Wayne, et al:
I also recommend that you perform a Megger test on the DC Source Circuit
conductors before recommissioning the system. There could be wiring
faults caused by the lightning strike that may go undetected.
It's also possible that an undetected ground fault might have occurred
during initial construction. The presence of a longitudinal imbalance on
the PV conductors could make the equipment more susceptible to lightning
induced voltage.
I was contracted to troubleshoot and determine the extent of damage for
a lightning strike on a 21 module (3-strings of 7) ground mount system
located about 180' from the garage where the string inverter was located.
The lightning irreparably fried the 7 modules in the middle landscape
oriented string (furthest from the N-S support posts) and the string
inverter. The other two strings were unaffected.
When I did a Megger test on the PV conductors for all 3 strings, I found
that the home run wiring for the lightning damaged middle string had a
4.5 k-Ohm ground fault on the PV+ conductor to ground. The ground fault
resistance was too high to blow the inverter's 1A GFDI fuse.
If left uncorrected, the ground fault would have seriously affected the
performance of this string. I measured the performance of this string
with my Solmetric PVA1000 analyzer after the damaged modules were
replaced. The ground fault caused a 44% reduction in PV production as
compared to the other two strings.
It was not possible to replace just the faulty conductor without
damaging the other wires in the buried conduit. The solution was to
install the replacement inverter at the ground mounted array, then reuse
the remaining good wiring for the inverter's PV output circuit.
Regards,
Gary Willett PE
Icarus Solar Services / Engineering
Irving TX USA
On 5/21/15 7:35 PM, Richard L Ratico wrote:
Wayne,
Never had an entire array fried. My experience consists of a total of less than
10 modules out of a total of maybe 50 at two different sites. One site had the
much more common (these days) modules with leads and diodes potted in an
epoxy-like material. We use a Dremel tool with a burr bit to access the diodes.
Pretty labor intensive, but modules of the right size were no longer available.
If the junction boxes have removeable covers, that's half the battle won. You
can test the individual diodes and cell strings. Diodes are inexpensive and not
too hard to replace. I think we got them through Mouser.
Dick Ratico
Solarwind Electric
--- You wrote:
Hi Wayne,
Several years back I had all sixteen SolarWorld modules on a tracker get
zapped. The two other trackers adjacent to this one had no damaged
modules. The same strike blew out the phone box at the end of the road
(some distance away).
The SolarWorld jboxes were all sealed with no way to get to the diodes.
The homeowners insurance covered the loss and I replaced the modules with
something similar (SW had since stopped manufacturing 175s). It would have
been nice to have had access to the diodes.
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