Batteries for my 48v off grid solar system

Aloha,
I have a 48 volt solar system with 6.2kw worth of panels on my roof. ( recently upgraded to 6.2kw from 3.2kw)  I started 8 years ago with 16 interstate L16 which crapped out after 3.5 years . I replaced them with 8 DEKA L16 which have lasted 4 years. My question is should I stay with 8 L16s or go back to 16 since I can now truly charge them to 100%. Options I'm looking at are 16 US battery USL16HCS or 4 12 volt industrial batteries from GB.  The Lithium Ion Sulfate are still too expensive so I thought I'd stay lead acid for the time being. I appreciate any guidance as I've got one shot at this financially  MAHALO!!
Jim

Your batteries dieing early may be an indication that the battery bank is not large enough. If your repeatedly pulling them down too far it drastically can reduce their life(I'm also guilty of this, so don't feel bad) if you can try to size your battery bank large enough so that you don't pull them below 80 percent they will have the longest longevity. As far as types of batteries to buy....after long amounts of research, my next battery will be from an electric forklift. They are designed super heavy duty and can last 15 to 20 years in solar applications. The problem is the weight. They can be 1500 to 2000 lbs. Not a big deal for me, but could pose a problem for you. I encourage you to look into them.

Also as a side note, do you use a refractometer to check specific gravity and charge level? I LITERALLY use mine every day. My system is an outback. While the system indicated 100 percent charge and the voltage also was congruent with a fully charged battery, it turned out by checking specific gravity I found out my batteries were really only charged 75 percent. I was under charging my batteries for over 4 months.  I went in the charge controller and increased the absorption time to 4 hours and it solved my problem. I still check one cells specific gravity daily to give myself a baseline of actual state of charge. Undercharging batteries can also kill them early, and even if you have the right amount of panels there could be a setting that needs changed for actual full charging.

Mahalo Eric,
Yes living off grid has been a learning experience. I have an outback system as well, but it turns out my charge controller wasn't tracking the panels correctly....I've now added a second charge controller and 9 more panels ( total 24 now)
My hope is that I can now truly charge my bank to 100%  I too check the specific gravity and regardless of what the mate was telling me, they weren't getting to 100%  Now my tired abused bank is fully charged by the afternoon ( but it's not holding the charge well at all).
I've ordered 16 Surette Rolls S550 6v 428 AH batteries and I'm going to limp along until they arrive. If I could get a forklift battery on to my property here in Hawaii I would do it, but the weight makes it cost prohibitive ( I'm picking up my Rolls 8 at a time from the harbor here).  I'm going to go one more round of lead acid, and then see if Lithium ion phosphate become cheaper and more tried and true for off grid application.
All the best
Jim

jim ward wrote:Mahalo Eric,
Yes living off grid has been a learning experience. I have an outback system as well, but it turns out my charge controller wasn't tracking the panels correctly....I've now added a second charge controller and 9 more panels ( total 24 now)
My hope is that I can now truly charge my bank to 100%  I too check the specific gravity and regardless of what the mate was telling me, they weren't getting to 100%  Now my tired abused bank is fully charged by the afternoon ( but it's not holding the charge well at all).
I've ordered 16 Surette Rolls S550 6v 428 AH batteries and I'm going to limp along until they arrive. If I could get a forklift battery on to my property here in Hawaii I would do it, but the weight makes it cost prohibitive ( I'm picking up my Rolls 8 at a time from the harbor here).  I'm going to go one more round of lead acid, and then see if Lithium ion phosphate become cheaper and more tried and true for off grid application.
All the best
Jim

Living off grid definitely has it's challenges, I hear you there.  I started small just learning the solar ropes. My "big" system went online 2 years ago. Big is a relative term, I'm running 1.4 kws of poly panels and my system is 24 volt with only 225 amp hour capacity.  This worked fantastic as a weekend setup running power tools etc while I was building my house but once we started living here, it's obvious my power reserves and charging needs to be increased.  I can run a window unit air conditioner all night but I've regularly been pulling my batteries down to 60 percent. Haven't had to rely on the generator a whole lot, but it's definitely saved me more then once.  I'm going to upgrade to 4000 watts of monocrystaline panels and 1000 amp hours of battery.  I've got 1000 watts of mono panels on my well pump and it works fantastic in low light conditions.  I hope your new batteries work out better for you. 856 amp hours seems on the light end to me depending on what your running of course. How deep do you regularly pull yours? Pulling out only 20 percent and leaving about 80 percent capacity should have a much longer life then you have experienced in the past.

Kindest regards,
Eric Hammond

Hi Eric,
The only thing that's really power hungry is my Grundfos 1horse water pump ( pulls 1800 watts for 30 seconds....) I'm looking into a smaller pump , but bigger pressure tank ( I draw water from my 22,000 gl tank) other than that everything is LED, Propane stove, water heater, dryer. LED lighting has helped a lot. The new Vizio 60 inch lcd draws Half what the 46 inch sony ( eight years old) does.  I'm hoping to draw a max 25% at night on the new bank of 16. I've been drawing 50% on the eight I now have combined with the fact they weren't getting fully charged. ( with 24 panels that issue should go away:)
best,
Jim

Answering your question really has to ask what your site characteristics/resource and orientation are, along with what your daytime, night time and seasonal use loads look like... peaks and constants over time.

You seem to have enough charging capacity for either 8 or 16 of the l16s, but use and solar exposure could flop the best choice either way. At 90a to 100a charging, you can run a 840ish to 1100 amp hour battery very nice, even with generous daytime use and standby loads. There is power left to charge at 40 to 50 amps while using 40 or so amps! Alternatively, if weather or site horizon, practical pitch angle, etc., (trees, mountains buildings other obstructions) are an issue, then your 6200w array can run to diversion or simply be limited at the max amps setting to fit the single string of l16s. All depends critically on expected use and solar availability, along with any other back up power and charging sources.

If you are using outback or midnite charge controls, be sure to set your absorb time long and your return amps to the correct setting for your battery capacity at 20/hr. rate.  2% of capacity for flooded, but do reference this spec.

Then you can tune with specific gravity for match and age over time. I have never done much more than keep electrolyte levels correct and once i learned how to set the profile for my battery types correctly, capacity and service life are surely improved. I have seen marked improvement in capacity from these changes on several systems.

Systems adopting battery sizing done on a budget limitation to capacity must actively limit loads to within the budget in order to not cause premature wear vs expectations...

Battery sizing is often required to be much larger than ideas of where budget within the system should be placed. Storage power and longevity are indicated by capacity vs use. 10% overnight is a great mark. It seems like a waste, but trouble free- long service life and meeting expectations and requirements has value.

I have undersized and under charged my share of USED(!) batteries....

Mahalo Frank!,
Great info. I'm waiting for my 16 x 6v 420ah batteries to ship. Realistically I'm hoping for a 20-25% nightly discharge, and I'm hoping they go 5-6 years. I got 3.5 years on the 8 6v that I have now, but they were never charging fully ( I've added panels) and I over watered them so I've ordered a "watering kit" that shuts off when the batteries are at optimal level) I appreciate the info about absorb time etc. Hoping in 5-6 years I can switch to Litihium ion Phosphate ( $10,000 now!) 16 6v Rolls are $5000 so that's what I'm going with for now
Best,
Jim

UPDATE TO BATTERY SAGA,
Well it appears the semi truck carrying my batteries from Canada to shipping point in California was stolen over the holiday weekend. As I can't wait another 4 weeks to have storage I ordered 3 Simpliphi 3.4KW 48v 67ah lithiumferrousPhosphate batteries that will be here next week. The cost was considerably more ($7800) for the same 10.2 KWH of the lead acid, but these are warrantied for 10 years, and apparently if I keep at a daily 80% DOD they will go 15-20 years. Big leap of faith here but it's nice they're non toxic, don't need watering, equalization etc.
Aloha!
Jim

jim ward wrote:UPDATE TO BATTERY SAGA,
Well it appears the semi truck carrying my batteries from Canada to shipping point in California was stolen over the holiday weekend. As I can't wait another 4 weeks to have storage I ordered 3 Simpliphi 3.4KW 48v 67ah lithiumferrousPhosphate batteries that will be here next week. The cost was considerably more ($7800) for the same 10.2 KWH of the lead acid, but these are warrantied for 10 years, and apparently if I keep at a daily 80% DOD they will go 15-20 years. Big leap of faith here but it's nice they're non toxic, don't need watering, equalization etc.
Aloha!
Jim

Jim, how are the new lifepo4's? I have only seen them in catalogs. A users perspective would be helpful and the saga never ends! Hope you are keeping warm.... or cool.

The cheapest li-ion batteries (besides free/reclaimed ones) are reportedly li-po hobby types.  http://www.genstattu.com/lipo-battery.html  

Aloha Frank,
We've been very happy with the SimpliPHi batteries so far. With the holidays we have guests running the shower at all hours ( after being asked not to...) and I'm impressed how the batts can take continual hits from the 1 horse water pump and still have reserve. I did add a 4th battery as we have 2 buildings , 2 fridges etc. We aren't seeing a discharge past 50%, and they're guaranteed 10 years even if taken down to 0%. They behave much different that lead acid ( a good thing) Charge really fast.
Happy Holidays
Jim

Yes Jim; Please do keep us posted on these battery's.