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Hello kids!

Three years ago I purchased a 4kw 48v Solar package. 9 panels, Magna Inverter/Controller, 8 Rolls 440 ah FLA batteries. In all honesty, I knew little about batteries and little about using them properly. That lack of knowledge led to the loss of all 8 batteries after only 4 months of use. That being said, I've learned a bit more since, won't repeat the same error and let's leave it at that.

So, for three years, I've had these 9 solar panels that are doing absolutely nothing, I now have the opportunity to get some batteries and put the system back in operation, but.....

The caveat to that is I cannot afford the 440ah batteries I once had and I am faced with creating a lower power system, which is fine. I was originally going to go with 220aH AGM batteries, but again, the price is out of reach. So now I have my sights set on some 130aH batteries. I have one question.

If I get (8) 6v 130aH AGM batteries to make up my 48v system, can I add more batteries later to increase my power(aH)/storage capacity?

I was told once a while ago that if I wanted to add more batteries to my then 440ah system for more storage I would have to wire the batteries differently. Parallel vs. Series I believe I was told.

Thank you for your help and suggestions in advance.

Ted
 

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Mixing batteries of different ages is bad.

A second string of batteries can be added a month after the first string, but any longer than that will be bad.

Batteries need to be the same age.

If you have multiple strings of batteries, the oldest / worst string will pull the other string down to its performance level.
 

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Who set you up with a 4kw system to power 21000 watts of battery bank?

Let me guess, your batteries were ruined because they were never fully charged up every couple days and they sulfated the plates?
 

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Who set you up with a 4kw system to power 21000 watts of battery bank?

Let me guess, your batteries were ruined because they were never fully charged up every couple days and they sulfated the plates?
Sorry, typo, 2.61 KW system and 430aH battery bank. Wholesalesolar.com
The batteries froze solid during a 5 day stretch of -25 degree days. Now that we got that out of the way....
 

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Sorry, typo, 2.61 KW system and 430aH battery bank. Wholesalesolar.com
The batteries froze solid during a 5 day stretch of -25 degree days. Now that we got that out of the way....
Setting up a 20kw battery bank with a 2.61 KW solar system is like using a motorcycle engine (solar panels) to power a concrete truck (battery bank).
WholesaleSolar is a very expensive place to purchase stuff. Go to Renvu.com and log in.. much better pricing and frequently half of what others are.

Your batteries froze because of the mismatch in power generation vs power storage. The battery charge dropped, which means your specific gravity of your electrolyte dropped, which raised the freezing point of the electrolyte.

Your problem isn't that they froze solid, its that they weren't being charged properly because a 2.61kw solar array is not even remotely enough to keep a 20KW (48v x 430ah) battery bank charged.

Go ahead and get your 130ah batteries, that's about all your solar panels can support anyhow and it would be a far better matched system between generation and storage. Just don't get crap batteries.. stick with a good quality unit.

There's a website called Battery University you should visit.. Read the entire website... twice.. then read it again. Probably one of the best places to learn about batteries.

When you are using a solar system to charge off-grid batteries, you have to monitor the batteries closely. Only Lithium batteries allow you to pretty much ignore them.

When cold weather is coming, its important to cut back on power use and not let battery voltage drop too low. Make sure to get a hydrometer and I would also suggest a refractometer. Hydrometers are good for quick checks, refractometers are good for high precision checks and calibrations.

Batteries are like women, they require a lot of attention and foreplay to keep them happy.
 

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Setting up a 20kw battery bank with a 2.61 KW solar system is like using a motorcycle engine (solar panels) to power a concrete truck (battery bank).
WholesaleSolar is a very expensive place to purchase stuff. Go to Renvu.com and log in.. much better pricing and frequently half of what others are.

Your batteries froze because of the mismatch in power generation vs power storage. The battery charge dropped, which means your specific gravity of your electrolyte dropped, which raised the freezing point of the electrolyte.

Your problem isn't that they froze solid, its that they weren't being charged properly because a 2.61kw solar array is not even remotely enough to keep a 20KW (48v x 430ah) battery bank charged.

Go ahead and get your 130ah batteries, that's about all your solar panels can support anyhow and it would be a far better matched system between generation and storage. Just don't get crap batteries.. stick with a good quality unit.

There's a website called Battery University you should visit.. Read the entire website... twice.. then read it again. Probably one of the best places to learn about batteries.

When you are using a solar system to charge off-grid batteries, you have to monitor the batteries closely. Only Lithium batteries allow you to pretty much ignore them.

When cold weather is coming, its important to cut back on power use and not let battery voltage drop too low. Make sure to get a hydrometer and I would also suggest a refractometer. Hydrometers are good for quick checks, refractometers are good for high precision checks and calibrations.

Batteries are like women, they require a lot of attention and foreplay to keep them happy.
 

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Thanks for the info, greatly appreciated. I will head to that site and check it out. Hopefully it'll work out to my benefit.

Very appreciated!!
 

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Thanks for the info, greatly appreciated. I will head to that site and check it out. Hopefully it'll work out to my benefit.

Very appreciated!!
Happy to help.

I would recommend you DON'T purchase your new batteries until you've read and understood everything on Battery University.. Then you can make informed choices on what you have, what you need, and what fits your budget.
 

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I've been doing a little research on my own. I'm actually considering getting (4) 12v batteries and wire them in Series-parallel and in that case I can get away even cheaper and still get the power I want.

By the way, I checked out Renvu.com and they're about the same with pricing on the battery banks. I have a very low budget right now and I need to get this system up and running, even if it means I have to dumb it down to 130 ah (which Renvu didn't have any of).

I'll look into Battery University, but I'm not the brightest bulb in the closet and I'm afraid my aging brain matter might not retain all that I read. But I'll give it a shot but if they get all techie and start throwing math at me, they will lose me in a snap.

Thanks again!!
 

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I've been doing a little research on my own. I'm actually considering getting (4) 12v batteries and wire them in Series-parallel and in that case I can get away even cheaper and still get the power I want.
If you're system is 48volts, you'll need four 12v batteries wired in series only. Check around for your local golf cart dealership or call a golf course and ask them were they purchase their 6 volt golf car batteries.

I'll look into Battery University, but I'm not the brightest bulb in the closet and I'm afraid my aging brain matter might not retain all that I read. But I'll give it a shot but if they get all techie and start throwing math at me, they will lose me in a snap.

Thanks again!!
If you purchase more batteries without a comprehensive understanding of how they work and how to take care of them, you'll just be out of the money you spent again in a short while.

If you want to operate a lead acid battery bank, you MUST know what you are doing. This isn't like driving a car, its more like taking out someone's appendix. You either have the knowledge and equipment or you don't, and if you don't, your batteries aren't going to last long at all.

I'd hate to see you waste you your money so read Battery University and you might even want to log onto one of the solar renewable energy websites that have battery sub-forms to ask questions.
Or I can answer them if you post.
 

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If you're system is 48volts, you'll need four 12v batteries wired in series only. Check around for your local golf cart dealership or call a golf course and ask them were they purchase their 6 volt golf car batteries.



If you purchase more batteries without a comprehensive understanding of how they work and how to take care of them, you'll just be out of the money you spent again in a short while.

If you want to operate a lead acid battery bank, you MUST know what you are doing. This isn't like driving a car, its more like taking out someone's appendix. You either have the knowledge and equipment or you don't, and if you don't, your batteries aren't going to last long at all.

I'd hate to see you waste you your money so read Battery University and you might even want to log onto one of the solar renewable energy websites that have battery sub-forms to ask questions.
Or I can answer them if you post.
I appreciate your help, really do.
Because of where my cabin is, upstate NY, I will not ever us FLA again. I'm going AGM this time.
Why would I go 6v, if 12v will do the trick?

The plan is to use the system when we're there, shut it down when we're not, keep the charge above 50% and use it in conjunction with a generator to keep it all on an even keel. When our previous FLA battery setup was functional, it was glorious. We were never below 80% power on the batteries, we were frugal with our power usage, all of our lighting is LED, our fridge is one of the most energy efficient ones you can get, all of our electronics are LED and low power consumption products and everything in our little 624 sf cabin worked just like any normal household. The only thing that I have that consumes a crap load of power is the well pump, other than that, all is normal. Only once did I use the generator to add additional power and that was only for a few hours while I used power tools (they do drain a little bit more as you can imagine). I have a power meter on the system that tells me what my power usage is and most times, I'm using less than 200 watts.

It's been a learning experience. Hopefully, Battery University won't make my hair hurt.
 

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I appreciate your help, really do.
Because of where my cabin is, upstate NY, I will not ever us FLA again. I'm going AGM this time.
AGM batteries are a lot more expensive but do have some advantages. A lot of folks who have battery banks would still say they'd rather spend the extra cash on more capacity though.

Why would I go 6v, if 12v will do the trick?
At the 130 AH size, I don't think it would matter much in your case.

The plan is to use the system when we're there, shut it down when we're not, keep the charge above 50% and use it in conjunction with a generator to keep it all on an even keel.
Your lead acid battery should NEVER be discharged to the 50% level except under emergencies and it should then be charged back up immediately! In fact, with the flooded batteries, they even say to "smoke em".. which means that its more important to get the battery back up to full charge quickly than it is to worry about over-voltage concerns. AGM batteries are sensitive to over-charging so don't do it.

When batteries are discharged, they begin to immediately sulfate.. Sulfation is "battery cancer", and once they have it, you can't undo it.
Your batteries, under normal circumstances, should never be discharged past 80% of their fully charged capacity.. So lets say you need 2 kW of power per day to run your house and you want a battery bank that can sustain your home for one day. That means you need a battery bank with 10 kW of storage!
Now lets say something happens and you need 3 kW of power one day instead of 2 kW.. it would be acceptable for you to run the battery down to 70% once in a while... but only so long as you charge it right back up as soon as possible.

But run a lead acid battery down to 50%?? NO FREAKING WAY! Not unless it was a dire emergency like the house is flooding and the pump needs to continue running.. and you better not leave it there at that deep of a discharge or you won't have a useful battery in a few weeks.

Your batteries need to be stored fully charged 100% and then they need a float charger to keep them charged while your away.. And even then, they need to be exercised at least once or twice a month to maintain optimal performance and health.

Please make sure you read the Battery University information.

When our previous FLA battery setup was functional, it was glorious. We were never below 80% power on the batteries, we were frugal with our power usage, all of our lighting is LED, our fridge is one of the most energy efficient ones you can get, all of our electronics are LED and low power consumption products and everything in our little 624 sf cabin worked just like any normal household. The only thing that I have that consumes a crap load of power is the well pump, other than that, all is normal. Only once did I use the generator to add additional power and that was only for a few hours while I used power tools (they do drain a little bit more as you can imagine). I have a power meter on the system that tells me what my power usage is and most times, I'm using less than 200 watts.

It's been a learning experience. Hopefully, Battery University won't make my hair hurt.
Yes! 80% is a good number.. 90% is even better, but not really practical economically.. Most off-grid people try to maintain normal battery discharge cycles at 70% to 80% and will only dip below the 70% number in emergencies. And then they always look to recharge the battery back up to 100% as quickly as possible.

Always calculate your available power at 20% of the battery bank's capacity for good health. A 10 kW battery bank is good for just 2 kW of daily use and cycling.

Lithium batteries can go all the way down to just 10% of their total capacity and then even be stored there for a while without damage. But they are super duper expensive.. like crazy expensive.
 

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Sorry... anxious fingers again. I meant to say 80%. We never had our FLA system go below 80% and we have no intention of letting the new AGM's get below that number either. If I need to use power tools, I'll fire up the generator.

Dude, the same battery bank I had in Lithium is $13K!!!! Insane!!
 

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Sorry... anxious fingers again. I meant to say 80%. We never had our FLA system go below 80% and we have no intention of letting the new AGM's get below that number either. If I need to use power tools, I'll fire up the generator.

Dude, the same battery bank I had in Lithium is $13K!!!! Insane!!
Tell me about it. I have a 7.56 kW grid tie solar system and I wanted the option of going completely off grid if some national disaster ever happened. (we're preppers). I looked into Lithium and the best deal, by far, was the Tesla Powerwall. Its 14.5 kW lithium with its own built in 5.5 kW split phase inverter for $5500.
The only reason I didn't jump on it is that they have a 4 month backlog and they insist on having their own certified installer ($1500 extra) install it.

I'm like "Dude, I'm an electrical engineer, I'm fully capable of installing anything".. Then they mail me an application and tell me they want me to become one of their Tesla certified installers.. LOL (rolling eyes)

It has a 10,000 cycle life expectancy.. assuming they're exaggerating and its only half that, its still far better than lead acid in all respects.

When they come to their senses, I'll probably spring for the Tesla Powerwall.. until then, I purchased an Outback Radian 8048 (8 kW split phase inverter) for $4000 and stored it in a Faraday cage for safe keeping.

I have 7.56 kW of solar up and running and another 5.4 kW of panels in safe storage so I can support that kind of power generation if I ever needed.

Personally, if I were you, I'd take your batteries home with you if you leave that cabin for more than a month.. keep them where you can keep your eye on your investment.
 

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Sorry, typo, 2.61 KW system and 430aH battery bank. Wholesalesolar.com
The batteries froze solid during a 5 day stretch of -25 degree days. Now that we got that out of the way....
Assuming they used an MPPT controller:

48*430 = 20,640wh
20,640/2610 = 7.9 That's on the fast end of C/8 to C/12 range that is recommended for FLA batteries.

Another way to calculate it:

2610/58= 45a
430/45 = 9.55 Again well in the C/8 to C/12 range for FLA batteries.

I don't see where wholesale solar made a mistake.

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Assuming they used an MPPT controller:

48*430 = 20,640wh
20,640/2610 = 7.9 That's on the fast end of C/8 to C/12 range that is recommended for FLA batteries.

Another way to calculate it:

2610/58= 45a
430/45 = 9.55 Again well in the C/8 to C/12 range for FLA batteries.

I don't see where wholesale solar made a mistake.

WWW
One of the very first things engineers learn in school is that mathematics are only about 50% of the story, and I'm being generous.

The key to his story is "cold spell of -25 degree weather". This means he's in the northern latitudes and even on a fully sunny summer day, he'd be lucky if his 2.61 kW system generated 2.5 kW.. and that's on a perfectly sunny day. Fast forward to winter where the angle of the sun drops substantially, and his 2.61 kW system will be lucky to generate even 1.5 kW.. and then, because of the short days, it will only do that for two or three hours per day if its sunny.

The reality is that in the northern latitudes, you must account for the drop in the sun's irradiance due to the drop in its angle, snow cover, cloudy weather, and most importantly, short days.

Your math is using the maximum theoretical perfect conditions and does not account for the real world.

Unfortunately, when it comes to off grid power using lead acid batteries, you can not starve them of a full charge, doing so is like starving a fire of oxygen.... eventually the fire will smolder out (battery sulfation), and once it does, the battery is junk.

Properly done, your winter calculations need to be able to charge the batteries.. of course, this means the summer calculations mean you'll have a lot of excess energy.. there's nothing that can be done about this with current technology. Maybe in the future our technology will evolve to use the excess summer energy to electrolyze water into hydrogen for compression and storage to be used in the winter, or maybe to charge lithium batteries or a flow battery.. But we're not there yet.

Probably the best (current) solution is to set up a system that detects sustained low battery voltage and automatically starts a small generator.. this way, all you need to do is keep a tank of fuel filled and the generator will make up for any shortfalls.

But the one rule you can not break is to allow a lead acid battery remain discharged for an extended time.
 

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Being that I've had my off-grid place in central Montana for 17 years I know all about northern latitudes and cold weather problems. Oversizing the array to the battery bank is not the solution for poor winter production. It creates more problems than it solves.

Strictly cold weather would increase the arrays output. Cloudy days it doesn't matter how much array you have as there isn't the sun for it to produce. The only workable solution is to add/use an addition power source. Hence the backup generator.

Ted - I would suggest you inquire at www.solarpaneltalk.com for advise. I can not (in good concious) advise any that would unbalance the array to battery ratio or parallel strings. If you decide to go with a smaller bank I can only suggest that you also don't use the full array.

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All,
Thanks for your input. I have registered on several solar forums and I'm getting good advice from everyone. Sadly and unfortunately, all solutions are out of my financial grasp for the foreseeable future. I can't do much with a $1500 budget and what batteries I would buy with that money, will be so undersized it may make it difficult run a completely solar household. I'm trying to eliminate or certainly minimize the use of my generators, which as you can imagine is costly and noisy. When my solar array was functioning, it was the greatest 3 months ever. Nice and quiet and really do miss that.

We'll see what happens in the next couple of weeks and I'll keep you all posted.
 

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Being that I've had my off-grid place in central Montana for 17 years I know all about northern latitudes and cold weather problems. Oversizing the array to the battery bank is not the solution for poor winter production. It creates more problems than it solves.
What problems do you think it creates?

Strictly cold weather would increase the arrays output. Cloudy days it doesn't matter how much array you have as there isn't the sun for it to produce. The only workable solution is to add/use an addition power source. Hence the backup generator.
I'm not sure what kind of panels you have, but mine produce about 20% of their output under gray skies in the winter and about 40% to 50% of their output under gray skies during the summer. (on average anyhow).

Back up generator would work, but the more solar panels one has, the less they need the backup generator. Also, when you compare the cost of fuel used alone by the generator over the course of years, and then factor in the cost of the extra solar panels, you quickly discover that the solar panels end up being cheaper in the long run.. and of course, the added benefit is that when you have excess power, you can waste electricity like wasting oxygen and it doesn't cost anything.

The simple fact is, when you have too much power, you can dump it.. but if you don't have enough, you end up having to supplement it with other more expensive sources.
This might not have been true 17 years ago when you purchased your panels.. but PV panels are really cheap these days and petrol fuels are really expensive.

Now, if he had natural gas available, I might be willing to suggest an NG Generator... much cheaper to run a generator on NG than on gasoline or diesel.
 
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