String sizing Question [RE-wrenches]

[Allan Sindelar]

Referring to original post:
> > Wrenches,
> > Originally an off-grid system, then brought in grid, now new owner with
> > different needs: Is there a batteryless grid-tied inverter that will
work
> > with ten BP275 75W 12V modules?
> >

Michael, thank you. I was wrong, and you gave me reason to look at the SB700
more closely. I also spoke with Paul Mync at SMA tech support about this,
and it brings up a closely related question, which I am posting to this list
in hopes of a good answer.

The SB 700 in the 250V configuration is the better choice, as it has a full
700W output and the same string sizing parameters. Using the online string
sizing, ten BP275 modules bumps up against the low-temperature max VOC of
250 VDC at -4 degrees F. This is unlikely but possible at our 7,000'
elevation in New Mexico.

What we both discussed is that the ten modules are 8 years in service. We
both understood that output degradation may be the factor that lets us get
away with this right-on-the-edge array low-temperature voltage. We also
think we recall that output degradation happens as loss of voltage, more
than as loss of current. If this is true, we should be OK. Can anyone verify
this, please?

Thanks again,
Allan at Positive Energy

----- Original Message ----- 
From: "Michael Cook" <mike at powerupco.com>
>
> A SB700 in a 200V configuration seems to work.
> >


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