A method in core drilling, wherein a tubular drill bit being arranged at the end of a tubular drill string is driven under rotation against a material intended for drilling, and wherein for the purpose of core retrieving, a tool is brought inside the drill string to an operative position in the area of the drill bit. The vacuum fan module includes a controller that performs navigation and control functions for both the vacuum fan module and the cleaning head module. The local power point optimizer may be configured to determine an optimum operating condition for a corresponding group of solar cells.