<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
</head>
<body style="background-color: rgb(255, 255, 255); color: rgb(0, 0,
0);" bgcolor="#FFFFFF" text="#000000">
Wrenches,<br>
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.<br>
<br>
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. <br>
<br>
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"). <br>
<br>
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?<br>
<br>
Thanks, Allan<br>
<div class="moz-signature">
<div class="WordSection1">
<p class="MsoNormal"><b>Allan Sindelar</b><br>
<span style="font-size:10.0pt"><a
href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a></span><br>
<span style="font-size:10.0pt">NABCEP Certified PV
Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), <span style="mso-bidi-font-weight:bold">Positive
Energy,
Inc.</span><br>
<b>505 780-2738 cell</b><br
style="mso-special-character:line-break">
<br style="mso-special-character:line-break">
<b><o:p></o:p></b></span></p>
<p class="MsoNormal"><o:p> </o:p><br>
</p>
</div>
</div>
</body>
</html>