[RE-wrenches] PV testing

Tue Oct 6 09:54:23 PDT 2015

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 <david at evcl.com 
>> <mailto: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
>>     <mailto: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
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