A method and apparatus are disclosed for controlling a hybrid energy system including at least an energy source having a maximum energy output and an energy storage device. The method includes determining a first amount of energy indicative of an amount of energy associated with the current operating condition of the energy source and determining a second amount of energy indicative of energy associated with the energy storage device. The method also includes estimating a third amount of energy indicative of a difference between the first amount of energy and the maximum energy output. The method further includes controlling the energy source as a function of the second and third amounts of energy.
