Hey Jay,
From what I've heard form battery manus, the C rates likely even in a
well PV-ed system still will not produce C-rates high enough to approach a high
or "longevity reducing" internal battery temp, assuming a typical bulk, absorb,
float cycle. Of course, battery environmental location (typical temps) would
set a baseline from which batt temp would rise from. Here in the Sierra,
ambients are not very high 95% of the time.
Just curious, how does the wiz bang account for all loads...2 shunts?
Thanks,
Bill
Feather River Solar Electric
----- Original Message -----
From: jay peltz
To: RE-wrenches
Sent: Thursday, May 21, 2015 8:07 PM
Subject: Re: [RE-wrenches] FLA battery setpoints with larger arrays
Hi Allan,
I like the classic/wiz bang jr. This allows really good end amp control as
all loads are accounted for.
Higher C rates equal higher internal temps which definitely will shorten the
life.
On Thu, May 21, 2015 at 10:56 AM, Allan Sindelar <[email protected]>
wrote:
Wrenches,
In the last few years I have changed my approach to off grid system sizing,
primarily due to higher battery costs and lower module costs. Rather than
shooting for a traditional 80-90% of winter load profile target, I will size a
larger array and smaller battery bank, figuring (especially here in the sunny
Southwest) that batteries will recharge more quickly, will spend more of their
time full (and thus last longer), and will be at least partially charged during
cloudy weather. This even allows for smaller battery banks that are cycled more
deeply (as long as there's a backup gennie in the mix); the lower cost of a
smaller size may allow for a set of higher-quality industrial cells.
I first began to rethink my design approach after reading Christopher
Freitas' Solar Pro article on large battery banks a few years ago. Being able
to refill in a day was part of his strategic approach to battery bank design. I
used and wrote about this approach in my tiny house article in the current Home
Power. However, I'm just beginning to get owner feedback about greater water
consumption and the need for more frequent watering. This is especially the
case when I add array to an existing system, and the old watering schedule is
suddenly not enough.
When I design new systems I now encourage larger arrays and smaller battery
banks, as the batteries spend more of their time happily full and recover more
quickly after a discharge period. But I am thinking that I will have to begin
changing charging setpoints in response. Flooded batteries have a range of
recommended bulk setpoints, from 28.8 to 29.6 volts on a 24V system. When
arrays were smaller we set to the higher end of the range to take advantage of
topping off when available, and a two hour or longer absorption was considered
beneficial, as long as the CC could transition to float at 2% of capacity or
so. With a larger array a better approach may be to lower the bulk/absorption
setting, as well as reduce absorption time and raise the float transition
current ("done amps").
I'm writing to encourage a discussion among off grid Wrenches. Are you
changing the relative relationship between array and battery capacities? If so,
how are you adjusting charge controller setpoint programming? For example, how
would you program a Midnite Classic, Outback FM or Schneider XW if you could
achieve a C/10 or C/15 charge rate?
Thanks, Allan
Allan Sindelar
[email protected]
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
505 780-2738 cell
--
Jay Peltz
Peltz Power
[email protected]
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