In this research, an educational approach to the concept of energy is proposed. It is based on the history of physics. In 1854 Hermann Helmholtz gave a popular lecture on the recent discovery that energy is conserved. Such lecture is used as a guide to introduce the pupils within several nuances of this concept. Not much mathematics is used, so Helmholtz's work, with several additions proposed here, is an excellent guide to understanding, from a qualitative point of view, the reasons that led scientists to establish the principle of conservation of energy. At the same time, it allows us to grasp two other concepts which are fundamental in reference to energy: work and heat. This panorama will be drawn in the first section. In the second one, some more mathematical and physical details on the teaching of energy in mechanics and thermodynamics will be offered. Finally, in the Conclusion, the interdisciplinary value of a historical approach to physics education will be pointed out.
