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diy solar

How many inverters do I need in parrallel?

sabo

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May 26, 2021
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Sunny So Cal
I am wondering since this unit has dual PV inputs and "high PV input 250V (Voc)"

https://www.mppsolar.com/v3/splitphase-lv6548/

Does this mean that I can do up to 6 of the below panels per input?
My confusion is these show 37.6 Open circuit voltage (VOC). Does the spec "high PV input 250V (Voc)" mean max per input?

37.6 V x 4 = 150.4
37.6 x 5 = 188
37.6 x 6 = 225.6

These are the panels I am looking into

https://store.santansolar.com/product/santan-solar-t-series-250w-silver-frame-solar-panel/

I want to get 20 panels. 5 panels equals 188 VOC per input, do I need two of these units in parallel?

Thanks
 
You may be able to parallel two PV strings, 5s2p, into one MPPT input. That would depend on max short circuit current of MPPT input.
So you might be able to put 20 panels on one inverter with two MPPT inputs, two arrays of 5s2p.
If you make that one 5s oriented SE and another oriented SW, peak power should be about 0.7x as high, but more hours of production.

"Manufacturing labels have been removed. Panels have been tested and have good output. These would need to be for off grid applications."

Not advisable for on-grid systems. Would probably fail inspection. Could be an issue for fire insurance if roof mounted.

You can select other panels at somewhat higher price that produce maybe 50% more power per unit area. Fewer panels, less labor and cost to mount.
 
These will be ground mounted with no vegetation nearby. There won't be any batteries to start. Off grid power that will fail over to house power when the sun power goes away.
What is 5s2p Is this 5 on one cable 2 strings in parallel?
 
Yes, 5 panels in series, another 5 panels in series, then those two strings connected in parallel.

Still, look at cost per watt, size & weight, mounting hardware needed.
SanTan says they test the panels, so should have good output (and he'll take care of any bad ones.)
But, panels do vary in how rapidly output degrades and various failure modes.
At today's prices, PV panels are getting to be a smaller fraction of system cost. A different panel at higher price per Wh may be worth considering.
My old panels from 17 years ago are similar efficiency to these. I bought premium panels (SunPower) which put out 50% more power in the same ground-mount area.
 
Which Sun Power panels did you purchase? Is max short circuit current called by any other name? I downloaded the manual but I dont see Max Short Circuit listed in the specs.
 
I got the E20 series 327W panels. Eight in series stays below 600Voc for my location.

Short circuit current is called Isc on PV panel data sheet.

Charge controller may or may not quote a short-circuit current limit. Usually a maximum operating current per MPPT input.
 
Ah ok I looked at the panel specs and found.
Short circuit current (ISC): 8.85 A

And from the Inverter manual the MPPT has
Max. Input Current 18A x 2

Max AC Input Current 60A
 
OK, two parallel strings into each MPPT fits the current limit.
Then you need to stay within Voc on a record cold day, and have Vmp be within MPPT range over temperature.
Also see how total PV watts compares to what inverter can process. Multiple angles of panels could be considered.
 
I do like the idea of multiple angles. I am thinking of doing a roof mounted array facing west to catch the evening sun more directly
 
In some US jurisdictions, roof mount now requires RST (isolation between panels) or fireman safety. Certain walkways/clearance for firemen to hack vent holes. AFCI to shut down if bad connections arc. Not all do, however.
 
I live in Inland Southern CA. It's sunny almost all the time. Even if it rains it clears up pretty quickly. It's basically desert here without all the imported water.

I have noticed from observing roof solar installations in Riverside county. That there seems to be some setback requirement from the edges of the roof line. I'll bet that's why.
 
It keeps changing.
Used to be a 3' walkway on both sides and the top. Some jurisdictions say 3' within the supporting wall so eaves don't count.
More recent code is 3' walkway on street side and the 3' at ridge can be 18" on either side.
Never seen any reason why rails or panels couldn't extend beyond lower edge of roof.

AFCI is built into many inverters and some charge controllers.

RSD is what could be an expensive pain. It is a box per panel (or 2 or 4 panels.) Only for large arrays wired together; microinverters already segment the array and AC can be turned off outside.
 
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