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.
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.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 10/6/2015 10:09 AM, David Coale wrote:
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.
David
On Oct 6, 2015, at 4:58 AM, Chris Mason wrote:
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.
As you can string test, which will identify any strings with bad
panels, I think this should be a minimum for any commissioning report.
On Tue, Oct 6, 2015 at 12:57 AM, David Coale <da...@evcl.com
<mailto:da...@evcl.com>> wrote:
Hi Wrenchers,
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.
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.
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.
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.
David
On Oct 5, 2015, at 7:46 AM, Starlight Solar Power Systems wrote:
> Bill,
>
> 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:
http://www.amazon.com/Programmable-Electronic-Load-360VDC-CSI3710A/dp/B00D7QGSV4).
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.
>
> I also use the Daystar DS-05A (seen here:
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)
irradiance meter to calculate power by holding it in the same
plane as the module to determine actual irradiance striking the
surface.
>
> Another tool I use is a simple instant read, non contact
infrared thermometer to check the cell temperature under test.
>
> 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.
>
> Larry
>
> On Oct 4, 2015, at 7:56 PM, frenergy <frene...@psln.com
<mailto:frene...@psln.com>> wrote:
>
> Wrenches,
>
> 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.
>
> 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.
>
> 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?
>
> Bill
> Feather River Solar Electric
>
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