The invention relates to a medical device (1) with an energy storage unit (2), which is embodied for supplying with solar energy. The device (1) is embodied.for an evaluation of a charging state of the storage unit (2) according to a medical workflow and for the output of information related to the result of the evaluation or a signal related to the evaluation. In this way, it is ensured that a supply of energy is guaranteed during the workflow. Fig. 3