Modern era is looking at the sustainable energy for a permanent solution to the future power demand all over the world whereas the countries of the third world like Bangladesh is still failure to meet the present basic power demand. St. Martin Island is one of those places which are still out of national grid in Bangladesh. It is the most beautiful tourist island in the Bay of Bengal, which is in the most southern part and 17 km far away from the main land of Bangladesh. Grid connected electric system is quite impossible even in future because of costs and geographic location. Present electricity demand is partially fulfilled by stand-alone diesel generators only for four hours per day with large amount of CO2 emission. This paper is documented to give a solution of the power crisis of St. Martin Island with optimizing hybrid power generation scheme concentrating on sustainable energy. Using HOMER analysis, an optimum configuration is established among a set of systems to supply electricity to about 1400 families, 150 shops, 100 hotels and various organizations. The load calculation for the whole island has an outcome of a demand of energy about 4000kWh per day with a peak load of 504kW. This system incorporates a combination of 600kW decentralized Solar PV, 3 wind turbines of 1.8kW each, 2000 batteries of 800Ah each, 300kW biogas generator and 15kW diesel generator to fulfill the whole power demand of St. Martin Island. This configuration gives lowest cost of energy (COE) as BDT 15.04/ kWh (US$ 0.2/kWh) with a renewable fraction of 99.3%. It reduces CO2 emission significantly. This hybrid system may be an effective solution to the present electricity demand of St. Martin Island without hampering the environment. Besides, it may be an ideal example of a renewable hub because of its high renewable fraction.