[RE-wrenches] MPP Tracking Notes: Solectria PVI13kW, Module VMPs

[Dave Click]

Hi all,

I did an inspection recently that had 3 Solectria PVI13kW units 
installed. I was surprised to note that the MPPT window on the nameplate 
was 225-380VDC, as the online spec sheet and manuals all note a 
205-385VDC window. When I asked tech support about this, they replied 
that the window has been 225-380 for a while. The rep was surprised that 
the online documentation is wrong and since my inverter was almost a 
year old, it's apparently been wrong for a year. No update as of today 
either, even though it's been a few weeks since I called. So, just an 
FYI in case you're looking to spec those inverters.

This inconsistency ended up being a big deal on this inspection, as the 
module manufacturer chose to custom-label each module with its actual 
output. Turns out that the actual VMP values were about 9% lower than 
the spec sheet indicated, which pushed the expected summer array VMP 
down to around 217VDC. I'm not sure how widespread this tolerance issue 
is, but since many manufacturers don't always provide flash test 
results, and UL 1703 allows these values to vary by as much as 10%, this 
is another good reason to try to max out your string sizes and stay as 
far as you can above the MPPT minimum voltage. These modules have a 
power tolerance of +/-3%, which they accomplish with higher current 
values that in some cases actually exceeded the 10% UL tolerance limit! 
After 20 years, the VMP on these modules will be about 20% lower than spec!

Dave