AGM vs flooded

JLC alaska

Hello All
I have a remote place in Alaska and we currently have 32 6 volt L-16 as our battery power reservoir.
The problem is we are only there 8 weeks out of the year and due to a lack of monthly maintenance the lifespan of these batteries has come to an end in only 7 years so I am looking at the replacing them with the Sun Extender AGM sealed battery.
Does anybody have experience with these in a RE system and how well do they hold up and what can I expect for a typical life span I know the charging requirements are different and I can program my inverter to handle that but 18K investment every 7 years is tough to swallow.

Thank You for any help

Cariboocoot

Re: AGM vs flooded

AGM's tend to be more expensive than FLA's. They are also more current tolerant but less Voltage tolerant.

Many people on this forum use AGM's, including the Sun Extender line and are quite happy with them.

What we'll all be wondering is what sort of issues you had with the L16's. The inevitable questions will be: how much panel have you got on them? What sort of charge controller? Was it set for routine equalization charging? System configuration? And is the problem that they run out of water because you can't be there often enough to check levels?

Seven years from a set of batteries is not bad, but I can sure understand why you'd want to get more life out of that much $ invested.

JLC alaska

Re: AGM vs flooded

The main issue is keeping them from freezing, in the winter we have a small Toyo stove that i run to keep the winter time temps around 50 deg F in the battery box it is a small power draw but it is enough to take the batteries down in the winter, come spring there is aolt of wind so keeping them charged is not an issue but with charging comes water loss and the cycle begins again.
here is a break down of my system.
i have two Whisper H80 48 VDC wind generators with controlers.
32 L-16 batteries, 375Ah @ 6 VDC ea, 1500 Ah @ 48VDC (73.8 KWh, 59KWh useable @80%)
six Sharp 170W PV modules
Outback MX60 3.3 KW solar charge controler
and a Xantrex/Trace Swp5548 Inverter (5.5KW @120 VAC, 60HZ) i also use this as a three stage charger.

BB.

Re: AGM vs flooded

Wow--A lot of batteries... I assume you really need that amount of power? (fewer batteries, lower costs)...

7-10 years is probably about what you would get from good L-16 batteries. "Typical good quality" AGM's are probably not going to last any longer (from what I understand--I am not a battery guy).

Back to your current battery bank--What temperature do you run them at (for every ~10C/18F drop below 25C/77F is, roughly, a doubling of battery shelf life and reduction in sulfation). Are you "boiling" the batteries dry when you are not there? Are there loads that need to be supported when you are not there (radio repeaters, etc.)?

My personal suggestions (as a starting point):

• Install a Battery Monitor (Victron is another good brand) if you do not have one to understand what is happening (charging/discharging/etc.)
• Review battery bank capacity--Does it need to be this large?
• Review winter/unoccupied operations (a few battery monitors can set alarms based on state of charge falling below XX%--turn off loads, start genset, etc.)
• Why is the current bank failing before its time (if it is). Deep discharges, boiling water below top of plates, over charging, etc...
• Look at Fork Lift type traction batteries for 20+ year life

A battery monitor does have its limitations--but it allows you to better understand what is happening to your battery bank from the battery's point of view. Do you have enough charging current for that size bank, are going below 50% state of charge (deep/frequent cycling shortens battery life), "storing" below ~75% state of charge (sulfation issues).

In the "old'en" days of off grid solar--Many folks recommended installing larger battery banks to address capacity issues... I think, most of us today are more comfortable to go with a "designed to load" battery bank (usually somewhere between 2-6x daily load) and then work on the Solar/Wind/backup genset charging setups to ensure the battery bank is "kept happy".

Some basic rules/guidelines: Generally, try to get above ~90% state of charge every few days or so. Avoid cycling below 50% state of charge (deep cycling reduces life). Never go below 20% state of charge (can kill a battery bank immediately). Never let a battery set below 75% state of charge for days/weeks/etc. (will increase sulfation). Use a charger with remote battery temperature sensor (solar, back genset, etc.) (will allow battery to recharge faster, and help prevent excessive charging voltage--hot batteries need lower charging voltages). Only equalize a battery bank when needed (see battery manual--generally once every month or so--And only equalize until all cells stop rising in specific gravity--Over equalization is very hard on battery banks (and for AGM and especially GEL, can dramatically shorten life).

Do you have any reasons why you think the battery bank is not lasting as long as it should? Since you have some paralleled battery strings, I would suggest getting a DC Current Clamp Meter (here is one with DMM functions for ~$60 in the lower 48). I am not a big fan of paralleled battery strings--I would prefer to see one string, or a maximum of three strings in parallel--if possible. Note you can buy L-16 (and other form factor) batteries in 4 volt and even 2 volts which reduces the amount of parallel strings--but keep the cells light enough to move around with one or two people. If you have a DC current clamp meter, you can monitor the charging/discharging current between strings. Many times, you can have silent/hidden failures (open/shorted cell, poor connection in wiring, even temperature imbalance between strings can cause issues) in a parallel string and unless you monitor the current sharing--you will not see it until something gets damaged. You need to make sure that the strings have "balanced wiring". Also, the fewer parallel strings, the less battery cells you have to check/maintain water levels in (how often do you have to add water--Probably more than once a month is too much charging, less often than once every 4-6 months, probably not enough charging).

For long life, 20+ year life fork lift batteries (some folks even buy reconditioned batteries with good results). They can last a long time and take lots of deep cycling (as long as they are quickly recharged)--However, the downsides is they tend to use more water (distilled water can be difficult to get/make and/or expensive). Also, they are not quite as efficient (need a bit more solar power to make for more self discharge/less efficiency).

AGM's are probably the ideal Lead Acid batteries (and really nice if you have high surge currents to support from a small(er) battery bank). Virtually no maintenance/cleaning required. However, they are 2x the price and, in general, probably have similar or slightly less life than a similar flooded cell battery.

Anyway--I will stop typing here. Your thoughts?

-Bill

Cariboocoot

Re: AGM vs flooded

Wow! 1500 Amp hours @ 48 Volts? That's a lot of battery power.
1050 Watts of panel, even with the wind turbines (wind being a fickle thing you can't count on), isn't going to keep that charged. Even in Alaska/Cariboo winters FLA's will not freeze if kept charged. To keep that much battery charged you'd need a massive array of about 10 kW and two FM80 controllers.

I'm going to suggest that before you invested megabucks in new batteries you re-evaluate your power needs and make sure you really have enough panel to recharge with (I tend to think of wind as supplemental to solar, rather than additive). It sounds like your shortened battery life may be due to falling short on charging. L16's in particular need lots of current and definitely benefit from EQ as they are prone to stratification. Likely you've been "putting back the Amp hours" but not getting a fast Bulk, full Absorb, and Float charge. This means that over time (years) the batteries have been steadily declining in capacity until they hit the point where they no longer have enough to be useful.

niel

Re: AGM vs flooded

i'll have to say you definitely need to revisit your loads to determine if you are over-batterying your system.

as to which to go with that can be tricky because my research has shown agms lose a bit more capacity in the cold than fla types. on the other hand the agm types don't normally gas. agms cost more, but also have lower self discharge rates.

8 years isn't too bad imo so i'd say go with the fla type for you've proven it to work, but just need to be sure of the battery capacity truly needed. (yes, i'm recommending fla over agm. write that down as it doesn't happen often.;)) if that ampacity is needed then you may wish to add more pv to help properly cover that much battery capacity as i wouldn't rely on wind that well.

of course mounting the pvs high to avoid being buried in the snow and having a steep angle on the pvs to help shed snow from building up on them helps.

vtmaps

Re: AGM vs flooded

JLC alaska wrote: »

The main issue is keeping them from freezing, in the winter we have a small Toyo stove that i run to keep the winter time temps around 50 deg F in the battery box it is a small power draw but it is enough to take the batteries down in the winter, come spring there is aolt of wind so keeping them charged is not an issue but with charging comes water loss and the cycle begins again.

I don't understand something... you mentioned that you're only there 8 weeks a year... does that mean there is no charging the other 44 weeks? If there is charging, you don't need the battery heater (batteries won't freeze if charged). If there is no charging, the heater is drawing down the batteries. Perhaps you should turn off the heater and use a few solar panels to maintain the batteries over the winter.
--vtMaps

Mangas

Re: AGM vs flooded

I cannot speak to the AGMs' as forum members who use them will weigh in.

I replaced 64 L-16s' installed in late 2005 when our system was built. The reason I replaced them was I wanted to take advantage of the receding solar tax credit despite they were about 60% or so through their planned life. I say planned life as I had budgeted to replace them between 6-7 years regardless of their condition. For me, cost of doing business with a large off grid system.

Also, using AGMs' would have been prohibitive costwise especiallly if I make a mistake mid-stream or have a charge controller failure

After 2 years the new L-16 REBs' use practically no water compared to the older version (as far as I can tell about 35%) and have a different paste and specific gravity. They come up very quickly and so far I think they are a significant improvement over my previous banks. I expect these to last more than 7-8 years.

Given the cost of bringing in the grid against losing ranch landscape conservation values and the unreliability of our rural grid (outages and spikes), I feel replacement costs are a wash. That said, running large battery banks to power off grid living is significantly more expensive than the grid. But, we all have different priorities.

The calculus we all go through is lifestyle and convenience objectives versus cost minimized through judicious conservation measures.

niel

Re: AGM vs flooded

vtmaps wrote: »

I don't understand something... you mentioned that you're only there 8 weeks a year... does that mean there is no charging the other 44 weeks? If there is charging, you don't need the battery heater (batteries won't freeze if charged). If there is no charging, the heater is drawing down the batteries. Perhaps you should turn off the heater and use a few solar panels to maintain the batteries over the winter.
--vtMaps

that's a good catch and point. if nobody is there the pvs should be sufficient to keep the batteries at 100% and prevent freezing. upon your return the capacity may be slightly lower due to colder batteries, but will creep upward in temperature due to use. if that's insufficient you can flip the heater on for a few hours too, but don't do this long term when you aren't there.

_OS_

Re: AGM vs flooded

I have used two 305Ah 12V Sun Xtender batteries in parallel in my remote cabin in Norway for four years now and they have functioned flawlessly. The temperature has been as low as -30C and as high as +28C.

Since you have a very large battery bank I recommend contacting Concorde before ordering since the Sun Xtender batteries have a very low internal resistance which requires you to put special attention to the wiring of the batteries. In fact Concorde does not recommend putting more than three of the 12V batteries in parallel because of this.

Ole

toothy

Re: AGM vs flooded

You didn't say how far north you are? If the sun doesn't bother coming up for a few months and then the wind dies for 2 weeks that may explain some things. I'm in south central Alaska and the sun even here, lacks it's usual punch from November until mid February. At the solstice we are supposed to have 5 hrs but that doesn't take into account Mtn's and trees.

We live here full time so our use is a lot higher than yours in the winter, I added more panels as they are relatively cheap, now at a bit over 5K. We went with 4 volt 1350Ah fla's @48v.

My suggestion would be more panels, way less but bigger batteries and no heat or a drip stove if you really feel the need.

Wade

techntrek

Re: AGM vs flooded

Just to drive home this important point - mentioned several times above - you definitely want to let your batteries get cold. Very cold. A quote from Wind Sun's battery FAQ:

Even though battery capacity at high temperatures is higher, battery life is shortened. Battery capacity is reduced by 50% at -22 degrees F - but battery LIFE increases by about 60%.

http://www.windsun.com/Batteries/Battery_FAQ.htm#Temperature%20Effects%20on%20Batteries

You WANT them to get cold when you aren't around - not stay at 50 F all winter. I take advantage of this with my camper and leave my battery in place over the winter (disconnected) instead of bringing it into my garage. Not only does it extend the life, but it reduces the self-discharge rate so I only have to top it off every couple of months over the winter.

I also would bet you can cut your battery bank size in half, maybe a quarter and be fine, especially for a place that is only used 2 months a year. Note in my signature I have a fairly large battery. It is enough to run everything normally (TVs, lights, wood stove fan, other smaller loads for a few hours in the evening, then 200-300 watts for wood stove fan and smaller loads overnight) for 17-20 hours.

waynefromnscanada

Re: AGM vs flooded

techntrek wrote: »

Just to drive home this important point - mentioned several times above - you definitely want to let your batteries get cold. Very cold. A quote from Wind Sun's battery FAQ:



http://www.windsun.com/Batteries/Battery_FAQ.htm#Temperature%20Effects%20on%20Batteries

You WANT them to get cold when you aren't around - not stay at 50 F all winter.

Agree! They just need to be kept charged so they don't freeze. Shouldn't be difficult as they aren't used all Winter.
The fact that my L-16's are kept in an outside shed year round, with months at a time of battery temperature averaging no warmer than 0 C, may well be the reason they're 10 years old and still appear to work like new. And this in spite of the abuse they endured early in life as I was learning.

techntrek

Re: AGM vs flooded

Oh, and to tie in the original question "agm vs. flooded" to what I said earlier, with the minimal charging necessary over the winter (by keeping the batteries cold) you should have no problems with FLA. They won't boil all their water away while you are gone. By sticking with FLA, keeping them cold and cutting your battery size way down you'll come out way ahead - less money spent on the batteries, no money spent keeping them warm, and they'll last longer.