Understanding the energy profile of a complex, multi-faceted software system is difficult. In this thesis, we present a novel methodology, called SMURF, a five-step methodology that gives insights into the energy consumption of a complex system. The methodology is broadly applicable, supports informed decision-making, and closely involves and engages stakeholders. We evaluate the methodology with a case study on MUST, a software system used in spacecraft operations. In the case study, SMURF successfully finds energy hotspots and wasteful components in MUST, and is used effectively to formulate actionable recommendations. Through the case study, we find that the SMURF methodology serves as an effective engagement tool to get developers, users, and product owners interested in sustainable software ideas.