In this paper we analyze, whether energy consumption in a wireless sensor network (WSN) can be evaluated realistically and accurately using the Avrora simulation tool. For this purpose, results from a reference experiment using SANDbed, a WSN testbed with focus on energymeasurements, and Avrora, a wireless sensor network simulation tool, are compared. In this experiment, we found a difference in total energy consumption up to 20% between simulation and reality. The analysis revealed several issues that influenced the accuracy of Avrora simulations. We thus implemented an improved version of Avrora that deals with the identified issues. A concluding evaluation shows that the improved Avrora+ reduces the difference between simulation and testbed to < 5%.