CN-115940805-B - Method for measuring forbidden bandwidth of photovoltaic module

Abstract

The invention discloses a method for measuring the forbidden bandwidth of a photovoltaic module, which belongs to the technical field of physical property analysis of solar cells and comprises the steps of firstly, continuously measuring the current-voltage characteristics output by the photovoltaic module in an outdoor environment, and recording a plurality of groups of data and module temperature during measurement. And secondly, establishing a three-diode model by using the obtained current-voltage data, wherein two diode ideal factors are fixed to be 1 and 2, the other diode ideal factor is a variable parameter, and extracting model parameters by using a nodes parameter decomposition technology and an optimization algorithm. And finally, calculating the forbidden bandwidth of the photovoltaic module by utilizing the change relation between the reverse saturation current with the ideal factor of 1 and the temperature. Compared with the existing forbidden bandwidth measurement method, the method does not need to use expensive spectrometer or X-ray photoelectron spectrometer equipment, does not need destructive operation, is suitable for the packaged photovoltaic module with any size and unknown ideal factors, and has the advantages of low cost, simplicity and easiness.

Inventors

• XU JIE
• ZHAO HAIKUN
• REN QINGYING
• CHEN DEYUAN
• LI WEI

Assignees

• 南京邮电大学

Dates

Publication Date

20260505

Application Date

20221231

Claims (2)

1. 1. The method for measuring the forbidden bandwidth of the photovoltaic module is characterized by comprising the following steps of: (1) Under an outdoor illumination environment, continuously measuring the current-voltage characteristics output by the photovoltaic module, and recording a plurality of groups of current-voltage data and module temperature during measurement; (2) Establishing a three-diode equivalent circuit model by using the obtained current-voltage data, wherein the model comprises three diodes connected in parallel, a current source, a parallel resistor and a series resistor, the ideality factors of the two diodes are respectively fixed to be 1 and 2, the ideality factor of the other diode is a variable parameter, and related model parameters are extracted by using a Benders parameter decomposition technology and an optimization algorithm, wherein the three-diode model is that , Wherein I is current, V is voltage, and f (I, V) function is represented by The definition formula gives that E is a natural base number, I ph is a photo-generated current, I s1 is a reverse saturation current of a diode with an ideal factor of 1, I s2 is a reverse saturation current of a diode with an ideal factor of 2, I s3 is a reverse saturation current of a diode with an ideal factor of N 3 , R s is a series resistor, G sh is a parallel conductance, N 3 is an ideal factor of a third diode, V T is a thermal voltage, and V T =N S kT/q is defined, wherein N S is the number of series units in a photovoltaic module, k=1.38e-23J/K is a boltzmann constant, q=1.602E-19C is an electron charge amount, and T is a module temperature in kelvin; Model fitting adopts a Nelder-Mead algorithm to solve the following optimization problem after being decomposed by the parameters of the Benders: , Wherein N 3 and R s are two independent parameters, (I i ,V i ) are current-voltage data points of a certain group of data, subscript I takes values from 1 to N, N is data point data, I cal,i is a current value calculated by using a three-diode model at voltage V i , superscript T represents transposition, superscript-1 represents matrix inversion, M and b are respectively a matrix and a vector for performing Benders parameter decomposition, and they divide the parameters Conversion to dependent parameters related to n 3 and R s , the specific definition of M and b being , , Where all sums contain all data points, i.e., from i=1 to i=n, and, in addition, , , , Obtaining all 7 model parameters by solving the optimal optimization problem Extracting three-diode model parameters from the current-voltage data at different temperatures; (3) Calculating the forbidden bandwidth of the photovoltaic module by utilizing the change relation between the reverse saturation current and the temperature of the diode with the ideal factor of 1; The inverse saturation current I s1 of diode with ideal factor of 1 is linear with the reciprocal of absolute temperature T, a data image with 1/T as independent variable and ln (I s1 ) as dependent variable is made, the slope of straight line is fitted by least square method and recorded as slope, the forbidden bandwidth of photovoltaic module Calculation using the following formula , Where k=1.38E-23J/K is boltzmann constant and q=1.602E-19C is electron charge amount.
2. 2. The method of claim 1, wherein the current-voltage test circuit in step (1) comprises a power supply, an adjustable resistor and an ammeter which are connected in series with the photovoltaic module, and the voltmeters which are connected in parallel with two ends of the photovoltaic module.

Description

Method for measuring forbidden bandwidth of photovoltaic module Technical Field The invention belongs to the technical field of physical property analysis of solar cells, and particularly relates to a method for extracting forbidden bandwidth from an outdoor test volt-ampere characteristic curve of a photovoltaic module. Background The forbidden bandwidth is one of important property parameters of a solar cell or a photovoltaic module, and refers to the energy level difference of a cell material at the bottom of a conduction band and the top of a valence band of a wave vector space. By measuring the forbidden bandwidth, the solar cell or photovoltaic module can be effectively identified, the manufacturing process is estimated and improved, and the working state is inspected and inspected. Currently, there are some methods for measuring the forbidden band width of semiconductor materials. For example, the energy of the photons which are intrinsically absorbed by the semiconductor material is not lower than the forbidden bandwidth, so that the energy corresponding to the lowest frequency of the intrinsically absorbed photons is equal to the forbidden bandwidth by measuring the absorption spectrum in the visible light range, or the energy level position at the top of the valence band is deduced by utilizing the X-ray photoelectron energy spectrum, and the energy level position at the bottom of the conduction band is determined by utilizing the backlight electron energy spectrum, wherein the difference value of the energy level position and the energy level position is the forbidden bandwidth. However, spectrometers and X-ray photoelectron spectroscopy equipment are expensive, complex to operate, and require certain sample size and surface treatment, such as for larger sized and packaged photovoltaic modules, which must be subjected to cumbersome operations such as destructive cutting and removal of packaging materials to allow measurement using the spectrometer or photoelectron spectrometer. In addition, for an ideal diode, i.e., when the ideality factor is equal to 1, the sensitivity and the forbidden bandwidth of the diode can be measured by measuring the variation relationship of the forward voltage and the temperature thereof. However, this approach is also not applicable to photovoltaic modules because the ideality factor of the photovoltaic module is unknown and is typically greater than 1, even greater than 2. Therefore, how to measure the forbidden bandwidth of the photovoltaic module simply, conveniently and reasonably with low cost is still a problem worthy of overcoming in the technical field. Disclosure of Invention Aiming at the defects of the prior art, the invention provides the method for simply, conveniently and reasonably measuring the forbidden bandwidth of the photovoltaic module with low cost, does not need destructive operations such as cutting and the like on the photovoltaic module packaged in a large size, and is simultaneously suitable for the photovoltaic module with unknown ideal factors. The technical scheme adopted by the invention is that the method for measuring the forbidden bandwidth of the photovoltaic module comprises the following steps of: And 1, continuously measuring the current-voltage (I-V) characteristics output by the photovoltaic module by using a standard test circuit in an outdoor illumination environment, and recording a plurality of groups of I-V data and module temperature T during measurement. The standard I-V test circuit comprises a power supply, an adjustable resistor, an ammeter and voltmeters, wherein the power supply, the adjustable resistor and the ammeter are connected in series with the photovoltaic module, and the voltmeters are connected in parallel with the two ends of the photovoltaic module. And 2, performing three-diode model fitting by using each group of I-V data obtained in the step 1 to obtain related model parameters. The three diode I-V model is as follows Where I is current, V is voltage, f (I, V) function is given by the definition after the symbol "≡", E is natural base, I ph is photo-generated current, I s1 is reverse saturation current of diode with ideal factor 1, I s2 is reverse saturation current of diode with ideal factor 2, I s3 is reverse saturation current of diode with ideal factor N 3, R s is series resistance, G sh is parallel conductance, N 3 is ideal factor of the third diode, V T is thermal voltage, defined as V T＝NS kT/q, where N S is the number of series units in the photovoltaic module, k=1.38e-23J/K is boltzmann constant, q=1.602E-19C is electron charge quantity, and T is the module temperature recorded in step 1 under the kelvin temperature scale. The three-diode model has 7 unknown parameters (I ph,Is1,Is2,Is3,Gsh,Rs,n3) in total, and the number of independent parameters is reduced to 2 by adopting a Benders parameter decomposition method, namely two independent parameters of n 3 and R s. Next, for a certain set of