This manuscript describes different methods for transferring, in the most efficient way, power from the solar cells to the battery system, and from the battery system to all loads..Since overcharging a battery can cause damage to the battery, this project describes/analyzes DC-DC Buck choppers that will not just reduce/regulate the voltage for solar cell charging.. In order to understand the use of PI controller in minimizing the output voltage oscillation cycles and its magnitude, the model is provided with a manual switch and PI controller. Using the manual switch provided, the model of a time varying DC voltage source is provided as the input to simulate the effect of variation of the input voltage from its normal value. Thus we can visually observe the effect of variation of input voltage on the output, both by including and excluding The PI controller in the same model. This report is intended to provide the designer with a method of buck/step down DC voltage from high Voltage to low Voltage, by using a DC-DC switching buck chopper designed specifically for this task, the results are validated by using MATLAB/SIMULINK.