The concept of energy is widely employed in introductory science courses. However, the term energy is defined and utilized in different ways depending on the context, even within a given discipline. Through the lens of metaphor theory, these various definitions of energy are seen as metaphors that highlight and obscure characteristics of energy. Working under this framework, undergraduate students in introductory biology, chemistry, and physics courses were asked to write analogies that reflect their understanding of the role of energy in the context of ecosystems (n=49), chemical reactions (n=36), mechanical systems (n=65), and electrical circuits (n=44). These analogies were analyzed qualitatively using metaphor theory to gain understanding of how students conceptualize energy in these different contexts. The results of this study indicate that students use seven different conceptual metaphors to explain the role of energy in various scientific contexts: energy as a substance that can be accounted for, energy as a substance that can flow, can change forms, can be carried, can be lost, can be an ingredient or a product, and energy as a process or interaction. This result gives teachers a framework to use in evaluating student ideas about energy.