Asymmetric Multi-core systems are the current way in which both embedded systems and data-centers are organized to obtain the best trade-off between the conflicting goals of saving energy and obtaining high performances. The idea is to have two different execution environments, capable of running exactly the same set of applications, but one tailored for energy efficiency at the expense of performance, and the other fast but more demanding in terms of resources. Such systems become even more interesting when combined with intermittent renewable energy sources, such as solar panels, that can reduce the impact of high performance cores, increasing the opportunities for their usage. In this work we will present a simple, yet effective, queuing network model that can expose and explain many of the critical aspects of these systems.