How Are My Panels Connected?
I hope this is the right forum to post this. My question is for grid-tie, batteryless systems that already exist, that's of a troubleshooting nature.
A few months ago my roof was 'totaled' by a devastating hail storm. The storm was a pretty news worthy event, particularly in the Dallas area. My PV system survived just fine. It was a good lesson on why you want to install, or have installed, class A UL listed panels, and done so properly on a roof using a racking system.
My PV system is the one that's illustrated in the 'sticky' posting at the top of the Beginners Forum here. Here's a picture of the system: http://www.welserver.com/WEL0043/ .
It's worked fine over the years, within the design limitations noted in the postings, with zero maintenance ever needed. It's performance remains unchanaged and was a good lesson on grid-tie batteryless solar PV design tradeoffs. Last year it averaged about 67% efficiency, about half way between PV Watts 77% default and utility company minimum performance expectation of 62%. See http://www.welserver.com/perl/plot/WEL0043/SolarPVefficiency.png .
Fast forward to now. Looking at http://www.welserver.com/perl/plot/WEL0043/DailySolarEnergyProduction2.png for a picture of the daily kWh for the past 13 months, we see where the PV system was taken down for the roof to be replaced. It's between the -4 and -5 marks on the X-axis (starting 5 months ago, 'restored' 4 months ago).
The system is a 3 string design, with 12 panels each per string.
Included in the re-roofing job was outsourcing of the removal of the whole system, and then later re-installation. Since there are no 'as built' documents supplied by the installer when installed in 2009, the roofer was instructed to include effort to mark, document and photograph everything such that each panel would be put exactly where it was, and ground and string connections would be connected just as before removal.
You know what's coming. The roofer's subcontracted electrician didn't do any the expected 'as built' documentation. As a result, the system is virtually non-operating.
At the moment:
String 1 = 551 VDC OC - it's disconnected because it's close to the 600 DC maximum system voltage.
String 2 = 294 VDC OC - when connected as the only circuit, in the morning it's cool enough such that it gets above the Sunny Boy 7000W inverter's minimum 300 VDC starting voltage and stays running all day.
String 3 = 271 VDC OC - when connected as the only circuit, it doesn't get high enough to trigger start up of the inverter.
Total panels = 35 (one's removed to fix wire damage).
Here's my key question: is it possible to determine how many panels, and which ones, are connected to each string?
Here's an image of each panel's specs: http://www.pbase.com/neukranz/image/119532803 . For example, Voc = 37.33 .
Is this a reasonable approximation of what's connected to each string?
String 1 = 17 panels
String 2 = 9 panels
String 3 = 9 panels