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Which batteries should I buy (rhetorical question)


Chris Hobson
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My battery bank is failing and I am contemplating what sort of batteries I should buy as replacements. We are limping along and the batteries last a couple of hours until we go to bed but do not last through the night.

I am going to discuss batteries in general and try and avoid specifics so that folk considering battery purchases are aided in their own decision.

I think the first decision is deciding whether you want to go vented or not. In our case the "power room" is a corner in our TV/study/workroom so unless I end up with an innovative battery box that vents outside I would not want vented batteries inside our home. Battery boxes are common in the US which is considerably colder than SA and batteries are kept indoors to prevent them freezing. There are lots of designs on the net and I thought I would put a piece of 32mm conduit through just below the window sill. This would not be easy as the walls are over just over 450mm thick. This would enable me to have Trojans the only vented batteries I would consider.

If I were to go with sealed batteries one could add Lithium batteries to the smorgasbord of options available to you.

The second but probably deciding factor is cost. Lithium and 2V cells (both VRLA and vented) cost a whole whack but should outlast the other options available. I would have to be sure that the Lithium batteries I looked at were compatible with my inverter. I don't think my funding would stretch to a Lithium bank but if I have to replace my inverter too it would make it an exercise in futility.

The third deciding factor (for me) would to have batteries with sufficient Ah rating so that I could have a single string of batteries. This would exclude doubling up on the current brand of batteries I already have along with the bulk of the VRLA batteries on the market.

So what are my options if money is no object:

  1. Lithium that is compatible with my inverter
  2. VRLA "sealed" 2V cells
  3. Trojan batteries in a vented battery box.

My budget is probably going to reverse that order :P.

 

 

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I have CB Solar AGM batteries which have lasted there allotted time I have done just shy of 800 cycles and they had service through two hot summers where ambient temperatures were for the large part  over 30°C. So they have the equivalent of about 900 cycles.

I had neither considered Edison  nor saltwater batteries. Pricing seems based on what the lead acid market sustains rather than the value of the product plus some profit. This makes them very expensive and makes one apprehensive about spending that amount of money.

 

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14 hours ago, DeepBass9 said:

What about those iron Edison batteries? Do they need Venting?

Very low round trip efficiency, and really heavy. The old ones used to last ages, but that was old tech and the energy density was low. The new ones have much higher energy density (modern manufacturing allows increasing the surface area of the active materials), but that again lowers their lifetime. Gases just as much if not more than lead acid. Needs electrolyte replacement after some time because the electrolyte degrads. DIY Tesla PW made some videos on it (is it just me, or are these videos with text and the same sound track in EVERY video somewhat irritating? Still, info is good).

Edit: Also two spelling mistakes that seriously gets my OCD... he spells the name of the inventor incorrectly even though it is right there on the screen, and then there is "theif" instead of thief... :-)

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I know that the forumites recommend against parallel strings, but I think that 2 strings that are well terminated with battery balancing and a cheap 3-30v DC voltmeter on each battery will be a very low risk installation.

image.jpeg.8c812630770c3acfe035aacd00e0cc31.jpeg

The above meter is about R40 on Bid-or-Buy.

The issue with parallel strings is when one battery goes belly-up resulting in the rest of your string being toasted, with permanent monitoring you could immediately see if this is happening and react before permanently damaging the rest of the bank (in the case of sealed batteries by replacing the faulty unit).

What size bank are you considering?

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13 hours ago, Chris Hobson said:

saltwater batteries

Aquion? No longer in business. The idea looked cool but you could not discharge them at the kind of discharge rates required for off-grid... unless you had a LOT of them!

Perhaps I'm biased now that I'm leaning in this direction myself, but if you could beg, borrow or steal the money... 1kwh of lithium Ion costs around 10k now, and does 7000 cycles to 70%.

10000/(0.7*7000) = R2.04/kwh. That's within cents of Cape Town Domestic rate. Don't think you can buy any smaller than 4kwh at 48V (really 51.2V), so you're talking 40k for something that is technically no more than 100Ah, but because they cycle so much deeper and charge so much more efficiently, you really don't need the same size as you would for lead acid.

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18 minutes ago, plonkster said:

Perhaps I'm biased now that I'm leaning in this direction myself, but if you could beg, borrow or steal the money... 1kwh of lithium Ion costs around 10k now, and does 7000 cycles to 70%.

Some of the more mainstream Li+ manufacturers want there batteries paired to certain inverters and my Axpert is yet to be invited to the party.:P On a more serious note if I was a Li+ battery manufacturer I don't think an Axpert would be my inverter of choice to pair with my product.

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1 minute ago, Chris Hobson said:

Some of the more mainstream Li+ manufacturers want there batteries paired to certain inverters and my Axpert is yet to be invited to the party.:P On a more serious note if I was a Li+ battery manufacturer I don't think an Axpert would be my inverter of choice to pair with my product.

SolarMD pairs their battery with the Axpert. They are the only ones though. I still feel like BlueNova or FreedomWon present better options, but I'll be completely honest and tell you how I came to this unscientific conclusion: These guys integrate with a more expensive inverter, in other words, they keep high-class company, or to put it bluntly: I judge them by their choice of inverter :-) But... on the inside, everyone fits Winston cells that come from China. The big difference is in the BMS.

Also, with some of the other batteries, the BMS sometimes have dry contacts that can be used to disconnect chargers/loads when a cell is critically high or low, so you could wire it such that the PV is disconnected when there is a high cell, or everything is disconnected on a low cell. Then all you need is a battery charger profile for the lithium cells. See for example the Victron vebus BMS that can combine with the Cyrix disconnects.

Honestly though, I feel like you should get another AGM bank and slug it out another 2 years or so. Or maybe look at L16RE from Trojan (370Ah). All that bothers me about that, is this is a 6k battery, of which you need 8. For 48k you can get a pretty decent entry-level lithium bank.

This article suggests that cost is about on par now, which suggests you need to look at high end flooded lead acid. Ie L16RE-B.

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The Victron Gel Long Life 2v 600Ah looks like an option for you, seems to have charge requirements suited to Axpert SCC and brilliant life expectancy (1500cyc at 80% and 2500cyc at 50%) - no idea what they cost!

From the attached pic's it seems remarkably similar to the FNB OPzV - which may be a viable alternative subject to more research.

Victron -GEL_AGM.pdf

OPzVPowerGel-2015-.pdf

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17 minutes ago, pilotfish said:

The Victron Gel Long Life 2v 600Ah looks like an option for you, seems to have charge requirements suited to Axpert SCC and brilliant life expectancy (1500cyc at 80% and 2500cyc at 50%) - no idea what they cost!

572 Euro each. You need 24. They weight 50kg a piece, so it's 1.2 tons :-)

At the present exchange rate it's just a tad more than 200k. In Europe...

Selection_022.png

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For around 250k you can get a 300Ah Lithium bank... that will comfortably fit your requirements and last three times longer. Look specifically at the 300Ah 12.8V smart battery (you also need the BMS right at the bottom, cheap compared to the batteries).

Selection_023.thumb.png.00577a2fd58f9c4e42016682d0210d93.png

Keep in mind that buying a LiFePO4 battery locally will be at least a third cheaper. Not only measured by the Victron stuff... an LG-chem is also up at around 70k, while you can get the same sort of thing locally for less than 50k (probably).

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9 hours ago, plonkster said:

Honestly though, I feel like you should get another AGM bank and slug it out another 2 years or so. Or maybe look at L16RE from Trojan (370Ah). All that bothers me about that, is this is a 6k battery, of which you need 8. For 48k you can get a pretty decent entry-level lithium bank.

I might be looking at old prices but I thought the L16RE-Bs were just over R4k. 6kWh of Li is not going to do it for me, 8-9 is probably where I should be aiming. My reasoning is that I just, just squeak through on 260Ah LA overnight. (40% DOD). If my family are home we don't make it. In winter our base draw is between 250 and 350W  - perhaps a bit high. The sun disappears behind the mountain 3:30 pm and starts meaningful production at 8:30 am. So I have about 17hrs where we are entirely reliant on batteries or other sources of power. A wind turbine would help but often the Karoo can have weeks during winter of little or no wind. I have done 2 years with a a bank that is too small supplementing the shortfall with the gennie. Phase 2 is to get my staff also onto solar and then the gennie should only run in an emergency.

The idea of  8 x 260 Ah does not frighten me as even without busbars I think I can have a 2 string system wired up optimally - it is just been there done that. For not much more money I could have 8 x L16RE-Bs or if I am feeling energetic 16 x T105REs.  1st prize would still be Lithium.

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5 minutes ago, Chris Hobson said:

I thought the L16RE-Bs were just over R4k

I just googled a price last night, I could be totally off the mark with that. If you can get them at 4k, this is what I'd vote for. Also gives you a sub R3 price per kwh and a sub 40k initial investment. At 6k I start to get into that "oh, what a pitty, it's sooo close" feeling because it starts to encroach on low-end lithium :-)

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19 minutes ago, plonkster said:

572 Euro each. You need 24. They weight 50kg a piece, so it's 1.2 tons :-)

At the present exchange rate it's just a tad more than 200k. In Europe...

Under those circumstances I would look at vented Hoppecke 520Ah R75k excl vat. Rack and acid etc included.

or R100k for the gel 2v cells - still an extraordinary amount of money.

 

12 minutes ago, plonkster said:

For around 250k you can get a 300Ah Lithium bank... that will comfortably fit your requirements and last three times longer. Look specifically at the 300Ah 12.8V smart battery (you also need the BMS right at the bottom, cheap compared to the batteries).

Selection_023.thumb.png.00577a2fd58f9c4e42016682d0210d93.png

Keep in mind that buying a LiFePO4 battery locally will be at least a third cheaper. Not only measured by the Victron stuff... an LG-chem is also up at around 70k, while you can get the same sort of thing locally for less than 50k (probably).

A LG Chem 10kWh for R80k excluding VAT but then there is the little problem of a compatible inverter.

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Good day Chris.

I have installed a Freedomwon bank on an axpert inverter. Quite easy, they set the BMS parameters a bit further for the axpert (Still within range) you set the charging voltage 55.6V for float & bulk charge. the axpert throws full amps into the batteries & once it reaches the set volts the amps tapers down to about 1A & they are full.

Annycase, they are expensive initially.

Have a look at these, I think mantech made a booboo with their price on these. I bought x8, 2 weeks ago, with 4 voltage meters on each 12v battery. I also did a H bridge connection between the parallel banks for balancing.

The DG range of batteries does about 1100 cycles @ 50%

http://www.mantech.co.za/ProductInfo.aspx?Item=370M0075

 

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15 hours ago, Jako said:

Have a look at these, I think mantech made a booboo with their price on these. I bought x8, 2 weeks ago, with 4 voltage meters on each 12v battery. I also did a H bridge connection between the parallel banks for balancing.

The DG range of batteries does about 1100 cycles @ 50%

http://www.mantech.co.za/ProductInfo.aspx?Item=370M0075

 

That is a very good price, I'm considering 4 of them. Are they suitable with the axpert 5Kva inverter? 

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Verry good price :P

Max charging amps for a single string 30A. Max charging for 5kva 60A solar + 60A utility.

Just limit the max charging amps in your settings.

But my experience you can leave it on 60A due to the agm battery drawing less & less amps the higher the soc. So at 50% DOD the batteries does not pull anything close to 30A. You cannot push amps into a battery. It draws what is required. But you can limit the initial current draw.

Yes they will work for you.

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40 minutes ago, Jako said:

You cannot push amps into a battery

Oh you absolutely can! Just make the voltage high enough :-)

While that sounds like a silly thing that nobody would do, that is precisely what happens when a cell is shorted, the voltage across the rest rises.

Even with a healthy battery, if it has been discharged deeply it might "draw" more than is good for it on the recharge cycle.

I tend to agree that you can push the limits a bit with AGM, maybe up to 40A, but I would not go up to 60 on a 150Ah battery :-)

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I see Mantech is also doing a 2v OPZV2-490 - they are charging R2233/battery if you buy 24.

  • Total cost R53,600 for a single string 490Ah (C10) bank,
  • No noxious gases in the TV/study/workroom,
  • 3500cyc at 50% DOD
  • At 50% DOD that is about 42,000kWh so about R1.30 per kWh,
  • That makes it worthwhile to be completely off grid!

I think it is the best spec/cost ratio that I have seen that suits the Axpert SCC, I am going to order right now before Chris buys them all.:D

OPZV2-490.pdf

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