Understanding energy with a focus on sustainable development requires further knowledge beyond traditional conceptual understanding. This paper presents the result from one main investigation and two smaller follow-up studies. The main study (step 1) consists of an interpreting, iterative analysis of statements made by experts on contents for physics education on energy with focus on sustainable energy systems gathered from a questionnaire, which results in subject-specific contents for physics teaching presented as a category system of objectives. The categories from step 1 are used as means for analyses in steps 2 and 3, which involve the study of educational material and one physics class. The results show that the content of physics for upper secondary, in order for students to reach insight, should comprise certain physical concepts and relations not only in 'limited contexts' but also in relation to greater contextual connections, in which problematisation and insight in solutions for the future is necessary. These parts should have a similar weight according to the statements of the experts. This is not to be found in either the typical educational material (textbooks) or in one physics class, which has been studied.