The electrical power system (EPS) is an essential part of a satellite. It distributes, stores and generates the electric power for autonomous operation of the satellite in space. Through standardizations in the CubeSat community a common structure of EPS is established. The thesis explains both the functioning and the requirements of electrical power systems. Furthermore, two EPS are presented that are currently commercially available and have been used in other CubeSats. The Naval Postgraduate School (NPS) is currently developing a 1U Cubesat (NPS-SCAT) and the EPS board used has insufficient specifications for accurate operation. To avoid problems in the advanced stage of development, the EPS has to be simulated. This research lays the foundation for an EPS computer model based on PSpice simulation software. At the outset the design of a solar panel and Lithium-Ion battery model was possible. In particular, the models are modifiable at any time so that technical changes can be incorporated as needed. This thesis was finished in April 2010 and is part of the small satellites programme of the Space System Academic Group at the NPS