<html><body><span style="font-family:Verdana; color:#000000; font-size:10pt;"><div>Thanks for sharing your experience with these batteries, Dan.</div><div>I have similar SOC issues with an off-grid customer who has the Aquion Hybrid Ion batteries.</div><div>It has difficulty reaching full charge from solar, requiring the genny to kick on each morning even in the summer.</div><div>This is even worse in cold winter weather.<br></div><div>Your explanation of the change in Peukert's exponent above 80% SOC with NiFe batteries sounds like what is happening here as well. </div><div>Do you have any experience with Aquion batteries that you can share?</div><div><br></div><div>Thanks<br></div><div>Don Barch </div><div>Energy Solar</div><div> <a href="mailto:don@energysolarnow.com">don@energysolarnow.com</a><br></div><div><br></div><blockquote id="replyBlockquote" webmail="1" style="border-left: 2px solid blue; margin-left: 8px; padding-left: 8px; font-size:10pt; color:black; font-family:verdana;"><div id="wmQuoteWrapper">
Message: 2<br>
Date: Mon, 25 Jan 2016 15:51:26 -0700<br>
From: Dan Fink <<a href="mailto:danbob88@gmail.com">danbob88@gmail.com</a>><br>
To: RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>><br>
Subject: Re: [RE-wrenches] LiFePO4; WAS Availability of Powerwall<br>
Batteries<br>
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<br>
Hello Mark;<br>
My NiFes went in last March, I'm almost at a year living with them off the<br>
grid.<br>
To avoid writing a novel here I'll group my comments into Oddities,<br>
Advantages and Disadvantages.<br>
<br>
Advantages:<br>
~ at least 25 year lifespan<br>
~ 10 year warranty<br>
~ Can add more parallel strings at any time/age, just drain and replace<br>
electrolyte of old batteries<br>
~ 80% depth of discharge no problem, so can size smaller amp-hour capacity<br>
<br>
Oddities:<br>
~ alkaline electrolyte, neutralize spills and clean tops with white vinegar<br>
~ Specific gravity of electrolyte does not change with state of charge so a<br>
hydrometer is useless<br>
~ Charge / discharge efficiency changes greatly with state of charge.<br>
Sometimes my Magnum ME-BMK amp hour meter matches the Midnite Whizbang Jr<br>
exactly, sometimes they are way off from each other. For ground truth, the<br>
state of charge vs. voltage curve from the battery manufacturer seems right<br>
on, not counting false readings when the batteries are not at rest for a<br>
couple hours.<br>
~ Fooling PV MPPT charge controllers into dealing with NiFes involves<br>
setting a very long and high Absorb voltage<br>
~ Charge efficiency is great up to 80% state of charge, but after that<br>
drops way off. Above 80% SOC these batteries want to see 1.65v per cell to<br>
really fill up. No problem for modern MPPT PV controllers, but-<br>
~ Some inverter / chargers (Magnum here) freak out and shut down at 1.6v<br>
per cell, so the solution from the battery manufacturer is-<br>
~ Run fewer cells during times of year when charging is frequent from the<br>
generator, put the extra cells back in the string during times of year when<br>
the charging is mostly PV. Sitting uncharged does not damage these "extra"<br>
cells.<br>
~ So I am running a 10.8v battery bank right now, will bring it back to 12v<br>
this spring. No big deal, but does affect inverter surge capacity. Would<br>
not be as much of a problem at 24v or 48v.<br>
~<br>
<br>
Disadvantages:<br>
~ The high Absorb voltage to get that last 20% SOC efficiently bubbles<br>
through a lot of distilled water. My schedule is 1-2 gallons every 40 days,<br>
and the company sends a reminder email at that interval.<br>
~ The bubbling gets the tops dirty fast. A cleaning every 40 days is about<br>
right.<br>
~ High cost<br>
~ Twiddling with string voltages semi-annually. This would not be an issue<br>
if most charging is from PV.<br>
<br>
My thoughts:<br>
My overall impression of being married to NiFes way off the grid has so far<br>
been <a href="http://favorable.In">favorable.In</a> a grid standby situation, I think string voltage<br>
twiddling would be a non-issue, who cares about the last 20% of SOC charge<br>
efficiency in that situation? Off the grid with daily cycling, generator<br>
use, etc, I would not consider these to be batteries for off-grid<br>
beginners. But anyone who has been off grid for a few years with lead acid<br>
batteries will immediately appreciate the advantages and only occasionally<br>
curse the quirks of Nife.<br>
Plans here: Increase my PV by about 30%. Cheap and easy, no more taking<br>
cells in and out of the string, and less winter generator run time. Get 'em<br>
to 80% on genny during tough snowbound times and let PV do the rest. Figure<br>
out some Arduino solution for monitoring when Peukert's exponent changes<br>
depending on SOC. Complain to inverter/charger manufacturers to make them<br>
work better with NiFe.<br>
<br>
Best regards;<br>
<br>
Dan Fink<br>
Adjunct Professor, Ecotech Institute<br>
IREC Certified Instructor? for:<br>
~ PV Installation Professional<br>
~ Small Wind Installer<br>
Executive Director, Buckville Energy<br>
NABCEP Accredited Continuing Education Providers?<br>
970.672.4342<br>
<br>
<br>
<br>
<br>
</div>
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