Hello,
I need some help, I have a older ST2000 Suntie with 4 24vdc Sharp 165w panels 2 pv input legs into the inverter.
For a total input wattage of 165w x 4 = 660w right? The inverter only display 300w - 320w
even on the best solar days. I live in Nebraska with big blue skies, no fast moving clouds. I'm I wrong I my math?? Any thoughts would be Great.
Thanks,
Gus.

Hello Gus,

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The 165 Watt rating is at a specific operational point , this is called Standard Test Conditions , STC for Short.

STC , is for an irradiance of 1000 watts per meter square and a cell tempature of 25C deg C.

This only happens in VERY cold climates (it would have to be below freezing for air temps and at solar noon).

Silicon Cells drop .08 volts for every degree C in tempature increase , the Sun , even at solar noon is typically in the 900-930 wmsq range only when there is refracted light, partly cloudy conditions have I recorded above 930 wmsq


So , typical rise is 40-50 C for the panels , this translaes into a 3.2 volt drop (this is for 12 volt panels) from STC conditions , so for a pair of your sharps , the voltage will be 12.8 volts lower than the STC test rating. Roughly speaking , 68 volts is vmp on the sharp pair , subtract 12.8 volts and your real vmp is 55.2 volts , this times your currect of 4.85 amps equals your real power ... 267 watts , add on more derating for less than 1000 wmsq , use 940 or .94 * 267 and your looking at 250 watts (times 2 ) so figure 500 Watts DC PEAK

The Suntie older Suntie , running n the 200-400 watt power range is only 80-82 percent effiecent ... One big drain is the fan is running full on , this is almost 5% (15 watts). So 500 * .8 = 400 watts

More issues with the old Suntie in mpp tracking , 8 bit resolution on voltage and it typically is 2-3 volts above true vmp when it is working , also the reported AC power is not very exact on the older Sunites

So , I don't see anything "wrong" so to speak .. You should get your inverter upgraded , you will probably see about a 20-30% improvement , but your only talking 60 - 80 watts with such a small system.

One of the Suntie UPG beta testers had the same configuration , 4 sharps and a Suntie ... I did ALLOT of code work to get the small system performance improved over the old Suntie

Hope this helps