Low power on my 9kw ground mounted PV system

[Lenerd]

Hi all I plugged in the system like 5 months ago but didn't notice that it was producing less than half the power it should. Using SMA 7700 sunnyboy Inverter (it's not the Inverter)
DC at the inverter reads 350v .8 Amps on one string and 350v 1.4 Amps on the other. I imagine it must be bad wiring (3 strings -12 modules each running 165 ft 8 awg) Hopefully it's the MC4 connectors i put on without a good tool at the start of each string, - odd that all 3 strings are bad- Why would that be ? Does anyone have a good troubleshooting procedure for checking Hot - Installed wires I guess for Amps. Would using a clamp meter somehow help? Thanks Len

[Mike90250]

Sears has a <$100 clamp on DC amp meter that will help narrow it down,
You say you have 3 strings, and list amps for 2 of them, does the 3rd work OK ?

You may find using a handheld IR thermometer may be good for finding bad connectors,

at least it's a ground mount, and not up on a roof.

[inetdog]

Lenerd,

You did not mention the specifications of your panels, so we do not know what the Imp and Isc are supposed to be.
A single bad panel whose bypass diodes are not all working properly and is partially shaded can limit the current through the whole series string.
You would need to measure panel voltage under load, or maybe look at panel surface temperatures to figure out which panels are not healthy.

A bad connection alone will not be able to limit the current without dropping the string voltage considerably and getting very very hot. Like boiling water or melting plastic.

[bcroe]

If the clamp on meter and hot wiring tests fail to find the problem, you could check your modules with
an infared thermometer. A failed module or sections of, can reduce the voltage to the point where it
can't match the string operating properly at MPPT. At that point I'd stick a 3 way MC4 at the center
(in the dark please) of a failing string and measure the voltage to either end. Or 3 of them and
measure quarter strings. Expectation is some partial strings will measure higher voltage; others
lower. The panels not delivering are in a lower voltage section. Use taps to divide up the bad
section and expect to find an individual panel running at 2/3, 1/3, or no significant voltage. Bruce Roe

[Lenerd]

there are 3 strings but two are doubled up on the SMA inverter that has only 2 ports Its the suggested way to do it as long as those 2 strings are identical/
IMP is 8.2A
ISC is 8.7A
Thanks all

[inetdog]

there are 3 strings but two are doubled up on the SMA inverter that has only 2 ports Its the suggested way to do it as long as those 2 strings are identical/
IMP is 8.2A
ISC is 8.7A
Thanks all

Doubling up to one input is fine as long as the panel strings are identical AND there is no partial shading on either string at any time within two or three hours before and after solar noon.

[Lenerd]

So Hi Again guys To be clear I am getting under 50 percent of what PV Watts or the SMA design tool projected. Considering i'm only getting 1.4A on the doubled up string and .8 Isnt it weird that I have a problem on both strings? Does that somehow Identify the problem? But anyway How could I use a meter t o check my connections I really don't understand meters especially clamp ones. If i run it across a line , would it read higher amps before the trouble and lower after the bad connection? Any help would be appreciated

[bcroe]

Your design tools don't read todays weather; I often see output in the 20% range under clouds. If you have
several identical strings with none shaded, the best check is compare the output currents of the string. The
situation most likely to show a problem is under best sun, but they should track. The voltage of all strings
should be nearly the same; you may be able to read out your 2 inverter sections. It varies little.

Found a mismatch, refer to above methods to isolate the fault. Bruce Roe

[Lenerd]

Thanks bcroe but from July to January ( a good cross section of the year I got just 2.472 MWh The SMA design tool Projected 12,577.00 KWh for the year or approximately 5.240 MWh for that period. So, knowing that and just reading .8 A and 1.4 A , am I correct in thinking I have low output?
If so, can someone help me understand using a meter to find a weak spot in wiring or a module? How its done and what i am looking for.

[bcroe]

1. Get a DC clamp on ammeter and read the instructions how to operate it.
2. Follow our instructions above. Bruce Roe