Method for testing heating performance of photovoltaic and photo-thermal integrated water heater

Abstract

The invention discloses a method for testing the heating performance of a photovoltaic and photo-thermal integrated water heater and relates to the field of water heater testing, the photovoltaic and photo-thermal integrated water heater comprises a heat storage water tank and a photovoltaic and photo-thermal integrated assembly, and the testing method comprises the steps that water with the temperature not lower than 20 DEG C is adopted, and water circulation treatment is conducted on the heat storage water tank at the flow of 400 L / h to 600 L / h; under the condition that the temperature change of the water inlet of the heat storage water tank within at least 5 min is not larger than 1 DEG C, the water inlet temperature is determined as the effective water inlet temperature of the heat storage water tank; a heating mode of the photovoltaic and photo-thermal integrated water heater is started, heating is stopped after heating is conducted for 8 h, and the photovoltaic and photo-thermal integrated assembly is shielded; a water mixing pump located in the hot water storage tank is started, water in the hot water storage tank is evenly mixed, and the effective water outlet temperature of the hot water storage tank is obtained; and determining a daily heat gain value according to the effective water inlet temperature and the effective water outlet temperature. The method has the advantage of improving the test accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of water heater testing, and in particular to a method for testing the heating performance of a photovoltaic-thermal integrated water heater. Background Art

[0002] With the widespread application of photovoltaic thermal water heaters in the field of renewable energy, their performance evaluation technology has become a key factor restricting the development of the industry. The existing testing system has significant limitations in environmental simulation, data collection, efficiency evaluation and other aspects, making it difficult for test results to truly reflect actual working conditions. For example, the initial conditions (such as the water temperature of the hot water storage tank and the cold water inlet temperature) lack precise control, the parameter fluctuation range is large and there is no unified standard, resulting in poor comparability of data between different test batches or equipment; the dynamic monitoring capability is insufficient, relying only on low-frequency sampling or key node recording, unable to capture transient changes in the heat output process, and it is difficult to fully reflect the thermal response characteristics of the system; in addition, the existing methods generally ignore the heat loss factors such as insulation loss and pipe heat dissipation during the heat output process of the water heater, resulting in an inflated heat output rate calculation result that cannot truly reflect the performance in actual usage scenarios.

[0003] The above problems together lead to low reliability and poor data comparability of photovoltaic thermal water heater performance test results, which makes it difficult to meet the needs of product design optimization, market access certification, etc. There is an urgent need to establish a standardized and high-precision testing method to scientifically evaluate the system's thermal output performance. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems in the related art to a certain extent. To this end, the present invention provides a method for testing the heating performance of a photovoltaic-thermal integrated water heater, which has the advantage of improving the test accuracy.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for testing the heating performance of a photovoltaic-thermal integrated water heater, wherein the photovoltaic-thermal integrated water heater includes a heat storage tank and a photovoltaic-thermal integrated assembly. The testing method includes: Use water with a temperature of not less than 20°C and a flow rate of 400L / h to 600L / h to circulate water in the hot water storage tank; When the water inlet temperature of the hot water storage tank changes by no more than 0.1° C. within at least 5 minutes, the water inlet temperature is determined as the effective water inlet temperature of the hot water storage tank; Starting the heating mode of the photovoltaic-thermal integrated water heater, stopping the heating after 8 hours, and shielding the photovoltaic-thermal integrated component; Starting a water mixing pump in the hot water storage tank to mix the water in the hot water storage tank and obtain an effective water outlet temperature of the hot water storage tank; The daily heat gain is determined according to the effective water inlet temperature and the effective water outlet temperature; wherein the daily heat gain is one of the performance indicators of heating performance.

[0006] By circulating water at a temperature of no less than 20°C and requiring the inlet temperature of the heat storage tank to fluctuate by no more than ±0.1°C within 5 minutes, the water temperature at the start of heating is ensured to be highly consistent, eliminating the impact of initial water temperature differences on the test results. Furthermore, a mixing pump is used to pump water from the bottom of the heat storage tank to the top for circulation, avoiding measurement errors caused by temperature stratification. The inlet flow rate is set to 400L / h to 600L / h to avoid uneven water temperature distribution or changes in heat exchange efficiency due to excessive flow fluctuations, further ensuring the stability of the test conditions. Furthermore, the average temperature over 5 minutes is used as the water temperature at the start and end of heating, avoiding the impact of instantaneous temperature fluctuations on the results. Through strict control of each step, errors caused by operational differences are reduced, improving the accuracy of the test results.

[0007] Optionally, obtaining the effective water outlet temperature of the hot water storage tank includes: Continuously obtaining the outlet temperature of the hot water storage tank, and determining the outlet temperature as the effective outlet temperature of the hot water storage tank when the outlet temperature of the hot water storage tank changes by no more than 0.1° C. within at least 5 minutes; The calculation formula of the daily calorific value is shown in formula (1): (1) where c pw is the specific heat capacity of water at constant pressure, t e is the effective outlet temperature, t b is the effective water inlet temperature, m is the total mass of water in the water tank, in kilograms (Kg).

[0008] Optionally, the heating mode includes a photovoltaic heating mode, a solar thermal heating mode, and a photovoltaic-thermal integrated heating mode; wherein the solar thermal heating mode includes any one of a photovoltaic short-circuit condition, a photovoltaic open-circuit condition, and a photovoltaic load condition; In case the heating mode is a photovoltaic heating mode, the starting of the photovoltaic-thermal integrated water heater in the heating mode includes: connecting the photovoltaic-thermal integrated component to an electric heater; When the heating mode is the solar thermal heating mode, the heating mode of the photovoltaic-thermal integrated water heater is started, including: connecting the positive and negative cables of the photovoltaic-thermal integrated component under the photovoltaic short-circuit condition; disconnecting the positive and negative poles of the photovoltaic-thermal integrated component under the photovoltaic open-circuit condition; and connecting the positive and negative poles of the photovoltaic-thermal integrated component to a pure resistance module under the photovoltaic load condition, and immersing the pure resistance module in a constant temperature water tank; In the case where the heating mode is the photovoltaic thermal heating mode, starting the heating mode of the photovoltaic thermal integrated water heater includes: connecting the photovoltaic thermal integrated component to the electric heater and connecting the direct thermal heating circulation pipeline.

[0009] Optionally, the performance index also includes the solar radiation amount on the surface of the photovoltaic thermal integration component is 5kWh / m 2 The nominal daily heat gain per unit photovoltaic installation area is calculated as shown in formula (2): (2) Where H is the daily solar radiation on the surface of the photovoltaic and thermal integrated components, in kWh / m 2 , A is the area of ​​the lighting surface of the photovoltaic thermal integration component, in square meters (㎡).

[0010] Optionally, the performance index also includes the solar radiation amount on the surface of the photovoltaic thermal integration component is 5kWh / m 2 The nominal daily heat gain per unit photovoltaic installed capacity is calculated as shown in formula (3): (3) Where H is the daily solar radiation on the surface of the photovoltaic and thermal integrated components, in kWh / m 2 , P peak It is the actual measured value of photovoltaic installation capacity, in watts (W).

[0011] Optionally, obtaining the effective water outlet temperature of the hot water storage tank includes: Continuously injecting inlet water of different temperatures into the water inlet of the hot water storage tank, and discharging the hot water in the hot water storage tank from the water outlet of the hot water storage tank at a constant flow rate, measuring the temperature of the drainage water at least once every 1 second until the volume of the drainage water is greater than three times the volume of the hot water storage tank and the temperature difference between the drainage water and the inlet water temperature is less than 1°C, and determining the temperatures of the multiple drainage water as multiple effective water outlet temperatures; The calculation formula of the daily calorific value is shown in formula (4): (4) Wherein T1 is the water inlet temperature, T2 is the effective water outlet temperature, C is the constant pressure specific heat capacity of water, is the mass flow rate of water at the outlet, in kilograms per second (kg / s).

[0012] Optionally, after starting the heating mode of the photovoltaic-thermal integrated water heater, heating is stopped after 8 hours, and the photovoltaic-thermal integrated component is shielded, and then the method includes: The cumulative photovoltaic power generation during the heating period is obtained using an electric energy meter. The heating efficiency of the photovoltaic-thermal integrated water heater is determined based on the daily heat value and the cumulative photovoltaic power generation. The calculation formula for the heating efficiency of the photovoltaic-thermal integrated water heater is shown in formula (5): (5) Among them, E PV is the cumulative photovoltaic power generation.

[0013] Optionally, after that, it also includes: After adjusting the water temperature in the hot water storage tank to 65℃±3℃, turn off any power heating mode; Continuously injecting cold water at a temperature of 15°C ± 2°C into the water inlet of the hot water storage tank, and continuously discharging hot water from the water outlet of the hot water storage tank; After 15 seconds from the start of drainage, the inlet water temperature and outlet water temperature are measured every 5 seconds. If the outlet water temperature is 20°C lower than the maximum outlet water temperature, drainage is stopped. Obtain the average inlet water temperature, average outlet water temperature and total drainage mass during the drainage period; The hot water output rate is determined according to the average water inlet temperature, the average drainage temperature, and the total drainage mass.

[0014] Optionally, the calculation formula for the hot water output rate is shown in formula (6): (6) Wherein, m is the total mass of the drainage, t p is the average drainage temperature, t c is the average inlet water temperature, m p The mass of the released water is in kilograms (kg), and m is the total mass of the water in the water tank, in kilograms (Kg).

[0015] Optionally, before starting the water mixing pump in the hot water storage tank to mix the water in the hot water storage tank and obtaining the effective water outlet temperature of the hot water storage tank, the method includes: Stop injecting water into the water inlet of the hot water storage tank.

[0016] Optionally, before the water storage tank is circulated with water having a temperature of not less than 20° C. at a flow rate of 400 L / h to 600 L / h, the method further comprises: Clean the surface of the photovoltaic-thermal integrated component and completely shield the photovoltaic-thermal integrated component.

[0017] These features and advantages of the present invention will be further disclosed in the following detailed description and accompanying drawings. The preferred embodiments and means of the present invention will be fully illustrated in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. Furthermore, although multiple features, elements, and components may be present in each of the following text and accompanying drawings, they may be labeled with different symbols or numbers for convenience, but all represent components with the same or similar structure or function. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings: Figure 1 A flow chart of a testing method according to an embodiment of the present invention; Figure 2 This is a connection diagram of the photovoltaic heating performance test system in the above embodiment; Figure 3 This is a drainage curve of another embodiment of the present invention Figure 1 : Figure 4 The drainage curve of the above embodiment Figure 2 .

[0019] Among them, 1. Photovoltaic thermal integration component; 2. Grid power supply; 3. Heat storage tank; 4. Electric heater; 5. Controller; 6. Three-way valve; 7. Bypass water pump; 8. Heat storage tank inlet temperature sensor; 9. Heat storage tank outlet temperature sensor; 10. Global pyranometer; 11. Outdoor temperature sensor; 12. Indoor temperature sensor. DETAILED DESCRIPTION

[0020] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described in the embodiments are intended to explain the present invention and are not to be construed as limiting the present invention.

[0021] Reference in this specification to "one embodiment," "an example," or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment itself can be included in at least one embodiment of the present patent disclosure. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0022] The present invention provides a method for testing the heating performance of a photovoltaic-thermal integrated water heater, wherein the photovoltaic-thermal integrated water heater comprises a heat storage tank and a photovoltaic-thermal integrated component, such as Figure 1 As shown, the test method includes: In step S110, water with a temperature of not less than 20°C is used to circulate water through the hot water storage tank at a flow rate of 400 L / h to 600 L / h; In step S120, when the water inlet temperature of the hot water storage tank does not change by more than 0.1°C within at least 5 minutes, the water inlet temperature is determined as the effective water inlet temperature of the hot water storage tank; In step S130, the photovoltaic-thermal integrated water heater is started in a heating mode, and the heating is stopped after 8 hours, and the photovoltaic-thermal integrated component is shielded; In step S140, a water mixing pump in the hot water storage tank is started to mix the water in the hot water storage tank and obtain the effective water outlet temperature of the hot water storage tank; In step S150, the daily heat gain is determined according to the effective water inlet temperature and the effective water outlet temperature; wherein the daily heat gain is one of the performance indicators of heating performance.

[0023] By circulating water at a temperature of no less than 20°C and requiring the inlet temperature of the heat storage tank to fluctuate by no more than ±0.1°C within 5 minutes, the water temperature at the start of heating is ensured to be highly consistent, eliminating the impact of initial water temperature differences on the test results. Furthermore, a mixing pump is used to pump water from the bottom of the heat storage tank to the top for circulation, avoiding measurement errors caused by temperature stratification. The inlet flow rate is set to 400L / h to 600L / h to avoid uneven water temperature distribution or changes in heat exchange efficiency due to excessive flow fluctuations, further ensuring the stability of the test conditions. Furthermore, the average temperature over 5 minutes is used as the water temperature at the start and end of heating, avoiding the impact of instantaneous temperature fluctuations on the results. Through strict control of each step, errors caused by operational differences are reduced, improving the accuracy of the test results.

[0024] During the testing process, the requirements for the test object and test environment are as follows: 1. During the test, the photovoltaic-thermal integrated water heater operates in heating mode, and the photovoltaic heating function will not be turned off due to the water temperature in the hot water storage tank reaching the maximum protection temperature value of photovoltaic heating; 2. The test day shall include at least one full day, with the test period being 4 hours before and 4 hours after local solar noon; 3. During the test period, the daily solar radiation on the surface of the photovoltaic thermal integrated module is 4.5kWh / m 2 ~6kWh / m 2 within the scope; 4. The water storage tank is placed indoors. The water temperature of the water storage tank is 20.0℃±1.0℃ at the beginning of the test. The average temperature of the environment where the water storage tank is located during the test is within the range of 15℃~30℃. 5. All components of the photovoltaic water heater should be installed according to the manufacturer's instructions; 6. The photovoltaic and thermal integrated modules shall be installed on the mounting brackets provided by the manufacturer, or at the mounting angles specified by the manufacturer; 7. Connect the photovoltaic water heater to the photovoltaic heating performance test system; The photovoltaic heating performance test system includes a photovoltaic thermal integration component 1, a power grid power supply 2, a heat storage tank 3, an electric heater 4, a controller 5, a three-way valve 6, a bypass water pump 7, a heat storage tank inlet temperature sensor 8, a heat storage tank outlet temperature sensor 9, a global pyranometer 10, an outdoor temperature sensor 11, and an indoor temperature sensor 12. The connection method is as follows: Figure 2 shown.

[0025] 8. The pyranometer tests the solar irradiance on the plane where the photovoltaic and thermal integrated components are located; 9. The horizontal distance between the outdoor temperature sensor and the photovoltaic thermal integrated component shall not exceed 3m, and the horizontal distance between the indoor temperature sensor and the water storage tank shall not exceed 3m.

[0026] Optionally, obtaining the effective water outlet temperature of the hot water storage tank includes: Continuously obtaining the outlet temperature of the hot water storage tank, and determining the outlet temperature as the effective outlet temperature of the hot water storage tank when the outlet temperature of the hot water storage tank changes by no more than 1° C. within at least 5 minutes; The calculation formula of the daily calorific value is shown in formula (1): (1) where c pw is the specific heat capacity of water at constant pressure, which should be determined based on the average water temperature before and after startup, and is expressed in kilojoules per kilogram per degree Celsius [kJ / (kg‧℃)], t e is the effective outlet temperature, t b is the effective water inlet temperature, m is the total mass of water in the water tank, in kilograms (Kg).

[0027] The water at the bottom of the hot water storage tank is pumped to the top through a mixing pump and circulated for at least 5 minutes to ensure that the water temperature in the tank is evenly distributed and to avoid measurement errors caused by temperature stratification. The water temperature fluctuation during the mixing process does not exceed the requirement of ±0.1°C, which further ensures the accuracy of temperature measurement.

[0028] Optionally, the heating mode includes a photovoltaic heating mode, a solar thermal heating mode, and a photovoltaic-thermal integrated heating mode; wherein the solar thermal heating mode includes any one of a photovoltaic short-circuit condition, a photovoltaic open-circuit condition, and a photovoltaic load condition; In case the heating mode is a photovoltaic heating mode, the starting of the photovoltaic-thermal integrated water heater in the heating mode includes: connecting the photovoltaic-thermal integrated component to an electric heater; When the heating mode is the solar thermal heating mode, the heating mode of the photovoltaic-thermal integrated water heater is started, including: connecting the positive and negative cables of the photovoltaic-thermal integrated component under the photovoltaic short-circuit condition; disconnecting the positive and negative poles of the photovoltaic-thermal integrated component under the photovoltaic open-circuit condition; and connecting the positive and negative poles of the photovoltaic-thermal integrated component to a pure resistance module under the photovoltaic load condition, and immersing the pure resistance module in a constant temperature water tank; In the case where the heating mode is the photovoltaic thermal heating mode, starting the heating mode of the photovoltaic thermal integrated water heater includes: connecting the photovoltaic thermal integrated component to the electric heater and connecting the direct thermal heating circulation pipeline.

[0029] The resistance of the pure resistance module is determined by the electric heating resistor in the integrated photovoltaic / thermal water heater. Immersing the module in a constant-temperature water bath maintains a constant resistance. By testing the water heater under various heating modes, the comprehensive evaluation of the heating performance of the integrated photovoltaic / thermal water heater is enhanced.

[0030] Optionally, the performance index also includes the solar radiation amount on the surface of the photovoltaic thermal integration component is 5kWh / m 2 The nominal daily heat gain per unit photovoltaic installation area is calculated as shown in formula (2): (2) Where H is the daily solar radiation on the surface of the photovoltaic and thermal integrated components, in kWh / m 2 , A is the area of ​​the lighting surface of the photovoltaic thermal integration component, in square meters (㎡).

[0031] In an optional embodiment, the performance index also includes the solar radiation amount on the surface of the photovoltaic thermal integrated component is 5kWh / m 2 The nominal daily heat gain per unit photovoltaic installed capacity is calculated as shown in formula (3): (3) Where H is the daily solar radiation on the surface of the photovoltaic and thermal integrated components, in kWh / m 2 , P peak It is the actual measured value of photovoltaic installation capacity, in watts (W).

[0032] Optionally, obtaining the effective water outlet temperature of the hot water storage tank includes: Continuously injecting inlet water of different temperatures into the water inlet of the hot water storage tank, and discharging the hot water in the hot water storage tank from the water outlet of the hot water storage tank at a constant flow rate, measuring the temperature of the drainage water at least once every 1 second until the volume of the drainage water is greater than three times the volume of the hot water storage tank and the temperature difference between the drainage water and the inlet water temperature is less than 1°C, and determining the temperatures of the multiple drainage water as multiple effective water outlet temperatures; The calculation formula of the daily calorific value is shown in formula (4): (4) Wherein T1 is the water inlet temperature, T2 is the effective water outlet temperature, C is the constant pressure specific heat capacity of water, is the mass flow rate of water at the outlet, in kilograms per second (kg / s).

[0033] By measuring the temperature of the drain water frequently, it is possible to draw a Figure 3 The drainage curve shown in Figure 1 can more accurately describe the change of water temperature over time. f(T) is obtained by quadratic fitting through the drainage curve. In combination with the drainage curve, by changing the cold water temperature T1 entering the storage tank, the actual solar heat gain of the solar energy system under different water inlet temperatures can be obtained. In addition, Figure 4 As shown, by setting the usage temperature line, the total volume and total calorific value of hot water that the user can actually use can also be obtained.

[0034] In an optional embodiment, after starting the heating mode of the photovoltaic-thermal integrated water heater, heating is stopped after 8 hours, and the photovoltaic-thermal integrated component is shielded, the method further includes: The cumulative photovoltaic power generation during the heating period is obtained using an electric energy meter. The heating efficiency of the photovoltaic-thermal integrated water heater is determined based on the daily heat value and the cumulative photovoltaic power generation. The calculation formula for the heating efficiency of the photovoltaic-thermal integrated water heater is shown in formula (5): (5) Among them, E PV is the cumulative photovoltaic power generation.

[0035] Optionally, after that, it also includes: After adjusting the water temperature in the hot water storage tank to 65℃±3℃, turn off any power heating mode; Continuously injecting cold water at a temperature of 15°C ± 2°C into the water inlet of the hot water storage tank, and continuously discharging hot water from the water outlet of the hot water storage tank; After 15 seconds from the start of drainage, the inlet water temperature and outlet water temperature are measured every 5 seconds. If the outlet water temperature is 20°C lower than the maximum outlet water temperature, drainage is stopped. Obtain the average inlet water temperature, average outlet water temperature and total drainage mass during the drainage period; The hot water output rate is determined according to the average water inlet temperature, the average drainage temperature, and the total drainage mass.

[0036] Before testing, turn off the power heating mode to ensure consistent water temperature at the start of the test, eliminating the impact of initial conditions on test results. By continuously draining water until the water temperature is 20°C below the maximum drain temperature, the test covers the entire heat output process and avoids underestimating performance due to premature cessation of draining.

[0037] In addition, the drainage flow rate can be controlled by a valve installed at the water outlet of the hot water storage tank. When the drainage volume is not more than 10L, the drainage flow rate is 2L / min; when the drainage volume is between 10L and 50L, the drainage flow rate is 5L / min; when the drainage volume is between 50L and 200L, the drainage flow rate is 10L / min; when the drainage volume is greater than 200L, 5% of the nominal capacity of the hot water storage tank is discharged per minute.

[0038] In an optional embodiment, the calculation formula of the hot water output rate is shown in formula (6): (6) Wherein, m is the total mass of the drainage, t p is the average drainage temperature, t c is the average inlet water temperature, m p The mass of the released water is in kilograms (kg), and m is the total mass of the water in the water tank, in kilograms (Kg).

[0039] Optionally, before starting the water mixing pump in the hot water storage tank to mix the water in the hot water storage tank and obtaining the effective water outlet temperature of the hot water storage tank, the method includes: Stop injecting water into the water inlet of the hot water storage tank.

[0040] Before starting the test, stop the water circulation and cut off the bypass loop to ensure that the water flows completely through the main circulation system to avoid flow or temperature abnormalities caused by the bypass loop.

[0041] Optionally, before the water storage tank is circulated with water having a temperature of not less than 20° C. at a flow rate of 400 L / h to 600 L / h, the method further comprises: Clean the surface of the photovoltaic-thermal integrated component and completely shield the photovoltaic-thermal integrated component.

[0042] Before testing, the photovoltaic and thermal integrated components were completely shielded to avoid interference of photovoltaic power generation on the initial water temperature.

[0043] The above are only specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes but is not limited to the contents described in the drawings and the above specific embodiments. Any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A method for testing the heating performance of a photovoltaic-thermal integrated water heater, wherein the photovoltaic-thermal integrated water heater comprises a heat storage tank and a photovoltaic-thermal integrated assembly, characterized in that: The test method includes: Use water with a temperature of not less than 20°C and a flow rate of 400L / h to 600L / h to circulate water in the hot water storage tank; When the water inlet temperature of the hot water storage tank changes by no more than 0.1° C. within at least 5 minutes, the water inlet temperature is determined as the effective water inlet temperature of the hot water storage tank; Starting the heating mode of the photovoltaic-thermal integrated water heater, stopping the heating after 8 hours, and shielding the photovoltaic-thermal integrated component; Starting a water mixing pump in the hot water storage tank to mix the water in the hot water storage tank and obtain an effective water outlet temperature of the hot water storage tank; The daily heat gain is determined according to the effective water inlet temperature and the effective water outlet temperature; wherein the daily heat gain is one of the performance indicators of heating performance.

2. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 1, characterized in that: The obtaining of the effective water outlet temperature of the hot water storage tank comprises: Continuously obtaining the outlet temperature of the hot water storage tank, and determining the outlet temperature as the effective outlet temperature of the hot water storage tank when the outlet temperature of the hot water storage tank changes by no more than 0.1° C. within at least 5 minutes; The calculation formula of the daily calorific value is shown in formula (1): （1） where c pw is the specific heat capacity of water at constant pressure, t e is the effective outlet temperature, t b is the effective water inlet temperature.

3. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 2, characterized in that: The heating modes include photovoltaic heating mode, photothermal heating mode and photovoltaic-photothermal integrated heating mode; wherein the photothermal heating mode includes any one of photovoltaic short-circuit condition, photovoltaic open-circuit condition and photovoltaic load condition; In the case where the heating mode is a photovoltaic heating mode, the heating mode of starting the photovoltaic-thermal integrated water heater includes: Connecting the photovoltaic and thermal integrated components to electric heating; In the case where the heating mode is a solar thermal heating mode, the step of starting the photovoltaic-solar thermal integrated water heater includes: Under photovoltaic short-circuit conditions, connect the positive and negative cables of the photovoltaic thermal integrated module; Under photovoltaic circuit-breaking conditions, disconnect the positive and negative poles of the photovoltaic thermal integrated module; Under the photovoltaic load condition, the positive and negative electrodes of the photovoltaic thermal integrated assembly are connected to the pure resistance module, and the pure resistance module is immersed in a constant temperature water tank; In the case where the heating mode is a photovoltaic-thermal heating mode, the heating mode of starting the photovoltaic-thermal integrated water heater includes: Connect the photovoltaic and thermal integrated components to the electric heater and connect the direct solar thermal heating circulation pipeline.

4. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 3, characterized in that: The performance index also includes the solar radiation amount on the surface of the photovoltaic and thermal integrated component is 5kWh / m 2 The nominal daily heat gain per unit photovoltaic installation area is calculated as shown in formula (2): （2） Where H is the daily solar radiation on the surface of the photovoltaic and thermal integrated components, in kWh / m 2 .

5. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 3, characterized in that: The performance index also includes the solar radiation amount on the surface of the photovoltaic and thermal integrated component is 5kWh / m 2 The nominal daily heat gain per unit photovoltaic installed capacity is calculated as shown in formula (3): （3） Where H is the daily solar radiation on the surface of the photovoltaic and thermal integrated components, in kWh / m 2 .

6. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 1, characterized in that: The obtaining of the effective water outlet temperature of the hot water storage tank comprises: Continuously injecting inlet water of different temperatures into the water inlet of the hot water storage tank, and discharging the hot water in the hot water storage tank from the water outlet of the hot water storage tank at a constant flow rate, measuring the temperature of the drainage water at least once every 1 second until the volume of the drainage water is greater than three times the volume of the hot water storage tank and the temperature difference between the drainage water and the inlet water temperature is less than 1°C, and determining the temperatures of the multiple drainage water as multiple effective water outlet temperatures; The calculation formula of the daily calorific value is shown in formula (4): （4） Wherein T1 is the inlet water temperature, and T2 is the effective outlet water temperature.

7. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to any one of claims 2 to 6, characterized in that: After starting the heating mode of the photovoltaic-thermal integrated water heater, heating is stopped after 8 hours, and the photovoltaic-thermal integrated component is shielded, and then the method includes: The cumulative photovoltaic power generation during the heating period is obtained using an electric energy meter. The heating efficiency of the photovoltaic-thermal integrated water heater is determined based on the daily heat value and the cumulative photovoltaic power generation. The calculation formula for the heating efficiency of the photovoltaic-thermal integrated water heater is shown in formula (5): （5） Among them, E PV is the cumulative photovoltaic power generation.

8. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 1, characterized in that: Afterwards, it also includes: After adjusting the water temperature in the hot water storage tank to 65℃±3℃, turn off any heating mode; Continuously injecting cold water at a temperature of 15°C ± 2°C into the water inlet of the hot water storage tank, and continuously discharging hot water from the water outlet of the hot water storage tank; After 15 seconds from the start of drainage, the inlet water temperature and outlet water temperature are measured every 5 seconds. If the outlet water temperature is 20°C lower than the maximum outlet water temperature, drainage is stopped. Obtain the average inlet water temperature, average outlet water temperature and total drainage mass during the drainage period; The hot water output rate is determined according to the average water inlet temperature, the average drainage temperature, and the total drainage mass.

9. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 8, characterized in that: The calculation formula of the hot water output rate is shown in formula (6): （6） Wherein, m is the total mass of the drainage, t p is the average drainage temperature, t c is the average inlet water temperature.

10. The photovoltaic-thermal integrated water heater heating performance testing method according to claim 1, characterized in that: Before the water storage tank is circulated with water having a temperature of not less than 20° C. at a flow rate of 400 L / h to 600 L / h, the method includes: Clean the surface of the photovoltaic-thermal integrated component and completely shield the photovoltaic-thermal integrated component.

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