I'm over my head

[Brush Ape]

I just reread your last post. So I need 24 2v batteries? Can I build this 12v at a time? Or is it bad to add new batteries to batteries already in service as the older ones will drag the new ones down?

[Brush Ape]

So if I use something like the Rolls S-1400EX in series, then I'll only need 12v? But don't run them parallel to make multiples of 12v? Weight is not an issue, I built the shed for all the solar stuff to hold battery weight. Also can I set them directly on a wood floor or do they need a table or a shelf?

[Sunking]

They're specialty batteries for the most part, used pretty heavily in the telecom industry among others. You'd do best if you could find a local telecom getting rid of used ones because they're often taken out of service at a specified date rather than based on their condition, and they've been known to be good for years and years afterward (because they've only been used for backup the same as you intend, without a lot of cycling).

Not a good choice. Telecom batteries are made like car batteries. They are not made for cycle service. Telecom industry goes on the Calendar life of the battery, not cycles. Batteries have two life specs. 1 is cycles, and 2 is calendar life. Whichever comes first.Telecom batteries have 100 to 300 cycles and 5 to 10 year Calendar life.

When they sell them to the public is to turn a liability into an asset. It cost them thousands of dollars to dispose of them and a mountain of EPA red tape. Or they can sel them dirt cheap to the unsuspecting public. Most of that cash goes to the engineer and warehouse personnel pockets. They get rid of a huge problem and put the monkey on the buyers back.

I know, I have worked in the telecom sector for 35 years in DC plants. We always cycled starting in October to make Xmas cash. Once you sign the papers, you own the problem.

[Live2BFree]

Howdy, love your enthusiasm but I dont think any battery is currently going to give you 20 years in a daily cycled off-grid solar setup, hopefully one day

I agree, but unless I miss my guess the OP isn't really looking for daily cycle on his batteries. I think his intention--conceived improperly, as it were, when the build was started--is to have a backup source of power charged/cycled on occasion but to be primarily grid-tied. Given less than daily cycling and some improvements to his system, I'd bet he'd get ten years out of quality batteries if he maintains them properly...

[Sunking]

Sunking and Live2bFree thank you. Now we are getting somewhere. What batteries do I look at. I've never even heard of 2v batteries, other than the little discs for welding helmets and calculators.

That is because you are stuck inside a 12 volt box. Lead acid batteries are 2 volts, not 12 volts like a 6-cell car battery. A 12 volt lead acid battery is actually 6 batteries in a common case. The issue is capacity vs weight. In a 12 volt battery the largest AH you can find is around 200 AH. Any larger and they become to big and heavy to handle.

12 volt battery is just fine if your application requires 200 AH or less. But what if you need say 12 volts at 1000 AH? A 12 volt 200 AH battery weighs around 120 to 150 pounds or roughly 50 to 60 pounds per Kwh of capacity. that means a 12 volt 1000 AH battery would weigh in around 750 pounds. Is that a problem for you? It is for me and the battery using public

True Deep cycle batteries are even heavier. You typical 6 volt golf cart battery weighs twice as much. A 6 volt 200 AH battery weighs as much as a 12 volt 200 AH starter or hybrid battery. They have a lot more lead in them. OK I think you get the point. Lead acid batteries come in 2, 4, 6, 8, 12, 24, and 36 volt cases. 24 and 36 are used in marine and trucking. 12 volt is a car battery and the box you are stuck in. Time to get out of that box.

Good Deep Cycle batteries come in 2, 4, 6, 8, and 12 volts. At 48 volt battery with 8000 watts of panels requires a minimum 1250 AH's. That is roughly 3600 pounds. You want to avoid Parallel battery strings. at 1250 AH's demands you use 2-volt 1250 AH batteries. Or as close as you can get. In this class you are talking a commercial battery like Rolls, Crown, and Trojan.Example Rolls makes a few that would fit the bill. Models like S-1725, S-1400 EX, and even a 4-volt 4KS25P. It would take 24 units in the 2 volt cells and 12 in 4-volt batteries. If you think these are large batteries think again. I served with the Silent Service and we used a 2-volt 10,000 AH battery in strings of 220 cells in series. Each cell weighed 1200 pounds. Those were for propulsion, and there are more for
communications and life support.

Back to your application. You will go into sticker shock when you find out what a 48 volt 1250 AH battery cost. That is what it takes to handle 8000 watts of power at 48 volts. Just the way it works. So I hope you understand my urgency when I say your batteries are way undersized. They can only handle 4800 watts being the AGM's that they are. I sugges tin the future you get away from AGM because they cost twice as much as FLA and only last half as long as FLA.

[solar pete]

They're specialty batteries for the most part, used pretty heavily in the telecom industry among others. You'd do best if you could find a local telecom getting rid of used ones because they're often taken out of service at a specified date rather than based on their condition, and they've been known to be good for years and years afterward (because they've only been used for backup the same as you intend, without a lot of cycling). They're fairly big, fairly heavy, and fairly expensive--but they pack a lot of power and they're not as heavy as, say, a forklift battery. You'd install them in series up to your system's intended voltage, giving you a lot of amp-hours--way more than you'd get installing typical 6 or 12 volt versions of a "comparable" (and I use the word lightly) size. To put 2 volt batteries into some cost perspective, however, you're looking at a couple grand or more for six of them from a typical battery sources--Trojan, for instance--and you'll obviously need six to get to twelve volts (just to start). If you move to a higher voltage system, you'll need to double that, etc. It can be pricey. On the other hand, properly maintained quality 2v batteries are rated as high as 20-40 YEARS life expectancy. That's a lot of bang for the buck.

Howdy, love your enthusiasm but I dont think any battery is currently going to give you 20 years in a daily cycled off-grid solar setup, hopefully one day

[Live2BFree]

They're specialty batteries for the most part, used pretty heavily in the telecom industry among others. You'd do best if you could find a local telecom getting rid of used ones because they're often taken out of service at a specified date rather than based on their condition, and they've been known to be good for years and years afterward (because they've only been used for backup the same as you intend, without a lot of cycling). They're fairly big, fairly heavy, and fairly expensive--but they pack a lot of power and they're not as heavy as, say, a forklift battery. You'd install them in series up to your system's intended voltage, giving you a lot of amp-hours--way more than you'd get installing typical 6 or 12 volt versions of a "comparable" (and I use the word lightly) size. To put 2 volt batteries into some cost perspective, however, you're looking at a couple grand or more for six of them from a typical battery sources--Trojan, for instance--and you'll obviously need six to get to twelve volts (just to start). If you move to a higher voltage system, you'll need to double that, etc. It can be pricey. On the other hand, properly maintained quality 2v batteries are rated as high as 20-40 YEARS life expectancy. That's a lot of bang for the buck.

It should be noted that I'm by no means an expert, and I'm going purely from memory. It should also be noted--and I suspect you've gotten the gist of this already--that your mindset of being prepared for the worst, being self-reliant, etc., will not be well received by everyone on this forum. I've been here less than a day and have already decided this is not the forum for me. You'll have to decide if you can deal with the bile (particularly that aimed at "preppers" and others of us who are not much interested in the first-world conveniences, nor afraid of the work that comes with living apart from them) in order to get simple answers to relatively simple questions. I'd bear in mind what you already know, especially if you are a farmer on a large scale...that is, you go with the simplest thing that gets the job done. Duct tape, WD40, a can of ether, a come-along, channel locks, and a whole host of similar things--they're all simple products that we use every day to get things done. Might not be pretty, might not be up to someone's "code", but we put food on the table and live until we're 100. Folks who don't do what we do will never understand that.

I also know that a lot of smart, smart people are worried that things won't always be the way they are now. If the day ever comes that the world ceases to be as we've come to expect it, I'm confident that I'll be better able to handle it than most. That's a sort of peace of mind that can't be understated. I'm sure you know exactly what I mean. I'm not sure that others, who don't live or think as we do, will ever understand what I've just said...and that's okay; it isn't meant for them.

You've made mistakes before--in what you've planted or how you've fertilized, where you located your silo or deciding to go with the International Harvester rather than the John Deere. The same can be said of your solar installation, perhaps--but you'll get it figured out and working perfectly for what you intend, just like you did with that old Farmall.

Again, it's what we do.

Don't let anyone rain too much on your parade. Above all, don't be told that "it can't be done". How many times have you been told that, right before you did it?

[Brush Ape]

Sunking and Live2bFree thank you. Now we are getting somewhere. What batteries do I look at. I've never even heard of 2v batteries, other than the little discs for welding helmets and calculators.

[Live2BFree]

I'm no expert by any means, as many who have already posted are. However, you've come looking for solutions and, if you think on this a bit, there are several you could consider. As you've stated, you're too far in to stop now.

Start with what you've learned here--the system as you've designed it will not work safely, if at all. That doesn't mean you can't correct the errors. Those AGM batteries are not wasted yet, and can be sold on Craigslist at very little loss given the current desire for them. You could note in your listing that you've upgraded to a system too large for them to handle, so they are barely used/virtually new. Pain in the neck because it's an extra step you hadn't planned for, but at least you'll salvage most of what you have in them. Then invest the funds from reselling them together with more (I know, it sucks) money to put together a decent bank comprised of 2-volt batteries.

The same could be done with all of your equipment. I personally would carefully take panels offline a few at a time, at first, downsizing to a more proper configuration for your controllers. If you have the funds for it, I'd build a bank of batteries right now that is sized for the remaining panels but with future expansion in mind as funds become available to replace your controllers (or as components are sold and replaced). You're looking at a large system that you want to be able to count on in a grid-down situation. Do it right from here, using the right batteries, and expand it as you can.

Speaking of grid-down, this is why I posted in the first place. You mentioned that you're a farmer, so I believe I understand what you were thinking when you went battery and grid-tie. I am a good ole' boy myself, so I know the mentality that put you here to begin with. Let me see if I can address this issue from the angle you came at it.

I believe there should be a way to HAVE a battery bank that is available for SHTF scenarios, which is charged (and discharged) on an occasional basis, with some sort of manual switching available to allow you to grid-tie for the majority of the time. You want to sell your excess power back to the power company in orderer to recoup some of your investment, but you want to have the ability to go off-grid when necessary. I'd be asking these experts what you need to do to make that possible. Batteries are meant for storage--so store. A tractor kept in the barn will eventually rust, but that doesn't mean you use it every second of the day. Batteries shouldn't be any different. It may not be optimal (on a cost basis) to have batteries that aren't being used as anything more than "energy silos", but you're not going to destroy them by only occasionally cycling them. They may not live as long or as cost-effectively as they would if you were using them regularly, but you want BACKUP. That's what you have intended. Find a way to have that, while also being able to utilize your array on a regular basis AND sell the excess harvest back to the power company.

Lastly, don't be so hard on your friend as all these people have. He likely did what he thought was best, with the very best of intentions, and probably for free (or near it). It's not hard for even the smartest people to get lost in all of this--and it's even easier to get in over your head when dealing with a system of your size. His "mistakes" were likely small errors that simply compounded themselves due to the increased size of your project. He designed a small system, probably similar to his own, that he tried to scale. As you can see, solar only scales to a limited extent before it becomes a whole other animal.

You've come to the right place and asked (mostly) the right questions. You're here for solutions, not berating. Take the "attitude" with a grain of salt and listen for the nuggets of wisdom--then fix your problem.

It's what we farmer-types do.

[Sunking]

Sinking, there must be some confusion here. The OP has an Outback Radian GS8048 inverter and a 48 volt 350AH battery bank. As it is, it looks like he is going to have to shut off PV to 2 of his controllers. 2 controllers using 4000 watts of this array should output up to 83 amps charging under perfect conditions. From what I have read, AGM's need a charge rate of about 20 percent of capacity or 70 amps in this case. So, is 83 too much, what do you think. Of course, the long term solution is a properly sized battery bank.

Crap you are right. Not sure how I got off on 24 volts, but think because he is using 4 controllers which was a mistake. 48 volts did not make sense with 4 controllers. It does changes things a bit and gives him a few more options. But he stil has a dangerous situation. Click his link on his battery. to get maximum charge current. Short story is max charge current is 50 amps per 175AH of battery. He has 8 batteries in 2 x 4 configuration or 48 volts @ 350 AH. In other words he can pump up to a maximum of 100 amps or a maximum of 4800 watts is still the limit he can use. So the panel wattage does not change and 8000 watts is still very dangerous. So that modifies the recomendation, and gives him another option of adding batteries now if he wants to use all of his 8000 watts.

At 48 volt battery, his 60 amp controller limits goes up to 3200 watts, but because the battery has a limit of 4800 total he can use 2 controllers with 2400 watts on each. Each array would produce 50 amps and 100 amps amps total. That makes it safe and usable. Still does not change the fact he has to remove and store 2 charge controllers and 3200 watts of solar panels.

However being at 48 volts, he CAN ADD one more string of batteries, use another controller, and an other 2400 watts of panels if he wants, but not a good idea. It i snot a good idea because one should not use parallel battery strings. With two or three strings in parallel he is going to be replacing the batteries in 1 to 2 years. That is what happens with Parallel strings of low quality batteries.

What I would s reccomend from an economic POV is to run 2 2400 watt panel arrays with 2 of his controllers, store the rest and wait until it is time to replace the batteries. When the time comes to replace the batteries. then reconfigure the panels to 2 arrays with 3200 watts and 1 with 1600 watts to total 8000 watts. Throw the 3rd charge controller away. Then for replacement battery the minimum size at 8000 watts input 800 AH of a Flooded Lead acid battery using 2 or 4 volt 800 AH cells so as to make one single string tha can last 5 to 7 years.

Another suggestion is to trade all four controllers for two Midnite Solar 80 amp controllers. Those will easily handle 800 watts up to 10,000 watts. .

[Logan005]

Before you buy any new Batteries you need to study and understand how batteries work. I recommend lot's of reading especially the sticky's and wiki's

[Brush Ape]

So another battery bank would satisfy the other two controllers?

[Raj]

Sinking, there must be some confusion here. The OP has an Outback Radian GS8048 inverter and a 48 volt 350AH battery bank. As it is, it looks like he is going to have to shut off PV to 2 of his controllers. 2 controllers using 4000 watts of this array should output up to 83 amps charging under perfect conditions. From what I have read, AGM's need a charge rate of about 20 percent of capacity or 70 amps in this case. So, is 83 too much, what do you think. Of course, the long term solution is a properly sized battery bank.

[Sunking]

I don't care if you use small monosyllabic words. Explain to me what this stuff does, why the charge controllers aren't smart enough to know when to stop charging, etc. I need to make this work, I'm too far in to quit.

We already told you what it takes to make it work, but will fall short of your intended usage. What you have now is extremely dangerous.

As for the Charge controllers they have Input limits you cannot exceed. If you do you let the magic smoke out, and it never works again. That does not matter because even if the Controllers could tolerate the higher wattage would still limit the output current to its rated maximum. In your case 60 amps. In other words it changes your panel wattage from 2000 watts to 1600 watts. So with 4 x 2000 watt (8000 watts) watt array you are limited to 6400 watts.

Lastly your batteries make everything above a moot point and even more dangerous. Batteries can only handle so much charge current. Go above what you batteries can safely handle and they over heat. As they heat up, the internal resistance goes lower causing more more current to flow. More current causes more heat which causes more current. More current cause more heat and more heat cause more current. More current causes more heat which causes more current. Do you get it? It is caused Thermal Runaway and the AGM's go BOOM!

You only have one option with what you have and I already spelled it out for you along with 3 or more knowledgeable folks concur. You batteries can only handle 4800 watts maximum, you have 8000. Sorry we cannot fix your system, only try to help you at least make it safe. You are going to have to live with your mistake.

In the very near future, 2 years maximum, you will have to replace the batteries. That will be the time to fix your nightmare and it is going to be very expensive. When that times comes based on all those panels you have to take off and store away, put most of them back up in 3 sections using your 3 of your 4 controllers, charging a 48 volt 1300 ah, and replace your 24 volt inverter with a 48 volt Inverter. There is no other option you have with 8000 watts of panels and 4 controllers to operate at 24 volts.

Your so called friend really screwed you big time. He is either clueless, or wanted to do great harm to you financially and physically. What I can say with almost certainty, is if you use what you have now set up like it is now, you have a FIRE in your very near future. You are in grave danger and your friend is to thank for it.

[Brush Ape]

I don't care if you use small monosyllabic words. Explain to me what this stuff does, why the charge controllers aren't smart enough to know when to stop charging, etc. I need to make this work, I'm too far in to quit.