The CubeSat standard makes development, launch, and operation possible for those with no experience in space technology to participate. The power demand coverage by the power supply system during all modes of operation is a critical issue that needs to focus on to avoid satellite mission failure. Therefore, the solar array (SA) and battery pack should be sized precisely based on the satellite architecture and flight orientation scenarios. A 3U Cube-Satellite has been used as a case study to evaluate the effect of satellite flight orientation (Nadir and sun tracking) on the energy balance between the supply system and the load demand and find out the appropriate flight orientation for achieving the mission successfully. The orbit simulation has been done via STK environment for both flight orientation scenarios with the same load profile where the electrical power system (EPS) has confronted the worst-case scenario of operation. Furthermore, the unregulated bus configuration has been selected to simulate EPS response during the orbit period using SIMULINK for different orientation flight scenarios.