In this paper, the different aging mechanisms taking place in photovoltaic modules are discussed, and the cause-effect links, which exist among such mechanisms, are evidenced. It is also shown that a closed-loop link exists between aging and mismatching since aging (which is nonuniform by its nature) causes mismatching among cells, whereas mismatching, in turn, mainly due to its thermal effects, leads to nonuniform aging.

The starting point for the proper design of an efficient wireless sensor node (WSN) supply system that is based on the adoption of a resonant electromagnetic vibration energy harvester (REVEH) is represented by the choice of a REVEH with a proper resonance frequency. But further likewise important design guidelines need to be also taken into account especially if, as in the case of freight wagons applications, vibrations are nonsinusoidal and their characteristics change with time. In this paper, the guidelines leading to the development of a smart power electronics interface between the REVEH and the WSN are provided with reference to freight wagons applications. In particular, for the most widely used double stage ac/dc architecture for REVEH applications, such guidelines not only allow the choice of the proper dc/dc converter topology, but they also allow the development of a suitable maximum power point tracking control strategy that allows to avoid the waste of energy and the consequent necessity to oversize the REVEH.

In PV applications, under mismatching conditions, it is necessary to adopt a maximum power point tracking (MPPT) technique which is able to regulate not only the voltages of the PV modules of the array but also the DC input voltage of the inverter. Such a technique can be considered a hybrid MPPT (HMPPT) technique since it is neither only distributed on the PV modules of the PV array or only centralized at the input of the inverter. In this paper a new HMPPT technique is presented and discussed. Its main advantages are the high MPPT efficiency and the high speed of tracking which are obtained by means of a fast estimate of the optimal values of PV modules voltages and of the input inverter voltage. The new HMPPT technique is compared with simple HMPPT techniques based on the scan of the power versus voltage inverter input characteristic. The theoretical analysis and the results of numerical simulations are widely discussed. Moreover, a laboratory test system, equipped with PV emulators, has been realized and used in order to experimentally validate the proposed technique.