[RE-wrenches] PV testing

Tue Oct 6 04:58:22 PDT 2015

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 <david at 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 <frenergy at 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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-- 
Chris Mason
NABCEP Certified Solar PV Installer™
Solar Design Engineer
Generac Generators Industrial technician

www.cometsolar.com <http://www.cometenergysystems.com>
264.235.5670
869.662.5670
Skype: netconcepts
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