The use of solar panels as an energy producer has revealed a real need to study it in order to optimize and therefore develop the exploitation of this source of clean renouvenable energy [1] . The research has shown that the functioning of the solar panels is strongly dependent on several parameters: some are external i.e. sunshine and temperature and other internal such as the development of device technology [2] .

Therefore, the experiment should lead to results similar to the theory [3] .

Thus, to cope the demand and competition from other energy sources, it is necessary to have a good knowledge on the conversion process of sunlight which will allow designing powerful solar cells and low cost [4] [5] .

Our study focuses on the characteristic I-V and the temperature of a solar cell using an experimental device automatic of the resistive load with a microcontroller [6] [7] that is running a C language program code [8] [9] .

With the automation of the change in operating point, based on a mathematical control law, we can impose a particular operation for the study of a phenomenon with given parameters.

Also we can move from static study to dynamic study with the same experimental device. This work helps to characterize the solar cell to optimize its use.

The basic circuit for the characterization of the solar generator is shown in Figure 1.

We designed a device who gets this characterization so the microcontroller will execute two programs: a program for the static mode and one for the dynamic mode.

The choice of the temperature sensor is made on a sensor that does not require external calibrations to give an accuracy of ±0.5˚C over a temperature ranging between −40˚C and 85˚C. This sensor is characterized by the equation:

The sensor is placed directly on the solar panel. Indeed, according to the technical data we consulted, manufacturers offer solar panels operating in a temperature range between −40˚C and 85˚C. So that with a solar panel whose maximum operating temperature T_max = 85˚C, we will have a voltage.

This voltage is low compared to the voltage which the microcontroller used for conversion which is between 0 - 5 V. In addition to this, the temperature is an analog quantity. The goal is to use all the microcontroller conversion range for better accuracy; we will have to use an amplifier. The characteristic amplifier is adapted to solar panels having operating temperatures between −40˚C and 85˚C. We can look Figure 4.

This amplifier will enable us to achieve a tension close to the microcontroller voltage conversion using its characteristic equation:

is the gain of an amplifier

So with a solar panel with a maximum operating temperature T_max = 85˚C, we have:

This leads with a voltage of 5 V we will gain: 5 V = 0.85 ´ G where G = 5.88.

As the temperature an analog quantity and the peak processes digital data it will have to use a digital to analog converter to pass the signal peak.

This work was performed in the laboratory of the Semiconductor and Solar Energy (LASES) of the Faculty of Science and Technology in Dakar. Here is our diagram of the automatic experimental processus for the solar panel which is shown in Figure 8.

Our PCB (printed circuit board) is shown in Figure 9.

The results are obtained with an analog oscilloscope. The microprocessor PIC 16F877A issued for the controlling part of the automatic experimental. Throughout the manipulation, we calibrated our oscilloscope to 1 V/div for voltage and 0.2 V/div for current and used a temperature sensor to measure the ambient temperature. The following are results taken for different values of the ambient temperature. Figures 10-17 represent the characteristic I-V at different temperature:

The I-V characteristic in the static mode under illumination polychromatic at 35˚C under an ambient temperature of 33.1˚C.

The I-V characteristic in the static mode under illumination polychromatic at 36˚C under an ambient temperature of 33.3˚C.

The I-V characteristic in the static mode under illumination polychromatic at 37˚C under an ambient temperature of 32.3˚C.

The I-V characteristic in the static mode under illumination polychromatic at 38˚C under an ambient temperature of 33.1˚C.

The I-V characteristic in the static mode under illumination polychromatic at 39˚C under an ambient temperature of 33.5˚C.

The I-V characteristic in the static mode under illumination polychromatic at 40˚C under an ambient temperature of 33.1˚C.

The I-V characteristic in the static mode under illumination polychromatic at 42˚C under an ambient temperature of 34.8˚C.

The I-V characteristic in the static mode under illumination polychromatic at 45˚C under an ambient temperature of 33.8˚C.

Here is an example below to calculate current and voltage. Throughout our handling we took 1 V/div for voltage and 0.1 V/div for current see following Figure 18.

This work was performed in the laboratory of the Semiconductor and Solar Energy (LASES) of the Faculty of Sciences and Techniques of Dakar.

It allowed us to design and implement an automatic experimental device for the acquisition of the characteristic I-V and temperature for solar panel silicon.

The concept of resistance equivalent to several cable resistors in parallel to obtain a digitally controlled variable resistor has been highlighted.

The electronic binary signals have helped us through static switches considered here as transistors, for changing the wiring resistance of the parallel combination.

For this we used a microcontroller that executed a C language program.

The results allowed us to conclude that the change in temperature affects the characteristic I-V. The increase in temperature leads to an increase of the current Icc short

circuit and a decrease in the open circuit voltage Voc. Thus it means that the temperature rise causes a slight increase in the creation of electron-hole pairs. Finally the work has allowed us to become familiar with some components such as the microprocessor.

In this section, we present our execution program of our simulation.

The program:

void main() {

unsigned short int T;

unsignedint N;

unsignedint Compteur;

TRISD=0;

TRISB=0;

TRISC.RC0=0;

TRISC.RC1=0;

TRISC.RC2=1;

TRISC.RC3=1;

TRISA=1;

ADCON1=0;

ADCON1.F7=1;

ADCON0.F6=0;

ADCON0.F7=1;

ADCON0.F0=1;

while (1)

{

while (PORTC.RC2==0);

if (PORTC.RC3==0)

{ PORTD=0; PORTC=0x01;

Delay(t3);

PORTC=0x02;

Delay(t3); }

else

{

ADCON0.F3=0;

ADCON0.F4=0;

ADCON0.F5=0;

Delay_us(20);

ADCON0.F2=1;

while (ADCON0.F2==1);

N=ADRESL+512*ADRESH.B1+256*ADRESH.B0;

T=0.084268716081*N;

if (T<10) PORTB=T;

else if (T>=10&&T<20) {PORTB=T-10; PORTB.RB4=1;}

else if (T>=20&&T<30) {PORTB=T-20; PORTB.RB5=1;}

else if (T>=30&&T<40) {PORTB=T-30; PORTB.RB4=1; PORTB.RB5=1;}

else if (T>=40&&T<50) {PORTB=T-40; PORTB.RB6=1;}

else if (T>=50&&T<60) {PORTB=T-50; PORTB.RB4=1; PORTB.RB6=1;}

else if (T>=60&&T<70) {PORTB=T-60; PORTB.RB5=1; PORTB.RB6=1;}

else if (T>=70&&T<80) {PORTB=T-70; PORTB.RB5=1; PORTB.RB6=1; PORTB.RB4=1;}

else if (T>=80&&T<90) {PORTB=T-80; PORTB.RB7=1;}

else {PORTB=T-90; PORTB.RB4=1; PORTB.RB7=1;}

PORTD=0;

PORTC=0;

Compteur=0;

while (Compteur<1024)

{

if (PORTC.RC4==1)

Delay(t1);

else Delay(t2);

PORTD++;

if (PORTD==0) PORTC++;

Compteur++;

} } } }

The authors gratefully acknowledge the managements of laboratory of the Semiconductor and Solar Energy (LASES) of the Faculty of Sciences and Techniques of Dakar, Polytechnic School of Thiès, Sénégal Université Alioune DIOP de Bambey, Sénégal and the University Institute of Technology, University of Thiès, Sénégal.

Dione, B., Sow, O., Wade, M., Ibrahima, L.Y., Mbodji, S. and Sissoko, G. (2016) Experimental Processus for Acquisition Automatic Features of I-V Properties and Temperature of the Solar Panel by Changing the Operating Point. Circuits and Systems, 7, 3984-4000. http://dx.doi.org/10.4236/cs.2016.711330