# A Comparative Study of Storage Batteries for Electrical Energy Produced by Photovoltaic Panels
## 4 Building the Experimental Stand  
A picture of the experimental stand is presented in Figure 10. This stand is composed of the following: 1--Arduino Uno development board; 2--ACS 712 current sensor; 3--buck-type DC-DC convertor; 4--adjustable current-controlled voltage source; 5--ammeter; 6--voltmeter; 7--batteries; 8--laptop. To control the battery charge, a program was developed based on the MPPT algorithm for incremental conductance. The ACS 712 current sensor can measure currents of up to 20 A and has a sensitivity of 0.1 V/A. It supplies a voltage signal to the A2 channel of the Arduino Uno development board. The characteristics and running mode of the DC-DC buck-type convertor have been presented in ref. [26]. In ref. [26], a calculation method for the signal supplied by the ACS 712 current sensor is presented, as well as a calculation method for the signal supplied by the voltage sensor composed of a resistive divider, R1-R2. In ref. [26], a buck-type DC-DC convertor was used to supply a resistive load. In the current study, the same buck DC-DC convertor was used, but instead of a resistive load, batteries were connected. The electrical setup of this convertor also included a voltage divider made from resistors to measure the voltage of the convertor input. The current-controlled voltage source had the following features: an adjustable voltage range of (0-30) V D.C. and a range of (0-5) A for the variation in the current as a function of the load connected to the source terminals. This source was used in the laboratory instead of photovoltaic panels. The ammeter used was an analog instrument that measured the current intensity of the battery charging within a measuring range of 0 to 5 A. The voltmeter used was a digital instrument that could measure voltage rates within the range of (0-200) V D.C. The batteries used were acid-type batteries with a charging capacity of 80 Ah each. Two 12 V D.C. car batteries, connected in series, were used because the buck-type DC-DC convertor was designed and built to produce an output voltage of 24 V D.C. The batteries were connected to the voltage source by means of the buck-type DC-DC convertor. After connecting the adjustable voltage source to the input of the DC-DC buck-type convertor, and connecting the batteries to the convertor output, the following measurements were taken within one charging cycle of the batteries (as per Table 2):The experimental stand simulated a storage system for electrical energy produced by photovoltaic panels. By means of the algorithm for incremental conductance, the maximum required power for charging the batteries was supplied. Analysis of the experimental results revealed that during battery charging, along with an increase in the charging voltage, an increase in the filling factor of the PWM signal that controls the DC-DC buck convertor also takes place, as per Figure 11. In the future, more studies on Lithium-Ion batteries will be conducted.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Time** & **Usource** & **Isource** & **Ibattery** & **Ubattery** & **PWM Factor** \\ \hline
12.25 & 26.1 & 0.98 & 1.32 & 22.95 & 130 \\ \hline
12.30 & 26.1 & 1.07 & 1.37 & 23.12 & 146 \\ \hline
12.35 & 26.1 & 1.20 & 1.47 & 23.27 & 157 \\ \hline
12.40 & 26.1 & 1.28 & 1.57 & 23.30 & 161 \\ \hline
12.45 & 26.0 & 1.37 & 1.65 & 23.38 & 176 \\ \hline
12.50 & 26.0 & 1.48 & 1.70 & 23.46 & 188 \\ \hline \end{tabular}
\end{table}
Table 2: Experimental determinations.  
Figure 10: Picture of experimental stand for battery charging.