[RE-wrenches] Voltage Degradation with Uni-Solar laminate

[boB at midnitesolar.com]

Partial shading will also reduce the MPP voltage and to a much smaller 
extent, the Voc.

I don't suppose there are some new trees or something at the site ?

Jarmo, I like your presentation.

boB


On 6/1/2015 11:21 AM, Starlight Solar Power Systems wrote:
> Luke,
>
> For reference, we sold/installed many hundreds of Uni-Solar products 
> since 2002. I have never seen anywhere near that much Voc loss.
>
> Since the PVL-68 has an open circuit of 23.1V (92.4V) but you only see 
> 14.2V (71V), a loss of 25%, I do not believe degradation is the 
> culprit even at 15 years. The rated degradation is 0.73% per year. 
> That should put you at 82.3 Voc. But, Uni-Solar consistantly outputs 
>  at least 10% more than rated power, even with age it should be higher 
> than 82 volts.
>
> Proper Uni-Solar installation required 2 screws into the roof up near 
> the top. A misplaced screw and time or an open seam may be causing a 
> ground fault, pulling down the voltage of the array. Start by using a 
> Megger at the combiner to check for leakage. No one likes crawling in 
> a hot attic but I think you may need to.
>
>
> Larry Crutcher
>
>
>
> Hello Off-Grid Wrenches,
>
> I recently made a periodic maintenance visit to a residential off-grid 
> system I take care of here in Southern CO, and discovered an 
> interesting problem.
>
> This system has an array of 48x Uni-Solar PVL-68 laminate modules 
> applied directly to standing-seam metal roofing.
>
> The data logging on the controller (Outback MX-60) indicated that the 
> system was having trouble completing a charge cycle and going to 
> float. Initially I assumed was due to heavy electrical use by the 
> occupants (renters). After a little checking, I noticed that the 
> module string voltage was only about 0.5V above the battery voltage!
> This was a cool late morning, with full sun, and the array was 
> charging almost 2kW at 54.5V. The module strings were running at 55V. 
> I've noticed the module voltage being lower than I'd like before, but 
> it has never been this low. I suspect this is the real reason the 
> system hasn't been able to complete a charge cycle.
>
> By removing the loads I was able to get an open-circuit voltage of 
> 71V, but that still seems pretty low.
>
> Has anyone else experienced a voltage degradation issue with the 
> Uni-Solar laminate? What was the expected annual voltage degradation 
> for this technology?
>
> These modules do have some age on them. The system was installed about 
> 15 years ago (by a competent installer who is now retired). The system 
> was installed before MPPT controllers were common, so I assume the 
> modules are wired in strings of 4 for 48V nominal.
>
> Any experiences or opinions are appreciated.
> Thanks in advance.
>
> -Luke
>
>
> Luke Christy
>
> NABCEP Certified PV Installation Professional™: Certification #031409-25
> NABCEP Certified Solar Heating Installer™: Certification #ST032611-03
> CoSEIA Certified PV Installer
>
> Solar Gain Services, LLC
> PO Box 531
> Monte Vista, CO. 81144
> SGSRenewables at Gmail.com <mailto:SGSRenewables at Gmail.com>
> 719.588.3044
> www.sgsrenewables.com <x-msg://40/www.sgsrenewables.com>
>
>

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