Net - zero energy systems are a key to making the Internet of Things (IOT) and the associated edge devices more ubiquitous. The power management unit for such edge devices should be able to harvest maximum energy from whatever is available in the device’s surrounding environment while actively managing the battery charge/discharge and generating all the rails for the sensors/actuators, compute, and communication sub-systems. This paper will present an overview of all the useful sources of ambient energy harvesting along with its power densities while also providing an insight into some of the work ongoing in academic and research institutions to showcase trends that can be expected as we move forward to making these systems more ubiquitous. The paper will also provide an overview of the various characteristics that is expected in a power management architecture that can keep these IOT sub-systems charged and ready for the next sense, compute or communicate event. Features that will make these power management units lower cost, higher efficiency and smaller form factor will also be presented. Some of the challenges and design considerations that are vital to making these systems feasible will also be presented in this paper.