Bill and all,
To elaborate a bit on Ray's accurate suggestion with a bit of history...
in the early days the general consensus developed that for general use,
36 cells (given that one cell produces just shy of 1/2 volt, regardless
of cell size) was the standard cell count for battery charging. This was
based on the understanding that a typical Vmp of 17.1-17.6 for a 36 cell
module was necessary to equalize a 12V FLA battery to ~15.5 VDC in hot
ambient daytime temperatures after all system losses due to various
resistance in wire, connections, controllers, etc., were accounted for.
You'll occasionally see early modules with 35, 33, 32 and even 30 cells,
tried as "self-regulating" modules - didn't work, as it couldn't account
for voltage variations due to temperature. Anyway, 36 cells is the
default standard to charge a 12V battery. Extrapolating from this,
there's a direct correlation between cell count and voltage in most
applications: as 36 cells > 12Vnom, 72 cells > 24V and 60 cells >
20Vnom. Go outside of these rules of thumb only with clear understanding
of these limitations.
Three 60 cell modules is a nominal 80V; ideal for a 48 Vnom battery
bank, while still below the 150V limit of many standard controllers in
record cold temperatures. Three 72 cell modules, or 72 Vnom, is on the
ragged edge of voltage compliance in cold winter climates.
Allan
On 9/12/2018 10:30 AM, Ray wrote:
A 2nd option: A pair of 72 cell modules should be enough.
Ray Walters
Remote Solar
303 505-8760
On 9/12/18 9:21 AM, Mac Lewis wrote:
Hi Bill,
I agree with Allen. We get similar peak temps here and two 60 cell
modules doesn't charge a 48V battery bank adequately. This effect
would become worse over time with voltage degradation. I try to be at
least 15% above highest expected battery voltage with Vmp of the
strings. With 150V input limit on the Outback controllers, that
leaves you with only one option, strings of 3, with our low temps.
On Tue, Sep 11, 2018, 4:24 PM Sindelar Solar <al...@sindelarsolar.com
<mailto:al...@sindelarsolar.com>> wrote:
Bill, I wouldn't, especially with FLAs. I have seen this
situation here, where the summer highs are similar, with a few
homeowner/hack installations and no, 60-cell modules will not
finish the charge in hot weather. Strings of three work just
about perfect with modern charge controllers, especially in
winter, as they range high enough but well below 150VDC limits.
Allan
On 9/11/2018 4:04 PM, Bill Battagin wrote:
I've been on hold with OB for about 40 minutes now and I need to
know if 2 SW PVs with a Voc of 39.9 and a Vmpp of 31.3 will do
an effective job of charging a 48 volt LA battery especially
with temps of 95 degrees. Anybody have experience with this or
similar, Appreciate the feedback. It just seems I'm a little
low in Vmpp if I want to equalize when its hot. Will it be even
more questionable in 10 years as PVs age?
OB did just pickup only to tell me I need Java for the string
sizing tool and he can't help me with this configuration.
Bill
--
*Allan Sindelar*
al...@sindelarsolar.com <mailto:al...@sindelarsolar.com>
NABCEP Certified PV Installation Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
*505 780-2738 cell*
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*Allan Sindelar*
al...@sindelarsolar.com <mailto:al...@sindelarsolar.com>
NABCEP Certified PV Installation Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
*505 780-2738 cell*
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