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

[Ray Walters]

Yes, amorphous modules degrade faster then crystalline cells. 15 years 
will really start catching up with you, that's why we always tried to 
stick to monocrystalline when we could.
I think your best option for now is to rewire the array for much higher 
voltage.  Even your current voltage problem aside, the system will run 
more efficiently at higher voltage:  Less current = less voltage drop.  
I would probably just jump the 4 module sets in series in the combiner 
box to 8 in series.  Should be a quick fix, and really show an 
improvement.  I've seen this same issue with low voltage polys and 
undersized wiring.  Usually the MPP controllers like some room to play 
with; as soon as the MPP voltage gets close to or less than battery 
voltage, the current drops off substantially.




R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 5/31/2015 11:55 AM, Luke Christy wrote:
> 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
> 719.588.3044
> www.sgsrenewables.com
>
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