Oooo... Or maybe a module or more are shorted and being bypassed ?
A FLIR can sometimes come in handy to look at the entire array and of course
detect bad/hot connections.
But a shorted module will be almost as hot as a working module at MPP
voltage.
boB
On 6/1/2015 11:28 AM, b...@midnitesolar.com wrote:
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
sgsrenewab...@gmail.com <mailto:sgsrenewab...@gmail.com>
719.588.3044
www.sgsrenewables.com <x-msg://40/www.sgsrenewables.com>
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