A hybrid (face-to-face and online) professional development (PD) course focused on energy science for middle and high school teachers (N = 47) was conducted using the teaching science as inquiry (TSI) framework. Data from the PD indicates that online opportunities enhanced participation and that the TSI structure improved teachers' inquiry implementation. Teachers found the TSI modes of inquiry easily accessible and effectively implemented them (modes correspond to the inquiry mechanisms of investigation, such as product evaluation, authoritative, inductive, deductive, and descriptive). On the other hand, the TSI phase structure (i.e. learning cycle) was most helpful for teachers novice to inquiry teaching, suggesting that modification of the PD is needed to promote more in-depth use of the phases in the TSI framework. In terms of content, teacher interest in energy science was high, which resulted in implementation of energy science activities across a range of disciplines. However, teachers' confidence in teaching energy science through inquiry was low compared to similar TSI PD courses on other subjects (mean perceived pedagogical content knowledge = 8.96 plus or minus 2.07 SD for energy compared to 15.45 plus or minus 1.83, 16.44 plus or minus 1.81 and 15.63 plus or minus 1.69, for elementary astronomy, high school aquatic science, and college aquatic science, respectively). These data support current findings on the complexities of teaching and understanding energy science content and suggest the need for additional teacher PD opportunities in energy science in order to provide opportunities for teachers to increase both their content knowledge and their confidence in teaching energy science. (Contains 5 tables and 4 figures.)