Experimenting a distributed passive MPPT based on mini-battery-packs to cope with short-term critical partial shadings on PV-generators

Abstract

The common use of by-pass diodes, to contain power generation losses and to avoid "hotspot" phenomena in presence of short-term, repetitive and critical partial shadings on a PVfield, is experimentally investigated, for demonstrating that bypass diodes are not the optimum choice. Active distributed maximum power point trackers (DMPPTs) can offer a better solution; nevertheless, they are based on complex circuitries and control algorithms, with a reduced reliability and additional power losses. In this contest, the aim of the paper is to present and discuss experimental results obtained by testing a homemade PVgenerator prototype in which only a wisely designed and distributed mini-storage based on commercial rechargeable batteries is introduced, to be employed as a "passive" DMPPT, without any active DC/DC converter. The prototype is also experimented to make a comparative performance analysis (i) without bypass diodes, (ii) with bypass diodes and (iii) by introducing our mini-battery-pack, under identical partial shadings, artificially caused and characterized by different degrees of criticality. Experiments demonstrate that wisely designed distributed mini-battery-packs, based on commercial rechargeable batteries, can effectively operate as a passive DMPPT able to cope with short-term critical partial shadings for avoiding "hot-spot" issues and for guaranteeing a significant improvement of the net generated power together with the conventional storage task.