Degradation analysis of Photovoltaic modules operating under local conditions

Abstract

Solar power has the abilit y to play a major role in the electrification of the developing and developed world. Autonomous energy system s based on solar photovoltaic is a feasible alterna tive to a grid connection. Solar power can also be used as a complement to a weak grid, for facilities that require a higher re- liabilit y of power. Photovoltaic (PV) modules deployed outdoors can degrade due to exposure to various conditions. This includes exposure to UV light, a range of uctuatin g temp eratures and humidities and exposure to variances in operating currents and voltages. Different climates have an important in uence on degrada tion rate. Therefore, degradation rate studies from diverse geograph- ical locations are of great interest. Evidence indicates that not only degradation but also failure mechanisms are locat ion dependent. There exists a huge knowl- edge gap on the degradation forms and mechanisms of solar panels over medium to long term usage. A larger gap tending towards almost total absence of this knowledge, for the Kenyan environment, does exist. This research investigated the mechanisms and causes of degradation, how a module degrades and how the degradation can be avoided. The study involved identification and analysis of modules that had been deployed in various locations in Kenya and had been in operation for an extended period of time. A sun simulator and curve tracer were used to generate and study PV module power output. Imaging instruments were used to study visible signs of weathering and other physical defects. This work was carried out in collab oration with Ubbink E.A Ltd, the only solar module factory in East and Central Africa. The results indicate d that despite the fact that panels are designed to operate in outdoor environment, numerous cases exist whereby panels degrade physically and consequently exhibit either total failure,

diminished performance or just physical manifestation of wear. The main forms of degradation observed were defects on the encapsulan t. Power derating was observed to be directly proportional to degradation. As such, PV modules ex- hibiting higher forms of degradation also exhibit high power deratings. It was noted that PV modules operating in regions of elevated temp eratures and higher annual precipitation experience more degradation forms and consequently higher power deratings. Apart from manufacturer defects, user ignorance on installation and usage also contributed to the diminished life span of some panels.