The present invention seeks to improve upon existing energy-generation technologies by providing methods, systems, and devices for converting mechanical power into electrical power. More specifically, the present invention relates to fluid-powered generators and methods, systems, and devices for generating power by way of such fluid-powered generators. The present invention includes devices for generating energy comprising fluid turbine generators having variable inlet(s), wherein the fluid velocity, volume, and/or mass of fluid collected by the inlet can be varied to control turbine speed to provide a reasonably steady, continuous, and/or sufficient source of energy over a wide range of conditions presented by natural fluid resources.