Energy Harvesting for Sensors: DC Harvesters
Nowadays, photovoltaic (PV) panels and thermoelectric generators (TEGs) constitute the most important direct current (dc) energy transducers that can be used to harvest energy from the environment and power an autonomous sensor node. They generate a direct current and voltage for constant operating conditions. A current–voltage (I–V) curve is defined for each operating condition in which an optimum bias point exists where maximum power is achieved. The voltage at the maximum power point (V MPP) depends on the operating conditions and it changes as these conditions vary with time. Several energy conditioners have been proposed and commercialized to transfer the energy to a storage unit or a load. The small magnitudes of the currents and voltages of such transducers constitute the main challenge in the design of these circuits. Ultralow-power consumption energy conditioners have to be designed to make feasible the use of these power sources.