The present disclosure relates to a method, system and device for power generation planning in a power generation system. The power generation system comprises a plurality of Power Generation Units (PGUs). The system receives a power demand data indicative of power required over a pre-defined time period, by a load. A pattern in variation of power among various patterns is identified for each of one or more intervals in the pre-defined time period. An operation technique and a repair technique are determined for each of the one or more intervals based on the pattern. A plurality of working patterns for operating the plurality of PGUs is determined in each of the one or more intervals based on determined operational technique and repair technique for corresponding one or more intervals. System determines individual power outputs to be generated by the number of PGUs determined in each of the plurality of working patterns.