More than a thousand Grade 10 Physical Science learners from four South African provinces participated in a study that probed their conceptions of energy. The purpose was to determine the learners' conceptual resources, i.e. their initial conceptions, and identify the potentially productive resources from which they may construct physics concepts. The conceptions revealed by the learners in their responses to a questionnaire were categorised as core intuitive, implicit, conscious or verbal-symbolic. Notwithstanding learning the curriculum theme Energy and Change in their preceding school years, the results show that many of the learners have not yet mastered the concept of energy and related concepts ontologically well enough for progression to formal physics in the FET phase. However, their initial conceptions contain resources that can be refined to the science concepts. Implications and recommendations for learning and teaching in the FET phase are discussed in the framework of the conceptual refinement model.