[RE-wrenches] Trickle Charging?

[Drake]

We have an AC coupled  backup system at our house 
in S.E. Ohio. In the winter we have many cloudy 
days. We are using two 40 W Sunwise modules in 
series with a Morningstar PWM CC to maintain a 
415 AH, 24 V set of Full River AGM batteries. We 
don't need to use the AC charger for around 1/2 
the year. In the winter, we charge regularly from the grid.

Colorado has a lot more winter sun that SE Ohio. 
If I did ours over again, I'd double the 
maintainer array. But we have many periods, of 
several days in a row, where it is so dingy that 
our main array produces almost nothing, with no 
snow cover. I've never seen these prolonged, low 
light conditions in Colorado. If the price 
difference for a larger maintainer array isn't 
too much, I'd likely go bigger, especially since 
your battery bank is twice as big.

Drake Chamberlin
Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV
740-448-7328
<http://athens-electric.com/>http://athens-electric.com/



At 11:19 PM 10/8/2018, you wrote:
>Lots of questions this season..... I'm 
>winterizing a cabin for a customer that will not 
>be there for the next 8 months (summer use 
>only). Inverter and loads will be off. The 
>rooftop array will probably be covered with snow 
>for extended periods of time, and he has a brand 
>new 800 AH set of AGM batteries.  I've read 
>that AGMs can handle sitting for longer periods 
>of time, but my experience is that they are a 
>bit finicky.  I'm planning on adding a small 
>wall mounted array on a small Morningstar PWM 
>controller that's sole purpose is to trickle 
>charge the batteries and off set the self 
>discharge in heavy snow.  What is the minimum 
>size array needed? I've calculated self 
>discharge rates from 2% to 5% /month, and I'm 
>seeing a very small array would offset 
>that.  Even at 5% monthly losses, and 4 hrs of 
>sun/ day, I'm seeing a 10 watt array could meet 
>that.  My current plan is a pair of 30 watt 
>modules wired in series for the 24 v 
>battery.  Is that too small? Or should I not 
>even worry, because enough sun will creep 
>through the snow to the main array? Thanks, -- 
>Ray Walters Remote Solar 303 505-8760 
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