  Moisture in the form of humidity has a significant impact on the operation of
photovoltaic (PV) cells and panels. Moisture is often diffuse through the
encapsulant film (Ethylene Vynil Acetate (EVA), PVB, PVF, PMMA) or the
breathable back-sheet. Moisture is known to accelerate the degradation and
reduce the performance of a PV while operating in a wet environment. SCAPS 1 D
is widely used to simulate and estimate the operation of PV. In this work, we
showed the effect of moisture on the operation and performance of a PV, made
from monocrystalline silicon. Namely, the influence of defects and impurities
generated by moisture was investigated. We studied the simultaneous effects of
Silanlols (Si-OH), Hydrogen ions H$^+$, and the metallic ions generated from
the corrosion of contacts, encapsulant and transparent conducting oxide (TCO)
when there is production of acid (Al$^{3+}$; Zn$^{2+}$), or from dust
(Fe$^{3+}$).
  The numerical simulation showed that : starting with PV cells without
moisture, the Fill Factor (FF) and the Power Conversion Efficiency (PCE) drop
respectively from 82.80 $\%$ to 81.78 $\%$ and 18.57 $\%$ to 11.46 $\%$ , when
there is moisture in the cell and PVB used as encapsulant. Further degradation
of parameters was observed, when the moisture leads to the production of acetic
acid on the EVA, or when there is dust having iron (Fe). FF and PCE were
further dropped to 79.20 $\%$ and 7.04 $\%$ respectively, using the same
initial photovoltaic cells. Furthermore, a net decrease in key electrical
parameters of the PV was observed throughout the study, with maximal power (
P$_{max}$), the short circuit current ( J$_{SC}$), the current density at
maximum power J$_{MP}$ reducing by more than 50\%. This study paves the way for
the improvement of performance, and the understanding of degradation process in
panels used in wet environments and tropical area.
