[RE-wrenches] Unisolar Intermittent Ground Fault

Tue Nov 27 08:49:18 PST 2012

Let us know what the megohmmeter says. FWIW: There is some precedent for premature product failure in a roof-integrated product manufactured by Energy Conversion Devices (Uni-Solar):

http://www.utsandiego.com/news/2012/sep/14/tp-flawed-solar-panels-removed-at-schools/?print&page=all

On Nov 27, 2012, at 10:12 AM, Larry Crutcher, Starlight Solar Power Systems wrote:

> Robert,
> 
> Having installed hundreds of Uni-Solar modules, the only failure I every experienced was a framed US64 that had the PV negative short to frame. Flexing the module would create intermittent failure. You have PV laminates so your ground fault may be to the metal roof.  I might be stating the obvious but here's my list of tests:
> 
> I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, Installation Guide, AA4-3670-05, 10/05). 
> If that does not produce results, apply pressure with a heavy roller up and down the edges where the diodes and cell interconnect traces are while testing.
> Check all wire penetrations into the channel.
> Make sure all wire expansion rules were followed, look for stressed wire.
> Check for any screws installed in other than the two approved areas. There are two versions of laminates. One has a VERY narrow area. 0.65" by 2.75",  for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, 10/05). A misplaced screw may have allowed water to migrate to the trace areas and be providing a path through the screw.
> 
> RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever.
> 
> Larry Crutcher
> Starlight Solar Power Systems
> 
> 
> 
> 
> 
> 
> On Nov 26, 2012, at 5:55 PM, Robert Nuese wrote:
> 
> Dear Wrenches
> 
> I've been experiencing a troubleshooting problem that you may be able to
> help me with.  Or, can anyone refer me to someone, maybe an electrical
> engineer?, who I could hire to help.
> 
> About 7 years ago I installed Unisolar modules on all the roofs of a complex
> of 12 mixed use buildings and one commercial building. These fed the
> grid through a variety of Fronius IG and SMA SunnyBoy inverters.
> 
> Ever since, we have had occasional intermittent ground faults on a few of
> the roofs, and more frequent ones on one roof. At least some of these I
> suspect were caused by the roofer. Standard procedure on the Unisolar
> modules is to put two screws through them that hold on the roof ridge
> z-strip metal closure piece. These also keep the modules from sliding off
> the roof in extreme hot weather. I found a number of screws placed
> slightly outside the allowed screw zone. After I'd moved the screws
> (and removed the raised metal edges the screws had made in the roof,
> and put insulation between roof and module in those locations), this has
> seemed to fix some problems. Similarly, putting tefzel patches, per Uni-
> solar instructions, on some big dings and scratches may have fixed some
> others.
> 
> However, I still occasionally, rather rarely, get ground fault indications
> on some inverters, and rather regularly get them on one specific IG 3000.
> Some times the indication is just in the software, and the problem disappears
> through resetting by disconnecting the inverter and reconnecting to reset the
> software. However, on that worst Fronius, it has usually blown the 1 amp
> ground fault fuse, indicating that there very likely has been a ground fault.
> 
> I suspect that these ground faults are brought on by thermal expansion and
> contraction, that may only occasionally, and briefly, bring hot and ground
> elements of the system into close enough proximity. Dampness seems to
> play a part, the ground faults almost always occur during the rainy season,
> and usually during a rainy period.
> 
> But whenever I get out to the site to test the system, the ground fault is
> always gone. I test by disconnecting both wires of each string, measuring
> the total voltage across, and then the voltage from each to ground. If there
> is a clear voltage to ground, then there is a ground fault, and its location in
> the string can be easily determined. If the voltage steadily goes toward
> zero, then a ground fault is not clearly present, and the location of where
> one had been is totally obscure.
> 
> I've done very thorough visual inspection of the roofs, and also of the
> disconnects, junction boxes, and gutters that the wires pass through.
> As mentioned, the modules have had some problems, and I've fixed them
> all, as well as can be done. The wires all seem fine. Well connected, neat,
> not close to raw metal edges, insulation ok, etc.
> 
> I've asked Unisolar (before they went bankrupt, now they don't answer the
> phones), and they've just recommended the testing I've done, and not had
> any other ideas. Same with Fronius - they think it's outside of the inverter,
> and the blown fuses support that position.
> 
> I could go on with more details about what I've done and thought about,
> for instance, is the Fronius too sensitive? But I'll catch my breath and see
> if anyone else has some input before I go into more detail.
> 
> SO what am I missing? What test should I do? How can I fix this problem?
> 
> OR does anyone know of somebody with more expertise who I could hire
> to help? I'm a fairly experienced solar installer, but I think this might be
> something that requires an electrical (or electronic?) engineer with a deep
> understanding of electrical theory, and with some advanced test equipment.
> Any recommendations? Probably needs to be someone within 100 miles of
> Sebastopol CA.
> 
> Thanks,
> Robert Nuese
> 
> 
> 
> 
> 
> 
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