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

[Luke Christy]

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