles of the embodiments, their practical applications, or the improvements to the technology in the market, or to enable other ordinary technicians in the technical field to understand the embodiments disclosed in this document.

[0048] The above are only alternative embodiments of this application and are not intended to limit this application. For those skilled in the art, various changes and modifications can be made to this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A photovoltaic-thermal integrated production, storage and supply system, characterized in that The integrated system includes: Electrical system: The power output end of the photovoltaic panel (1) is connected to the user load distribution box (3) through an inverter, and the redundant power output end of the inverter is connected to the lithium-ion battery pack (5) through a bi-directional converter (4); The discharge end of the lithium-ion battery pack (5) is connected to the power distribution controller (6) through a DC bus, and the output end of the power distribution controller (6) is connected back to the user load distribution box (3); Thermal system: The heat medium outlet of the PVT module (7) is connected to the evaporator inlet of the absorption heat pump (9) through a first plate heat exchanger (8), and the condenser outlet of the absorption heat pump (9) is connected to the input end of the phase change heat storage tank (11) through a second shell-and-tube heat exchanger (10); The output end of the phase change heat storage tank (11) is connected to the water inlet main pipe of the user heating pipe network (13) through a variable-frequency circulating pump (12); Auxiliary heat source unit: The water outlet of the geothermal well (14) is in parallel with the water outlet of the air source heat pump (16) through a first three-way regulating valve (15), and both are jointly connected to the water inlet main pipe of the user heating pipe network (13).

2. The integrated photovoltaic-thermal power generation, storage and supply system according to claim 1, characterized in that The phase change heat storage tank (11) is a stratified domestic hot water tank. The condenser outlet of the absorption heat pump (9) is connected to the inlet of the spiral coil at the bottom of the stratified domestic hot water tank through the second shell-and-tube heat exchanger (10), and the hot water outlet at the top of the stratified domestic hot water tank is connected to the user domestic hot water pipe through a constant temperature mixing valve.

3. The integrated photovoltaic-thermal power generation, storage, and supply system according to claim 2, wherein It further includes an inter-seasonal heat storage unit, and the inter-seasonal heat storage unit includes a geothermal well (14) and a ground source heat pump (18); The heat medium outlet branch of the PVT module (7) is connected to the heat injection port of the geothermal well (14) through a third plate heat exchanger (17). The input end of the ground source heat pump (18) is connected to the geothermal well (14) through a U-shaped buried pipe (19), and the output end of the ground source heat pump (18) is connected to the water inlet main pipe of the user heating pipe network (13) through a fourth shell-and-tube heat exchanger (20).

4. The integrated photovoltaic-thermal power generation, storage and supply system according to claim 3, wherein The electrical system further includes a proton exchange membrane electrolyzer and a hydrogen storage bottle group; The redundant power output end of the bi-directional converter (4) is connected to the DC input end of the proton exchange membrane electrolyzer through a rectifier, and the hydrogen outlet of the proton exchange membrane electrolyzer is connected to the inlet valve of the hydrogen storage bottle group through a high-pressure compressor; The gas outlet end of the hydrogen storage bottle group is connected to the anode inlet of the hydrogen fuel cell through a pressure reducing valve. The power output end of the hydrogen fuel cell is connected to the DC bus of the power distribution controller (6), and its cooling water outlet is connected in parallel to the input end of the phase change heat storage tank (11) or the water inlet main pipe of the user heating pipe network (13) through a fifth plate heat exchanger.

5. The integrated photovoltaic-thermal power generation, storage, and supply system according to claim 4, wherein, The cooling water outlet of the hydrogen fuel cell and the heat medium outlet of the PVT module (7) converge through a second three-way regulating valve and are jointly connected to the heat injection port of the geothermal well (14) of the inter-seasonal heat storage unit; A temperature compensation valve is provided between the output end of the ground source heat pump (18) and the water inlet main pipe of the user heating pipe network (13) through the fourth shell-and-tube heat exchanger (20).

6. The integrated photovoltaic-thermal power generation, storage and supply system according to claim 5, characterized in that, The PVT component (7) includes: an installation housing (21), which is of a rectangular frame structure with both ends open. One end is for installing the photovoltaic panel (1), and the other end is provided with a sealing cover plate (22). It further includes: a heating box (23), which is arranged inside the installation housing (21). One side of the heating box (23) is provided with a heat conduction plate (24), and the heat conduction plate (24) is arranged close to the photovoltaic panel (1). A plurality of serpentine conduits (25) are arranged inside the heating box (23), and each serpentine conduit (25) is respectively arranged at each vertex inside the heating box (23). A high-temperature chamber (26) is further arranged inside the heating box (23). The outer wall of the high-temperature chamber (26) is slidably connected to the inner wall of the heat conduction plate (24). A hydraulic rod (27) is arranged in the sliding direction of the high-temperature chamber (26). One end of the hydraulic rod (27) is connected to the outer wall of the high-temperature chamber (26), and the other end is connected to the inner wall of the heating box (23). One end of each serpentine conduit (25) communicates with the high-temperature chamber (26) through a corrugated pipe (28), and the other end passes through the outer wall of the heating box (23) and is connected to a water supply pipe (29). A plurality of water supply pipes (29) are provided. The plurality of water supply pipes (29) are respectively connected to one end of each serpentine conduit (25) away from the high-temperature chamber (26). Each water supply pipe (29) is respectively arranged in the interval between the high-temperature chamber (26) and the heating box (23). One end of each water supply pipe (29) away from the serpentine conduit (25) passes through the installation housing (21). An L-shaped pipe (30) is arranged at one end of the high-temperature chamber (26) away from the heat conduction plate (24). One end of the L-shaped pipe (30) communicates with the inner wall of the high-temperature chamber (26), and the other end passes through the heating box (23) and the installation housing (21). The L-shaped pipe (30) is slidably sealed with the heating box (23) and the housing.

7. The integrated photovoltaic-thermal power generation, storage, and supply system according to claim 6, characterized in that, A slide rail (31) is arranged on the surface of the heat conduction plate (24). A slide groove (32) is arranged on the side of the high-temperature chamber (26) close to the heat conduction plate (24), and the slide groove (32) is slidably matched with the slide rail (31). Oil guide pipes (33) are arranged at intervals inside the high-temperature chamber (26). Both ends of the oil guide pipes (33) communicate with the heating box (23). The oil guide pipes (33) are arranged parallel to the slide rail (31), and the heating box (23) is filled with heat conduction oil. A number of water guide plates (34) are arranged inside the high-temperature chamber (26), and each water guide plate (34) is distributed in an S shape inside the heating box (23).

8. The control method of the integrated system according to any one of claims 1-7, characterized in that, The power distribution controller (6) switches the charge and discharge modes of the lithium-ion battery pack (5) according to the user load demand, and realizes the grid-connected or off-grid control of photovoltaic electric energy and the power grid through the bidirectional inverter (4). The variable-frequency circulating pump (12) adjusts the flow according to the signal of the heating network pressure sensor, and the first three-way regulating valve (15) switches the water supply ratio of the medium-deep geothermal energy and the air source heat pump (16) according to the signal of the total water inlet temperature sensor. During the transitional season, the waste heat of the PVT module (7) and the waste heat of the cooling water of the hydrogen fuel cell are injected into the geothermal well (14) through the third plate heat exchanger (17). In winter, the heat stored in the geothermal well (14) is extracted by the ground source heat pump (18) and input into the user heating pipe network (13).

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