Delfi-C3 is a nanosatellite developed by MSc students of the Faculty of Aerospace Engineering and Electrical Engineering, Mathematics and Computer Science at the Delft University of Technology. It will serve as an in-orbit test bed for three innovative technologies. Delfi-C3 is scheduled for launch in August 2007 by an Indian PSLV launcher. This report focuses on the design process of the electrical power system. Because Delfi-C3 applies a constant voltage power bus, a power conversion system is introduced to transport power from the solar arrays to the power bus. Additional conversion systems are designed for power supply to the various electronics boards. Furthermore, designs are made for interfaces between the electrical power system and the other subsystems. These designs will be presented and discussed in this report. Because electrical power is a scarce resource in spaceflight, a power budget has been generated and maintained throughout the complete Delfi-C3 project. Interface control is applied to ensure efficient cooperation between the various subsystems. In this report, the power budget and interface control process will be presented. A second focus in this report is the simulation and verification process of the electrical systems of Delfi-C3. To generate an adequate impression of the behaviour of the Delfi-C3 spacecraft in orbit, several orbit simulations are performed. As simulation output, the orbital position is calculated. In addition, the control and disturbance torques are used to reconstruct the attitude profile of the spacecraft. These parameters are subsequently used to calculate the incoming solar power. It will be shown that the incoming solar power is sufficient to supply Delfi-C3 with electrical power. Electrical system verification is part of the spacecrafts testing process. It has to be verified whether the electrical power system is successful in converting solar array power to bus power. The power distribution system has to be tested to guarantee that power arrives at every subsystem in the correct conditions. It will be shown that the electrical power system performs in accordance with requirements and is qualified for spaceflight.