Adding new panels to old

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Zee

Senior Member
Location
CA
Here's a fun one:
Customer has existing system of 6 @ SHARP NU-U235F1 panels (235W). Mono. Totally covers small South roof.
He needs more power.
I am adding 6 panels facing West.
Roof pitches both about 35 degrees, steep.

Existing inverter stays..... and is a PV POWERED PVP2000.

SHARP has Vmp of 30 V.

I will combine both circuits of 6, old and new, on roof into existing #10 home run wiring. (combine in parallel)

How critical is it to match the new V to the old V? Or rather what does "match" mean, to what degree?

I am already planning to use matching number of modules (6) and 60 cell mod.s.
Specifically, my V options in panels range from 30.6 Vmp to 32.8 Vmp.
I want to get him max power...and myself max $.....so I prefer the 32.8 V times 6 panels, as it corresponds to the LG 310 watt, the most powerful panel.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
With a string voltage (Vmp) match within 5% you can run both strings in parallel into one MPPT input with minimal (~1%?) wasted power over the course of the day.
 

Zee

Senior Member
Location
CA
I thought that with panels facing different directions, they need separate MPPT handling?

Cheers, Wayne

GoldDigger: Thank you. That is what I recalled...vaguely.:roll:
So if the 30 V is given...... at 5% diff...30 V x 1.05 = 31.5 V is max for new panel.
So, maybe 32.8 V on a new panel is pushing it...but then again with these higher V panels, he could be getting 310 W per panel, instead of 265W...so I may go that route. He is in high cost, tier 4 rates...... and could benefit from as many W as possible.

wwhitney: yes and no: never split a string over orientation! but having separate strings on separate orientations is actually fine!
Not to mention..... the split orientation here actually allows me to overload this inverter in Watts a bit more than my customary 20%, as both strings will not reach their peak power simultaneously but spread out throughout the day. Of course E and W would be even better in this regard.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I thought that with panels facing different directions, they need separate MPPT handling?

Cheers, Wayne
No. It turns out that as long as the string lengths and panel voltages match *and* neither string is partially shaded, you can use a single MPPT input.
The value of Vmp is almost independent of insolation even though Imp will vary linearly.
SMA had published a paper on this, as have others.
 
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