There is a vast amount of existing work that investigates energy aware computing. However to exploit the best possible solution requires a system wide approach to design. To design and optimise a whole system at once is not scalable. A viable alternative is component-based engineering approaches where individual parts of the system are designed whilst allowing for the interactions with the rest of the system. The contributions of this paper are a method by which flexibility in the design of applications can be exploited to give the most energy efficient requirements in a computationally efficient way and an exploration of how different computational models relate to the most energy efficient requirements. The results show that the most obvious choice of requirements is not always the best and the overheads due to specific computational models are significant. While carrying out this work, power / energy anomalies, similar in nature to the timing anomalies already identified for worst-case execution time and multiprocessor systems, have been uncovered.