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I agree, many module failures only show up under load. I just use a
clamp on meter while the modules are still wired to the batteries. <br>
The PV150 can capture operating current and power as well, so it
should be able to identify most module fails. I'm just not sure if
it can do this without a load. I don't believe it's an actual IV
tester.<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
<div class="moz-cite-prefix">On 10/6/2015 10:09 AM, David Coale
wrote:<br>
</div>
<blockquote cite="mid:FC3B7423-2757-4B23-8199-B15B88B345EA@evcl.com"
type="cite">An Isc test will not find a series resistance problem.
You have to put a real load on the panel or string to find this
type of problem.
<div><br>
</div>
<div>David</div>
<div><br>
<div>
<div>On Oct 6, 2015, at 4:58 AM, Chris Mason wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
<div dir="ltr">If you use the PV150 tester, it will do this
test, giving you the Isc for each panel you test. The Isc
should be the same for all panels given the same
irradiance. It does all the other tests at the same time,
and you can record the results to an Excel format report,
including the irradiance at the moment of the test.
<div>As you can string test, which will identify any
strings with bad panels, I think this should be a
minimum for any commissioning report.</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Oct 6, 2015 at 12:57 AM,
David Coale <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:david@evcl.com"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:david@evcl.com">david@evcl.com</a></a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi
Wrenchers,<br>
<br>
I have found on the older panels, especially the
AstroPower line, the problems tend to be bad solder
joints. This shows up as a series resistance. As
such, the open circuit voltage and short circuit
current will read good. It is not until you put an
external load on the panel that you will see any
problems. If you want to draw out a simple circuit
with a voltage source, a current source and a series
resister, you will see this quite clearly.<br>
<br>
On these older systems I am just looking for the few
bad panels to be replaced or fixed (more info on
fixing if requested). I am not looking to find the
MPP output or the corrected performance of the panel
with all the relevant parameters accounted for. A
very easy way to do this is to just have one or two 50
watt 12 volt halogen bulbs as a load and measure
voltage and current across each pane with this load.
I try one bulb and then two bulbs in series and use
whatever set up gives me the highest wattage reading
and then use this load for the rest of the testing.
Bad panels (AstroPower) tend to be 1/2 the output
relative to the good panels, or almost no output at
all depending on where the bad solder joint is.<br>
<br>
If you have a bunch of panels you can take down the
measurements and then sort through them and get the
best panels for your system (I have an excess of
panels at this point). It is helpful to have an
irradiance meter to make sure you are testing all the
panels with about the same input for comparison. The
panels of course have to have about the same angle to
the sun and similar temp to make the comparison
valid. I usually have the panels in the shade and
then pull them out for testing so that the temp is all
about the same. They can also be tested in place if
you can access the leads for testing.<br>
<br>
I have built a tester with several bulbs and a toggle
switch that will let you easily switch between Voc,
Isc and with a load using two meters, one for voltage
and one for current to make the readings at the same
time. No fancy testers required for just finding the
few bad panels.<br>
<span class="HOEnZb"><font color="#888888"><br>
David<br>
</font></span>
<div class="HOEnZb">
<div class="h5"><br>
On Oct 5, 2015, at 7:46 AM, Starlight Solar Power
Systems wrote:<br>
<br>
> Bill,<br>
><br>
> In the shop I have two electronic loads that
I use nearly every day with batteries and PV
modules. One is a programmable 150W, 360V that can
be set for constant power, current or voltage
(like this: <a moz-do-not-send="true"
href="http://www.amazon.com/Programmable-Electronic-Load-360VDC-CSI3710A/dp/B00D7QGSV4"
rel="noreferrer" target="_blank">http://www.amazon.com/Programmable-Electronic-Load-360VDC-CSI3710A/dp/B00D7QGSV4</a>).
It’s small enough to take to the field. The other
is a 2kW model that I use for battery load and
discharge testing. It’s too big to move.<br>
><br>
> I also use the Daystar DS-05A (seen here: <a
moz-do-not-send="true"
href="http://www.amazon.com/Daystar-DS-05A-Solar-Digital-Meter/dp/B00YVTXZJ4/ref=sr_1_fkmr0_1?s=electronics&ie=UTF8&qid=1444055204&sr=8-1-fkmr0&keywords=Daystar+PV+irradiancePV"
rel="noreferrer" target="_blank"><a class="moz-txt-link-freetext" href="http://www.amazon.com/Daystar-DS-05A-Solar-Digital-Meter/dp/B00YVTXZJ4/ref=sr_1_fkmr0_1?s=electronics&ie=UTF8&qid=1444055204&sr=8-1-fkmr0&keywords=Daystar+PV+irradiancePV">http://www.amazon.com/Daystar-DS-05A-Solar-Digital-Meter/dp/B00YVTXZJ4/ref=sr_1_fkmr0_1?s=electronics&ie=UTF8&qid=1444055204&sr=8-1-fkmr0&keywords=Daystar+PV+irradiancePV</a></a>)
irradiance meter to calculate power by holding it
in the same plane as the module to determine
actual irradiance striking the surface.<br>
><br>
> Another tool I use is a simple instant read,
non contact infrared thermometer to check the cell
temperature under test.<br>
><br>
> With these tools and a little information, I
can measure instant power and calculate module
degradation. Others have suggested higher cost
tools but these low cost tools have been reliable
for many years.<br>
><br>
> Larry<br>
><br>
> On Oct 4, 2015, at 7:56 PM, frenergy <<a
moz-do-not-send="true"
href="mailto:frenergy@psln.com"><a class="moz-txt-link-abbreviated" href="mailto:frenergy@psln.com">frenergy@psln.com</a></a>>
wrote:<br>
><br>
> Wrenches,<br>
><br>
> As time passeth, we're bumping more into
older PVs/arrays that have questionable outputs.
After minimizing the variables (dust, temps, sun
angle, wiring, expected deterioration with age,
etc) and still coming up with low numbers.
Testing individual PVs' Voc and Isc don't seem to
tell the whole story as they often look good.<br>
><br>
> Would not a definitive test be to wire a
suspect PV to an inexpensive mppt CC (oxymoron?)
and then to an orphaned battery. The battery
would have to have a mondo (surplus) rheostat
paralleled to it to maintain a steady voltage
during the test. With appropriate metering in
place, you would then have Vmmp and Immp as the
rheostat is tweaked to hold a steady batt voltage
and the CC finds the knee.<br>
><br>
> Help me here. I know its a little
spendy to cobble up but the value of nailing an
offender might be worth it. Am I missing
something? Is it common for inverters to fall off
in output gradually?<br>
><br>
> Bill<br>
> Feather River Solar Electric<br>
><br>
>
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-- <br>
<div class="gmail_signature">
<div dir="ltr">Chris Mason
<div>
<div style="color:rgb(136,136,136)"><span
style="font-size:13px">NABCEP Certified Solar PV
Installer™</span></div>
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style="color:rgb(34,34,34)">Solar Design
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style="font-size:13px">Generac Generators
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style="font-size:13px"><br>
</span></div>
<div><a moz-do-not-send="true"
href="http://www.cometenergysystems.com/"
target="_blank">www.cometsolar.com</a></div>
<div>264.235.5670</div>
<div>869.662.5670</div>
<div>Skype: netconcepts</div>
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