The Nano satellite that respects the standard form CubeSat present various engineering challenges due to its small size and surface area. The challenge is to incorporate a large amount of technology in a cubic form no bigger than 10cm3 and consumes only 1W. This paper details the design of a photovoltaic-battery based power supply utilizing direct energy transfer for solar array regulation and battery charging. Also the simulation results for the management of the power system in the nanosatellite are displayed.