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What are the best batteries for off grid solar


Bowsie
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Hi Guys.

 

I'm looking for opinions on the best batteries to use on small economic off grid systems from 1-5 kw peak.

 

Has anyone had experience with gel or AGM over a period of time?

 

Bowsie

 

 

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1 hour ago, Bowsie said:

I'm looking for opinions on the best batteries to use on small economic off grid systems from 1-5 kw peak.

One should not be using the words "economic" and "batteries" in the same sentence.

It is very difficult to determine what for you would be"the best batteries to use". Rather than a 1-5kW peak we would need to  know what overnight draw you are planning to supply. Your geographic location may influence the size of one's battery bank. Thirdly one would need to know where you are planning to house your batteries? Are you going to be able to have vented batteries or are you going to be restricted to VRLA (Gel or AGM) batteries?

I have AGM batteries which are two years old and have given me fine service. They are nearing the end of their useful life and I have had some sobering moments recently. With some fancy footwork I have manged to get them to behave themselves again, but the warning signs are there and I am in the market for some new batteries.

 

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23 minutes ago, Chris Hobson said:

I am in the market for some new batteries.

Ja like a Victron MPPT with the Axpert and Trojan's. :P

@Bowsie agree to what Chris said re. "economic" and "batteries" in the same sentence.

Batteries are more expensive than Eskom. Unless you are off-grid and rely on a generator, then batteries are very much viable and economical - T&C's apply with pages and pages of small print obviously, "Needs" vs "Wants" on said battery bank.

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Sorry. Let me rephrase. Not economic batteries, rather on an economic system, so not top end equipment.
Presuming the batteries are speced correctly and ventilation was not an issue and you had a choice over AGM or gel in an off grid application which would you chose? @Chris Hobson your AGM's have lasted two years. Is that cycling every day?


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9 hours ago, Bowsie said:

@Chris Hobson your AGM's have lasted two years. Is that cycling every day?

HI Bowsie

Yes I have cycled every day. DOD 41% on a 260Ah battery. (108 Ah).

9 hours ago, Bowsie said:

Sorry. Let me rephrase. Not economic batteries, rather on an economic system, so not top end equipment.

Perhaps have a look at top end equipment. TTT's beloved Trojan's are not badly priced here is a spreadsheet based on powerstore prices.

 

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@Chris Hobson I have T105 batteries and they are not suitable if your inverter is an Axpert. The maximum charge voltage of the Axpert is 58.4V and T105 requires 59.2V bulk charge and 62.4V equalisation of the top of my head.. So purchasing the T105s was a mistake and if I have to buy again it will be AGM batteries. Having to top up the electrolyte with distilled water every so often is a pain. Best to check that the specs of batteries and inverters match for best results. That said, Trojans have a fine reputation as proper deep cycle batteries and if one has an Axpert, their AGM or VRLA batteries will make a great match. Just stay away from the flooded LA Trojans if you have an Axpert.

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2 minutes ago, ebrsa said:

@Chris Hobson I have T105 batteries and they are not suitable if your inverter is an Axpert. The maximum charge voltage of the Axpert is 58.4V and T105 requires 59.2V bulk charge and 62.4V equalisation of the top of my head.. So purchasing the T105s was a mistake and if I have to buy again it will be AGM batteries. Having to top up the electrolyte with distilled water every so often is a pain. Best to check that the specs of batteries and inverters match for best results. That said, Trojans have a fine reputation as proper deep cycle batteries and if one has an Axpert, their AGM or VRLA batteries will make a great match.

As previously discussed that 0.5V difference is not that serious. You can get your batteries 100%  charged if you cheat and use a bit of Eskom. What it means is your Trojan bank goes into absorb sooner than it should and ultimately into float too soon. If you are cycling your batteries lightly I think there is enough solar day left to get to 100% SOC. If however you are cycling deeper you may find that you don't hit 100% before the end of the day. Allowing Eskom to do the job solves your dilemma. It still does not allow you to equalise.

My current thinking is to replace the AGMs I currently have (when I have wrung the last Ah out of them) with 2 strings of Trojan T105 REs. I preferably would want a single string but cannot find 400Ah+ batteries that would be cost effective. I would then include  a Victron charger in the setup. I would lose the Solar Power Balance ability of the Axpert but this would matter less in that the larger battery bank could accept the entire capacity of the panels I currently have. Not ideal but entirely workable.   

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On 5/12/2017 at 8:36 AM, Chris Hobson said:

As previously discussed that 0.5V difference is not that serious. You can get your batteries 100%  charged if you cheat and use a bit of Eskom. What it means is your Trojan bank goes into absorb sooner than it should and ultimately into float too soon. If you are cycling your batteries lightly I think there is enough solar day left to get to 100% SOC. If however you are cycling deeper you may find that you don't hit 100% before the end of the day. Allowing Eskom to do the job solves your dilemma. It still does not allow you to equalise.

My current thinking is to replace the AGMs I currently have (when I have wrung the last Ah out of them) with 2 strings of Trojan T105 REs. I preferably would want a single string but cannot find 400Ah+ batteries that would be cost effective. I would then include  a Victron charger in the setup. I would lose the Solar Power Balance ability of the Axpert but this would matter less in that the larger battery bank could accept the entire capacity of the panels I currently have. Not ideal but entirely workable.   

 

@ Chis Hobson - I feel you would be better off with one string of batteries, even if that means a slightly smaller bank resulting in an increased in DOD. The ability to charge and discharge a battery equally will greatly increase service life. 

@ 108ah draw per night, you would have a DOD on the 450 AH bank of 24% and a DOD on the 370ah bank of 29%. So only a 5% increase in DOD. 

If it were me, I would rather put in one 370ah bank than two 225ah banks, and yes, I have actually had both;-) 

There is a 435AH Trojan signature line battery the L16H-AC, the other choice would be the L16RE-B 370Ah. The RE-B may be the better choice, as it all round a superior battery to the signature line. Hence the jump from a 1yr warrant to 3 yr.

Also, with 2 banks you will have 48 cells to water and check.

 

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1 hour ago, LivSol said:

 

@ Chis Hobson - I feel you would be better off with one string of batteries, even if that means a slightly smaller bank resulting in an increased in DOD. The ability to charge and discharge a battery equally will greatly increase service life. 

@ 108ah draw per night, you would have a DOD on the 450 AH bank of 24% and a DOD on the 370ah bank of 29%. So only a 5% increase in DOD. 

If it were me, I would rather put in one 370ah bank than two 225ah banks, and yes, I have actually had both;-) 

There is a 435AH Trojan signature line battery the L16H-AC, the other choice would be the L16RE-B 370Ah. The RE-B may be the better choice, as it all round a superior battery to the signature line. Hence the jump from a 1yr warrant to 3 yr.

Also, with 2 banks you will have 48 cells to water and check.

 

Agreed. Fewer batteries = fewer problems. 

Back to the OP, the best battery for solar, IMO is a battery made up of 2V cells. 

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55 minutes ago, LivSol said:

... 48 cells to water and check ...

And then you have the watering kit for that: http://www.rvpowersupply.com/pro_fill.htm 

To add onto what LivSol said @Chris Hobson, like I am helping a guy solarise his Van. Batteries are a "Need" in both your cases.

Alternative is a gennie, in the Van's case the diesel enjin idling for hours (noooo ... ). We all know gennies are rather expensive in a off-grid scenario

 

Just a left around the tree thought.
The flip side Chris, now that you KNOW your needs and wants with the training wheels off, you can now also consider, with data to back your decision, the loads are over 24hour periods, when and how high the peak loads are, but more importantly, you know the 24/7 loads that costs ito batteries.

Because the high peaks may be few and far in daytime to boot, it most definitely makes sense to look at 2v cells (I agree with Siver).

Like 1849ah 2800 cycles at 50% DOD 2v batteries.
Or a 1520Ah 2v bank?
Or a 1270ah 4v bank?
Or a 925ah 6v bank?
All of the 2800 cycles at 50% DOD with a watering kit added.

But you know a 48v / 2 = 24 batteries. Damn , one can by the neighbors farm for that price?! 

Fear not, TTT always has a curve ball to share.

Their high AH puts you in a very unique position. BECAUSE of the data you have accumulated so far, you could make a case for a 24v system, even a 12v.

12v system with 2 x 925ah 6v batts @ 2800 cycles @ 50% DOD for few evening peak loads yet taking care of the constant loads with ease at less than +-R40k with watering kit.

Makes a LOT of sense to me to look at a 12v 5kva inverter.

Problem. We know the panels may be too much for 12v system, as you pointed out to me a while ago. So one could argue and split the array with multiple smaller controllers (cheaper) in parallel charging the bank from the array split optimally between said controllers?

That's what I would consider if I was off-grid.

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20 minutes ago, The Terrible Triplett said:

12v system with 2 x 925ah 6v batts @ 2800 cycles @ 50% DOD for few evening peak loads yet taking care of the constant loads with ease at less than +-R40k with watering kit.

Makes a LOT of sense to me to look at a 12v 5kva inverter.

Problem. We know the panels may be too much for 12v system, as you pointed out to me a while ago. So one could argue and split the array with multiple smaller controllers (cheaper) in parallel charging the bank from the array split optimally between said controllers?

That's what I would consider if I was off-grid.

I think we have discussed this before. 12V for a 5KVA inverter is not even close to ideal...  You are talking about a current draw of roughly 450A at full load - that is insane for a small 5KVA system.

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57 minutes ago, superdiy said:

I think we have discussed this before. 12V for a 5KVA inverter is not even close to ideal...  You are talking about a current draw of roughly 450A at full load - that is insane for a small 5KVA system.

Correct, we have had and I am being shot down time and time again, for then most was fairly new to solar, and when it was said, watts constantly <1000w = 12v  <2000w is 24v and above 3000w is definitely 48v, it made little sense.

Since back then new information has come to light in that we all now have Emon data so we started seeing patterns in that the majority of the loads are <500w, loads that are on 24/7, loads that cost ito batteries.

We also saw some loads are now and then 1500w range and infrequently there are ad hoc loads above 3000w for very "short" periods. It all depends on YOUR data, which differs from mine and others data. See my comment on knowing your peak loads and time they are on.

And daytime it is not an issue as the panels run the show. 

It is all about peak loads and the time they are on that may make a case for 12v/24v bank for the AH are sorted on the large banks, and one can save on lot on the costs of a 48v battery bank if you do not run above 3000w 24/7. Everything is not the 5 4 3 rule. :D

So with our newfound data I am saying again is to make a call on YOUR data to see if you can save on said batts by getting less batts with the same or higher AH, without compromising too much on the amps risk IF you need to draw 3000w for 5 minutes, even 5000w for 5 sec twice a week.

And also to add, large AH batteries can handle said amps drawn, your 200ah banks no.

So get thicker cables, and you need less for there are less batts, and ja, bigger fuses, for I really don't see the problem IF you know your loads and manage it wisely, to make a massive saving on a bank whilst powering the <500w on said bank for a decade or more.

 

Come on, pray tell me you have not seen the same pattern as I have and the above is not starting to make some sense into the future?

It is all in your data.

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1 hour ago, The Terrible Triplett said:

seen the same pattern

Well yeah, but car analogy time again.

Petrol engines are often tuned to combine fuel efficiency with good power. If you think about it, that can't ever actually work, not in this century. There is an optimum fuel/air mixture, known as stoichiometrically correct, where you have exactly the right amounts of fuel/air so that very little fuel is left after combustion (unburnt hydrocarbons) and you minimise your bad gases, that is Carbon monoxide (not enough air in the mixture) and Nitrogen oxides (Nox, which causes acid rain). The computers in cars are very good at getting this right, which means that power is pretty much directly proportional to how much fuel you squirt in there, and that is pretty much proportional to the amount of airflow you can arrange. So there is no such thing as having both power and fuel efficiency at the same time, the engines that can do both cannot do them at the same time.

What manufacturers to is build an engine that is deliberately detuned at lower RPMs to get better fuel consumption, and when you rev past 4000rpm the VTEC/VVTi/whatever kicks in and the spare wheel spins three quarters of a turn before you fly off. What they've done, essentially, is sell you two engines: One that is fuel efficient, and one that makes power.

What you want in an inverter, is two inverters: One that is efficient at low loads, but one that can also scale up to 5kw when you need it.

So far such a thing doesn't really exist. Some people split the loads and use a smaller inverter for some loads, others may use a small inverter and grid-tie it to fall back if there is a big load, but for someone who is off-grid, the only option is a large inverter with the corresponding high costs of the battery and the high quiescent draw.

24V are for people who have occasional peaks of no more than 3kw. Everyone else should have 48V systems.

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25 minutes ago, plonkster said:

24V are for people who have occasional peaks of no more than 3kw.

Depends. How occasional on for how long?

Guys, seriously, stop and think for a moment. I have said BEFORE that I am NOT saying all and sundry must go lower volts.

I am saying look at your data and make an informed decision, not stick to the 5 4 3 principal because everyone says so so it must be so because you THINK you are going to use 5000VA all the time.

You need a big bank as cost effectively as possible off grid. 48v may not be the only answer to every single person our there for we all have done all we can to protect our existing banks, now carry that forward and think further. 

You may just be quite surprised and realise you can go lower volts and bigger bank by going 2v that last 10+ years because your never really went over 1500w on average, 500w at night with 1 or 2 peaks of maybe 3kw very infrequently during the day for a very short period of time ad hoc - manage that if it bothers you.

Don't forget, I am all for more batts. Lots and lots of batts. Translates into lots and lots more profit. Why would anyone talk themselves out of profits?

 

Re. your car analogy.  Jhb to Cpt in 14 hours flat, with roadworks, at a cool 16.2km/l over the entire trip. Just 1 ticket at Worcester .. bliksims.

Was done with a 1.6 diesel engine (2v) like in the new Nissan Xtrail - power and fuel efficiency and no need for high revs in 6th gear - up and down all the hills.

My 2.8l (48v) can do that too ... down a 2.5km deep mine shaft.

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5 hours ago, LivSol said:

 

@ Chis Hobson - I feel you would be better off with one string of batteries, even if that means a slightly smaller bank resulting in an increased in DOD. The ability to charge and discharge a battery equally will greatly increase service life. 

@ 108ah draw per night, you would have a DOD on the 450 AH bank of 24% and a DOD on the 370ah bank of 29%. So only a 5% increase in DOD. 

If it were me, I would rather put in one 370ah bank than two 225ah banks, and yes, I have actually had both;-) 

There is a 435AH Trojan signature line battery the L16H-AC, the other choice would be the L16RE-B 370Ah. The RE-B may be the better choice, as it all round a superior battery to the signature line. Hence the jump from a 1yr warrant to 3 yr.

Also, with 2 banks you will have 48 cells to water and check.

 

Thanks for the tips LivSol. Nice to have practical experience.  

I don't know whether I will  find a 400+Ah battery reasonably priced. My 108 Ah draw is due to the gennie still running in the evening for my staff. The next expansion will bring them onto solar too and therefore I know 260Ah is too little. In my ideal world there would be a 24 x 2V bank the same capacity and for the same sort of money as two strings of T105 REs.

One bank of L16RE-B would be marginally cheaper than two banks of T105REs but I am after Ah. Unfortunately one you get to that sort of size you better like your batteries a lot. The Trojan industrial line is going to be with you for a while. I am not set on any particular battery yet but one string is preferable over two strings but 400-500Ah is probably not negotiable for me being completely off grid.I see DB9 has 150Ah of batteries. Somehow we just do not seem to be that energy efficient. Probably (700W for 5 hours and 350W for 7 hours). Plus I know the more power you have the more you use. Creature comforts are great especially in winter. A bigger bank would also help with losing the Axpert's Solar Balance capability.

My batteries are behaving themselves at the moment. I had a good talking to them and said any funny business they will be shipped to Bellville for an unknown fate that includes sparks and smoke.

5 hours ago, LivSol said:

Also, with 2 banks you will have 48 cells to water and check.

Hmmm that might just swing it into a single string's favour.

 

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The thread is about: What are the best batteries for off grid solar?

The answer: 2v high Ah batteries that will last you 10+ years.

Cons: Costs.
Cons: Be careful for running at too high amps for too long on 12v / 24v.
Pro's: 12v is cheaper than 48v by a whopping large margin.

So either spend more on batteries or save a dingese klomp geld by managing the peak loads better.

Like don't run the kettle with the oven and microwave together - 4500w. One at a time staying as close to your preferred limit to not stress yourself or your system.

Or just go 5 4 3 and be done. 

That is the next level of off grid solar efficiency.

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Been doing a bit of surfing the "http://forum.solar-electric.com/discussions" site and amazed at home many 24V system there are... I think this is almost the middle ground.  Less batteries - higher ah @Chris Hobson but still the ability to run big loads for small periods.  Most people also have a gennie to use when the welder needs to be used for example.  Off grid you probably have one anyway.

@Chris Hobson I would explore the 24V option for your situation.  NOT 12V ;)  ( @TTT is about to step in :unsure:)

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1 hour ago, The Terrible Triplett said:

The tread is about: What are the best batteries for off grid solar?

The answer: 2v high Ah batteries that will last you 10 years.

Cons: Costs.
Cons: Be careful for running at too high amps for too long on 12v / 24v.
Pro's: 12v is cheaper than 48v by a whopping large margin.

So either spend more on batteries or safe a dingese klomp geld by managing the peak loads better.

Like don't run the kettle with the oven and microwave together - 4500w. One at a time staying as close to your preferred limit to not stress yourself or you system.

Or just go 5 4 3 and be done. 

That is the next level of off grid solar efficiency.

I know a couple guys who drain their 2V cells to 0%, recharge them again the next day and run them flat again. And some suppliers have confirmed that you could easily get more than 20 years from those cells if they're maintained properly.

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45 minutes ago, Mark said:

Been doing a bit of surfing the "http://forum.solar-electric.com/discussions" site and amazed at home many 24V system there are... I think this is almost the middle ground.  Less batteries - higher ah @Chris Hobson but still the ability to run big loads for small periods.  Most people also have a gennie to use when the welder needs to be used for example.  Off grid you probably have one anyway.

@Chris Hobson I would explore the 24V option for your situation.  NOT 12V ;)  ( @TTT is about to step in :unsure:)

24V is fine for smaller installations but at some point (6 or 7Kw), 48V just makes a lot more sense. Thinner cables, smaller fuses and less risk of fire.

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42 minutes ago, SilverNodashi said:

... at some point (6 or 7Kw) ...

I concur 100%.

Risk of fire is everywhere, even 220v AC. All depends on who dunnit and how wise / stupid they where.

12v is the bottom left, for the brave and the strong of spirit that wanting the max bang for your buck - bank replacements do not break the bank.

48 is the top right - all problems solved bar the price tag at replacement time - with data at hand justifying 48v bank.

In between is 24v as @Mark said. No argument there at all - quite a comfy place to be settling on - IF that blows you hair back. :D

@SilverNodashi pointed out, that is also an idea. Go less batts, smaller bank, and hit it hard like 2800 cycles at 50% DOD on the industrial Trojans in a off-grid scenario. They will give you quite a few years and you can nurse them for a few more - or what say you @Chris Hobson ?

 

3 minutes ago, Gerald_db said:

Just topped up my 24 × Trojans. 72 cells. Took a while.

Watering kit is not that expensive if you want. Have seen them at wot +-R2.6k for 48v system. Once a week / month go and pump it and your are done.

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1 hour ago, Mark said:

 

@Chris Hobson I would explore the 24V option for your situation.  NOT 12V ;)  ( @TTT is about to step in :unsure:)

I have given it some thought. In an off grid situation I want Ah. We already are butting heads over multiple strings and I would consider 24V with something like a Willard 2V cell. Where I would plum for perhaps 48V 400Ah battery bank, but the same battery also comes in a 900 - 1200Ah and the price increase in not linear. So a 24V 900Ah bank is actually cheaper than a 48V 400Ah bank.

You don't want to be carrying your heavy loads off batteries. That why the sun shines in the day - so you can see what you're doing wielding that precision angle grinder and plasma welder combo . Batteries are there for the low wattage over night draw. That been said you don't want to start the gennie just because the system cannot handle a microwave.

You lucky folk in the city always have the grid to fall back on. For us rural dwellers it is go big or go home having gone small (energy efficiency) in the first place. We need to be able to power 95% of our loads. Gennie is there for that 5% and rainy days.

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3 hours ago, The Terrible Triplett said:

Cons: Costs.
Cons: Be careful for running at too high amps for too long.
Pro's: 12v is cheaper than 48v by a whopping large margin.

You do realize that saying "12V is cheaper than 48V" is like saying "a scooter is cheaper than a 4 door sedan". Yes, it is, but the scooter won't accomplish the end goal - same as a single 12V battery won't accomplish the end goal if indeed 4x 12V batteries are needed, regardless if it's in a 12V configuration or 48V. 

 

IF the end result was 1Kwh over say 20 hours, then a single 200A 12V battery would not deliver the needed energy. No matter how much you ask it to you. You would need a whole bunch of 12V/200A batteries to deliver the required 1Kwh over just about any period of time. 

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43 minutes ago, SilverNodashi said:

You do realize that saying "12V is cheaper than 48V" is like saying "a scooter is cheaper than a 4 door sedan". Yes, it is, but the scooter won't accomplish the end goal

No, I never said that.

Taking your analogy, what I have said is if you have bought a 4 door sedan and after years of using you realise one day it is always just yourself driving in it, you drive 2 km every day with the 4 door sedan, never over 60km/h IF the robots are green, then the scooter makes a lot more sense.

So then you may say you will get wet once in a while ... I say, get a raincoat. :P

You just need to decide, you want the 4 door sedan with all the associated costs or can the scooter do the job as good at a 100th of the cost of said sedan? :D

That is what I said and am saying. Check your data, does it justify your system or can you get really clever 2nd time around.

It is far more efficient to run a solar system at max all the time, with spare watts on inverter (!), than oversize it all just in case, having to replace it in a few years not having used it to its fullest potential.

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