Mitigation of hot-spot effect via back side cooling techniques: A potential for electrical and thermal performance improvement

Abstract

Hot-spot mitigation is an ever-present issue in photovoltaic system and it significantly affects the performance of photovoltaic (PV) panels. Most of the hot-spots are actually partial hot-spots which cover only a part of PV cell, or part of PV panel. In this work an influence of cooling mechanism on hot-spot mitigation is investigated by using previously developed numerical model. Specific parameters such as insolation, hot-spot intensity, convection intensity, cooling medium temperature and number of affected cells were varied for single panel. By varying parameters, it was found that partial hot-spots with less than 15% shade percentage on up to 4 cells (corresponds with 1% of total shade on PV panel) can be mitigated with adequate cooling technique applied on the PV panel. The hot-spot cases with larger shade can be mitigated, but only with high cooling intensity which makes the feasibility of the mitigation highly questionable. Hot-spot cases with more than 15% shade percentage on more than 10 affected cells (corresponds with 2.5% of total shade on PV panel) practically cannot be completely mitigated with any back side cooling technique. Nevertheless, cooling technique still provides additional electrical energy gain even with intense hot-spot cases. Results gained in this investigation can also be used to estimate potential in higher electricity output with specific cooling technique, and to estimate thermal energy potential such as house or hot water heating. A simplified case study is presented, where result application is explained step-by-step. These results are of particular interest for PV panels installed in urban areas with lots of obstructions and where regular cleaning is not practical. Such applications are rooftop PV systems, facade PV and photovoltaic-thermal (PVT) systems.