A method and system for supplying energy to an electrically operable, medical device (100) implanted in ′ a patient. Wireless energy is transferred from an external energy source (104) located outside the patient to an internal energy receiver (102) located inside the patient and connected to the medical device. An internal control unit (108) determines an amount of energy currently required for the operation of said medical device. A control signal is transmitted to the external energy source, reflecting the required amount of energy. An external control unit (106) controls the amount of transferred energy in response to the control signal, by adjusting the energy transfer efficiency from the external energy source to the internal energy receiver. The energy transfer efficiency is adjusted by adjusting the position of a primary coil, serving as the external energy source, relative to an implanted secondary coil, serving as the internal energy source.
