[RE-wrenches] Outback settings adjustment so batteries consume less of PV output

[Kent Osterberg]

Jerry,

No doubt about it lithium battery chemistry is more efficient than 
lead-acid battery chemistry. That is a good reason to choose lithium 
batteries. However, 98% RTE is wrong. While being charged the terminal 
voltage for lithium iron phosphate batteries, in a 48-volt system, is 
typically 54.4 volts. While being discharged at light load the terminal 
voltage is about 51 volts; it is even lower if being discharged rapidly. 
The RTE efficiency cannot be greater than 51/54.4 or 94% and typically 
it will be even lower than that. Many battery manufacturers claim over 
95% RTE but that is only possible when the battery doesn't go through a 
full discharge cycle. There are many sources on the internet that say 98 
or 99%, but that is wrong, among us let's get it right.

Kent Osterberg
Blue Mountain Solar


On 3/20/2021 7:01 PM, Jerry Shafer wrote:
> Wrenches
> So what l got from the question is why when my batteries are at 100% 
> isn't everything just passing through. Well, your batteries may be the 
> issue, l stopped using AGM batteries because of what l called spill 
> over, the batteries are never full and are leaking out as they are 
> getting full. This can just be loss because of the chemical reaction 
> and the electrons, even waist heat. AGM might have a RTE of 82% (round 
> trip efficiency) so some battery storage energy is lost to the cosmos. 
> Lithium ion phosphate can have a RTE of 98%, lead acid 75% Edison 
> batterys maybe 60%. So what l am getting at is different batteries 
> have different losses internally, AGM's are cheaper then some so you 
> pick your efficiencies and losses, a solution may be to fatten up the 
> array to compensate for the storage losses. I am sure someone may have 
> an alternate solution
> Jerry
> NABCEP PV Inspector
>
> On Fri, Mar 19, 2021, 9:49 AM Christopher Warfel 
> <cwarfel at entech-engineering.com 
> <mailto:cwarfel at entech-engineering.com>> wrote:
>
>     I have not been able to find a way to set my customers battery
>     charging parameters so that the AGM batteries do not consume less
>     of the pv output to maintain charge. Here is an Optics view of the
>     situation with a small image embedded. (If you can answer, please
>     remove image per Mr. Welch's request.
>
>     I have the absorb voltage at 54.3 for one hour, the float
>     voltageat 54, the equalize at 56 (disabled for this battery type).
>
>     It seems like this is a lot of energy being used by the batteries,
>     but I am hoping that some one with more experience in these
>     settings can weigh in on any changes I should make, or if this is
>     just how it is.  Thank you, Chris
>
>
>
>
>
>     -- 
>                             Christopher Warfel
>     ENTECH Engineering, Inc.
>     PO Box 871, Block Island, RI 02807
>     401-466-8978
>     <http://entech-engineering.com>
>
>
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