[RE-wrenches] Extensive Lightning Damage to Modules

Fri Sep 7 11:37:31 PDT 2012

Hey Larry,

The four poles of ten modules in each row are each a separate string, combined at a fused DC combiner on the west most pole.  A 1 inch PVC conduit runs down each pole directly to a buried hand hole box at the west pole of each row.  Each conduit contains a #8 EGC along with the current carrying conductors.  In the hand hole boxes the four #8 wires are irreversibly spliced to the bare #6 that is laid in and runs the length of the 39 foot trench connecting the four poles.  An acorn attaches the bare #6 to a ground rod at each end.  The #8 EGC at each pole is irreversibly spliced to the EGC from the rails, rack and pole, each of which have lay in lugs.  The module are grounded to the rails with WEEBs.  We're following Burndy's paper on how to ground DP&W top of pole mounts.

The #6 should not have any tight bends, it should just leave the hand hole box and go in a straight line 39 feet east in the bottom of the trench.  This, combined with each pole being 5-7 feet into the ground should be sufficient grounding, I'd have thought.  It's about 100 times more surface area than the average house with a single ground rod.

Jeff
Hudson Solar

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Larry Crutcher, Starlight Solar Power Systems
Sent: Friday, September 07, 2012 11:54 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Extensive Lightning Damage to Modules

Hello Jeff,

I am curious about the network of ground rods and #6 wire. Can you describe how the modules and mount are connected to this ground system?
Are there any tight bends anywhere in the #6 wire?
Are any of the poles or mounts connected to other poles/mounts before going to the ground system?
Are any PV wires running between the poles before going to the combiner?

As most wrenches know, lightning strikes can induce very high voltage on any nearby wire runs and that voltage is looking for a path to ground. Equipment is damaged when it contributes to that path. If the voltage was induced on the PV module frames or wire, an effective ground system will disperse it to ground. Key word here is effective. I have seen grounding systems where the installer made nice, neat and tight 90° bends in the ground wire. This is a huge mistake which can greatly diminish the effectiveness of the ground system.

Larry Crutcher
Starlight Solar Power Systems

On Sep 7, 2012, at 8:40 AM, Jeff Irish wrote:

A customer of ours has recently suffered lightning damage to 31 out of 160 top of pole mounted modules.  This is the first time in 10 years that I've seen modules damaged by lightning.  Lots of inverter GF fuses and a few inverters, but never modules.  We're trying to determine if it was caused by the lightning flash irradiating the modules or ground currents.

The array consists of 16 DP&W top of pole mounts with 10 modules each, arranged in a square of 4 poles E-W and 4 rows N-S.  The poles are 13 feet center to center E-W and the N-S row spacing is about 50 feet.  The poles are 6 inch galvanized Technoposts, augured 5 - 7 feet into the firm ground, connected with a network of about 160 feet of bare #6 copper and at least 8 copper plated ground rods.  Altogether we have about 130 square feet of bare metal surface area connected and buried in the ground at and around the array.

The customer saw lightning strike just after dawn a few weeks ago a couple hundred feet to the southwest where it also destroyed two utility pole mount distribution transformers and ran along the utility wires 100 feet south of the array.  The inverters are 200 feet NW and suffered no damage.  The array and modules look totally fine, except some of the J-boxes are deformed from heat.  Opening the J-boxes shows varying levels of damage to one or more diodes, from discoloration to being broken and cracked open.

The odd thing is the pattern of damage (we've tested all the modules individually for Voc and Isc).  Only modules in the south row of 4 poles are damaged, and the damage is concentrated on the modules closest to the ground; modules higher up in the air appear OK.  Also, damage is less frequent as you move east, away from the direction of the strike.

If it was caused by ground currents, why would the current want to go up the poles, why only the southern row of poles, and why damage more modules closer to the ground and not those at the top?  Is it possible a flash near the ground irradiated the modules causing a current spike and the southern row shielded the other rows from most of the flash?  Anyone have experience with this?

Jeff Irish, PE
President
Hudson Solar
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Rhinebeck, NY 12572
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F.845.876.3912
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