A system includes a fuel burner disposed within a buoy, and at least one fuel tank coupled to the fuel burner. The fuel tank preferably contains ethanol or propane. The system comprises either a thermoelectric generator or an electrical generator mechanically coupled to a heat engine. The ethanol or propane is burned to generate electric power. At least a portion of the electric power that is generated is stored in a battery system so that the system can provide peak levels of electric power consumption that are relatively large. The system can be used in autonomous marine applications.