A photovoltaic panel cleanliness evaluation method based on twin system output

Abstract

The present invention discloses a photovoltaic panel cleanliness evaluation method based on the output of a twin system, and belongs to the field of data processing technology. The method considers the influence of the cleanliness of photovoltaic panels on the efficiency of photovoltaic power generation, and proposes a photovoltaic panel cleanliness evaluation method that can be applied online to the operation and maintenance of photovoltaic power stations. By building a twin system with the same characteristics as the photovoltaic power station to be applied, and utilizing the consistency between the cleanliness of the photovoltaic panels of the twin system and the photovoltaic power station, some photovoltaic panels in the twin system are cleaned, and the ultra-short-term fluctuations of the power generation of the twin system before and after cleaning are compared, and the influence of cleaning on the efficiency conversion of the photovoltaic panel is evaluated, thereby obtaining the photovoltaic panel cleanliness evaluation index value for the entire photovoltaic power station. This method avoids the fluctuation of the cleanliness of the photovoltaic panel on the power output of the photovoltaic power station caused by the cleanliness of the photovoltaic panel, and fills the gap in the field of photovoltaic panel cleanliness evaluation.

Description

Technical Field

[0001] The present invention belongs to the technical field of data processing, relates to the management of photovoltaic power stations in power systems, and specifically to a photovoltaic panel cleanliness evaluation method based on twin system output. Background Art

[0002] As a clean and renewable way of generating electricity, solar photovoltaic power generation accounts for an increasing proportion of the power grid year by year. However, in actual operation, photovoltaic power stations are generally seriously affected by air quality, especially in haze weather, when dust or particles in the air will accumulate on the surface of photovoltaic panels, hindering the photovoltaic panels from converting solar radiation into electrical energy, which not only affects the conversion efficiency, but also may form a "hot spot" phenomenon, causing damage to the photovoltaic panels.

[0003] There are many cleaning methods and devices for photovoltaic panels at present, but the cleaning effect may be different for photovoltaic panel surfaces with different cleanliness. Frequent cleaning not only wastes manpower and material resources, but also causes instability in photovoltaic power generation. Therefore, there is an urgent need for an evaluation method for the cleanliness of photovoltaic panels to provide guidance for the cleaning of photovoltaic panels. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a method for evaluating the cleanliness of photovoltaic panels based on the output of a twin system, builds a twin system of the photovoltaic power station to be used, and utilizes the high consistency of the cleanliness of the photovoltaic panels of the twin system and the photovoltaic power station. According to the ultra-short-term fluctuations of the twin system output, the cleanliness of the photovoltaic panels of the entire photovoltaic power station is evaluated.

[0005] A photovoltaic panel cleanliness evaluation method based on twin system output, the specific steps are as follows:

[0006] Step 1: Build a twin system with fewer photovoltaic modules than the photovoltaic power station to be used as a DC power source for the battery. The production batch, module orientation and installation angle of the photovoltaic modules used in the twin system are the same as those of the photovoltaic power station to be used.

[0007] Step 2: Select some panels in the twin system as clean panels and the rest as unclean panels. Based on the ultra-short-term fluctuations in the power generation of the twin system before and after the clean panels are cleaned on sunny days, the cleanliness of the photovoltaic panels of the entire photovoltaic power station is evaluated. The specific steps are as follows:

[0008] Step 2.1: Collect the power generated by the twin system during the sunny period P' ( k ) and the average temperature of the back of some non-clean panels as the operating temperature of the twin system T' ( k ),in k=1,2, …, n represents the discrete sampling time sequence number, n is the total number of sampling points in a natural day.

[0009] When photovoltaic power generation efficiency is the highest, k max , clean the cleaning panels in the twin system in the conventional dust removal manner.

[0010] Step 2.2: After cleaning is completed, collect the average temperature of the back of several clean panels as the working temperature of the clean panel. T cl , and record the sampled data as T cl ( k' ), k' =s, s+1, …, n , s represents the first sampling time after cleaning is completed.

[0011] Considering the output fluctuation of the twin system caused by various uncontrollable factors during the cleaning process, the power data collected during the cleaning process and the working temperature of the non-cleaning panel are discarded to obtain P ( k )and T ( k ), k =1, 2, …,(k max )-1,k max ,s,s+1, …, n .

[0012] Step 2.3: k≤k before cleaning max Power generation data of the twin system P ( k ) Estimated power generation of the uncleaned twin system P z( k' ).

[0013] Step 2.4: Estimated value by working temperature P z( k' ) to make corrections:

[0014] (1)

[0015] in, P z T ( k' ) represents the corrected estimate, which represents the power temperature coefficient of the component:

[0016] , i =1, 2, …30 (2)

[0017] (3)

[0018] Step 3: The actual collected twin system power generation P ( k ) and the revised estimate P z T ( k' ) to compare and calculate the cleanliness index of photovoltaic panels C :

[0019] (4)

[0020] Step 4: Calculate the cleanliness index of the photovoltaic panel according to step 3 C The cleanliness of photovoltaic panels in photovoltaic power plants is evaluated by numerical values. C When the value exceeds the set threshold, all panels in the photovoltaic power plant and the non-clean panels in the twin system are cleaned.

[0021] The present invention has the following beneficial effects:

[0022] Based on the ultra-short-term fluctuations in the output of the twin system that is consistent with the photovoltaic power station to be applied, the cleanliness of the photovoltaic panels of the entire photovoltaic power station can be evaluated. The cleanliness index can be used to objectively evaluate the cleanliness of the photovoltaic panel. Compared with the fixed-time cleaning strategy, the cleaning time is determined based on the cleanliness index, which can not only avoid the fluctuation of the power output of the photovoltaic power station caused by frequent cleaning, but also improve the power generation efficiency of the photovoltaic power station, filling the gap in the field of photovoltaic panel cleanliness evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a flow chart of the cleanliness evaluation method of photovoltaic panels based on the output of twin systems. DETAILED DESCRIPTION

[0024] The present invention will be further explained below with reference to the accompanying drawings;

[0025] like Figure 1 As shown, a photovoltaic panel cleanliness evaluation method based on the output of a twin system is shown, and the specific steps are as follows:

[0026] Step 1: Since the photovoltaic modules in the photovoltaic power station convert light radiation into electric current, forming a DC volt-ampere characteristic, it is converted by the inverter and then connected to the grid in the form of AC. In order to avoid the fluctuation of the power output of the photovoltaic power station caused by the cleanliness evaluation of the photovoltaic panel, a twin system with the same characteristics as the photovoltaic power station to be applied is built.

[0027] Taking into account the existence of certain internal random factors in the materials and processes used to manufacture photoelectric conversion devices, and assuming that the conversion efficiency follows a normal distribution, the number of photovoltaic modules in the twin system is set to 5% of the scale of the entire photovoltaic power station, and all photovoltaic modules that constitute the twin system are the same as those in the photovoltaic power station, that is, the production batches, module orientations and installation inclinations of the photovoltaic modules should be the same. At this time, the cleanliness of the photovoltaic panels of the twin system and the photovoltaic power station will be highly consistent.

[0028] Step 2: The twin system is used as a backup component and is not directly connected to the grid, but as a DC power source for the battery.

[0029] Since photovoltaic devices themselves will deteriorate over time, simply selecting a day with similar weather far away from the current day will not necessarily make the power generation of the twin systems comparable. Therefore, a local cleaning strategy is proposed, selecting 20% ​​of the panels in the twin system as clean panels and the remaining panels as unclean panels. Based on the ultra-short-term fluctuations in the power generation of the twin system before and after cleaning, the cleanliness of the photovoltaic panels of the entire photovoltaic power station can be evaluated.

[0030] Considering that when parameters such as temperature and humidity remain unchanged, photovoltaic power generation on sunny days has a larger output than on rainy and cloudy days, and the fluctuation range of the power generation curve has better recognition, we choose to conduct photovoltaic panel cleanliness evaluation on sunny days:

[0031] Step 2.1: Considering the relationship between light radiation and the rise and fall of the sun, according to the location of the photovoltaic power station and the differences in seasons, usually between 8:00 and 17:00 every day, use power meters, irradiance meters and temperature sensors to obtain the power generation of the twin system respectively. P' ( k ), and the average temperature of the back of some non-clean panels as the operating temperature of the twin system T' ( k ),in k represents the discrete sampling time sequence number, k =1,2, …, n , n is the total number of sampling points in a natural day. When the sampling period is 60 seconds, n =540.

[0032] The time when the photovoltaic power generation efficiency is the highest is set as 12:00 am in this embodiment, corresponding to the discrete sampling time sequence number k = 180, clean the cleaning panel in the twin system for half an hour in the conventional dust removal method.

[0033] Step 2.2: After cleaning is completed, collect the average temperature of the back of several clean panels as the working temperature of the clean panel.T cl , and record the sampled data as T cl ( k' ), k' =210, 211, …, n .

[0034] Considering the output fluctuation of the twin system caused by various uncontrollable factors during the cleaning process, the power data collected during the half-hour cleaning process and the working temperature of the non-cleaning panel are discarded to obtain P ( k )and T ( k ), k =1, 2,…180, 210, 211, …, n .

[0035] Step 2.3: After half an hour of cleaning, the irradiance and temperature of the cleaned panel will change, thus affecting the overall power generation of the twin system. Therefore, the power generation data of k≤180 before cleaning is used. P ( k ) The power generation of the uncleaned twin system is estimated by the least squares fitting method. P z( k' ).

[0036] Step 2.4: Clean the panel working temperature within a short period of time after cleaning. T cl The operating temperature of the non-cleaned panel will be significantly lower than T , so we need to estimate the value P z( k' ) to make corrections:

[0037] (1)

[0038] in, P z T ( k' ) represents the corrected estimate, which represents the power temperature coefficient of the component:

[0039] , i =1, 2, …30 (2)

[0040] (3)

[0041] Step 3: The actual collected twin system power generation P ( k ) and the revised estimate P z T (k' ) to compare and calculate the cleanliness index of photovoltaic panels C :

[0042] (4)

[0043] Where c is the cleanliness index scaling factor, which is used to convert the cleanliness index C The value of is scaled to a reasonable range. In this embodiment, c=25 is set.

[0044] Step 4: Calculate the cleanliness index of the photovoltaic panel according to step 3 C The cleanliness of photovoltaic panels in photovoltaic power plants is evaluated by numerical value. C The different numerical ranges of the cleaning parameters determine whether cleaning operations are required and take corresponding measures.

[0045] In this embodiment, when C ∈[0,0.1], it means that the PV panel is less polluted, the power generation efficiency is close to ideal, and no cleaning is required; when C ∈(0.1,0.3], it means that the photovoltaic panels are slightly contaminated and have caused a certain impact on the power generation efficiency. It is recommended to clean all photovoltaic panels in the photovoltaic power station and the non-clean panels in the twin system; when C When >0.3, it means that the pollution is serious and the power generation efficiency of the panel is significantly affected. All photovoltaic panels in the photovoltaic power station and non-clean panels in the twin system must be thoroughly cleaned immediately.

[0046] To verify the effectiveness of this method, two photovoltaic power stations A and B of the same size in the same region were cleaned using the traditional method and this method respectively. This method is based on the fluctuation difference of the power generation before and after the cleaning of the twin system of the photovoltaic power station, and calculates the cleanliness index of the photovoltaic panel to determine whether to clean it. The traditional method is to clean it once every three months. The difference in power generation of photovoltaic power stations under different cleaning strategies is compared, and the results are shown in Table 1:

[0047] Table 1

[0048]

[0049] According to the data in the table, it can be seen that the power generation of photovoltaic power station B, which uses this method to determine the cleaning frequency, is significantly improved in different months of a year compared with photovoltaic power station A, which is cleaned in a specified time period. The increase is between 3.54% and 7.52%, and the annual average increase is 4.80%, indicating that this method significantly optimizes the power generation performance of the photovoltaic power station and effectively improves the power generation of the photovoltaic power station.

Claims

1. A photovoltaic panel cleanliness evaluation method based on twin system output, characterized in that: The specific steps are as follows: Step 1: Build a twin system with a smaller number of photovoltaic modules than the photovoltaic power station to be used; Step 2: Select some panels in the twin system as clean panels and the remaining panels as non-clean panels; Collect the power generation of the twin system P'(k), where k = 1, 2, ..., n, and n is the total number of sampling points in a natural day; Clean the cleaning panels in the twin system; Use the power generation data P(k) of the twin system collected before cleaning to estimate the power generation Pz(k') of the twin system that has not been cleaned, k' = s, s+1, ..., n, s represents the first sampling time after the cleaning is completed; Step 3: Collect the average temperature of the back of the non-cleaned panel before cleaning as the twin system working temperature T'(k), and collect the average temperature of the back of the cleaned panel after cleaning as the cleaned panel working temperature T cl (k'); According to the twin system working temperature T'(k) and the working temperature of the clean panel after cleaning T cl (k') corrects the estimated value of the power generation of the twin system that has not been cleaned, Pz(k'), and compares the actual collected power generation of the twin system P(k) with the corrected estimated value P ZT (k′) to calculate the cleanliness index C of the photovoltaic panel: Where c is the cleanliness index scaling factor; Step 4: Evaluate the cleanliness of the photovoltaic panels in the photovoltaic power station according to the value of the photovoltaic panel cleanliness index C calculated in step 3. When it is determined that the value of the photovoltaic panel cleanliness index C exceeds the set threshold, clean all panels in the photovoltaic power station and non-clean panels in the twin system.

2. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1, characterized in that: The production batch, component orientation and installation inclination angle of the photovoltaic modules used in the twin system are the same as those of the photovoltaic power station to be used.

3. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1, characterized in that: The number of photovoltaic modules in the twin system is 5% of the number of photovoltaic modules in the photovoltaic power station to be used.

4. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1, characterized in that: 20% of the panels in the twin system are selected as clean panels and the remaining panels as non-clean panels.

5. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1, characterized in that: The power generation power and operating temperature are sampled between 8:00 and 17:00 on a natural day, with a sampling period of 60 seconds.

6. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 5, characterized in that: Select 12 o'clock on a sunny day as the time when photovoltaic power generation efficiency is highest, and set the cleaning time to 0.5 hours.

7. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1, characterized in that: Using the power generation data of the twin system collected before cleaning, the power generation of the twin system without cleaning is estimated by the least squares fitting method.

8. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1 or 7, characterized in that: P ZT (k′)=P Z (k′)×δ×(T cl (k′)-T′(k)) (2) Among them, Pz T (k') represents the corrected estimated value, and δ represents the power temperature coefficient of the component: Using the revised estimate P ZT (k′) replaces Pz(k') to calculate the cleanliness index C of the photovoltaic panel.

9. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1, characterized in that: Set the cleanliness index scaling factor c=25.

10. A photovoltaic panel cleanliness evaluation method based on twin system output as claimed in claim 1 or 9, characterized in that: When C∈[0,0.1], no cleaning is required; When C∈(0.1,0.3], it means that the PV panels are slightly contaminated, and it is recommended to clean all PV panels in the PV power plant and the non-clean panels in the twin system; When C>0.3, it indicates serious pollution, and all photovoltaic panels in the photovoltaic power plant and non-clean panels in the twin system should be thoroughly cleaned immediately.

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