Optimal Use of Batteries on PV Systems for Solving Problems Caused by Predictable Partial Shadings

In the current energy transition contest, photovoltaic (PV) systems stand out among the most efficient renewable electricity sources. Therefore, there is a strong collective interest in making this technology more efficient and in solving some important issues. In particular, partial shadings are one of the major drawbacks regarding electricity generation by PV-systems. Partial shading phenomena can be caused both by stochastic events (e.g. dirt, cloud passages, bird passages etc.) and/or by predictable and repetitive events (e.g. shadow projections created by a variety of fixed natural elements or artificial installations located in urban or industrial contexts). This last type of shading, turns out to be one of the main causes of generation reduction and also permanent damages or premature obsolescence of PV-components; they are also a real deterrent to a wide diffusion of PV-installations, as they frustrate the utilization of a variety of potentially useful surfaces in urban and/or industrial contexts. Against these baleful effects of predictable and repetitive partial shadings, in the paper, we propose a mitigation technique based on batteries distributed at the PV submodule level. More specifically, as an alternative to conventional bypass diodes, batteries and a proper battery control unit (BCU) are proposed to be installed at the terminals of partially shaded submodules, in order to improve its generation performance and to eliminate potential hot-spot phenomena. The operating principles are described along with the configurations and the used materials. Furthermore, the performance of two grid-connected PV-generators subjected to identical partial shadings are experimentally compared; only one PV-generator is equipped by the proposed battery-based solution while the other one is equipped by conventional bypass diodes.