The reactive power in non-sinusoidal circuits is determined here from an energy analysis instead of using the non-sinusoidal apparent power S. In the first of the two energy analyses, circuits previously examined by the currents' physical components power theory are re-examined using the principle of conservation of energy, the balance principle of the reactive power and the concept of reactive power compensation. This energy analysis yields a reactive power value substantiated by the aforementioned principles and power theory but it also suggests a value of S that differs from its traditional definition. The energy analysis performed with the circuit analysis technique based on geometric algebra, its GN domain power theory and M, a conservative power quantity based on the flow of energy, confirms the reactive power value attained in the former analysis. More importantly, M clarifies three intriguing issues about S: its value, its physical significance and whether this quantity can lead to erroneous conclusions. These, and previous results, demonstrate that the reactive power should be assessed on the energy flow but a multidimensional mathematical framework is needed to better understand energy flow in non-sinusoidal circuits.