Abstract: A power generation system including an engine and an electrical generator driven to rotate at rotational speed by the engine. The generator is configured to supply an adjustable amount of required electrical power having a voltage and a current to at least one electrical load. The system also includes a controller configured to adjust at least one operating parameter of the engine in order to maximize efficiency of the system. The system efficiency is a measure of the combined operation of generator and engine and load for a given load condition. The controller is configured to maximize system efficiency based only upon the required electrical power being supplied by the generator. The controller is configured so that the controller does not independently consider any one of the rotational speed, the voltage or the current being supplied by the generator when adjusting the at least one operating parameter.