Solar System Battery VS. Automotive High Performance Deep Cycle Battery

[vinniethePVtech]

I've been trying to figure out for awhile now why solar system batteries are so expensive.
I've been exploring automotive for cost comparison, how ever there is some confusion with automotive. Only because ampere hours arent listed as they can be on most solar batteries.

I did find a good automotive battery that claims deep cycle, listed as optima D35 , I'm just having some problems deciphering the AMPS. Its not listed at AMPER Hours, just listed as C/20 good for 770 AMPS @32* F, 620 AMPS @ 0*F. So when I do the break down for the battery in a 20 hour time frame I get 770/20=38.5 AMPS an Hour assuming this is the Ah of the battery. How ever the optima spec chart is referencing a number of 48? Spec sheet claims that is 48 amps per hour. So something to me is conflicting between the spec chart and references.
Here is the optima spec sheet for that battery.

http://www.optimabatteries.com/_media/documents/specs/D35.pdf

So in comparison I was looking at the Concorde Solar System Battery. This was the specs I could pull up. 12V at 49Amper Hours. That's all I could get from that.
Here are the claims.
Concorde batteries have a a lower self discharge rate—five times better than flooded batteries. Expected life cycles are 5000 cycles to 10% DOD, 1000cycles to 50% DOD. UL listed as a recognized system component. Meet DOT transportation requirements and are not restricted for shipment because they are exempted from hazardous materials category. All have copper alloy terminals and silicon bronze bolts.


Now between the optima and the Concorde the spec information is different and I cant fully decipher which one would be better. For the price I would rather go with the optima, no brainier there and it is back with a 1 year no hassle warranty. Concorde offers a 1 year warranty as well.

Automotive Optima I can get for $169.00
Solar System Concorde I can get for $190.00

My battery bank would look clean with the optima as well as I like to show off what I build. So what do you think would be the better performer in the long run?

[Sunking]

Vinny I think I can help you out with this. The Optima is a hybrid battery. It is neither a pure starting or a deep cycle battery. In other words it is considered a Marine Battery aka Golf Cart Battery.

Starting or cranking type of batteries have multiple, thin, spongy textured plates to maximize surface area so as to allow very high discharge currents for short periods of time, and then be recharged very quickly via an alternator. If pressed into deep cycle service will quickly deplete the thin plates and only last a short period of time..

A true Deep Cycle Battery has fewer but very heavy thick plates. This allows them to supply only moderate amounts of current (C/8 for FLA, C/4 for AGM), for long periods of time, and slowly recharged many times.

A Marine or GC battery is in between, and not something you want for true deep cycle applications. Optima are great as aux batteries in vehicles where the kids have very large wattage stereos or hydraulic pumps for low riders.

Here is a good example you can compare side-by-side. The Trojan T-105 is a very popular battery used in just about all golf carts. Another is the L-16 for floor machines. Just a few short years ago there were not many choices for Solar Stand Alone Battery systems and the T-105 and L-16 were the default choice... Now days Trojan makes a T-105 and T-105RE, L-16, and L-16RE. Look at the specs and note the weight of the batteries. Notice the RE models are heavier?

[vinniethePVtech]

Look at the specs and note the weight of the batteries. Notice the RE models are heavier?

That was one of the main things that caught my attention the concorde is a 36 LB battery, and the optima is a 36.7LB battery. The Exterior composition of the optima is using light wieght polymers. So should I expect the DOD between the 2 batteries to be the same because of weight and composition?

I believe I looked at a trojan 6V that I would have to run in series to get the same bang for my voltage and current.
Total weight of 2 6volt trojan batteries 236LB.
Optima or concorde is 36LB.s
That is a 200LB difference

The cost comparison is shocking though on a trojan a consumer would pay 75% more....
12V trojan for $666.00
12V optima concorde $170~$190

Now why can't I at the cost I could get the optima or concord can I just add a few more battery series in parallel and it would still be more cost effective than the trojan? That should keep the DOD down. right?

I don't see the warranty info on the trojan either, if its only 1 year its not worth it at the price sold for. Also according to BCI for sizing and dimensions the trojans are not only heavy, they are huge!!! BCI 903 is a very awkward size to be dealing with for a 6 volt.

Now I did also look into the Optima true marine battery that comes with a blue top. The weight of it is much heavier and the rating is at 55Ah. Reserve capacity is 120 minutes VS the 100minutes the concorde and optima yellow are rated for.
43.5Lb.s for a D34. You are right wieght has alot to do with it.

[Sunking]

I believe I looked at a trojan 6V that I would have to run in series to get the same bang for my voltage and current.
Total weight of 2 6volt trojan batteries 236LB.
Optima or concorde is 36LB.s
That is a 200LB difference

Vinny you are not comparing Apples to Apples. It is like comparing $10 worth of quarters to a $100 bill.

The Trojan T105 is a 220 AH battery compared to 48 AH Optima. Energy density of lead acid batteries is in the range of 40 to 50 wh/kg. So yes the Trojan is heavier because it has significantly more capacity.

[russ]

Very good - you just discovered that most folks with off grid systems are making a big mistake by buying true deep cycle batteries when they could be using far cheaper car batteries.

Guess that means they are all fools and you are the smart one?

Maybe Mike made a big mistake with the new battery system he just put in?

[vinniethePVtech]

Very good - you just discovered that most folks with off grid systems are making a big mistake by buying true deep cycle batteries when they could be using far cheaper car batteries.

Guess that means they are all fools and you are the smart one?

Maybe Mike made a big mistake with the new battery system he just put in?

I never said that. You are putting words into an idea that has not come to fruition.

I'm considering the sunny island inverter, and would need to achieve 48 volts.
Automotive is cheaper, and when comparing to the concorde solar battery there isn't much difference. Optima isn't a true automotive battery either its a hybrid. If I need to compensate for D.O.D then I can buy more for parallel.
The 6volt trojan is a nice idea, however that is double the amount of batteries for a series with a price tag that is ridiculously insane, not to mention install and disposal just based off weight is insane. Disposal for batteries cost money based on weight.
How ever as SunKing pointed out it it has far more capacity so for the price its actually slightly discounted to the capacity of the concorde or the optima. I won't need that much capacity though so I am building to the desired capacity needed. As adding more in parrallel could give me the desired capacity wanted. Wouldn't you agree?
Even if I had to replace a string/bank of 4 batteries in 1 year it is still cheaper than a string of trojan batteries in one purchase.
So why wouldn't it work?

I as well have been following SunKings tutorial advice.
Fourth step is to select a battery. If possible we want to only have one single string of batteries wired in series to obtain the voltage needed. We only want to use true deep cycle batteries made for renewable energy. This limits manufactures, and you will not find them at Walmart. A very good manufacture with the best warranty is Rolls-Surrette. They have a very good selection tool you can use. Check the RE battery option, input Desired AH, input +/- Percentage (10 to 15%), and 20 Hour Rate. Then you will see your choices to the right. Select a battery with enough AH capacity to construct with 1 string if possible. In this case the Rolls S1380 is the right choice. It is a 2 volt @ 1050 AH battery so you would need 12 of them wired in series to make 24 volts. The battery carries a 7 year warranty, with 2 years free replacement and last 5 prorated. You can expect 5 years of life out of it with excellent care.

I've noticed that lower volt batteries can have larger capacities how ever by the time they are all wired in a string the bank becomes huge. I unfortunately don't get a limitless sq/ft to install numerous strings. My fiancee and I consume on average 2.8KW and wanted to start with the sunny island inverter. For me its cost and warranty for chance opf replacement that matters.

[Sunking]

I've noticed that lower volt batteries can have larger capacities how ever by the time they are all wired in a string the bank becomes huge. I unfortunately don't get a limitless sq/ft to install numerous strings. My fiancee and I consume on average 2.8KW and wanted to start with the sunny island inverter. For me its cost and warranty for chance opf replacement that matters.

Vinny I don't think you have thought this through. If you consume 2.8 Kwh per day means you need a minimum battery capacity of 14Kwh period.

At 12 volts that is 1166 Amp Hours.
At 48 volts that is 290 Amp Hours

Either way it still weighs 900 to 1000 pounds and takes the exact same volume of space.

To do that with your Optima 34 requires 24 batteries with 4 parallel 48 volt strings That will be a nightmare and only last a couple of years at best before you need to replace them.

As I stated energy density and volume density are fixed with respect lead acid batteries. You cannot escape that. X amount of power will require X amount of weight and space.

What is not fixed is price and longevity (cycle life). Sure you can get a automotive battery that cost about $80 to $100 per Kwh. You will be replacing them every year. Or you could go with a marine type like the Optima for around $120 to $150 per Keh and get 2 to 3 years out of them. Or you can go with a true deep cycle battery, made to the size required and get 5 to 10 years @ the $180 to $220 per Kwh.

So you need a 14 Kwh capacity @ 48 volts. Your best best is a Rolls Surrette 12 CS 11P. It is a 12 volt 357 Amp Hour battery and you only need 4 of them, not 24 of them. They have a 10 year warranty and the best you can get. They are not cheap and would cost you about $2800 to $3000 and weigh 1088 pounds and take up 10 cubic feet of space.

My advice to you is do your homework and compare Apples to Apples.

[894tom]

Sunking, again the advise you give is priceless. Vinny I can tell you he sounds like he may be trying to sell you some huge expensive battery bank, but take it from a guy just like you, I have learned (the expensive way) that my way is not the best way. The point is battery solar systems are extremely expensive for a very small amount of power. When its all said and done you may be scratching your head wondering why you ever started down the off grid path.

Vinny, your prices are off pretty bad also and so are your weights. You can source a golf cart battery for about $100 bucks after a quick search. They only weigh 60lbs. I bought my bank for $760. 8 of them would give you the 48 volts your after. BUT...you will draw your bank down in about 12 hrs or so to 50%. You may get a couple years out of them at that rate if you go off grid full time.

[vinniethePVtech]

To do that with your Optima 34 requires 24 batteries with 4 parallel 48 volt strings That will be a nightmare and only last a couple of years at best before you need to replace them.


What is not fixed is price and longevity (cycle life). Sure you can get a automotive battery that cost about $80 to $100 per Kwh. You will be replacing them every year. Or you could go with a marine type like the Optima for around $120 to $150 per Keh and get 2 to 3 years out of them. Or you can go with a true deep cycle battery, made to the size required and get 5 to 10 years @ the $180 to $220 per Kwh.

I think you meant 24 batteries @ 6 parrallel Correct? Not 4 parallel 4X4=16
4 series X 12v=48
6 parrallel X 55Ah= 330Ah

24 batteries X $180 = $4320

Surrette 12CS 11PS 357Ah from (eco direct) = $1,072.95 + 4 + 4291.8

Difference of $28 and surrette offers the 10 year warranty! Its basically a $200 savings with the surrette after you add all the additions needed for the optima's, and offset the the difference in Ampere hours...LOL

4 Surrette wet weight is 1088 LB.s
24 Optima batteries is 1044 LB.s

Just based off the weight factor how ever I would be willing to do an experiment to see if optima could out live the Surrette just based on a difference of 44LB.s. Multiple batteries would cause numerous points of failure. Would be interesting to know.

[vinniethePVtech]

Vinny, your prices are off pretty bad also and so are your weights.

I pulled the prices directly from solar direct warehouse, I also pulled the battery weights directly from the spec sheets. Absolutely no math involved, and no room for error.

[894tom]

I pulled the prices directly from solar direct warehouse, I also pulled the battery weights directly from the spec sheets. Absolutely no math involved, and no room for error.

"I believe I looked at a trojan 6V that I would have to run in series to get the same bang for my voltage and current.
Total weight of 2 6volt trojan batteries 236LB.
Optima or concorde is 36LB.s
That is a 200LB difference"

[vinniethePVtech]

"I believe I looked at a trojan 6V that I would have to run in series to get the same bang for my voltage and current.
Total weight of 2 6volt trojan batteries 236LB.
Optima or concorde is 36LB.s
That is a 200LB difference"

Your point is moot at best 1, 6 volt trojan weighs 118LB.s
that means 2 trojans in series is 236 LB.s, seems pretty right to me.

[894tom]

I see what happened. Sunking and I were using the example of a T105 golf cart battery. This whole time you're refering to a L16. The amp hours are completely different on that battery compared to the T105 example given.

[vinniethePVtech]

4 series X 12v=48
6 parrallel X 55Ah= 330Ah

24 batteries X $180 = $4320

Surrette 12CS 11PS 357Ah from (eco direct) = $1,072.95 + 4 + 4291.8

16 batteries X $270 = $4320

$4320 for the trojan same price as the optima with less parallel strings!!! .
I haven't found any warranty specifications for the trojan AGM, if some one can find it that would be great!!

4 Surrette wet weight is 1088 LB.s
24 Optima batteries is 1044 LB.s

Total weight of 16 trojan batteries 1024LB.s, 20Lb.s pounds less than 24 optima batteries.

[Sunking]

I think you meant 24 batteries @ 6 parrallel Correct?

Correct my bad.

Difference of $28 and surrette offers the 10 year warranty! Its basically a $200 savings with the surrette after you add all the additions needed for the optima's, and offset the the difference in Ampere hours...LOL

4 Surrette wet weight is 1088 LB.s
24 Optima batteries is 1044 LB.s

Just based off the weight factor how ever I would be willing to do an experiment to see if optima could out live the Surrette just based on a difference of 44LB.s. Multiple batteries would cause numerous points of failure. Would be interesting to know.

Not sure I follow your logic. If the Surrette cost a whole $28 more than the Optimas, The Surrette battery is a bargain. Not only will it last 3 to 5 times longer but has 15% more capacity.