CN105281666B - A kind of method for improving solar cell irradiation sensor measuring accuracy - Google Patents

Abstract

The invention discloses a kind of method for improving solar cell irradiation sensor measuring accuracy, by analysis and solar cell area, the relation using circuit and load resistance and measuring accuracy in solar cell irradiation sensor, the careful design for high performance-price ratio solar radiation sensor provides direction.

Description

Method for improving test precision of solar cell irradiation sensor

Technical Field

The invention relates to a method for improving the testing precision of a solar cell irradiation sensor, and belongs to the technical field of photovoltaic systems.

Background

With the development of photovoltaic systems, the evaluation of photovoltaic efficiency is particularly important. The photovoltaic system efficiency generally refers to the ratio of actual power generation output to total irradiation amount reaching the surface of a photovoltaic square matrix, and accurate and rapid measurement of irradiation is crucial to photovoltaic system efficiency evaluation. The evaluation of the photovoltaic system is mainly realized by a solar radiation sensor, and one is composed of a combined thermopile circuit, which can accurately reflect the radiation intensity but cannot reflect the influence of the radiation spectrum difference on the arrival of photovoltaic power generation. And the other type adopts a solar cell as a solar total radiation sensor, the spectral response of the solar cell is basically consistent with that of the photovoltaic power generation, and the influence of the radiation spectrum difference on the photovoltaic power generation is eliminated.

The basic principle for manufacturing a solar cell as a total radiation sensor is as follows: the solar cell converts the irradiation intensity value into a short-circuit current value, then converts the short-circuit current value into a voltage value by connecting a high-precision resistor in series as a load, finally connects the resistor with a singlechip, and the singlechip adoptsAnd collecting voltage signals at two ends of the load to carry out operation (as shown in figure 1), and finally displaying the irradiation value on a Liquid Crystal Display (LCD). The parameters associated with the measurement process are: the voltage value U (unit: V) across the load, the circuit value I (unit: A) through the load, the resistance value R (unit: omega), the irradiation intensity H (unit: W/m)²)。

In the solar irradiation sensor circuit, an AD conversion module is responsible for collecting voltages at two ends of a solar cell load, converting an analog voltage signal into a digital signal and inputting the digital signal into a single chip microcomputer for operation. Several concepts related to sensors are:

1. number of bits of ADC (analog-to-digital converter)

An n-bit ADC represents 2 n-th power scales for this ADC. The 8-bit ADC outputs 256 digital quantities from 0 to 255, namely 8-power data scales of 2.

2. Reference source

The reference source, also called reference voltage, is an important index of the ADC, and if the signal input to the ADC is to be measured accurately, the reference source needs to be calibrated first, and the deviation of the reference source may directly result in the deviation of the conversion result.

3. Resolution ratio

Resolution is the variation of analog signal when the digital quantity changes by a minimum scale, and is defined as the full scale range and 2ⁿ-a ratio of 1. Assuming a 5.10V voltage system, and using 8-bit ADC for measurement, the 5.10V is divided into 255 parts equally by 256 scales corresponding to 0-255, and the resolution is 5.10/255 ═ 0.02V.

Disclosure of Invention

In the process of manufacturing the solar cell as the total radiation sensor, the guarantee of the radiation precision is particularly important. The invention provides a method for improving the test precision of a solar cell irradiation sensor by performing analysis on the reasonability of the design of a sampling circuit of an irradiation meter and the size selection of a solar cell, thereby ensuring the precision of the irradiation meter.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for improving the test precision of a solar cell irradiation sensor comprises the following steps:

1) assuming that the number of digital-to-analog converters in the solar cell irradiation sensor is n bits, and the reference voltage is X, the resolution X of the sampling circuit is:

2) assuming that the irradiation change Δ H' at a certain time and the voltage change Δ U, the minimum resolution Δ H of the irradiation sensor is calculated by the following relationship:

3) according to the formula (2), under the condition determined by the sampling circuit, the value of the minimum resolution Δ H of the radiation sensor can be reduced by increasing the voltage change Δ U, namely, the test accuracy of the radiation sensor is improved.

In the foregoing step 3), in the solar cell irradiation sensor, the voltage change Δ U is a voltage U at two ends of a load connected in series to two ends of the solar cell, and a specific method for increasing the voltage change Δ U is to increase the voltage U at two ends of the load includes the following steps:

3-1) for a certain type of solar cell, if the irradiation intensity H, the solar cell module efficiency eta and the solar cell area A are known, the output power P of the solar cell is as follows:

P＝H·A·η (3)

3-2) combination formula P ═ UI ═ U²The following results are obtained:

wherein I represents a current through the load, and R represents a load resistance;

3-3) if the irradiation intensity H, the solar cell module efficiency eta and the load resistance R are determined, according to the formula (5), the larger the area A of the solar cell is, the larger the voltage U at two ends of the load is, and the higher the precision of the irradiation sensor is;

if the irradiation intensity H, the solar cell module efficiency eta and the area A of the solar cell are determined, according to the formula (5), the larger the resistance value R of the load resistor is, the larger the voltage U at two ends of the load is, and the higher the precision of the irradiation sensor is.

In the foregoing step 3-3), the resistance value R of the load resistor must satisfy:

wherein, U_ocRepresents the open circuit voltage of the solar cell, I_scIndicating the short circuit current of the solar cell.

In the foregoing step 3-3), due to the size limitation of the solar cell used by the irradiation sensor, the open-circuit voltage value of the solar cell itself is within 10V, and the voltage U across the load connected to the solar cell must satisfy: u is less than 10V.

The foregoing is according to formula (1) and formula (2) to yield:

according to the formula, under the condition that the voltage change delta U cannot be increased, the digit n of the digital-to-analog converter of the irradiation sensor is increased, the value of the minimum resolution delta H of the irradiation sensor can be reduced, and the test accuracy of the irradiation sensor is improved.

The invention provides a simple circuit design scheme of the solar radiation sensor, and provides a direction for the accurate design of the solar radiation sensor with high cost performance by analyzing the area of the solar cell, adopting the relation between the circuit and the like and the test accuracy.

Drawings

FIG. 1 is a working schematic diagram of a solar cell irradiation sensor;

FIG. 2 is a diagram of the internal circuitry of the solar cell irradiance sensor of the present invention;

fig. 3 is a graph showing the relationship between the solar cell area and the irradiation accuracy in the embodiment of the present invention.

Detailed Description

The present invention will now be described in further detail with reference to the accompanying drawings and detailed description.

As shown in FIG. 2, the solar cell irradiation sensor circuit of the present invention comprises a single chip, a digital-to-analog converter, a GPS module and an LCD1602 screen display. Wherein,

the single chip microcomputer, namely U1 in fig. 2, is connected with an LCD1602 screen display, a digital-to-analog converter U2 and a GPS module. The singlechip U1 has a programmed irradiation instrument working program, and the singlechip U1 receives the digital signal output by the digital-to-analog converter U2, processes and calculates the digital signal through the irradiation instrument working program, and then sends the digital signal to the LCD1602 screen for irradiation display.

The digital-to-analog converter adopts PCF8951, namely U2 in FIG. 2, and is connected with the load resistance of the solar cell, and the right side of FIG. 2 is an analog signal input end. The digital-to-analog converter U2 converts the input analog voltage signal into a digital voltage signal and inputs the digital voltage signal into the singlechip U1 for calculation.

The GPS module (omitted in figure 2) can automatically receive the positioning information and send the positioning information to the singlechip U1 through a serial port, and a built-in program of the singlechip can analyze latitude, time information, latitude and time in the positioning information and take part in operation as necessary constants for calculating an irradiation value.

The LCD1602 screen display includes RP1 and RV1, receives the irradiation data that will show that singlechip U1 sent, and shows on the screen, and the program that supports the screen work is contained in the singlechip, constitutes irradiation appearance work overall program with other program groups.

The testing accuracy of the solar cell irradiation sensor is influenced by the following factors.

First, influence of sampling circuit precision

Assuming that the reference voltage of the single chip microcomputer AD converter is X and the number of ADC bits is n according to the requirements of the selected circuit, the resolution (the variation of the analog signal when the digital quantity changes a minimum scale) X is as follows:

if the irradiation change Δ H' at a certain time and the voltage change Δ U are set, the irradiation minimum resolution, i.e., the irradiation accuracy Δ H, is calculated from the following relationship:

if the reference voltage of the AD conversion module of the singlechip is 5.1V and the number of ADC bits is 8 according to the requirements of the selected circuit, the resolution ratio is as follows: x is 5 ÷ (2)⁸-1) ═ 0.02V, the irradiation change accuracy Δ H is calculated from the following relationship:

if the minimum value of change of irradiation intensity of the final irradiation meter is ensured, the value is 1W/m²(i.e. when using the sun's electricityWhen the voltage at two ends of the cell load is 0.02V, the corresponding irradiation intensity is 1W/m²) Then, under standard test conditions (irradiation intensity of 1000W/m)²) The voltage value corresponding to the two ends of the load isDue to the size limitation of the solar cell used by the radiometer, the open-circuit voltage value of the solar cell is generally within 10V, and the voltage at two ends of the connected load is necessarily less than 10V. Therefore, under the condition that the reference voltage of the current 8-bit ADC is 5.1V, the minimum variation (resolution) of the radiometer cannot reach 1W/m²。

The ADC digit is increased to 10 digits, the reference voltage is 5.1V, and the resolution isCorresponding minimum resolution of the irradiator is equal to 1W/m². Similarly, under the standard test condition, the voltage corresponding to the two ends of the load isCan meet the requirements of the solar cell.

Therefore, if the voltage value of the two ends of the load connected with the solar cell is larger, the resolution of the irradiation score is higher, but the size of the solar cell limits that the load voltage cannot be infinitely increased; at the moment, the resolution of the final radiometer can be improved by adopting a method for improving the ADC number of the radiometer.

Second, the influence of the solar cell on the final irradiation precision

The area of the solar cell determines the output power, which in turn determines the voltage across the load of the solar cell and the current flowing through the load.

For a certain type of solar cell, if the irradiation intensity H, the solar cell module efficiency eta and the solar cell area A (or side length) are known, the output power (unit: W) of the cell is

P＝H·A·η (3)

For example, at an irradiation intensity of 1000W/m²under the condition that the efficiency of the selected solar cell module is 15 percent, the size of the solar cell is 80mm × 80mm, and the output power P of the module is 1000W/m²×80×80×10^-6m²×15％＝0.96W。

Then by the formula

P＝UI＝U²/R (4)

From (3) and (4):

therefore, to improve the irradiation precision, in addition to increasing the ADC bit number, the value of the load voltage U can be improved by:

I. selecting a solar cell with higher photovoltaic efficiency eta, such as 19 percent;

selecting a reasonable solar cell size, and properly increasing the value of the area A of the solar cell;

and III, selecting a proper load resistor.

(1) Changing the area of the solar cell with a determined load resistance value R

The determination of the load resistance value can firstly measure the open-circuit voltage U of the solar cell_ocAnd short-circuit current I_scThen atThe load resistance is selected within the range. For example, a solar cell is measured at 1000W/m²U under the condition_oc＝6.05V，I_scA load resistance in the range of 10 Ω to 15 Ω can be selected, ensuring a linear dependence between the measured radiation intensity and the load voltage (current) ═ 0.2AIs described. At this time, if the load resistance R is 15 Ω, the solar cell efficiency is 20%, and the ADC bit number is 12, the relationship between the solar cell area, the load voltage, and the irradiation accuracy can be obtained according to the formula (5) as shown in table 1 below:

TABLE 1 relationship between solar cell area and load voltage, irradiation precision

Wherein the load voltage is calculated according to equation (5) and the minimum resolution Δ H of the radiometer is calculated according toIs calculated to obtain, hereThe load power is calculated according to equation (3).

From table 1, a graph of the solar cell area versus the irradiation accuracy is plotted as shown in fig. 3, and as can be seen from fig. 3, when the above conditions are not changed, the minimum resolution of the irradiator decreases with the increase of the solar cell area, meaning that the irradiation accuracy is improved.

(2) Selecting a suitable load resistance when the size of the solar cell is determined

According to the above conclusion, the larger the area of the solar cell is, the larger the voltage and current (also referred to as output power) which can be provided for the load under a certain irradiation condition is. According to the formula (5), the load resistance value is also a variable for determining the irradiation precision, and at this time, if the size of the solar cell is determined, the selected size of the solar cell is set to 70mm x 70mm at 1000W/m²U under the condition_oc＝6.05V，I_scwhen the solar cell efficiency is 20% and the ADC bit number is 12 at 0.2A, H, A and η are both fixed values, the load voltage U is related to the load resistance R, and the determination of the load resistance R can be utilized firstObtaining a maximum value R of R_mAccording to this R_mMultiplying by a certain proportion, and obtaining the relation between the irradiation precision and the load voltage through calculation and analysis in the same way. According to the above parameters, obtaining R_m30.25 Ω, then:

TABLE 2 relationship between load resistance and load voltage, irradiation accuracy

Wherein the load voltage is calculated according to the formula (5), and the irradiation precision is calculated according to the formulaIs calculated to obtain, here

It can be easily found by analyzing table 2 that the larger the actual load resistance is, the larger the voltage across the load is, and the higher the irradiation precision is. However, the value of the load resistance R cannot be increased infinitely, and when the load resistance is too high, the voltage, current and irradiation value at two ends of the load lose their own obvious linear relationship, so that the irradiation value at that moment cannot be measured accurately by the irradiator. At this time, according to the related data, the selection is satisfiedThe resistance value in the range can ensure the linear relation among load voltage, current and irradiation.

Claims (2)

1. A method for improving the test precision of a solar cell irradiation sensor is characterized by comprising the following steps:

1) assuming that the number of digital-to-analog converters in the solar cell irradiation sensor is n bits, and the reference voltage is X, the resolution X of the sampling circuit is:

$x=\frac{X}{2^n-1}---\left(1\right)$

2) assuming that the irradiation change Δ H' at a certain time and the voltage change Δ U, the minimum resolution Δ H of the irradiation sensor is calculated by the following relationship:

$\frac{{\mathrm{\ΔH}}^{\′}}{\mathrm{\Δ}H}=\frac{\mathrm{\Δ}U}{x}---\left(2\right)$

3) according to the formula (2), under the condition determined by the sampling circuit, the voltage change delta U is increased, namely the value of the minimum resolution delta H of the irradiation sensor can be reduced, namely the test precision of the irradiation sensor is improved;

in a solar cell irradiation sensor, a voltage change delta U is the voltage U at two ends of a load connected in series with two ends of a solar cell, and a specific method for increasing the voltage change delta U is to increase the voltage U at two ends of the load comprises the following steps:

3-1) for a certain type of solar cell, if the irradiation intensity H, the solar cell module efficiency eta and the solar cell area A are known, the output power P of the solar cell is as follows:

P＝H·A·η (3)

3-2) combination formula P ═ UI ═ U²The following results are obtained:

$U=\sqrt{P\·R}=\sqrt{H\·A\·\mathrm{\η}\·R}---\left(5\right)$

wherein I represents a current through the load, and R represents a load resistance;

3-3) if the irradiation intensity H, the solar cell module efficiency eta and the load resistance R are determined, according to the formula (5), the larger the area A of the solar cell is, the larger the voltage U at two ends of the load is, and the higher the precision of the irradiation sensor is;

if the irradiation intensity H, the solar cell module efficiency eta and the area A of the solar cell are determined, according to the formula (5), the larger the resistance value R of the load resistor is, the larger the voltage U at two ends of the load is, and the higher the precision of the irradiation sensor is;

the load resistor resistance value R must satisfy:

wherein, U_ocRepresents the open circuit voltage of the solar cell, I_scRepresents a short-circuit current of the solar cell;

due to the size limitation of the solar cell used by the irradiation sensor, the open-circuit voltage value of the solar cell is within 10V, and the voltage U at two ends of the load connected with the solar cell must satisfy the following conditions: u is less than 10V.

2. The method for improving the testing accuracy of the solar cell radiation sensor according to claim 1, wherein the following is obtained according to the formula (1) and the formula (2):

$\frac{{\mathrm{\ΔH}}^{\′}}{\mathrm{\Δ}H}=\frac{\mathrm{\Δ}U}{\frac{X}{2^n-1}}$

according to the formula, under the condition that the voltage change delta U cannot be increased, the digit n of the digital-to-analog converter of the irradiation sensor is increased, the value of the minimum resolution delta H of the irradiation sensor can be reduced, and the test accuracy of the irradiation sensor is improved.