Environmental sustainability is a major and relevant challenge facing computing. Therefore, we must start teaching theory, techniques, and practices that both increase an awareness in our student population as well a provide concrete advice to be applied in practical software development. In this experience report, we focus on energy consumption of executing software, and describe teaching approaches from three different universities that all address software energy consumption in various ways. Our main contribution is reporting lessons learned from these experiences and sketching some issues that teachers must be aware of when designing learning goals, teaching material and exercises.