Photovoltaic-thermal system and its control method

Abstract

The present application relates to a photovoltaic-thermal system and a control method thereof. The photovoltaic-thermal system includes: a photovoltaic-thermal integrated unit, which includes an alternative working photovoltaic power generation unit and a solar thermal water supply unit; a working mode control unit, which is connected to the photovoltaic-thermal integrated unit to control the alternative working of the photovoltaic power generation unit and the solar thermal water supply unit; a heating water tank, which is connected to the solar thermal water supply unit through a first circulation water pipe, and a first circulation water pump is connected to the first circulation water pipe; a heat-using unit, which is connected to the heating water tank through a water pipe; and an electricity-using unit, which is electrically connected to the photovoltaic power generation unit.

Description

Technical Field

[0001] The present application relates to a photovoltaic-thermal system and a control method thereof. Background Art

[0002] Solar energy, as a renewable energy source, has been widely used, such as in photovoltaic power generation, solar heating, solar thermal power generation, etc. Solar energy is also the main direction for the future development of green energy. There are two existing technical approaches for utilizing solar energy: namely, the technical products of photovoltaic power generation and solar heating have been popularized in every country in the world. The existing solar power generation devices and heating devices are two separate devices. Due to the respective advantages and disadvantages of the photovoltaic utilization and solar thermal utilization of solar energy, there is a problem that they cannot be installed simultaneously, that is, they can only generate electricity but not heat or can only generate heat but not electricity, so that the two cannot complement each other's advantages and cannot generate heat and electricity simultaneously, affecting the full and efficient utilization of solar energy.

[0003] When only photovoltaic power generation is carried out, the photoelectric conversion efficiency is low, and its conversion efficiency is generally 12%-17% of the solar energy radiation amount. That is to say, about 83% of the solar energy irradiated on the surface of the photovoltaic panel fails to be utilized and converted. A considerable part of the energy is converted into heat and lost. At the same time, the generated heat will also increase the temperature of the photovoltaic panel, resulting in a decrease in battery efficiency and further reducing the photoelectric conversion rate. Therefore, there are problems of low conversion rate and much solar energy loss in pure photovoltaic power generation.

[0004] When only solar heating is carried out, such as in a common solar water heater, the solar-thermal conversion efficiency is high, generally above 50% of the solar radiation amount. However, the problem is that the needs of household bathing are not required every day, resulting in the waste of hot water generated on most days. Especially for schools equipped with solar water heating systems, during the start of the semester, the solar hot water meets the use of students, but during the relatively long winter and summer vacations, and at this time the light intensity is the largest, the water heater is left unused, causing energy waste. In addition, for a solar water heating and heating system, in winter heating, the solar heating equipment is much more efficient than the photovoltaic power generation heating equipment. For example, for a 100-square-meter house in winter heating, if a 50-square-meter photovoltaic power generation device is installed, the electric energy generated on a sunny day cannot meet the requirements. If a 50-square-meter solar thermal utilization device is installed and heated by hot water, the absorbed heat energy can fully meet the requirements. However, the house is generally only heated in winter, and the heating time is about three months. The rest of the time is mostly in a standby state, and the collected heat energy is not used and wasted in vain. Therefore, there are problems of low usage frequency and long standby and shutdown cycles in pure solar heating.

[0005] In summary, the above problems existing in the current photovoltaic power generation and solar thermal heating methods of solar energy respectively lead to insufficient utilization of solar energy. Currently, solar energy-based products have not been popularized or widely applied in the market. The unique properties of solar energy as clean, readily available, and inexhaustible have not been well developed and utilized. Due to the lack of application and research and development of solar energy technology, the disadvantages of products using solar energy technology are more prominent. More seriously, products such as solar water heaters have even been abandoned in the market. Therefore, in the face of the current energy crisis and the pursuit of clean and pollution-free energy, the utilization technology of solar energy urgently needs to be innovated.

[0006] However, in practice, combining photovoltaic power generation and solar thermal heating has always been a difficult technical problem to overcome. There are many technical problems that need to be overcome in their combination, which is also determined by the current basic equipment of photovoltaic power generation and solar thermal heating: because most photovoltaic panels are a complete flat plate, and most solar thermal equipment is a set of heat collecting tubes arranged in an array, it causes the photovoltaic panel and the heat collecting tubes to be unable to be combined and work together to make up for the deficiencies of the two technologies respectively and maximize the utilization of solar energy, and it is impossible to obtain both hot water and electricity at the same time. Currently, there are very few devices on the market that combine photovoltaic power generation and solar thermal heating to produce heat and electricity simultaneously. Some existing devices set multiple heat collecting tubes on the back of the photovoltaic panel to utilize heat for heating. However, the problem with this method is that the heat collection tube heating still causes heat to be unable to dissipate, and the temperature of the photovoltaic panel will also rise, resulting in a decrease in battery efficiency and a shortening of service life. Therefore, the development of a photovoltaic-thermal integrated machine that can achieve photovoltaic-thermal switching in this application is of great significance and has an innovative meaning for the full utilization of solar energy and the formation of products for household applications. Summary of the Invention

[0007] The purpose of this application is: in view of the above problems, to provide a photovoltaic-thermal system that can achieve photovoltaic-thermal switching, and to provide a control method for the photovoltaic-thermal system.

[0008] The technical solution of this application is:

[0009] A photovoltaic-thermal system, comprising:

[0010] A photovoltaic-thermal integrated machine, which includes an alternative working photovoltaic power generation unit and a solar thermal heating unit;

[0011] A working mode control unit, which is connected to the photovoltaic-thermal integrated machine to control the alternative working of the photovoltaic power generation unit and the solar thermal heating unit;

[0012] A heating water tank, which is connected to the solar thermal heating unit through a first circulation water pipe, and a first circulation water pump is connected to the first circulation water pipe;

[0013] A heat unit, which is connected to the heating water tank through a water pipe; and

[0014] An electric unit, which is circuit-connected to the photovoltaic power generation unit.

[0015] On the basis of the above technical solution, this photovoltaic-thermal system of the present application further includes the following preferred solutions:

[0016] A heat storage water tank is provided on the water pipe.

[0017] The water pipe includes a second circulation water pipe connecting the heat storage water tank and the heating water tank, and a second circulation water pump is connected to the second circulation water pipe.

[0018] The water pipe further includes a third circulation water pipe connecting the heat storage water tank and the heat using unit, and a third circulation water pump is connected to the third circulation water pipe.

[0019] A second water temperature sensor is provided on the heating water tank, a third water temperature sensor is provided on the heat storage water tank, and both the second water temperature sensor and the third water temperature sensor are circuit-connected to the second circulation water pump.

[0020] A comparator is connected between the second water temperature sensor and the third water temperature sensor, and the comparator is circuit-connected to the second circulation water pump.

[0021] The heat storage water tank is connected to a water supply pipe.

[0022] The photovoltaic-thermal integrated machine includes:

[0023] A base frame,

[0024] A water passage cavity fixed on the base frame,

[0025] A heat collecting pipe arranged on the base frame and thermally connected to the water passage cavity, and

[0026] A photovoltaic panel arranged on the radial side of the heat collecting pipe and capable of rotating around the pipe axis of the heat collecting pipe;

[0027] The first circulation water pipe is connected to the water passage cavity, and the electric unit is circuit-connected to the photovoltaic panel.

[0028] The working mode control unit includes:

[0029] A motor connected to the photovoltaic panel through a transmission assembly to drive the photovoltaic panel to rotate, and

[0030] A motor controller circuit-connected to the motor.

[0031] At least two heat collecting tubes are provided, and each of the heat collecting tubes is arranged in parallel at intervals with each other. A photovoltaic panel that rotates around the tube axis of each heat collecting tube is arranged in parallel on the radial side of each heat collecting tube; the transmission assembly includes:

[0032] A synchronous gear coaxially sleeved outside the heat collecting tube and fixed to the photovoltaic panel, and

[0033] An idler gear meshingly connected between the synchronous gears;

[0034] The motor is connected to one of the synchronous gears or one of the idler gears.

[0035] A power controller is provided on the connection circuit between the power consumption unit and the photovoltaic power generation unit.

[0036] The power controller is connected to the public power grid circuit.

[0037] A first water temperature sensor is provided in the water flow cavity, a second water temperature sensor is provided in the heating water tank, and both the first water temperature sensor and the second water temperature sensor are connected to the first circulation water pump circuit.

[0038] A comparator is connected between the first water temperature sensor and the second water temperature sensor, and the comparator is connected to the first circulation water pump circuit.

[0039] The second water temperature sensor is connected to the working mode control unit circuit.

[0040] A control method for a photovoltaic-thermal system includes:

[0041] When the solar thermal heating unit is in a working state, the water temperature T2 of the heating water tank is obtained in real time. When T2≥T need At this time, the solar thermal heating unit stops working, and the photovoltaic power generation unit is adjusted to a working state.

[0042] On the basis of the above technical solution, this control method of the present application further includes the following priority solutions:

[0043] When the solar thermal heating unit is in a working state, the following control strategy is carried out:

[0044] When the water temperature T1 of the solar thermal heating unit≥T q At this time, the first circulation water pump starts; when T1≤T g At this time, the first circulation water pump is closed; T q >T g ;

[0045] When the water temperature T2 of the heating water tank≥T g At this time, Tq Reassign to the current T q Value and the sum of the increment Δδ1, and make T g Reassign to the current T q Value and the sum of another increment Δδ2.

[0046] It also includes the following second control strategy carried out independently:

[0047] When the water temperature T2 of the heating water tank ≥ T q1 , the second circulation pump starts to make the water in the heating water tank and the energy storage water tank exchange; when T2 ≤ T g1 , the second circulation pump starts to close; T q1 >T g1 ;

[0048] When the water temperature T3 of the energy storage water tank ≥ T g1 , make T q1 Reassign to the current T q1 Value and the sum of the increment Δδ 11 , make T g Reassign to the current T q1 Value and the sum of another increment Δδ 21 ;

[0049] When the T3 ≥ T need1 , close the second circulation pump and stop executing the second control strategy.

[0050] A control method for a photovoltaic-thermal system, characterized by including:

[0051] When the photovoltaic power generation unit is in the working state, the water temperature T2 of the heating water tank is obtained in real time. When T2 ≤ T low , the photovoltaic power generation unit stops working and the solar-thermal heating unit is adjusted to the working state.

[0052] T low = 30 °C.

[0053] A control method for a photovoltaic-thermal system, characterized in that when the solar-thermal heating unit is in the working state, the water level of the heating water tank is obtained in real time. When the water level of the heating water tank remains unchanged within a certain time period t, the solar-thermal heating unit stops working and the photovoltaic power generation unit is adjusted to the working state.

[0054] t = 48 hours.

[0055] This application can achieve the following beneficial effects:

[0056] 1. This proposed photovoltaic-thermal system combines photovoltaic power generation and thermal heating, allowing for the selection of power generation or heating as needed to achieve full utilization of solar energy, which has revolutionary significance for an energy-saving, pollution-free, and sustainable ecological development model.

[0057] 2. The photothermal conversion efficiency of solar energy can reach over 50%, while the photovoltaic conversion efficiency can only reach about 17%. However, it is impossible to use all solar energy for heating. For this reason, this proposed control method for the photovoltaic-thermal system automatically switches to the photovoltaic power generation mode when the photothermal conversion meets the usage requirements, making full use of solar energy throughout the day.

[0058] 3. This application uses the water temperatures of the photothermal heating unit and the heating water tank as basic parameters to regulate the water exchange state between them. Only when specific adjustments are met will the circulating pump between them be turned on, and a stepped control strategy is adopted, which is energy-saving and has low noise pollution.

[0059] 4. After the water temperature in the heating water tank rises to the required higher temperature, it directly switches to the photovoltaic working mode to maximize the utilization rate of solar energy.

[0060] 5. The photovoltaic power generation unit is connected to both the public power grid and household appliances. After the household electricity consumption is sufficient, the excess electricity can be transmitted to the public power grid, which is then allocated to power-deficient areas.

[0061] 6. If the volume of the heating water tank is made very large to meet the water consumption needs, it will take a long time to raise the water temperature in the heating water tank to the required value. If the floor heating, which is a heat-using unit, is directly connected to the heating water tank with a water pipe, the low-temperature water flowing back from the floor heating to the heating water tank will cause the water temperature in the heating water tank to drop rapidly, which will affect the normal use of some high-temperature heat-using equipment. In addition, different heat-using equipment has different water temperature requirements. If all heat-using equipment is directly connected to the heating water tank with water pipes, the heating water tank with a certain water temperature cannot supply water to different heat-using equipment with different temperature differences. For this reason, a storage water tank is set on the water pipe connecting the heat-using unit and the heating water tank in this application. The water in the heating water tank is first supplied to the storage water tank, and the storage water tank can be connected to tap water to mix and adjust the water temperature before supplying it to the corresponding heat-using unit. Moreover, the low-temperature water flowing back from some heat-using equipment such as floor heating is first sent to the storage water tank and will not directly enter the heating water tank, causing the water temperature in the heating water tank to drop rapidly.

[0062] 7. This application adopts a clever control strategy to conduct water exchange between the heating water tank and the storage water tank, avoiding the water temperature in the storage water tank being too low to meet the usage requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present application and do not limit the present application.

[0064] Figure 1 is the structural schematic diagram of the photovoltaic-thermal system in the first embodiment of the present application;

[0065] Figure 2 is the schematic diagram of the photovoltaic-thermal integrated machine in the first embodiment of the present application in the solar thermal working state.

[0066] Figure 3 is the schematic diagram of the photovoltaic-thermal integrated machine in the first embodiment of the present application in the photovoltaic working state.

[0067] Figure 4 is the planar structural schematic diagram in the first embodiment of the present application.

[0068] Figure 5 is Figure 4 the sectional view taken along the line A-A of

[0069] Figure 6 is the schematic diagram of the cooperation structure of the photovoltaic panel, pivot frame, heat collecting tube and synchronous gear in the first embodiment of the present application.

[0070] Figure 7 is the structural schematic diagram of the photovoltaic-thermal system in the second embodiment of the present application;

[0071] Figure 8 is the schematic diagram of the cooperation structure of the photovoltaic panel, connecting frame, heat collecting tube and synchronous gear in the third embodiment of the present application.

[0072] Wherein:

[0073] 1 - Photovoltaic-thermal integrated machine, 2 - Working mode control unit, 3 - Heating water tank, 4 - First circulation water pipe, 5 - First circulation water pump, 6 - Energy storage water tank, 7 - Second circulation water pipe, 8 - Second circulation water pump, 9 - Third circulation water pipe, 10 - Third circulation water pump, 11 - Electric heater, 12 - LED lamp, 13 - Power controller, 14 - Power grid, 15 - Electric meter, 16 - Water supply pipe, 17 - Solenoid valve;

[0074] 101 - Base frame, 102 - Water flow cavity, 102a - Water inlet interface, 102b - Water outlet interface, 103 - Six heat collecting tubes, 104 - Photovoltaic panel, 105 - Connecting frame;

[0075] 201 - Synchronous gear, 202 - Cross-over gear, 203 - Pivot frame. Detailed implementation manners

[0076] To make the objectives, technical solutions and advantages of the embodiments 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 embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0077] Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present application pertains. The terms "first", "second" and similar terms used in the patent application specification and claims of the present application do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, terms such as "a" or "an" do not denote a limitation of quantity, but mean that there is at least one.

[0078] Now, embodiments of the present application will be described with reference to the accompanying drawings.

[0079] Embodiment 1:

[0080] Figure 1 A specific embodiment of the photovoltaic-thermal system of the present application is shown. The system mainly consists of a photovoltaic-thermal integrated machine 1, a working mode control unit 2, a heating water tank 3, a heat-using unit and an electricity-using unit. Among them:

[0081] The photovoltaic-thermal integrated machine 1 includes a photovoltaic power generation unit and a solar thermal heating unit. And in actual use, the aforementioned photovoltaic power generation unit and solar thermal heating unit can only work alternatively, that is to say: when the photovoltaic power generation unit is in the working state and converts solar energy into electric energy, the solar thermal heating unit is in the non-working state; when the solar thermal heating unit is in the working state and uses solar energy to heat water, the photovoltaic power generation unit is in the non-working state.

[0082] The working mode control unit 2 is connected to the photovoltaic-thermal integrated machine 1, and is used to control the photovoltaic power generation unit and the solar thermal heating unit of the photovoltaic-thermal integrated machine 1 to work alternatively, that is, to control the photovoltaic-thermal integrated machine 1 to selectively be in the photovoltaic power generation state or the solar thermal heating state.

[0083] A first circulating water pipe 4 is connected between the heating water tank 3 and the solar thermal heating unit, and a first circulating water pump 5 is connected to the first circulating water pipe 4. The water exchange between the heating water tank 3 and the solar thermal heating unit can be realized by means of the aforementioned first circulating water pipe 4 and the first circulating water pump 5.

[0084] The heat-using unit is connected to the aforementioned heating water tank 3 through a water pipe, and the heating water tank 3 provides water at the required temperature for the heat-using unit. The aforementioned heat-using unit can include many heat-using devices, such as kitchen faucets, shower heads for bathing, and so on. Specifically, in this embodiment, the heat-using unit is a floor heating 11. Since the floor heating 11 only requires the heat of water and does not consume water, the aforementioned water pipe (i.e., the water pipe connecting the heating water tank and the floor heating) is also a circulating water pipe.

[0085] The power-using unit is electrically connected to the photovoltaic power generation unit, and the photovoltaic power generation unit provides electrical energy for the power-using unit. The aforementioned power-using unit can include many electrical devices, such as electric lights, computers, refrigerators, and so on, and can even include the public power grid.

[0086] Specifically, in this embodiment, the above-mentioned power-using unit includes the public power grid 14 and the LED lights 12. In this way, the electrical energy generated by the photovoltaic power generation unit can be directly transmitted to household appliances such as LED lights and refrigerators, or can be transmitted to the public power grid 14, and then allocated by the public power grid 14 to areas with power shortages.

[0087] In order to facilitate the selective transmission of the electrical energy generated by the photovoltaic power generation unit to the aforementioned LED lights 12 or the public power grid 14, and to perform relevant processing on the current when transmitting to the LED lights 12 or the public power grid 14, a power controller 13 is provided on the connection circuit between the power-using unit and the photovoltaic power generation unit in this embodiment. After passing through the power controller 13, the photovoltaic power generation unit is then connected to the power grid 14. The power controller 13 is not only connected between the LED lights 12 and the power controller 13, but also connected between the power grid 14 and the power controller 13.

[0088] Similar to some traditional power controllers, the above-mentioned power controller 2 includes a controller housing and a power control board provided inside the controller housing.

[0089] In practical applications, if the photovoltaic-thermal integrated machine 1 is in the solar thermal working mode, the solar thermal heating unit absorbs solar energy to heat the water flowing through the solar thermal heating unit. The heated water at a relatively high temperature enters the heating water tank 3 through the first circulating water pipe. The water at a relatively low temperature in the heating water tank 3 enters the solar thermal heating unit through the first circulating water pipe. In this way, the exchange of cold water and hot water between the heating water tank 3 and the solar thermal heating unit is realized, and finally the heating water tank 3 stores water at the required temperature for use. When the water temperature in the heating water tank 3 rises to a certain value, it means that the amount of hot water is sufficient. At this time, the working mode control unit 2 can be used to switch the photovoltaic-thermal integrated machine 1 to the photovoltaic working mode.

[0090] The switching between the solar thermal working mode and the photovoltaic working mode can adopt the following control strategy:

[0091] When the solar thermal heating unit is in the working state, the water temperature T2 of the heating water tank 3 is obtained in real time. When T2 ≥ T need , the solar thermal heating unit stops working, and the photovoltaic power generation unit adjusts to the working state. T need can be set manually and stored in the software program of the working mode control unit.

[0092] Furthermore, when the solar thermal heating unit is in the working state, the following control strategy is carried out:

[0093] When the water temperature T1 of the solar thermal heating unit ≥ T q , the first circulation pump 5 starts, and the solar thermal heating unit exchanges water with the heating water tank. When T1 ≤ T g , the first circulation pump 5 closes, and the water exchange between the solar thermal heating unit and the heating water tank stops. T q and T g values can be set manually and pre-stored in the photovoltaic-thermal system (such as stored in the following comparator). It is necessary to ensure that T q >T g . As the solar thermal heating unit continues to work, the water temperature of the heating water tank 3 will continue to increase with the water exchange. When the water temperature T2 of the heating water tank ≥ T g , T q is re-assigned as the sum of the current T q value and the increment Δδ1 (new T q = old T q + Δδ1), and T g is re-assigned as the sum of the current T g value and another increment Δδ2 (new T g = old T g + Δδ2). At this time, only when T1 ≥ new T q , the first circulation pump 5 starts; when T1 ≤ new T g , the first circulation pump 5 closes.

[0094] Until the water temperature T2 of the heating water tank 3 rises to the required temperature T need (T2 ≥ T need ), the first circulation pump and the solar thermal heating unit stop working, and the photovoltaic power generation unit adjusts to the working state.

[0095] To facilitate the reader to more intuitively understand the above working mode switching strategy, the following example is given:

[0096] The user manually adjusts the photovoltaic-thermal integrated machine 1 to the solar thermal working mode for the first time, obtains the water temperature (T1) of the solar thermal heating unit and the water temperature (T2) of the heating water tank 3 in real time, and sets the initial T q to 50 °C, and sets the initial T gis 40°C. Once the water temperature of the solar thermal heating unit (i.e., T1) reaches 50°C (i.e., T q ), the first circulation pump 5 starts, and water exchange occurs between the solar thermal heating unit and the heating water tank. Once the water temperature of the solar thermal heating unit is below 40°C (i.e., T g ), the first circulation pump 5 shuts down, and the water exchange between the solar thermal heating unit and the heating water tank stops. Obviously, performing the foregoing actions will cause the water temperature of the heating water tank 3 to continue to rise.

[0097] When the water temperature (T2) of the heating water tank 3 rises to 50°C, if the foregoing scheme is still executed, then the first circulation pump 5 will be in an operating state for a long time, which is not conducive to energy conservation and causes a large noise pollution. Based on the foregoing considerations, in this embodiment, after the water temperature of the heating water tank 3 rises to 50°C, the on and off temperature thresholds of the first circulation pump 5 are immediately raised by 10°C (i.e., Δδ1), that is: once the water temperature of the solar thermal heating unit reaches 60°C (i.e., the new T q ), the first circulation pump 5 starts; once the water temperature of the solar thermal heating unit is below 50°C (i.e., the new T g ), the first circulation pump 5 shuts down.

[0098] Similarly, when the water temperature of the heating water tank 3 rises to 60°C, the on and off temperature thresholds of the first circulation pump 5 are further raised by 10°C, that is: once the water temperature of the solar thermal heating unit reaches above 70°C, the first circulation pump 5 starts; once the water temperature of the solar thermal heating unit is below 60°C, the first circulation pump 5 shuts down.

[0099] When the water temperature of the heating water tank 3 rises to the required 70°C (i.e., when the artificially set T need is 70°C), if a similar instruction is executed again, it will be difficult or it will take a long time and a large amount of energy to raise the water temperature of the heating water tank 3 to a higher temperature such as 80°C (long time consumption and low energy conversion efficiency). Moreover, water at 70°C can already meet various daily needs. Based on this, in this embodiment, after the water temperature of the heating water tank 3 rises to 70°C, the above-mentioned similar instructions are no longer executed, and the operations of steps S1 to S3 are stopped. At this time, the first circulation pump 5 remains in the closed state, and the photovoltaic-thermal integrated machine 1 switches from the solar thermal working mode to the photovoltaic working mode.

[0100] To facilitate the automatic implementation of the above control strategy, the solar thermal heating unit of this embodiment is configured with a first water temperature sensor for detecting the water temperature, and the heating water tank 3 is configured with a second water temperature sensor. Both the first water temperature sensor and the second water temperature sensor are electrically connected to the first circulation pump 5. A comparator is connected between the first water temperature sensor and the second water temperature sensor, and the aforementioned comparator is electrically connected to the first circulation pump 5. Moreover, the second water temperature sensor is electrically connected to the working mode control unit 2, so that when the second water temperature sensor detects that the water temperature in the heating water tank 3 rises to the ideal value (70 °C), the working mode control unit 2 immediately switches the photovoltaic-thermal integrated machine 1 to the photovoltaic working mode.

[0101] If the volume of the heating water tank 3 is made very large to meet the water consumption requirements, it will take a long time to raise the water temperature in the heating water tank 3 to the required value. More critically: If the floor heating 11, which is a heat-using unit, is directly connected to the heating water tank 3 with a water pipe, the low-temperature water flowing back from the floor heating 11 to the heating water tank 3 will cause the water temperature in the heating water tank 3 to drop rapidly, which will affect the normal use of some high-temperature heat-using equipment. In addition, different heat-using equipment has different water temperature requirements. If all heat-using equipment is directly connected to the heating water tank 3 with water pipes, the heating water tank 3 with a certain water temperature cannot supply water to different heat-using equipment with different temperature differences.

[0102] For the above reasons, in this embodiment, an energy storage water tank 6 (buffer water tank) is provided on the water pipe connecting the heat-using unit and the heating water tank 3. The water in the heating water tank 3 is first supplied to the energy storage water tank 6. The energy storage water tank 6 can be connected to tap water to mix and adjust the water temperature and then supply it to the corresponding heat-using unit. Moreover, the low-temperature water flowing back from some heat-using equipment such as the floor heating 11 is first sent to the energy storage water tank 6 and will not directly enter the heating water tank 3, resulting in a rapid drop in the water temperature of the heating water tank 3. A water level sensor can be configured in the energy storage water tank 6 to detect the water volume therein in real time.

[0103] After the above-mentioned energy storage water tank 6 is provided on the water pipe connecting the floor heating 11, which is a heat-using unit, and the heating water tank 3, the aforementioned water pipe is divided into two parts - the first part connecting the heating water tank 3 and the energy storage water tank 6 and the second part connecting the energy storage water tank 6 and the floor heating 11. To facilitate the description of the technical solution of this embodiment, the aforementioned first part of the water pipe is hereinafter referred to as the second circulation water pipe 7, and the aforementioned second part of the water pipe is hereinafter referred to as the third circulation water pipe 9. The second circulation water pipe 7 connects the heating water tank 3 and the energy storage water tank 6, and the third circulation water pipe 7 connects the energy storage water tank 6 and the heat-using unit, that is, the floor heating 11. The second circulation water pipe 7 includes a water supply pipe for leading the water in the heating water tank 3 to the energy storage water tank 6 and a return pipe for leading the water in the energy storage water tank 6 to the heating water tank 3. The third circulation water pipe 7 includes a water supply pipe for leading the water in the energy storage water tank 6 to the floor heating 11 and a return pipe for leading the water in the floor heating 11 to the energy storage water tank 6. A second circulation pump 8 is connected to the second circulation water pipe 7, and a third circulation pump 10 is connected to the third water supply pipe 9.

[0104] Of course, the above first part of the water pipeline can also be a one-way pipeline with only water supply and no water return (instead of a circulating water pipe). The heating water tank 3 only supplies water to the energy storage water tank 6 and does not receive the cold water returned from the energy storage water tank 6. If the heat-consuming unit is not the floor heating 11 but a faucet that consumes water, then the second part of the water pipeline can also be a one-way pipeline with only water supply and no water return.

[0105] To prevent the water temperature in the energy storage water tank 6 from being too low to meet the usage requirements, the following second control strategy similar to the above control strategy is also adopted in this embodiment to ensure the water temperature of the energy storage water tank 6:

[0106] When the water temperature T2 of the heating water tank ≥ T q1 , the second circulation pump starts to enable the water in the heating water tank and the energy storage water tank to be exchanged. When T2 ≤ T g1 , the second circulation pump starts to close, and the water exchange between the heating water tank and the energy storage water tank stops. T q1 > T g1 . When the water temperature T3 of the energy storage water tank ≥ T g1 , reassign T q1 to the sum of the current T q1 value and the increment term Δδ 11 , and reassign T g to the sum of the current T q1 value and another increment term Δδ 21 .

[0107] It is not difficult to understand that theoretically, if the above second control strategy is continuously executed, the water temperature of the energy storage water tank 6 will continuously rise to be the same as the water temperature in the heating water tank 3. However, in some cases, it is not necessary for the energy storage water tank 6 to have a very high water temperature, as long as its water temperature can meet the normal requirements of the heat-consuming unit. Therefore, if it is detected that the water temperature of the energy storage water tank 6 reaches the required temperature value when T3 ≥ T need1 ), then the second circulation pump is closed, and the above second control strategy stops being executed.

[0108] To facilitate the reader to more intuitively understand the above second control strategy for the water temperature of the energy storage water tank, the following example is given:

[0109] The user starts the control strategy through the man-machine interface, and the water temperatures of the heating water tank 3 and the energy storage water tank 6 are obtained in real time. Once the water temperature of the heating water tank 3 reaches 50 °C (i.e., T q1 ), the second circulation pump 8 starts, and the heating water tank 3 and the energy storage water tank 6 conduct water exchange. Once the water temperature of the heating water tank 3 is at 40 °C (i.e., T g1)Next, the second circulation water pump 8 is closed, and the water exchange between the solar thermal heating unit and the heating water tank stops. Obviously, performing the foregoing actions will cause the water temperature of the heating water tank to continue to rise.

[0110] When the water temperature of the energy storage water tank 6 rises to 45 °C, the temperature thresholds for the second circulation water pump 8 to turn on and off are immediately raised by 5 °C, that is: once the water temperature of the heating water tank 3 reaches above 55 °C, the second circulation water pump 8 starts; once the water temperature of the heating water tank 3 is below 45 °C, the second circulation water pump 8 is closed.

[0111] Similarly, when the water temperature of the energy storage water tank 6 rises to 50 °C, the temperature thresholds for the second circulation water pump 8 to turn on and off are further raised by 5 °C, that is: once the water temperature of the heating water tank 3 reaches above 60 °C, the second circulation water pump 8 starts; once the heating water tank 3 is below 50 °C, the second circulation water pump 8 is closed.

[0112] When the water temperature of the energy storage water tank 6 rises to 55 °C, which can meet the demand of the floor heating 11, the above control strategy is no longer executed, and the actions of steps SⅠ to SⅢ are stopped. At this time, the second circulation water pump 8 remains in the closed state.

[0113] To facilitate the automatic implementation of the above water temperature control strategy for the energy storage water tank, the energy storage water tank 6 of this embodiment is equipped with a third water temperature sensor. The above second water temperature sensor and the foregoing third water temperature sensor are both electrically connected to the second circulation water pump 8. Another comparator is connected between the second water temperature sensor and the third water temperature sensor, and this comparator is electrically connected to the second circulation water pump 8. The foregoing third water temperature sensor is electrically connected to the second circulation water pump 8 so that when the third water temperature sensor detects that the water temperature of the energy storage water tank 6 rises to the ideal value (55 °C), the second circulation water pump 8 is kept in the closed state and the execution of this control strategy is stopped.

[0114] To prevent the heating water tank 3 from running out of water, this embodiment is also equipped with a water pipe that is connected to the above first circulation water pipe 4 to access tap water, and a water level sensor for detecting the water level of the heating water tank is arranged in the heating water tank 3. An electromagnetic valve 17 that is electrically connected to the above first circulation water pump 5 and the foregoing water level sensor is connected to the water pipe. When the water level sensor detects that the water level of the heating water tank 3 is lower than the set value, the electromagnetic valve 17 and the first circulation water pump 5 are turned on to inject tap water into the heating water tank 3.

[0115] When the photovoltaic water supply unit of the photovoltaic-thermal integrated machine is in the working state, the solar thermal heating unit is in the shutdown state and does not supply heat to the heating water tank 3. In this case, the heat consumption of the user for the system cannot be continuously replenished. To prevent the temperature of the heating water tank 3 from dropping to a level that cannot meet the usage requirements due to heat consumption in the photovoltaic mode, it is best to also obtain the water temperature T2 of the heating water tank 3 in real time in the photovoltaic mode. When the water temperature of the heating water tank drops to a set critical value such as 30 °C, the working mode control unit 2 switches the photovoltaic-thermal integrated machine 1 to the solar thermal working mode, the photovoltaic power generation unit stops working, and the solar thermal heating unit adjusts to the working state.

[0116] In some cases, such as in hot summer, when the house user is away for a long time, etc., heat is not used for a long time. If the system is operated in the solar thermal mode continuously or intermittently during this period, the heat generated is not utilized and is meaningless. For this reason, this embodiment also provides a control strategy with a higher priority: when the solar thermal heating unit is in the working state, the water level of the heating water tank 3 is obtained in real time. When the water level of the heating water tank remains unchanged for a long period of time (such as 48 hours), the working mode control unit 2 switches the photovoltaic-thermal integrated machine 1 to the solar thermal working mode, the photovoltaic power generation unit stops working, and the solar thermal heating unit adjusts to the working state.

[0117] The specific structure of the above-mentioned photovoltaic-thermal integrated machine 1 can be referred to Figures 2 to 6 As shown, the appearance of the photovoltaic-thermal integrated machine 1 is similar to that of an existing solar water heater. And the same as some existing solar water heaters, the photovoltaic-thermal integrated machine also includes a base frame 101, and a water flow cavity 102 and six heat collecting tubes 103 are fixedly arranged on the base frame 101.

[0118] The water flow cavity 102 has a water inlet interface 102a and a water outlet interface 102b. The water flow cavity 102 is connected to the above-mentioned first circulating water pipe through the water inlet interface 102a and the water outlet interface 102b thereon, so as to realize the connection between the water flow cavity 102 and the heating water tank 3. One end of each of the foregoing heat collecting tubes 103 is hermetically inserted into the water flow cavity (the mating part is sealed by a sealing ring), realizing the heat conduction connection between the heat collecting tube 103 and the water flow cavity 102, so as to transfer the solar heat absorbed by the heat collecting tube 103 to the water in the water flow cavity and heat the water in the water flow cavity. For the convenience of manufacturing and assembly, the foregoing heat collecting tubes 103 are arranged at equal intervals in the same plane. The base frame 101 serves as the support carrier of the entire photovoltaic-thermal integrated machine, and is used to support the foregoing water flow cavity 102 and heat collecting tubes 103 and various components described below, and defines the foregoing plane. Of course, in some other embodiments of the present application, the foregoing heat collecting tubes 103 can also be arranged at random intervals and not necessarily in the same plane.

[0119] The integrated photovoltaic and solar thermal device is also configured with six photovoltaic panels 104 that are equal in number to the heat collection tubes. These photovoltaic panels 104 are arranged one by one on the radial sides of the respective heat collection tubes, and each photovoltaic panel 104 can rotate around the tube axis of the corresponding heat collection tube. That is to say, the photovoltaic panels 104 are rotatably connected rather than fixedly connected to the integrated device, and the rotation axis of each photovoltaic panel 104 on the base frame 101 is exactly the tube axis of the corresponding heat collection tube 2.

[0120] For the convenience of describing the technical solution of this embodiment, if we Figure 2 and Figure 3 define a unit composed of a corresponding heat collection tube 103 and a photovoltaic panel 104 in Figure 6 as a photovoltaic-thermal unit, then the integrated photovoltaic and solar thermal device of this embodiment has a total of six photovoltaic-thermal units. In each photovoltaic-thermal unit, the rotation axis of the photovoltaic panel 104 on the base frame is exactly the tube axis of the heat collection tube 103 in that unit. In addition, in each photovoltaic-thermal unit, the photovoltaic panel 104 has an inner plate surface facing the heat collection tube 103 of that unit (i.e., Figure 6 the upper surface of the photovoltaic panel in Figure 6 ) and an outer plate surface facing away from the heat collection tube 103 of that unit (i.e., Figure 6 the lower surface of the photovoltaic panel in Figure 6 ), and the aforementioned outer plate surface of the photovoltaic panel 104 in this embodiment is the photovoltaic working surface for receiving sunlight for power generation.

[0121] It is not difficult to see that since the photovoltaic panel 104 can rotate around the tube axis of the heat collection tube 103 on the base frame 101, the relative position between the photovoltaic panel 104 and the heat collection tube 103 can be adjusted by rotating the photovoltaic panel 104. When it is necessary for the heat collection tube 103 to absorb light energy to obtain heat, the photovoltaic panel 104 is rotated to the backlight side of the heat collection tube 103 (i.e., the side away from the sunlight), and the heat collection tube faces the sunlight to generate heat. When it is necessary for power generation, the photovoltaic panel 104 is rotated to the sunlight-facing side of the heat collection tube 103 (i.e., the side facing the sunlight). At this time, the photovoltaic working surface of the photovoltaic panel 104 just faces the sunlight and is in the working state, and the photovoltaic panel 104 faces the sunlight to generate electricity.

[0122] It can be seen that when the integrated photovoltaic and solar thermal device is in the photovoltaic power generation working mode, the heat collection tube 103 is on the backlight side of the photovoltaic panel 104, and the sunlight is received and blocked by the photovoltaic panel 104 and will not shine on the heat collection tube 103. The heat collection tube 103 no longer absorbs heat to heat the water in the water flow cavity 102.

[0123] In practical applications, the solar thermal working mode and the photovoltaic working mode of the integrated device can be flexibly selected according to needs. For example: after obtaining a sufficient amount of heat energy in the solar thermal working mode, it is switched to the photovoltaic working mode for power generation, so as to make full use of solar energy for heating and power generation, increase the utilization efficiency of solar energy, realize the integration of solar power generation and heating, and save space resources.

[0124] In addition, to make the overall structure of the all-in-one machine more compact and reasonable, in this embodiment, the photovoltaic panels 104 and the heat collecting tubes 103 in each photovoltaic-thermal unit are arranged in parallel.

[0125] To prevent the photovoltaic panel 104 from touching the heat collecting tube 103 of an adjacent photovoltaic-thermal unit when rotating, which may lead to the rotation angle of the photovoltaic panel 104 being restricted by the heat collecting tube 103 in the adjacent photovoltaic-thermal unit, the photovoltaic panel 104 and the heat collecting tube 103 in each photovoltaic-thermal unit should be arranged as close as possible. Generally speaking, it is necessary to ensure that the distance value between the photovoltaic panel 104 and the heat collecting tube 103 in each photovoltaic-thermal unit is less than the distance value between the heat collecting tube 103 in this unit and the heat collecting tube in the adjacent unit. When the photovoltaic panel 3 rotates, it can pass through the gap between the adjacent heat collecting tubes.

[0126] As described above, the working mode of the photovoltaic-thermal integration is controlled by the aforementioned working mode control unit 2. Specifically, in this embodiment, the working mode control unit 2 mainly includes a motor and a motor controller. The motor is connected to the photovoltaic panel through a gear transmission assembly to drive the photovoltaic panel 104 to rotate. The motor controller is electrically connected to the motor to control the operating parameters of the motor. The second water temperature sensor for detecting the heating water tank 3 is electrically connected to the aforementioned motor controller.

[0127] The above-mentioned gear transmission assembly includes six synchronous gears 201 and six idler gears 202. The six synchronous gears 201 are respectively fixed to the six photovoltaic panels 104 (indirectly fixed, which will be introduced in detail below). The idler gears 202 are meshed with the synchronous gears 201. The motor can directly drive any one of the six synchronous gears 201 and the six idler gears 202, so as to realize the linkage of all the synchronous gears 201 and all the idler gears 202, and make each photovoltaic panel 104 in any predetermined orientation. The "synchronization" in the synchronous gears 201 means that under the drive of the aforementioned motor, the rotation angles and paces of these six gears are exactly the same, so that the rotation angles and paces of the six photovoltaic panels 104 are exactly the same.

[0128] The above-mentioned motor controller electrically connected to the motor can accurately control the rotation angle of the photovoltaic panel 104, and thus indirectly adjust the angle of the photovoltaic panel.

[0129] As described above, in this embodiment, each photovoltaic panel 104 is rotatably connected to the base frame 101. The following further introduces the rotational connection method between these photovoltaic panels 104 and the base frame 101:

[0130] A pivot frame 203 is fixed on each photovoltaic panel 104, and the pivot frame 203 is pivotally sleeved on the heat collecting pipe 103. The pivot frame 203 fixed on the photovoltaic panel 104 is rotatably sleeved on the heat collecting pipe 103, and the heat collecting pipe 103 is fixed to the base frame 101, so the rotational connection between the photovoltaic panel 104 and the base frame 101 is indirectly realized.

[0131] The above synchronous gear 201 is coaxially sleeved outside the heat collecting pipe 103 and fixed to the pivot frame 203.

[0132] A support bearing can be provided between the pivot frame 203 and the heat collecting pipe 103 to reduce friction.

[0133] The above synchronous gear 201 is directly fixed to the aforementioned pivot frame 203 rather than the photovoltaic panel 104. Since the pivot frame 203 is fixed to the photovoltaic panel 104, the synchronous gear 201 is indirectly fixed to the photovoltaic panel 104. The synchronous gear 201 drives the pivot frame 203 to rotate, and the pivot frame 203 drives the photovoltaic panel 104 to rotate relative to the base frame 101 and the heat collecting pipe 103. The aforementioned six synchronous gears 201 are coaxially arranged with six heat collecting pipes 103 respectively.

[0134] In actual application, the above-mentioned solar thermal and photovoltaic integrated machine (base frame part) is generally installed on the roof or outer wall of a building, especially a residence. The total area of all photovoltaic panels is preferably more than 20 m 2 above.

[0135] Embodiment 2:

[0136] Figure 7 Another specific embodiment of the photovoltaic and solar thermal system of the present application is shown. The photovoltaic and solar thermal system of this embodiment has basically the same structure as the photovoltaic and solar thermal system in Embodiment 1. It also includes a photovoltaic and solar thermal integrated machine 1, a working mode control unit 2, a heating water tank 3, a heat using unit, and an LED lamp 12 as an electricity using unit. Among them, the photovoltaic and solar thermal integrated machine 1 adopts exactly the same structural form as in Embodiment 1. The heat using unit is connected to the heating water tank 3 by a water circuit and is not shown in Figure 7 it.

[0137] This photovoltaic and solar thermal system adopts exactly the same solar thermal - photovoltaic working mode switching strategy as in Embodiment 1 - that is, by monitoring the water temperatures of the solar thermal heating unit and the heating water tank, the opening and closing of the first water pump 5 and the switching of the working mode are controlled.

[0138] Different from Embodiment 1, in this embodiment, the photovoltaic and solar thermal integrated machine 1 is not connected to the public power grid, and the water in the heating water tank 3 is not led to the floor heating through a buffer energy storage water tank.

[0139] Embodiment 3:

[0140] Figure 8Another photovoltaic-thermal integrated machine of structural form is shown, which is basically the same as the structure of the photovoltaic-thermal integrated machine in Example 1, with the only difference being that the heat collecting tube 103 is rotatably connected (rather than being fastened in Example 1) to the base frame 101, and the photovoltaic panel 104 and the heat collecting tube 103 in the same photovoltaic-thermal unit are fixedly connected to each other through a connecting frame 105. When the photovoltaic panel 104 rotates on the base frame 101, the heat collecting tube 103 fixed to the photovoltaic panel 104 also rotates accordingly. Naturally, when the heat collecting tube 103 rotates on the base frame 101, the photovoltaic panel 104 fixed to the heat collecting tube 103 also rotates with the heat collecting tube 103.

[0141] The rotating connection structure of the heat collecting tube 103 and the base frame 101 is specifically as follows: a heat collecting tube front plug-in hole is provided on the cavity wall of the water flow cavity 102, and a heat collecting tube rear plug-in hole is provided on the base frame 101, and the two ends of the heat collecting tube 103 are respectively pivotally inserted in the aforementioned heat collecting tube front plug-in hole and the heat collecting tube rear plug-in hole. Since the water flow cavity 102 and the base frame 101 are fixed, the relative position of the heat collecting tube front plug-in hole on the cavity wall of the water flow cavity 102 and the base frame 101 is fixed, so the heat collecting tube 103 pivotally inserted in the heat collecting tube front plug-in hole can also rotate (rotate) around the tube axis of the heat collecting tube relative to the base frame 101.

[0142] The heat collecting tube 103 and the photovoltaic panel 104 in the same photovoltaic-thermal unit are fixed to each other and can rotate around the same rotation axis (the tube axis of the heat collecting tube) on the base frame 101. By simply adjusting the rotation angle of the heat collecting tube 103 and the photovoltaic panel 104, the photovoltaic panel 104 can also be selectively placed on the backlight side or the light-facing side of the heat collecting tube 103.

[0143] In order to facilitate the rotation of the photovoltaic panel 104 and the heat collecting tube 103, the present embodiment is equipped with a driving device that is transmission-connected with the heat collecting tube 103 to drive the heat collecting tube 103 to rotate. The driving device also includes: a plurality of synchronous gears 201, a plurality of bridge gears and a miniature motor. The plurality of synchronous gears 201 are coaxially fixed to each heat collecting tube 103, respectively. The bridge gear is meshed and connected with the synchronous gear 201. The motor can directly drive any one of the plurality of synchronous gears 201 and the plurality of bridge gears, so that all the synchronous gears 201 and all the bridge gears can be linked, so that each heat collecting tube 103 and each photovoltaic panel 104 are in any predetermined orientation.

[0144] In the first embodiment, the heat collecting tube 103 is fixed to the base frame 101, and the photovoltaic panel 104 is rotatably connected to the heat collecting tube 103. In the second embodiment, the heat collecting tube 103 is rotatably connected to the base frame 101, and the photovoltaic panel 104 is fixed to the heat collecting tube 103. Both of the above methods can realize the switching of photovoltaic and solar thermal working modes, among which the first embodiment is more preferred, because:

[0145] The heat collecting pipe 103 can generally be divided into two structural forms: with water flow and without water flow. Whether it is a heat collecting pipe with water flow or without water flow, the end needs to be inserted into the water flow cavity 102. To prevent water from flowing out of the connection between the two, strict sealing is required. If the fixed heat collecting pipe structure of Embodiment 1 is adopted, the seal at the connection between the heat collecting pipe and the water flow cavity is a static seal and generally does not leak. However, if the rotating heat collecting pipe structure of Embodiment 2 is adopted, the following problems will exist:

[0146] For the heat collecting pipe with water flow, the connection between the heat collecting pipe and the water flow cavity is a dynamic seal. If the heat collecting pipe is rotated frequently, the dynamic seal is easily damaged, resulting in water leakage.

[0147] For the heat collecting pipe without water flow, it is generally mainly composed of an inner pipe and an outer pipe that are coaxially fixed. The hollow interlayer between the inner and outer pipes is a vacuum. An endothermic coating is coated on the inner wall of the inner pipe. A metal heat conducting rod and an aluminum foil sheet fixedly connected to the metal heat conducting rod are arranged inside the inner pipe. The aluminum foil sheet is arranged in contact with the endothermic coating. One end of the metal heat conducting rod extends outside the inner pipe to transfer heat to the water in the water flow cavity. If one end of the inner pipe, outer pipe, and metal heat conducting rod of the heat collecting pipe are all inserted into the connection with water in the water flow cavity, there will also be a problem that the dynamic seal is damaged and leaks after the heat collecting pipe rotates many times; if only one end of the metal heat conducting rod of the heat collecting pipe is inserted into the connection with water in the water flow cavity (the connection is a static seal), and the inner pipe and outer pipe are not inserted into the inside of the water flow cavity, during operation, the metal heat conducting rod is fixed and only the inner and outer pipes rotate. Although this can avoid the problem of water leakage, the aluminum foil sheet fixed to the metal heat conducting rod rotates relative to the inner and outer pipes. After long-term use, not only will the aluminum foil sheet be deformed and unable to maintain good contact with the endothermic coating, but also the aluminum foil sheet will scratch the endothermic coating, resulting in a decrease in its heat absorption performance.

[0148] The above is only an exemplary implementation manner of this application and is not used to limit the protection scope of this application. The protection scope of this application is determined by the appended claims.

Claims

1. A control method applicable to a photovoltaic-thermal system, characterized in that, The photovoltaic-thermal system includes: A photovoltaic-thermal integrated unit (1), which includes an alternative working photovoltaic power generation unit and a solar thermal heating unit; A working mode control unit (2), which is connected to the photovoltaic-thermal integrated unit to control the alternative working of the photovoltaic power generation unit and the solar thermal heating unit; A heating water tank (3), which is connected to the solar thermal heating unit through a first circulating water pipe (4), and a first circulating water pump (5) is connected to the first circulating water pipe (4); A heat-using unit, which is connected to the heating water tank (3) through a water pipe; and An electricity-using unit, which is electrically connected to the photovoltaic power generation unit; The solar thermal heating unit includes a water flow cavity (102) and a heat collecting pipe (103), the first circulating water pipe (4) is connected to the water flow cavity (102), and the heat collecting pipe (103) is thermally connected to the water flow cavity (102); A first water temperature sensor is provided in the water flow cavity (102), a second water temperature sensor is provided in the heating water tank (3), and both the first water temperature sensor and the second water temperature sensor are electrically connected to the first circulating water pump (5); A comparator is connected between the first water temperature sensor and the second water temperature sensor, and the comparator is electrically connected to the first circulating water pump (5); The control method includes: When the solar thermal heating unit is in the working state, the water temperature T2 of the heating water tank (3) is obtained in real time. When T2 ≥ T need , the solar thermal heating unit stops working, and the photovoltaic power generation unit is adjusted to the working state, where When the solar thermal heating unit is in a working state, the following control strategy is carried out: When the water temperature T1 of the photothermal heating unit ≥ T q , the first circulation water pump (5) starts; when T1 ≤ T g , the first circulation water pump (5) shuts down; T need > T q > T g ; When the water temperature T2 of the heating water tank ≥ T g , re-assign T q to the sum of the current T q value and the increment Δδ1, and re-assign T g to the sum of the current T q value and another increment Δδ2.

2. A control method as claimed in claim 1, wherein, Including: When the photovoltaic power generation unit is in the working state, the water temperature T2 of the heating water tank (3) is obtained in real time. When T2 ≤ T low , the photovoltaic power generation unit stops working, and the solar thermal heating unit is adjusted to the working state.

3. The control method according to claim 2, wherein T low ＝30℃。 4. A control method as claimed in claim 1, wherein, When the solar thermal heating unit is in a working state, the water level of the heating water tank (3) is obtained in real time. When the water level of the heating water tank (3) remains unchanged within a certain time period t, the solar thermal heating unit stops working, and the photovoltaic power generation unit is adjusted to a working state.

5. The control method according to claim 4, wherein t = 48 hours.

6. A photovoltaic-thermal system applicable to the control method according to any one of claims 1 to 5, characterized in that, Including: A photovoltaic-thermal integrated unit (1), which includes an alternative working photovoltaic power generation unit and a solar thermal heating unit; A working mode control unit (2), which is connected to the photovoltaic-thermal integrated unit to control the alternative working of the photovoltaic power generation unit and the solar thermal heating unit; A heating water tank (3), which is connected to the solar thermal heating unit through a first circulating water pipe (4), and a first circulating water pump (5) is connected to the first circulating water pipe (4); A heat-using unit, which is connected to the heating water tank (3) through a water pipe; and An electricity-using unit, which is electrically connected to the photovoltaic power generation unit; The solar thermal heating unit includes a water flow cavity (102) and a heat collecting pipe (103), the first circulating water pipe (4) is connected to the water flow cavity (102), and the heat collecting pipe (103) is thermally connected to the water flow cavity (102); A first water temperature sensor is provided in the water flow cavity (102), a second water temperature sensor is provided in the heating water tank (3), and both the first water temperature sensor and the second water temperature sensor are electrically connected to the first circulating water pump (5); A comparator is connected between the first water temperature sensor and the second water temperature sensor, and the comparator is electrically connected to the first circulating water pump (5).

7. The photovoltaic-thermal system according to claim 6, wherein A heat storage water tank (6) is provided on the water pipe.

8. The photovoltaic-thermal system according to claim 7, characterized in that The water flow pipeline includes a second circulation water pipe (7) connecting the energy storage water tank (6) and the heating water tank (3), and a second circulation water pump (8) is connected to the second circulation water pipe (7).

9. The photovoltaic-thermal system according to claim 8, characterized in that, The water flow pipeline further includes a third circulation water pipe (9) connecting the energy storage water tank (6) and the heat-using unit, and a third circulation water pump (10) is connected to the third circulation water pipe (9).

10. The photovoltaic and solar thermal system according to claim 8, characterized in that, The heating water tank (3) is provided with a second water temperature sensor, and the energy storage water tank (6) is provided with a third water temperature sensor. Both the second water temperature sensor and the third water temperature sensor are electrically connected to the second circulation water pump (8).

11. The photovoltaic-thermal system according to claim 10, characterized in that, A comparator is connected between the second water temperature sensor and the third water temperature sensor, and the comparator is electrically connected to the second circulation water pump (8).

12. The photovoltaic-thermal system according to claim 7, wherein The energy storage water tank (6) is connected to a water supply pipe.

13. The photovoltaic-thermal system according to claim 6, wherein The photovoltaic-thermal integrated machine (1) includes: A base frame (101), on which the water flow cavity (102) and the heat collection pipe (103) are both arranged, And A photovoltaic panel (104) arranged on the radial side of the heat collection pipe and capable of rotating around the pipe axis of the heat collection pipe; The electricity-consuming unit is electrically connected to the photovoltaic panel, The heating water tank (3) is configured with a water level sensor for detecting the water level of the heating water tank (3).

14. The photovoltaic-thermal system according to claim 13, characterized in that The working mode control unit (2) includes: A motor connected to the photovoltaic panel through a transmission component to drive the photovoltaic panel (104) to rotate, and A motor controller electrically connected to the motor.

15. The photovoltaic-thermal system according to claim 14, wherein At least two heat collection pipes (103) are provided, and each of the heat collection pipes (103) is arranged parallel to each other at intervals. A photovoltaic panel (104) that rotates around the pipe axis of each heat collection pipe is arranged parallel to the radial side of each heat collection pipe; the transmission component includes: A synchronous gear (201) coaxially sleeved outside the heat collection pipe (103) and fixed to the photovoltaic panel (104), and An idler gear (202) meshingly connected between the synchronous gears (201); The motor is connected to one of the synchronous gears (201) or one of the idler gears (202).

16. The photovoltaic and solar thermal system according to claim 6, characterized in that A power controller (13) is provided on the connection circuit between the electricity-consuming unit and the photovoltaic power generation unit, and the power controller (13) is electrically connected to the public power grid (14).

17. The photovoltaic-thermal system according to claim 6, wherein The second water temperature sensor is electrically connected to the working mode control unit (2).

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