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
[email protected]
719.588.3044
www.sgsrenewables.com
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