A hybrid electrical power supply control system for providing electrical energy to at least one load. The load may alternate between a first low energy consuming operational modus and a second high energy consuming operational modus. The control system may include a first power source comprising at least one battery unit and a second power source comprising at least one energy harvesting unit and arranged to harvest and convert energy into Direct Current, DC, energy, and wherein the converted DC energy is stored in a charge collecting unit. The control system further includes an operational modus detecting unit and a power source switching unit, connected to the operational modus detecting unit and arranged to alternately connect the first power source and the second power source to the load.