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Why backsheet standards are anything but standard
dards. While there is some overlap in the
tests, each has requirements the other does
not. These include varying requirements
for test data sources, along with different
methods for reporting test results.
Reconciling the lab with the field. Many
current standards have been borrowed
from other fields, and aren’t necessarily
applicable to photovoltaic testing. As a
result, these standards are not reliable
indicators of field performance. In fact, the
properties of PV module components are
often engineered to meet performance and
safety standards, as opposed to addressing
in-the-field durability and survival.
What are the tests?
With the above challenges in mind, here is
a sampling of material properties that are
most crucial to producing durable backsheet
with superior performance characteristics.
Comparative Tracking Index (CTI).
Rates resistance of an insulating material
to electrical breakdown, which would form
a conductive path on the surface.
Damp Heat (DHT). Required for module
certification, but not for backsheet.
However, poor performance of backsheet
under damp heat conditions—i.e. delamination,
degradation—can affect module
performance.
Flame Spread Index/Radiant Panel.
Measures the surface flammability of a
backsheet material when exposed to both
heat and flame.
Glow Wire Testing (GWFI/GWIT).
Examines the temperatures at which materials
ignite by simulating the effect of heat
that arises in malfunctioning electrical
equipment.
High Current Arc Ignition (HAI).
Determines the likelihood of a power
surge by simulating loose connections and
broken leads.
Horizontal Burn (HB). Determines the
rate, fast or slow, at which a particular
material will burn.
Hot Wire Ignition (HWI). Evaluates the
ignition properties of a polymeric material
when adjacent to or supporting an overheated
wire, whether insulated or uninsulated.
Partial Discharge (PD). Verifies the backsheet
is engineered with insulation properties
to suit the voltage requirements of the
module.
Relative Thermal Index (RTI). Ensures
the backsheet’s properties will not be unacceptably
compromised at the maximum
operating temperature of the module.
UV Resistance. Ensures appropriate resistance
to UV degradation, if and when the
end-use application requires the backsheet
to be in direct exposure to sunlight.
Vertical Burn (VB). Determines the rate at
which material will extinguish itself, once
the ignition source is removed.
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www.globalsolartechnology.com
Global Solar & Alternative Energies – May/June 2013 – 11