That 284 volt number is if the panel is at 25 degrees C. If the panels are in full sun and with little wind, they can be higher temperature than that even in cold weather.
An easy way to get a rough check on that is to disconnect the panels and temporarily haywire an extra panel in series from another string. I suspect the array might have to be rewired for 2 x 12. From: August Goers Sent: Thursday, February 03, 2011 5:01 PM To: RE-wrenches Subject: [RE-wrenches] Odd Inverter Behavior Hi Wrenches - We were called out today to check out an under performing system installed by another contractor. This is an odd case. The system has 24 Suntech 180s in three strings of 8 and a SMA Sunnyboy 4000us. Open circuit voltage for each string was about 330 Volts and we verified that everything appeared to be wired in correctly. There is no DC side grounding at all. Just a positive and negative coming down off the roof for each string. With all modules in direct light the inverter is only pumping out about 250 Watts steady state. We noticed that when we turn it off and on again that the power went up to about 1500 Watts as it started tracking the max power point. Then it slowly veers off course and settles out at about 250 Watts and is running very close to the open circuit voltage of about 330 volts. I would expect the MPP voltage to be closer to ~280 Volts. The inverter MPP tracking range goes down to 250 Volts so I don't think that's the problem. Anyone ever seen anything like this before? What might be causing the inverter to get confused? The only thing I can think of is that something fishy is going on with the lack of a DC side ground and that certainly needs to be fixed anyway. All thoughts welcome. Best, August -------------------------------------------------------------------------------- _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org Northern Arizona Wind & Sun - Electricity from the sun since 1979 -------------------------------------------------------------------- Online Solar Store Free Solar Discussion Forum --------------------------------------------------------------------
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