Method for measuring specular reflectance of tower type solar photo-thermal heliostat

Abstract

The invention discloses a method for measuring the specular reflectance of a tower type solar photo-thermal heliostat. The method comprises the following steps of: mounting a certain number of ultrasonic sensors on a heat absorption tower at a specified position below a heat absorber; measuring optical reflectivity and ultrasonic reflectivity by using a handheld optical reflectivity measuring instrument and an ultrasonic sensor, and constructing a data set; establishing a relationship between the ultrasonic reflectivity and the optical reflectivity; establishing a linear regression model of the relationship between the ultrasonic reflectivity and the optical reflectivity by using the measured data set, and solving a fitting coefficient through a least square method so as to obtain a fitted model; and detecting the heliostat to be measured by using an ultrasonic sensor, substituting the obtained ultrasonic reflectivity into the fitted model, and calculating to obtain the optical reflectivity of the heliostat to be measured. The method disclosed by the invention is simple and convenient to operate and high in measurement speed, reduces the measurement cost of the reflectivity of the heliostat, and does not affect the normal work of a heliostat field.

Description

Technical Field

[0001] The invention belongs to the field of solar thermal power generation and application, and in particular relates to a method for measuring the mirror reflectivity of a tower-type solar thermal heliostat. Background Art

[0002] As an important direction of new energy utilization, solar thermal power generation has gradually been valued and vigorously developed by people due to its characteristics of energy storage, peak regulation, continuous and stable power generation, clean and pollution-free. According to different focusing methods and structures, solar thermal power stations can be divided into tower type, trough type, dish type and Fresnel type.

[0003] In a tower solar power generation system, direct solar radiation is collected by heliostats and reflected to the heat absorption tower. The collected solar energy is used to heat the heat transfer medium, which generates high-temperature steam after passing through the heat exchanger, thereby driving the steam turbine to generate electricity. The reflectivity of the heliostat can directly affect the power generation efficiency of the tower solar thermal power station. Accurately assessing the reflectivity of the heliostat and timely cleaning the surface of the heliostat is an important guarantee for efficient power generation and smooth operation of the solar thermal power station and saving the operation and maintenance costs of the solar thermal power station.

[0004] The current method for measuring the reflectivity of heliostats requires a handheld reflectometer to measure each heliostat on a clear day. This method is time-consuming, has high labor costs, and can only be performed during the day, which seriously affects the normal work and operation of the mirror field. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for measuring the mirror reflectivity of a tower solar thermal heliostat, so as to achieve the purpose of simple operation, fast measurement speed and reduced cost of heliostat reflectivity measurement.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for measuring the reflectivity of a tower solar thermal heliostat, comprising the following steps:

[0008] Step 1, equipment installation: install a certain number of ultrasonic sensors on the heat absorption tower at the designated position below the heat absorber, ensuring that the detection range of the ultrasonic sensors can cover all heliostats;

[0009] Step 2, build the dataset:

[0010] Select n target heliostats and clean the mirror surfaces thoroughly to ensure that their initial reflectivity values ​​can be measured;

[0011] Using a handheld optical reflectivity measuring instrument, the selected target heliostat is measured to obtain an initial optical reflectivity, and an ultrasonic sensor is used to detect the ultrasonic reflectivity of the selected heliostat to obtain an initial ultrasonic reflectivity;

[0012] At certain intervals, the selected heliostat is measured using a handheld optical reflectivity measuring instrument and an ultrasonic sensor to obtain the optical reflectivity and ultrasonic reflectivity;

[0013] Step 3, establishing the relationship between ultrasonic reflectivity and optical reflectivity;

[0014] Using the measured data set, a linear regression model is established, and the regression coefficient is solved by the least square method to obtain a fitted mathematical model;

[0015] Step 4, reflectivity calculation:

[0016] The heliostat to be measured is detected by using an ultrasonic sensor, and the obtained ultrasonic reflectivity is substituted into the fitted model to calculate the optical reflectivity of the heliostat to be measured.

[0017] In the above scheme, the calculation formula for the number of ultrasonic sensors installed M is as follows:

[0018]

[0019] Where r is the average radius of the heliostat field, h is the detection field angle of the ultrasonic sensor, and S is the lighting area of ​​the heliostat field, that is, the sum of the lighting areas of all heliostats.

[0020] In the above scheme, the ultrasonic sensors are installed on the heat absorption tower at a position 20 meters below the heat absorber and distributed in a circle.

[0021] In the above scheme, the calculation formula of the ultrasonic reflectivity is as follows:

[0022]

[0023] Among them, E is the ultrasonic reflectivity, Er is the received reflected signal strength, and Ee is the transmitted signal strength.

[0024] In the above scheme, the number n of the target heliostats is 10 to 20, and the heliostats are selected in sequence according to different distances from the heat absorption tower.

[0025] In the above scheme, when the handheld optical reflectivity meter is used for measurement, five measurement points are selected on the mirror surface of each heliostat, the optical reflectivities of the five measurement points are measured respectively, and then the average value Q of the optical reflectivities of the five measurement points is calculated. In this way, all the selected target heliostats are measured in turn.

[0026] In the above scheme, measurements are taken every 3-5 days, for at least 10 times.

[0027] In the above scheme, the established linear regression model is as follows:

[0028]

[0029] In the formula, β1, β2, β3, β4, β5 are regression coefficients, Q ij is the optical reflectivity of the jth target heliostat measured at the ith time, E ij is the ultrasonic reflectivity of the jth target heliostat measured at the ith time, T i is the time of the i-th measurement.

[0030] Through the above technical solution, the method for measuring the mirror reflectivity of a tower solar thermal heliostat provided by the present invention has the following beneficial effects:

[0031] 1. The present invention establishes the relationship between the optical reflectivity and ultrasonic reflectivity of the heliostat, which minimizes the number of reflectivity measurements, can save labor costs, and help operators to optimize the mirror field cleaning plan.

[0032] 2. After the reflectivity calculation regression model is established in the present invention, the reflectivity of the heliostat mirror surface can be measured at night by an ultrasonic sensor without interrupting or affecting the normal operation of the mirror field during the day.

[0033] 3. The cost of the ultrasonic sensor used in the present invention is relatively low and can be easily integrated into an automated measurement system, thereby reducing the overall measurement cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0035] Figure 1 This is a schematic diagram of the operation process of a solar thermal power station;

[0036] Figure 2 A flow chart of a method for measuring the mirror reflectivity of a tower solar thermal heliostat disclosed in an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of installing an ultrasonic sensor according to an embodiment of the present invention.

[0038] In the figure, 1. heliostat; 2. absorber; 3. hot salt storage tank; 4. cold salt storage tank; 5. steam generator; 6. steam turbine; 7. generator; 8. condenser; 9. absorber tower; 10. ultrasonic sensor. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0040] like Figure 1 As shown, the heliostat 1 of the solar thermal power station collects and reflects sunlight energy. The heliostat concentrates solar energy to the absorber 2 to heat the molten salt passing through the absorber panel. The molten salt is heated to 565°C by the absorber and enters the hot salt storage tank 3. The hot molten salt is transported to the steam generator 5 to heat the water into water vapor. The high-temperature water vapor enters the steam turbine through the pipeline to drive the steam turbine 6 to work and make the generator 7 generate electricity. After passing through the steam generator 5, the molten salt releases heat, the temperature decreases, and enters the cold salt storage tank 4. At this time, the molten salt is about 265°C. After the high-temperature water vapor drives the steam turbine 6 to work, it passes through the condenser 8, becomes liquid water, and then continues to enter the steam generator 5 to exchange heat with the molten salt.

[0041] The present invention provides a method for measuring the reflectivity of a tower solar thermal heliostat. Figure 2 As shown, the following steps are included:

[0042] Step 1, equipment installation: a certain number of ultrasonic sensors 10 are installed on the heat absorption tower 9 at designated positions below the heat absorber, ensuring that the detection range of the ultrasonic sensors 10 can cover all heliostats.

[0043] like Figure 3 As shown, in this embodiment, the ultrasonic sensor 10 is installed around the heat absorption tower 9. In order to ensure the safety of the ultrasonic sensor 10, it is installed at a position 20 meters below the heat absorber 2. The number of ultrasonic sensors 10 installed is related to the lighting area S of the mirror field, which can ensure that the detection range of the ultrasonic sensor 10 can cover all the heliostat mirrors. The number M of ultrasonic sensors 10 that need to be installed can be calculated by the following formula:

[0044]

[0045] Where r is the average radius of the heliostat field (unit: m); h is the detection field angle of the ultrasonic sensor (unit: °); S is the daylighting area of ​​the heliostat field (unit: m 2 ), which is the sum of the daylighting areas of all heliostats.

[0046] The ultrasonic sensor 10 used in this embodiment is composed of four parts: a transmitter, a receiver, a signal processor and a display. It has the characteristics of high frequency, good directivity, and the ability to become rays and propagate in a directional manner. The frequency, amplitude and beam width of the ultrasonic wave emitted by the ultrasonic sensor 10 are usually known. The ultrasonic sensor 10 is used to emit an ultrasonic signal of known amplitude and frequency to the target heliostat. When the sound wave signal encounters the target heliostat, a reflection signal is generated. The reflection signal returns to the ultrasonic sensor 10 and is received by the receiver for signal processing. The calculation formula for ultrasonic reflectivity is as follows:

[0047]

[0048] Among them, E is the ultrasonic reflectivity, Er is the received reflected signal strength, and Ee is the transmitted signal strength.

[0049] Step 2, build the dataset:

[0050] Select n target heliostats (the number n of the target heliostats is 10 to 20, and the heliostats are selected in sequence according to different distances from the heat absorption tower 9), and clean the mirror surface thoroughly to ensure that the initial reflectivity value can be measured.

[0051] Use a handheld optical reflectivity meter to measure the selected target heliostats. During the measurement, select five measurement points on each heliostat (usually four corners and the middle), measure the optical reflectivity of these five measurement points respectively, and then calculate the average value Q of the optical reflectivity of the five measurement points. Use this method to measure all the selected target heliostats in turn to obtain the optical reflectivity of all target heliostats, which is marked as Q. 11 ~Q 1n .

[0052] At the same time, the ultrasonic sensor 10 is used to detect the ultrasonic reflectivity of the selected heliostat to obtain the initial ultrasonic reflectivity, which is recorded as E 11 ~E 1n .

[0053] Every 3-5 days, the specific number of days is determined by the surveyor according to the atmospheric environment on site, and the selected heliostat is measured using a handheld optical reflectivity measuring instrument and an ultrasonic sensor 10. In order to ensure the accuracy of the results, it is necessary to ensure that the measurement is completed 10 times, and the optical reflectivity Q of the i-th measurement is obtained respectively. i1 ~Q in and ultrasonic reflectivity E i1 ~E in .

[0054] Step 3, establishing the relationship between ultrasonic reflectivity and optical reflectivity;

[0055] Taking into account the existence of time effects, nonlinear relationships or interaction effects, the following linear regression model is established:

[0056]

[0057] In the formula, β1, β2, β3, β4, β5 are regression coefficients, Q ij is the optical reflectivity of the jth target heliostat measured at the ith time, E ij is the ultrasonic reflectivity of the jth target heliostat measured at the ith time, T i is the time of the i-th measurement.

[0058] The measured data set (optical reflectivity Q i1 ~Q in and ultrasonic reflectivity E i1 ~E in ) is substituted into the above model, and the regression coefficient is solved by the least square method, and finally a well-fitted mathematical model is obtained.

[0059] Step 4, reflectivity calculation:

[0060] The heliostat to be measured is detected by using the ultrasonic sensor 10, and the obtained ultrasonic reflectivity is substituted into the fitted model to calculate the optical reflectivity of the heliostat to be measured.

[0061] The method provided by the present invention does not affect the normal operation of the heliostat during the day, ensures the efficient operation of the power station, and maximizes the profit. In addition, the present invention adopts an ultrasonic method to measure the reflectivity of the heliostat. This method indirectly estimates its reflectivity through the reflection characteristics of ultrasonic waves on the surface of the heliostat, breaking the traditional mode of using light sources and relying on image recognition technology to evaluate the reflectivity of heliostats. Compared with light source detection, ultrasonic detection is not affected by the lighting conditions and atmospheric environment of the photothermal mirror field, thereby effectively improving the accuracy of the heliostat reflectivity calculation. Compared with optical measuring instruments, the ultrasonic sensor 10 has a lower equipment cost, has the advantages of simple operation and fast measurement speed, and reduces the cost of measuring and calculating the reflectivity of the heliostat.

[0062] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring the reflectivity of a tower solar thermal heliostat, characterized in that: The steps include: Step 1, equipment installation: install a certain number of ultrasonic sensors on the heat absorption tower at the designated position below the heat absorber, ensuring that the detection range of the ultrasonic sensors can cover all heliostats; Step 2, build the dataset: Select n target heliostats and clean the mirror surfaces thoroughly to ensure that their initial reflectivity values ​​can be measured; Using a handheld optical reflectivity measuring instrument, the selected target heliostat is measured to obtain an initial optical reflectivity, and an ultrasonic sensor is used to detect the ultrasonic reflectivity of the selected heliostat to obtain an initial ultrasonic reflectivity; At certain intervals, the selected heliostat is measured using a handheld optical reflectivity measuring instrument and an ultrasonic sensor to obtain the optical reflectivity and ultrasonic reflectivity; Step 3, establishing the relationship between ultrasonic reflectivity and optical reflectivity; Using the measured data set, a complex linear regression model is established, and the regression coefficient is solved by the least square method to obtain a well-fitted mathematical model; Step 4, reflectivity calculation: The heliostat to be measured is detected by using an ultrasonic sensor, and the obtained ultrasonic reflectivity is substituted into the fitted model to calculate the optical reflectivity of the heliostat to be measured.

2. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: The calculation formula for the installation quantity M of ultrasonic sensors is as follows: Where r is the average radius of the heliostat field, h is the detection field angle of the ultrasonic sensor, and S is the lighting area of ​​the heliostat field, that is, the sum of the lighting areas of all heliostats.

3. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: The ultrasonic sensors are installed on the heat absorption tower at a position 20 meters below the absorber and distributed in a circle.

4. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: The calculation formula of the ultrasonic reflectivity is as follows: Among them, E is the ultrasonic reflectivity, Er is the received reflected signal strength, and Ee is the transmitted signal strength.

5. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: The number n of the target heliostats is 10 to 20, and the heliostats are selected in sequence according to different distances from the heat absorption tower.

6. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: When measuring with a handheld optical reflectivity meter, five measuring points are selected on the mirror surface of each heliostat, and the optical reflectivity of these five measuring points is measured respectively. Then, the average value Q of the optical reflectivity of the five measuring points is calculated. All selected target heliostats are measured in turn in this way.

7. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: Measure every 3-5 days, at least 10 times.

8. The method for measuring the mirror reflectivity of a tower solar thermal heliostat according to claim 1, characterized in that: The established linear regression model is as follows: In the formula, β1, β2, β3, β4, β5 are regression coefficients, Q ij is the optical reflectivity of the jth target heliostat measured at the ith time, E ij is the ultrasonic reflectivity of the jth target heliostat measured at the ith time, T i is the time of the i-th measurement.

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