Battery Recommendation

97TJ · January 2012

Hi,
New guy here. I have been starting to put together a solar system for a small (750 sq ft) 1 1/2 story cabin. Location is Upper Midwest so it is a four season climate. Committed to 12 volt a while ago. So far I have 3 200 watt panels and a coleman air c80 charge controller (maybe larger than I need but was only a few dollars more at the time of purchase) and a 500 watt wind gen. ( I know the wind is not that practical but I am hoping it will add a little on those winter days when the sun isn't shining and the wind is blowing hard.) I am looking to purchase batteries and would like some feedback on type. I get up to the cabin a few times a month and then for a few one week stays per year. Some day I may make it a more permanent home. I am thinking about 600 to 700 amp hours of battery bank. I am wondering if I will need to vent if I go lead acid wet cell? How about AGM's due to their low maintenance and no need for venting. I want to set up my battery bank under my open stairway that goes to the loft area of the cabin.
Thanks for any input.
AxedadyC

westbranch · January 2012

Re: Battery Recommendation

97TJ wrote: »

Hi,
Location is Upper Midwest so it is a four season climate.
I get up to the cabin a few times a month and then for a few one week stays per year.
set up my battery bank under my open stairway that goes to the loft area of the cabin.

Welcome to the forum

First you need to list the panels specs to enable us to give you a detailed answer

my preference is AGM based on the sporadic use but mostly due to being inside in the open.
Not sure about the Controller matching with the AGM charging specs, a bit different from FLA.
You should use a temp sensor for adjusted charge V in the winter. Does your CC have one?
Roughly each of your panels should be good for a ~+-100Ah battery , depends on brand

HTH

97TJ · January 2012

Re: Battery Recommendation

Panels are:
Vmp 18.40 V
IMP 11.15 A
Voc 23.0
Isc 11.87 A

Not sure about the temp sensor but I can contact coleman air and find out.

BB. · January 2012

Re: Battery Recommendation

The Coleman C80 appears to be a diversion type controller... While it is the type used for Wind Turbines, it is not really the best type to use for solar panels.

Basically, it drops a large load on the battery bank when "full" and drops the load when charging is needed... So you end up "micro cycling" the batteries all day long. Diversion controllers do not charge batteries very well/accurately.

Second, large wattage panels (over 100 watts) tend to have Vmp ratings that are >>17.5 volts or so that we recommend for "12 volt" solar panels. Evergreen was one of the last vendors to make high wattage 12 volt panels (now out of business)--So you may have to choose a different controller anyway (MPPT type). If you have Vmp~17-18 volt panels, then a PWM controller can be used too:

All About Charge Controllers
Read this page about power tracking controllers

Next, normally we like to recommend that you estimate/measure your daily loads first (with lots of conservation before that).

Then, size the battery bank (1-3 days of "no sun" and 50% maximum discharge). That means your battery bank should be, roughly, 2-6x your daily loads (and losses).

Now, you size the solar array two ways... One to give a ~5% to 13% rate of charge to the battery bank (peak charging current). Second is to size the array to replace your daily usage plus losses. Note that an "extra large" battery bank really forces you to have a larger array.

And, long term, it is debatable if a "large bank" really saves any money... A bank that is 2x larger may last 2.2x longer (say 10 years vs 5 years). But that may force a larger solar array.

If your usage is random weekends right now... I would suggest a smaller battery bank (1-2 days of no sun) of ~2-4x your daily load. It will allow you to keep the system small and "inexpensive" (plus cost less if there is a theft). And get a Honda eu2000i or eu1000i (1,600 watt or 900 watt) inverter/generator (or Yamaha, others) for winter/cloudy weather charging/large appliance and tool power use.

For a weekend cabin, you will not "wear" the batteries out--they will probably "age" out or even get "killed" a few times by over discharging/under charging (or possibly even overcharging).

A small system/battery bank will allow you to lean and make cheaper mistakes (that we all have made).

The battery bank is the heart of your system and is the only part that (usually) damaged by misuse). A couple battery FAQs to read:

Deep Cycle Battery FAQ
www.batteryfaq.org

My suggestion is that you only get a large battery bank if you have large, unavoidable loads, (well pumping, cooking, tools, etc.). Otherwise, until the cabin is occupied 9 months of the year or more, using a genset to help with the power needs and propane appliances (stove, heat, fridge) is probably the more cost effective solution.

I would also suggest that you look into a Kill-a-Watt meter, a DC Amp*Hour/Watt*Hour meter, and/or a Battery Monitor. The first too to plan/measure your loads, the last one to manage your battery bank (especially nice if your spouse, kids, guests will be using your cabin... Much easier to read XX% battery capacity than to use a volt meter or hydrometer readings).

Assuming you will be using an AC inverter--Try to not get a very large model (if you do not need the 1-2kW of power). The smaller ones "waste" less power, and you can use the extra money saved to get a nice 300 watt TSW 12 vdc model from MorningStar (will not run a refrigerator, but will run most of your small appliances/LED and CFL lighting/computers/cell phone chargers very nicely).

All About Inverters
Choosing an inverter for water pumping

Do not buy anything until you have read a bit more--And make a paper plan of your system. You probably will do this several times until you get the optimum system for your needs (and understand all of the trade-offs being made).

In the end, most people underestimate their loads and over estimate the amount of power a solar PV system can generate (of reasonable size and cost).

If you want more exact answers--Let us know roughly where the cabin (nearest large city or what corner of state) and your major loads (watts*hours or Amps*Hours at what voltage of use, etc.).

Sounds like you will have a nice place when you are done.

-Bill

PS: Those panels are fine to connect with the Coleman or a (less costly) PWM type charge controller

97TJ · January 2012

Re: Battery Recommendation

So it sounds like I can still use my c80 for my wind gen and get a PWM controller for the solar panels. Any recommendation on type of batteries.

westbranch · January 2012

Re: Battery Recommendation

the next step is to determine your loads so you can size your batteries to support the loads then... etc etc etc

BB. · January 2012

Re: Battery Recommendation

Batteries... If this is your "first" solar PV system. A set of less expensive flooded cell batteries are generally the best answer. Pretty much everyone toasts their first bank years before they would wear out.

If you can get away with "golf cart" type batteries (220 AH @ 6 volts), they are not that expensive if they get killed. Also, if/when you decide to enlarge, you don't feel too bad taking them out of service/giving them to a friend, etc.

AGM are about the "perfect" lead acid battery... 90-98% efficient (vs flooded cell which are 80-90% efficient or so), no electrolyte mist/hydrogen gas in "normal" operation (still need to plan for venting if something fails and overcharges the battery bank and venting is a possible failure mode with old AGMs). If you freeze them, they will not leak (but normal reasonably charged flooded cell will not freeze either).

Down side is they are 2x as expensive and may not last quite as long as good quality flooded cell batteries. From the NAWS Battery FAQ:

Starting: 3-12 months
Marine: 1-6 years
Golf cart: 2-7 years
AGM deep cycle: 4-7 years
Gelled deep cycle: 2-5 years
Deep cycle (L-16 type etc): 4-8 years
Rolls-Surrette premium deep cycle: 7-15 years
Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years
Telephone (float): 2-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type.
NiFe (alkaline): 5-35 years
NiCad: 1-20 years

After you read the Battery FAQ's, you will wonder that batteries work at all for a typical solar PV installation... But if you treat them reasonably well, they do survive quite nicely.

But for Grid Tied Systems (like mine) and cabins that don't get a lot of use--It is difficult to justify a full blown, large, solar pv system + batteries. It ends up (usually) cheaper getting a nice/quiet genset and using it to power tools/large appliances and recharging a (smaller) battery bank when needed. And use Propane where possible for small fridge, cooking, hot water, etc.

-Bill

97TJ · January 2012

Re: Battery Recommendation

I appreciate the input. Would a small DC fan pushing air outdoors near the batteries provide enough ventilation? I have calculated my usage to be about 1800 watts per 24 hrs. I have several generators but I do not want to be dependent on them. Propane stove, wood heat etc.. Water will be pumped from a cistern to a tank inside and then pumped with a 12V pump to sink and shower. Instant hot water via propane.
Thanks again.

BB. · January 2012

Re: Battery Recommendation

Hydrogen rises... So a cover with draft pipe out the ceiling is common. Some folks will use the charge controller or voltage controlled switch to turn on a small DC fan to exhaust air when battery voltage is >14.x volts.

-Bill

westbranch · January 2012

Re: Battery Recommendation

here is a commonly mentioned vent http://zephyrvent.com/

97TJ · January 2012

Re: Battery Recommendation

"here is a commonly mentioned vent http://zephyrvent.com/"

That looks interesting, thanks. One more question. Northern Arizona Wind and Sun sells a Universal power group 12v 200 AH AGM battery that is not a whole lot more expensive that say a pair of Trojan wet cell 6v batteries. If I added Hydrocaps (really don't know if they are necessary) the cost is a little closer. Any comments on the batteries from UPG?

vtmaps · January 2012

Re: Battery Recommendation

97TJ wrote: »

One more question. Northern Arizona Wind and Sun sells a Universal power group 12v 200 AH AGM battery that is not a whole lot more expensive that say a pair of Trojan wet cell 6v batteries. If I added Hydrocaps (really don't know if they are necessary) the cost is a little closer. Any comments on the batteries from UPG?

I think BB. (earlier in this thread) gave you very very good advice:

BB. wrote:

If this is your "first" solar PV system. A set of less expensive flooded cell batteries are generally the best answer. Pretty much everyone toasts their first bank years before they would wear out.

If you can get away with "golf cart" type batteries (220 AH @ 6 volts), they are not that expensive if they get killed. Also, if/when you decide to enlarge, you don't feel too bad taking them out of service/giving them to a friend, etc.

Another Advantage of flooded batteries is that they are much more tolerant of your learning curve than other types.

97TJ wrote:

I want to set up my battery bank under my open stairway that goes to the loft area of the cabin.

I am not a believer in following National Electric Code for the sake of following code, but one thing I would not omit is a battery box. Before you omit the box, make sure you understand the consequences of something conductive falling through your open stairs onto the batteries.

Most folks here (including myself) will not advocate violating code, but one thing I have omitted in my setup (four L16 in series) is a powered battery vent. The lid for my battery box (home made plywood) is intentionally not airtight and vents adequately (in my possibly wrong opinion).

One more thing, search this forum for hydrocaps and water miser caps. Maybe you will form a different opinion on the need for hydrocaps.
--vtMaps

niel · January 2012

Re: Battery Recommendation

the upg batteries (non usa made) do not last as long as the concorde batteries.

97TJ · January 2012

Re: Battery Recommendation

I am really leaning toward AGM's because of the limited need for venting and I'm not sure I would be able to get up to the cabin enough for proper maintenance of wet cell batteries but It seems like I am hearing that newbies such as myself kill batteries and the like. Please forgive my Ignorance but according to Arizona Wind and Sun Battery FAQ, "Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage."

"Nearly all AGM batteries are "recombinant" - what that means is that the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost."

"The charging voltages are the same as for any standard battery - no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. The Concorde (and most AGM) batteries have no charge or discharge current limits."

"AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. The Concorde batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged."

"AGM's do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery."

Why does the consensus seem to be wet cell. If I get the proper panels and charge controller (do AGM's need a special controller?), where can I screw up and kill the batteries. I'm not trying to be a jerk and I really want to know. I have be reading about this stuff for a few years while building my cabin but some of it is still confusing and I'm no Einstein. Thank you for your patience.

waynefromnscanada · January 2012

Re: Battery Recommendation

97TJ asks: "Why does the consensus seem to be wet cell" ?
In general, they cost twice as much and don't last as long as flooded, and that's if everything is done right and they're treated with kid gloves. Beyond that, flooded are by comparison, far more tolerant of abuse that would very quickly kill the rest. Those are the main reasons why most go with flooded.

BB. · January 2012

Re: Battery Recommendation

Normally, a reasonably charged battery will not freeze for most people. A fully charged battery will go to something like -70F before freezing.

Yes, AGM's are cleaner, and require less maintenance. Good quality flooded cell will (probably) last longer at 1/2 the price.

Larger battery banks do use a fair amount of distilled water (can be 1 gallon a month or more). If access to distilled water is an issue--then AGM's may be worth it for you.

More or less, the recommendation is learn with a cheap flooded cell bank--then switch to AGM once you have your loads + charging all understood and dialed in.

That gives you ~3-5 years or so of "education" before you commit to XXX AH @ YY Volt$ Battery Bank.

If you have a good handle on your needs and are reasonably careful with your AGM bank (I also suggest a Battery Monitor is about mandatory with Sealed Batteries)--there is certainly are good reasons to start with a AGM set.

-Bill

westbranch · January 2012

Re: Battery Recommendation

As the saying goes, S**t happens. I know it quite well, luckily it was my 'marine' (RV) batteries....and I knew better... I just forgot to unhook them. Only a $100 each.

It WILL happen, that is why the recommendation to start with a learner set, can be small(er) and cheap(er).

It will save you money in the long or short run, wont say anything about frustration.

Vic · January 2012

Re: Battery Recommendation

AGMs are often seen in Float Service -- back-up applications. This is where they shine. Need almost no maintenance.

For cyclic use, FLAs are the most common. They do need maintenance, but at least one can directly measure SGs of each cell. That is, you do not need to try to infer the actual State Of Charge, YOU CAN MEASURE IT !!

Have read that AGMs do not deliver as many cycles when used on off-grid applications, where they are cycled every day. Recall that FLAs can deliver two or three times the number of cycles of most of the similarly-sized AGMs.

AND, with any VRLA battery, like AGMs, one should strive to have adequate capacity in A SINGLE STRING of batteries. The inability to measure the SG of each cell makes this almost mandatory.

A battery monitor, as BB suggests is almost mandatory, also.

Yes, FLA must be vented, but even passive venting from THE battery box should be fine -- inlet air low into the box, exhaust air outside from the top of the box.

FLAs are usually considerably less costly. The 24 cell FLAs here use about 1-1.5 gallons of H2O per month. Watering is done less than once per month. Cool batteries use less water.

EDIT: OH, regarding Charge Controllers, some CCs, like the Outback FM series seem to have difficulty regulating the charge voltage of VRLAs, at least AGMs. This can cause the battery voltage to rise above the max specified by the batt manufacturer. It may not really be a CC problem, and probably only occurs when the loads on the battery bank are low. And, perhaps other CCs, in addition to the OB FMs could have this issue. There are many tradeoffs in choosing off-grid components, especially batteries. (JMHO)

Good Luck, Vic

97TJ · January 2012

Re: Battery Recommendation

OK. Then I will go with something like Crown or Trojan. Will they go a few months at a time without adding water.

niel · January 2012

Re: Battery Recommendation

i'll add just a few things here on the agm batteries. most features you are aware of, but concordes do have a charge/discharge limit even though it is several times their ah ratings and some agm batteries are lower and similar to the limits fla types could have so no matter the battery bought you must research all specs on it including the voltage variation for a given degree in temperature and have a cc capable of that setting as some are fixed even though they have the temperature sensor ability. get the sensor too if it doesn't come with one. also, agms aren't as fragile as they make them sound as they can take some abuses better than a fla and they have better abilities in many cases over fla types. outgassing or overcharging is just not one agms are better at over fla types because you can't put the water back in. they are correct though that the cost of them is a factor, but if the batteries you are considering cost anywhere near what the agms do then go for the agms imo.

now it doesn't matter to me if you go to an fla type as they are cheaper in cost, but these days they all are expensive. some agms aren't as good as other agms just as some fla batteries aren't as good as others. the guys can make pointers on your 2 choices as i do not know how they would compare.

btw, if the controller you buy does sway up and down in voltage that it would not be an option to later try agm batteries with. i was not aware that there are mppt types out there that do this, but i know my c40 does which is a pwm.

Vic · January 2012

Re: Battery Recommendation

I have not run any AGM batteries, I am biased toward FLAs for off-grid cyclic uses.

Generally, the longer the charge cycle of FLAs, the greater the water use. And, the higher the charge voltage (Asorb), the greater the water use.
Also, as FLAs age, greater water use is reported.

I believe, but it is just a guess that very high-capacity L-16 batteries may have a bit less electrolyte "reserve" -- the amount of space above the plates and below the Vent Well. Any reduction in the reserve capacity, plus the other variables in water use affects the length of time between mandatory water addition.

So, at times when your cabin is not in use, there is considerably less time spent charging the batteries, and that should translate into less water use.

If your cabin is not in daily use, and has many weeks per year when it is unused, then perhaps AGMs could be a good choice ... if it is true that AGMs do not so as well as FLAs in the number of cycles to end of life. Many tradeoffs. But perhaps folks like me try too hard to make it seem too complex.

Good Luck, Vic

niel · January 2012

Re: Battery Recommendation

being vic brought up the subject of l16s, many have reported less water usage with trojan's new re l16s.

another point about agms is that you won't ruin the battery due to the electrolyte going below the plates like fla types do. personally, if you have the money to spend on the batteries, beginner or not, go for the agms.

no matter what battery type, you may want more capacity than the face value rating of the batteries due to temperature derating on the capacity and how much would depend on at what temp the batteries will be kept at worst case. this increased battery capacity may up the pv capacity needed to keep the batteries charging properly.

Mangas · January 2012

Re: Battery Recommendation

Neil, I can catagorically say the newer FLA L16 REBs water consumption have been practically nil in nearly 2 years. I cannot understand why, but I've had to add only about 8 gallons or so in almost 24 months with the new batteries (64). And, they really didn't need topping up. These batteries are running the ranch 24/7 including heavy 220 v loads.

I suspect increased plate density and newer paste formula may be part of the reason. Water misers on both sets. When I replaced the batteries, I upgraded to Flexmax 80s' which may have helped too.

My original 2006 vintage L16s' used about 6-8 gallons every 3-4 months.

Battery Recommendation

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