[RE-wrenches] PV Cell Temperature Variation

[Corey Shalanski]

On a recent utility-scale PV installation we noticed a strange phenomenon
on a single string on a single inverter. An IV curve (attached) reveals
that the measured performance characteristics for this string (solid line)
are significantly less than the expected values (dotted line). For
reference, the ambient temperature was 31°C and the irradiance was 1010
W/m².

The phenomenon that more so caught our attention is apparent on a thermal
image (also attached) of the modules in this string. For lack of a better
term I would describe the distribution of cell temperatures as resembling a
"checkerboard" or "scattershot" (random) pattern, ranging between roughly
55°C and 70°C. Interestingly this phenomenon was only apparent while the
inverter was operating, i.e. with the inverter turned off the modules
revert to a much more uniform temperature distribution nearer to 55°C,
instead varying by only a couple degrees across the entire module/string.

There was no apparent physical damage to the modules.

Can anyone offer any suggestions about what might be causing this
phenomenon?

--
Corey Shalanski
Joule Energy
New Orleans, LA
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