A self-optimizing energy harvester comprises a thermoelectric generator coupling to a thermal source, producing a source voltage greater than a minimum start-up voltage, where the thermoelectric generator drives a boost circuit and a feedforward circuit, delivering power to a load. A conventional boost circuit has a maximum output power only at the input voltage for which a fixed set point resistor is chosen. The feedforward circuit dynamically optimizes the boost circuit according to a dynamic set point resistance, thus increasing output power for a wide range of input voltages, relative to using a fixed reference resistor. The dynamic set point resistance is the sum of a variable resistance and a reference resistance. A sample element forms a differential voltage between the source and input voltage elements, and the variable resistance corresponds to the differential voltage. A reference resistor is chosen to establish the minimum start-up voltage.