# How Many Batteries?



## Tango (Aug 19, 2002)

how many batteries should I have for my three Kyocera panels totaling 365 watts. It is a 12 volt system with 12 volt batteries.


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## 12vman (Feb 17, 2004)

That would give you around 21aH/hour with a fixed array. Figuring the "4 hr. Window" (10 am to 2 pm) you could gather around 84aH in a good day. 2 golf cart batteries connected in series will suppply around 200 aH reserve. As long as your loads don't exceed say.. 60aH in a day, you would have plenty of reserve for a cloudy day and the battery could get caught up in the next day or so. More battery will give you more reserve but it will take longer to bring it back to full charge..

Too much battery is as bad as not enough panel. You need to "Work" batteries to keep them working..


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## wy_white_wolf (Oct 14, 2004)

Sizing batteries to your solar array is like going down and buying a pair of pants and then deciding your going to gain/lose wieght to fit the pants. 

Load has more to do with battery condition and longevitity the array. Any extra by trhe array will be handled by the charge controller and any shotage of charge should be handled by a genny. 

Battery banks need to be sized to the load. As a general rule they should be a min. of 5 times the average daily load for any season and a max. of 5 times your highest daily load for any season.


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## Tango (Aug 19, 2002)

The tech at backwoods solar told me to make the batteries work for the array, not the array for the batteries.I've taken that to mean that they should be able to be discharged daily and that a typical sunny day should be enough to recharge them. My load right now is minimal and I think my three batteries are doing well but was considering two batteries per panel when I add a fridge. Currently we have reserve power for two cloudy days when we accordingly reduce usage. I was going to add another array and a tracking mount so I could add a refrigerator (chest type freezer w/ thermostat) but I can't do any of that now. Was just wondering if others could explain the battery mystery to me better. I appreciate your input.


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## wy_white_wolf (Oct 14, 2004)

Tango said:


> The tech at backwoods solar told me to make the batteries work for the array, not the array for the batteries.I've taken that to mean that they should be able to be discharged daily and that a typical sunny day should be enough to recharge them. My load right now is minimal and I think my three batteries are doing well but was considering two batteries per panel when I add a fridge. Currently we have reserve power for two cloudy days when we accordingly reduce usage. I was going to add another array and a tracking mount so I could add a refrigerator (chest type freezer w/ thermostat) but I can't do any of that now. Was just wondering if others could explain the battery mystery to me better. I appreciate your input.



Shouldn't your system be built to fit (serve) your needs?

If no, than get about what was suggested earlier for batteries and hope it will carry the load.

If yes, than figure your loads and buy batteries accordingly. Then size the panels to fit the charging requirement of the batteries.

(I don't mean to sound condinsending (sp?) or anything)

Let's say we go by the suggestion for the array and get about 285ah of batteries. Then your load ends up being 150ah a day. When you hit a 2 day cloudy spell your batteries are dead. If you size the batteries and array to the load you will always have 5 day reserve. If your array is not big enough to keep the batteries charged then either a bigger array or backup genny is needed.


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## 12vman (Feb 17, 2004)

QUOTE.. 'How many batteries should I have for my three Kyocera panels totaling 365 watts. It is a 12 volt system with 12 volt batteries.'

In my suggestion above, I figured around a 3 days reserve at a 60aH load. Putting more batteries on this would not allow enough current to "Boil" the battery to keep the electrolite mixed up. Thats what I meant by "Working" them. The charge/discharge cycle should allow the battery to boil some daily..

Even though there isn't any bright sunlight, panels will still produce some current but only a small percentage. Not enough to boil the battery but will add some aH back in..

In using the 4-hour window, with a fixed array, some charge will accumulate before and after these times. This is a "Bonus" and covers battery losses and helps out on cloudy days..

It's important to keep a good balance with array/battery reserve. A 2-3 day reserve is good but the total size of system will depend on the demand load. A back up genny should only be used in extreme conditions..


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## Ramblin Wreck (Jun 10, 2005)

Thanks. This Summer I hope to complete a barn, and I want to build one wing of it as a combination garden/bee/canning room, and power it with solar (bascially lights and a DC powered freezer). Your discussion above has been helpful/enlightening.


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## mightybooboo (Feb 10, 2004)

12vman said:


> QUOTE.. Putting more batteries on this would not allow enough current to "Boil" the battery to keep the electrolite mixed up. Thats what I meant by "Working" them. The charge/discharge cycle should allow the battery to boil some daily..
> 
> Not enough to boil the battery but will add some aH back in..
> 
> .


12V,do you have a charge controller with equalize function?
Sometimes I wonder about equalizing,I do mine every few months or so,BIL NEVER equalizes his.His are going on 10 years I think,full off grid.Recharges though at about 85% I think.

If I was Tango,with approx. 400 watts I would use 4 t-105s ,would leave a little room for more panels,and genny up the shortages or cut out 2 batts if 400 watts is inadequate to keep them at least 85% charged.

Just my thoughts,could be wrong,as I dont know her full system and power generation vrs. withdrawals on a daily basis,time to talk trimetric meter numbers I think.

BooBoo


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## mightybooboo (Feb 10, 2004)

Oops,double post.


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## 12vman (Feb 17, 2004)

Boo Boo..

Yes, I have a C-40 controller but I never use the equalize function. The battery boils a little every sunny day so they get mixed. I've only added water to them once in the last 2 years so they don't boil much but enough..

IMO.. If a solar system is used for a back up and isn't used full time, the battery should be equalized to mix the electrolite. If a battery is used daily, the normal charge/discharge cycle will make them boil enough to keep them mixed up unless the battery is too big for the panels to get them boiling during a charge cycle. If this is the case, equalization won't work too well either because the panels can not produce enough current to make the battery boil. This is what I mean by "Working" the battery..

Different folks have different views on this but with my experience, this format works well for me. There's a fine line to how much battery and how much panel should be used. I feel a battery should show signs of charging every day. If you see some bubbles in each cell during the charge cycle, things are balanced pretty good. If you only see a bubble every now and then, I'd say you have too much battery. When I say boil, I don't mean like boiling water. It's more like a steady, small bubble action that is almost constant during full sunlight at noon. Even if the controller has kicked back to the float setting, there will still be some bubbles going on. You will see more if the controller is still in the bulk function..

Figuring in Ohio, in the winter, is a tough venture. To make a reliable system work all year round is over kill in the summer. I usually figure the amount of aH the panel array can provide in the 4 hour window with good conditions and gauge the battery to that. In my case, my panels can produce around 120aH in the 4 hour window. (30 amps/hr) My battery is slightly over 400aH. (4 golf cart batteries) I replace at least 1/4 of my total battery capacity in a good charge day. I know I collect more than 120aH in a day but I just forget about the extra before and after the window. This gives me a buffer for cloudy periods which can be days around here. Some days the controller never makes it to the float function but I know I have enough to get me by for another day or so. My loads are very light. I'll figure 60-70aH/day.. maybe. I've never really set down and figured it exactly. I watch the voltage. If it gets near 12/11.8, I worry and shut stuff down. That don't happen very often anymore. I haven't used my back up much in the last 2 years..

It takes an amount of current to make a battery boil. If too much battery is connected to an array, it's possible the battery will never achieve full charge if it's used on a daily basis. The controller should always get to the float level on a sunny day. At least on the second day if the 2 days are sunny, back to back, if the battery is run down pretty good during a cloudy period. The 4 to 1 theory seems to work well. (4 times the possible aH produced by the panel in the 4 hr. window for battery sizing) This will assure the battery is kept active and will get enough current to boil some without the need to equalize. This has worked well for me in installs I've done in my area. Winter is a killer and that's what I design for. Using this theory and figuring from the daily load amounts will assure almost fool proof operation year round..


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## Jim-mi (May 15, 2002)

..OOPPs.......

"being discharged daily'..........Carefull....How deeply..???

If you take them way down (discharge) then your bats will have a very short life.

As far as I know if you use Only 20% off the top of a fully charged bat. then the bat should live a long life.


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## 12vman (Feb 17, 2004)

I stated..

"The controller should always get to the float level on a sunny day"

If the battery is 4 times the possible aH output of the array and can achieve full charge in 1 sunny day, that would be around 25% discharge by design. That's if the array is designed to replace the user load daily..


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## mightybooboo (Feb 10, 2004)

12v,sounds like your system is nicely balanced,I shoot for solar to float on the Motorhome daily when in use.
But I just ordered my Honda eu2000I,so i can really do some nice power usage while dry camping,and plug in the neighbors too if needed,really excited about that little QUIET genny.The old ONAN is a beast,hate that thing!

BooBoo


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## Tango (Aug 19, 2002)

I don't have my generator connected to the array at all. I use it independently to pump water with an ac pump- and if we have too many cloudy days, like we had a couple of times over winter- I use it to charge my laptop and lanterns. Someday when I am in a position to finish what I've started I'd put in a back up generator like a guardian to kick in when the battery bank depletes. But for now, with so little power usage, three batteries get charged and discharged daily. I've gone from zero to minimal in the past past year with solar power. It's fun and educational. Sure appreciate everyone's help tweaking things and leanring more. I'll probably have too many batteries as summer approaches - I simply don't need that much right now. Would have been different with a frdige but that will probably be next year now.


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## 12vman (Feb 17, 2004)

Tango..
How many batteries do you have now? Were you getting more this summer? Are you using the Kyocera panels now?
Just curious..


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## Jim-mi (May 15, 2002)

Tango, I get hung up on the use of the word *discharged*. Thats why for my previous post.
A *discharged* battery can be a bad thing......to what degree of discharge is the question.------and here less (discharge) is better.
Any one who uses say 80% of the bats capacity *daily* will soon be buying new bats.
Being able to monitor your bats--like how full is your *fuel* tank--is very important.
The use of such as a "Tri Metric" meter will help YOU to prolong your bats life.


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