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Chapter 16 • Small-Scale PV Systems Used in Domestic Applications 347
They can grow over time due to thermal tension or seasonal and weather conditions, re-
sulting reduced power output.
16.5.4 Delamination and Moisture Ingress
In a panel production, three components of panels (the glass layer, the solar cells, and the
back sheet) are laminated under vacuum and designed to be weather proof. Delamination
is the separation of these layers during operation, resulting in moisture penetrating into
the panel, and causing internal corrosion which is visible as dark spots on the panel. Note
that panels manufactured using glass substrates and frameless/thin-film PV panels can
also suffer from moisture and corrosion problems.
16.5.5 Snail Trail Contamination
Snail trail is a discoloration of the panel, which usually becomes apparent after a couple of
years of production, and which is usually associated with the use of defective front mor-
alization silver paste during production of cells. This causes chemical breakdown on the
front of the panel that is visible in the form of snail trails affecting panel performance.
16.5.6 Interconnects
There are four levels of interconnects in thin-film modules such as gridlines (<1 mm thick)
in a cell, busbars connecting these gridlines in a single cell, cell interconnect ribbons (con-
necting multiple cells into a string), and string interconnect (connecting multiple strings
of cells) (Fig. 16.12). Failed connection of any of these interconnects decrease the perfor-
mance of a panel. Multiple ribbons and busbars may be accommodated to reduce this
problem but at increased cost and slightly reduced performance.
FIGURE 16.12 Four levels of interconnects in PV cells and modules.
