[RE-wrenches] PV testing

[Bill Hoffer]

Bill

Performance verification would be your first test that can be done with 2
clamp on meters ( idealy two Power meters like the Seaward Clamp Power
Meter ) , ie testing under load knowing the irradiance and cell
temperatures and measuring watts in and watts out of the inverter.  With
that data you should be able to tell if the array is at maximum power point
and/or if the Inverter is operating within spec.  You should account for
irradiance, cell temperature and Light Induced Power degradation ( 1% loss
per year unless module manufacturer warranty defines it differently),
voltage drop soiling etc...

IMHO Curve tracers are a huge investment in money and time to learn how to
get meaningful information out of them.  Also the 3 choices currently
available each have limitations that make it hard to decide which is the
best solution. That would be my last investment on the list of test tools.
Better to invest in a Insulation Resistance Tester and then something like
the PV150 tester ( which can also do DC Power measurements).

Bill

On Sun, Oct 4, 2015 at 6:56 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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-- 
William Hoffer
161 SE Fourth Ave
P.O. Box 1823
White Salmon, WA 98672-1823
sunengser at gmail.com <bhoffer at sunergyengineeringservices.com>
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