[Zack2000]

It depends on the kind of energy you intend to harvest, if it sound energy
Simple chips like the amplifier Ic and TDA Ic’s can be used in the device together with suitable sensors, if it light energy you intend to harvest component like the Light dependent Resistor (LDR) and the photo diode together with photo transistor will be useful…Every energy has a unique chip to be used for its implementation