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Wrenches,<br>
What a delight it is when a client is so fully able to understand
and follow directions! Albert, the homeowner of the 1997 system with
16 BP 75W modules on a tracker, sent the results below. In short, he
isolated each string and measured input and output voltage and
current as shown by the display on the MX60. <br>
<br>
The results suggest that while two of the four strings are worse
than the other two, all are severely degraded, and none put out
close to original MPP voltage or current. <br>
<br>
Given that the tracker has recently stopped operating (due to an
obviously failed internal electronic component, most likely from
lightning damage) and replacement controllers are no longer
available, SunXtenders that have reached the end of their life after
nine years of operation, and these modules, I'm not recommending
rebuilding this system with new batteries and modules. I have
suggested a batteryless grid-tied system, and either keeping this as
a modest backup resource for occasional outages (with new batteries,
of course) or using a home standby generator to meet backup needs.<br>
<br>
And both the client and I would be interested in any observations
and further conclusions that can be taken from the numbers below and
in the attached spreadsheet. It appears that string three pulls down
the overall output beyond what it contributes. We have one spare
module, if the client chooses to keep the existing array in
operation. The other three strings put out between 50% and 61% of
original nameplate current rating. All have decidedly low Vmp, which
at STC would be around 68V.<br>
<br>
Thank you,<br>
Allan<br>
<br>
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<p class="MsoNormal"><b>Allan Sindelar</b><br>
<span style="font-size:10.0pt"><a
href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a></span><br>
<span style="font-size:10.0pt">NABCEP Certified PV
Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), <span style="mso-bidi-font-weight:bold">Positive
Energy,
Inc.</span><br>
<b>505 780-2738 cell</b><br
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Date: </th>
<td>Sun, 28 Aug 2016 09:11:31 -0600</td>
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<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
Allan,
<div class="">I completed the test yesterday during late morning
sun. Results are shown in the attached spreadsheet. It appears
that both strings 3 and 4 gave lower Vmp, although 3 was worse.
</div>
<div class="">Albert<br>
<br>
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cellpadding="0" cellspacing="0" width="450">
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<tr class="" height="13">
<td colspan="2" class="" height="13" width="150">PV Array
Output</td>
<td class="" width="75"><br>
</td>
<td class="" width="75"><br>
</td>
<td class="" width="75"><br>
</td>
<td class="" width="75"><br>
</td>
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<td colspan="2" class="" height="13">Observation date:</td>
<td class="xl24" x:num="41147.0" align="right">8/27/16</td>
<td class=""><br>
</td>
<td class=""><br>
</td>
<td class=""><br>
</td>
</tr>
<tr class="" height="13">
<td colspan="2" class="" height="13">Observation time:</td>
<td colspan="2" class="">11:10 - 11:45</td>
<td class=""><br>
</td>
<td class=""><br>
</td>
</tr>
<tr class="" height="13">
<td colspan="4" class="" height="13">Values displayed on
MX-60 charge controller @ MPPT</td>
<td class=""><br>
</td>
<td class=""><br>
</td>
</tr>
<tr class="" height="13">
<td class="" height="13"><br>
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<td class=""><br>
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<td class=""><br>
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<td class=""><br>
</td>
<td class=""><br>
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<td class="xl26" height="13">String*</td>
<td colspan="3" class="xl27" style="border-right:.5pt
solid black">Input</td>
<td colspan="2" class="xl27" style="border-right:.5pt
solid black">Output</td>
</tr>
<tr class="" height="13">
<td class="xl26" height="13"><br>
</td>
<td class="xl26">V</td>
<td class="xl26">A</td>
<td class="xl26">W</td>
<td class="xl26">V</td>
<td class="xl26">A</td>
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<tr class="" height="13">
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</td>
<td class="xl26"><br>
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<td class="xl26"><br>
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<td class="xl26"><br>
</td>
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<td class="xl26" x:num="1.0" height="13">1</td>
<td class="xl26" x:num="52.0">52</td>
<td class="xl26" x:num="3.7">3.7</td>
<td class="xl26" x:num="184.0">184</td>
<td class="xl26" x:num="26.0">26</td>
<td class="xl26" x:num="7.1">7.1</td>
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<td class="xl26" x:num="46.0">46</td>
<td class="xl26" x:num="3.4">3.4</td>
<td class="xl26" x:num="153.0">153</td>
<td class="xl26" x:num="26.0">26</td>
<td class="xl26" x:num="6.0">6</td>
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<td class="xl26" x:num="38.0">38</td>
<td class="xl26" x:num="3.3">3.3</td>
<td class="xl26" x:num="122.0">122</td>
<td class="xl26" x:num="26.2">26.2</td>
<td class="xl26" x:num="4.7">4.7</td>
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<td class="xl26" x:num="4.0" height="13">4</td>
<td class="xl26" x:num="37.0">37</td>
<td class="xl26" x:num="4.2">4.2</td>
<td class="xl26" x:num="152.0">152</td>
<td class="xl26" x:num="26.2">26.2</td>
<td class="xl26" x:num="5.9">5.9</td>
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<tr class="" height="13">
<td class="xl26" height="13">1+2+3+4</td>
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<td class="xl26" x:num="16.0">16</td>
<td class="xl26" x:num="610.0">610</td>
<td class="xl26" x:num="26.2">26.2</td>
<td class="xl26" x:num="23.3">23.3</td>
</tr>
<tr class="" height="13">
<td class="xl26" height="13">1+2+4</td>
<td class="xl26" x:num="47.0">47</td>
<td class="xl26" x:num="12.3">12.3</td>
<td class="xl26" x:num="544.0">544</td>
<td class="xl26" x:num="26.2">26.2</td>
<td class="xl26" x:num="20.9">20.9</td>
</tr>
<tr class="" height="13">
<td class="xl26" height="13"><br>
</td>
<td class="xl26"><br>
</td>
<td class="xl26"><br>
</td>
<td class="xl26"><br>
</td>
<td class="xl26"><br>
</td>
<td class="xl26"><br>
</td>
</tr>
<tr class="" height="13">
<td class="xl25" colspan="4" height="13">*selected using
breakers on combiner box at array</td>
<td class="xl26"><br>
</td>
<td class="xl26"><br>
</td>
</tr>
</tbody>
</table>
<br>
<br>
Hi Allan,
<div class="">I would try turning off string #3 and see what
happens to the Vmp. </div>
<div class="">I'm guessing it'll go up to a more normal voltage.
<br>
</div>
<div class="">Replacement is my thought. <br>
</div>
<div class="">Jay</div>
<div class="">Peltz power. </div>
<div class=""><br class="">
</div>
<div class=""><br class="">
On Aug 25, 2016, at 7:04 AM, Allan Sindelar <<a
moz-do-not-send="true" href="mailto:allan@sindelarsolar.com"
style="color: blue;" class="">allan@sindelarsolar.com</a>>
wrote:<br class="">
<br class="">
</div>
Wrenches,<br class="">
Here's one I haven't seen before. 1997 grid-tie battery backup
system that was one of my first, although actual installation
was by another before I was licensed. 16 BP 275, 36-cell 12V
modules, the standard of that time. Early Outback MX60 replaced
C40 around 2005; array rewired to four 48V strings of four
modules at that time, serving a 24V battery bank. Tested with an
end-of-life 9-year-old AGM battery bank in the system, but in
Sell mode with a 26.4V Sell voltage setpoint.<br class="">
<br class="">
At 11 am, 68ºF, 900W/m<sup class="">2</sup><span
class="Apple-converted-space"> </span>on the Daystar, with the
array under charge, I measured 3.5A, 3.4A, 2.4A, and 3.6A.
Short-circuiting each string, I measured 4.0A, 3.7A, 3.8A, and
3.7A. Original rating was 4.45A, so except for the third string,
current is what I'd reasonably expect from 20-year-old module
degradation. However, watching the periodic MPPT sweep from the
MX60 at the array, the maximum power point voltage for the
entire 48V array settled at 14.6A at 37.2V, or about 540 watts
from a 1,200W (originally rated) array.<br class="">
<br class="">
I have commonly seen the current reduce substantially with
age-related degradation, while the MPP voltage remains fairly
close to original. I have never seen the voltage drop this far -
an average of 9.3V MPP per each 12V module. All of the cells are
seriously browned. I have other systems out there with the same
modules of similar age that don't exhibit this weird behavior.
Can anyone help me understand why the MPP voltage would drop so
far below what is typical?<br class="">
<br class="">
There is a slight possibility of corroded buried input
conductors, because of a serious but corrected issue of galvanic
corrosion from a ground fault (a Romex connector pinching a
conductor and allowing seepage to ground). This was corrected
years ago, but the input conductors were direct burial for ~100'
and there was never a bonding conductor between the array and
the house, so there is a potential for corrosion damage.
However, the voltage measured at both ends while charging was
identical, so I think that would indicate that high conductor
resistance isn't the issue.<br class="">
<br class="">
As usual, thank you for the collective and individual wisdom
shared here.<br class="">
Allan<br class="">
--<span class="Apple-converted-space"> </span><br>
</div>
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