Dollars per year: Batteries

Started by OlJarhead, January 13, 2015, 05:37:14 PM

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OlJarhead

Have been doing some number crunching and came across something someone suggested when considering batteries for an off-grid cabin:  Consider dollars per year.

So, thinking about this got me doing some math.  Last time I looked at Costco GCB's they were about $88/ea for 220AH 6v batteries.  For my system I would need 12 of them and have the 12 cores to trade in.  I can pick them up at the local Costco so no freight charges.  Total cost to replace my bank: $1056 Life expectancy?  ~5 years.  Cost per year: $211

Next I looked at the Trojan L16's I've been drooling over and they were $348/ea for the 370AH batteries.  Buying 8 of those (giving me 740AH@24vdc) would run me $2784 plus $250 shipping for a total of $3034 and if these batteries last 10 years the cost per year would be $303.  However, the specs show 4000 cycles at 20% discharge so in theory they ought to last twice that considering that I shouldn't discharge them 20% on a daily basis so for a 20 year life they would cost roughly $150/year or maybe $202 for 15 years.

So with all this math the question becomes:  will the L16's last me more than 10 years?  I can set my generator to start at a voltage that more closely represents a 20% discharge if I know what that actually is when the system is in operation. 

If the L16's will last more than 10 years than they are the better deal but if I abuse them like I have my GCB's than it wouldn't be....ahhh the dilema.  I'm almost thinking the $1000 for GCB's might be better just to give me more time to get better at maintaining my bank.

Feedback?

MountainDon

#1
1.  How about  some 370 AH Trojan L-16's at $330 with the chance of a free local pickup?  Thesolarbiz.com is the place to look. I know a few folks who have bought through thesolarbiz and picked up locally.  Local pickup usually means some largish city where you pick them up at a dealer or warehouse.   http://www.thesolarbiz.com/Solar_Panels/Batteries-for-Solar-RV-and-Marine?range=101%2C150%2C162#gsc.tab=0   check on page three.


2.  I have been told that with tall case batteries like the L-16 it is best if the PV system is large enough to ensure a C/10 rate for at least a portion of each day. With lower charge rates even if the batteries reach float stage, the electrolyte may not be "mixed" as well because of lower gassing. Lower gassing can lead to electrolyte stratification. Just something to think about.


3. Golf cart batteries from places like Costco and Sam's club are a great deal; lots of bang for the buck.


4.  Want to be on the cutting edge of technology?  Have a big wallet?  Lithium Ferrous Phosphate, aka LiFePO4, aka LFP.  There are also slight variations; LFMP, with manganese in the chemistry, for example.  Batteries with some benefits...
... LFP can be deeply discharged as a normal thing w/o damage. So more useful capacity means battery bank capacity can be reduced.
... LFP can sit in a partial state of charge for long periods w/o damage.
... LFP have a very low self discharge rate. Can sit for months without needing a maintenance charge.
... LFP have lower cell resistance so they recharge more rapidly. More amps into the batteries  in a given time, from the PV array for example
... LFP are lighter weight, not that it matters once the batteries are in place
... LFP have no need for ventilation.
... LFP basically only need a bulk charge, no need for a several hours long absorb charge, nor a float charge. No equalization needed.

Of course benefits do not come without costs. Downsides include...
... Cost. $$$  Initial outlay is high. IF they last as long as touted the annual cost could be lower than lead-acid.
... LFP can not be recharged if the batteries are below freezing.  Must be at 32 F or higher for recharging, although they can be safely discharged down to -45 F.
... LFP can NOT be discharged to too low a voltage, nor can they be charged to too high a voltage. Discharging too deeply will kill an LFP cell "right now". Charging to too high a voltage will also kill an LFP cell in a hurry!  To prevent either occurrences a battery management system that operates at the cell level is required.  This extra piece of equipment comes along with a good LFP battery. It will disconnect the discharge if/when any cell reaches too low a voltage. It will shift voltage from any cell that reaches the high set point while being charged.

NOTE: there are different types of Lithium Ion batteries. LFP are a safer technology than some. Some others have been known to cause fires.

The higher price scares me off. The no charge at freezing temperatures also is not good for our off grid situation, either. We would have to bring our batteries inside to use LFP. That would mean a lot of repositioning of equipment like the charge controller and inverter, and / or rewiring. The good thing is the PV system could be left shut down completely during the periods of absence.

5.  The learning curve regarding FLA batteries should be pretty much flat by now...   ;D    yes/no?
Just because something has been done and has not failed, doesn't mean it is good design.


hpinson

Dang, we need a "like" button Don.

MountainDon

Re LFP;  I meant to mention there are different shapes or configurations. Pouch, cylindrical and prismatic. Prismatic is what I am referring to. These are large cells so when picked correctly there is reduced need for parallel connections, unlike the cylindrical cells.

Like these, but the link is not necessarily a recommendation. I do know someone with one of these packs and so far he is happy. Only 4 months into it tho'.

http://www.balqon.com/store-2/#!/Lithium-Battery-Storage-5-2-kwhr-3-week-Lead-Time/p/39553969/category=2860254




http://www.balqon.com/store-2/#!/c/0/offset=0&sort=priceAsc


The metal encasement is required to prevent case swelling.


Just because something has been done and has not failed, doesn't mean it is good design.

OlJarhead

Little to spendy for me.

Don I've pretty much got the maintenance down these days but made my mistakes (like leaving the system in 'sleep' mode which allowed the gen charger to not charge thereby allowing the gen batt to die and the gen to not start when the bank dropped too low or when I set the auto start a little too low and the system failed in cold weather etc etc.).

My problem is trying to save money in ways that always costs me more!  d*


upa

I am envious of the $88 dollar Costco GC batteries  :(  I think they are north of $115 at our local  Canadian Costco. Still a great deal. I think once my batteries Kack  hopefully no sooner than  the next 4 years I will replace them again with GCs. The Lithium Ferrous Phosphate is interesting but still too expensive and limiting from a cold perspective. I am seriously entertaining augmenting my current 3kw array at some point as well. Perhaps having a separate array taking advantage of end of day light.

MountainDon

I've seen pictures of a few arrays divided into thirds, more or less, with east, south and west facing segments. Each with its own charge controller.   Some locations that offer subsidies to the homeowner also have a higher return rate on panels that face west. The overall power generation may be less in a 24 hour period but the later-in-the-day power is worth more to the power company.

If I was to add to our array I would aim a set of panels more to the east though. My thinking on that is that when we have cloudy days the clouds usually build after Noon. Two PM and later is often the cloudiest portion of our days while mornings dawn clear.
Just because something has been done and has not failed, doesn't mean it is good design.