Voltage drop musings [RE-wrenches]

[Allan Sindelar, Positive Energy, Inc.]

Jay and wrenches,
What a mindblowing idea. You are suggesting a 54 or 56 volt DC battery bank,
used with SW5548 and 4048 inverters? Have you successfully done it? Does it
work well in all other aspects, besides just MPP matching for sell-back? Can
it work in gird-backup stand-alone? Can you EQ the batteries occasionally?
Is DC overvoltage a problem?
I'm doing a big 48V system (posted Qs about it here some months ago); still
finalizing design. Total code-compliant. We're using a Pulse 500 for the DC
to get UL listing, so we have to use their controllers, rather than
not-yet-listed SB3048s on about 4kW of tracked array. One 5548 for house
loads; one 4048 (unstacked; all 230VAC loads will be grid-only) for pumps
and mechanical loads, and 3-4kW of Exeltech MX series for A/V/data loads.
Sell-back is NOT planned or requested by customer, but I'd like to design
for it to be added later. With 2V industrial cells, should I consider a
higher-than-48 nominal system voltage? What are pros, cons, and things to
watch out for?
Thanks for advice.
Allan at PosEn

----- Original Message -----
From: "jay peltz" <jay at asis.com>
> One way is to increase the number of batteries in the system.  This
increases the
> operating voltage ( more watts) without the need for a MPPT controller.
48v systems
> are pretty easy as you add another 6v ( if you are using 6v batteries.  If
you are
> using 2v cells, then maybe 8v would work better?) battery to the system,
works
> pretty slick- cell voltage is lower, overall voltage is higher= more watts
to the
> grid.
>
> And yes many people are using the MPPT controllers to get around this
problem called
> "batteries".


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