Last week I was chatting with my supplier and he pointed out that my system in not performing well. To be honest I was aware that the KHW numbers went down but just convinced myself that this year, we have more clouds and the Summer is hotter (which is true after all). However my supplier insisted that the system is not performing well and was asked to make somechecks for him.
The table below is the average daily production (KHW) for 2011 and 2012, as you can notice 2012 is lower for all months. The system has been in operation in December 2010.
Month 2011 - 2012
Jan 5.22 - 4.10
Feb 6.42 - 5.51
Mar 8.20 - 6.87
Apr 9.93 - 7.80
May 10.84 - 8.83
June 9.94 - 8.71
My system is grid tie, nine IBC 230W solar panels for a total of 2070W (configured as one string) and the grid tie inverter is the transformerless SMA SB 2100TL.
I Checked the Short Circuit current & Open Voltage for the nine panels at 11:00 local time (Panels should peak at about noon / 13:00...):
Today the thermometer reached 33 degrees Celcuis with a heat stress of about 40 degrees Celcuis (according to Met Office).
Panel 1 - 25.5 Voc / 6 Asc
Panel 2 - 27.5 Voc / 5.97 Asc
Panel 3 - 26.8 Voc / 5.92 Asc
Panel 4 - 29.0 Voc / 5.92 Asc
Panel 5 - 26.1 Voc / 5.81 Asc
Panel 6 - 27.8 Voc / 5.83 Asc
Panel 7 - 32.4 Voc / 6.39 Asc
Panel 8 - 32.2 Voc / 6.37 Asc
Panel 9 - 31.9 Voc / 6.3 Asc
The readings look fine at least in my opinion. Panels 1-6 are mounted in parallel to the building and are not facing truly South, in fact their output before noon is slightly less than the other three panels. Panels 7-9 are facing South.
I took the Open Circuit Voltage of all nine panels in series (261v) while the Short circuit current is 6.78Amps. These reading were taken on the roof.
I also took the Open circuit voltage of all nine panels in series (262v) while the Short circuit current is 7Amps at the Inverter input. (This was taken after the roof measurements in a time span of 10mins and there is a length of about 12 meters 10mm copper cable). From this I can conclude that the wiring is OK and there is no voltage drop from the panels to the inverter?
Once I connected the Inverter, as expected, the voltage went down to 200v while the current 5.42, the inverter exporting 989W. (All these last 3 readings taken directly from the inverter display)
At 16:00 I took more readings: 264Voc / 7.67Asc while the inverter was exporting only 1047W, Vpv 189. The inverter has been all day on MPP, no errors/ warnings and the max exported wattage has never exceeded 1200W.
I'm tempted to point my finger at the inverter MPPT... what's your opinion and if anyone has any recomendations for me to follow.