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Hi All,

I would really appreciate some advice please.

Currently got a 48V off-grid solar installation on a farm with:

Omnipower HT-B-S8000-48 8KW Pure Sine Wave Inverter

Outback FLEXmax 80 Charge Controller

24 x 2V First National solar lead-acid batteries (+-1100Ah at C10)

12 x JA Solar 335W panels (+-4KW)

Problem is that the lead-acid batteries has reached its end of life and we need to replace them.

Option is to replace with the same 24 x 2V First National solar lead-acid batteries (+-1020Ah at C5). Looking at R120k which seems to be very expensive.

Seems the better option is to look at maybe a bank of 4xPylontech US3000 (3.5KWh)

Problem is the Inverter and charge controller we have is probably more suited for lead acid type batteries. So we need to understand if the inverter and charge controller will be compatible with the Pylontech batteries, and if we will get the same capacity.

I also do not know how to compare the options as far as amp hours / capacity is concerned.

Is it correct to say the 2V First National solar lead-acid batteries is +-13kwh based on 25% discharge (1100 * 0.25 * 48) compared to 4 Pylontech US3000 +- 14Kwh (not sure what is the relevance or comparative C rating on Pylontech)

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Recently had a similar discussion, getting Lithium now will save you money in the long run even if it's slightly more expensive if you potentially need to upgrade your inverter. I'm not sure you do though? I'm not familiar with it, but does it have any settings to support Lithium batteries?

 

It's easiest to compare batteries with Watts and Watt Hours - Lithium is already quoted in WH

To get the lead acid equivalent you're already on the right track, AH * Voltage = WH

In your case you're making up a 48V bank so the AH stays the same. 1000AH * 48 = 48000 WH

Because you should only use 50% of that divide by 2. From there you can work out how long your loads will last etc.

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For Lithium you don't have to keep to a 50% discharge (80% is fine). So when swopping from from lead acid to lithium you need only about 60% of what you had in lead acid. There is a few calcs at the bottom of the Blue Nova product page here.

Those Omnipower unit does not have much in the sense of an interface you can change setting with if I remember correctly. You might need to swop out the inverter as well if you change battery types. LiFePO4 batteries are sometimes advertised as drop in replacements for lead acids. (Blue Nova advertise them like that), so perhaps the BMS is smart enough to sort that out. It might just take longer to charge the LiFePO4 on Lead Acid charger as they use a different curve. But the battery should not break. 

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Thanks. The Flexmax 80 charge controller got settings for absorb and float voltage. I see recommended values of absorption voltage of 52.5V and float at 51.8V for the Pylontech batteries in a another topic on the forum, and should be able to set that on the FM80.

50% DOD on the lead acid batteries MTE 21S only give about 2500 cycles (+- 7 years on paper). Only got about 5 years out of the previous set with 40% DOD.

https://www.battery.co.za/wp-content/uploads/2017/06/M_Solar_Dec_2016_.pdf

Pylontech claims 10 year warranty and giving 6000 cycles @ 80% DOD, so tempted to go with that.

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Each battery is different. Some have 16 cells and others have 15 cells. Your float\absorption values will depend on the battery and should be in the specifications when you buy it.

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On 2020/07/30 at 11:14 AM, Bielie said:

I also do not know how to compare the options as far as amp hours / capacity is concerned.

Is it correct to say the 2V First National solar lead-acid batteries is +-13kwh based on 25% discharge (1100 * 0.25 * 48) compared to 4 Pylontech US3000 +- 14Kwh (not sure what is the relevance or comparative C rating on Pylontech)

the basics of your sums look correct to me (Ah x V = kWh) so you know how to get to Ah and Wh for the comparisons but you must keep some things in mind. The lead acid 25% DOD is about longetivity of the battery bank. To make the batteries last a number of years you should not discharge them below a certain level, at least not on a regular basis - BUT you still have spare capacity that you CAN use. If you have another (backup) energy source ( like a generator) or if clouds are something you only get to see in books then you may not need all that extra capacity but if this is your only energy source and it powers very essential loads, what happens if you have 3 cloudy days in a row?

You would have to determine what your actual power need is for at least one day, and then decide how much autonomy (how many extra days) you need if running only on batteries. For that, 4 pylontechs could be enough but only you will know for sure. Also 4 pylontechs with BMS communication will more likely be ~11.3kWh (BMS will only let battery discharge down to 80%), and if installed without BMS comms should be ~12.7 kWh (only 90% discharge allowed by internal BMS) - your setup will not allow for BMS comms cable connection.

The C-rate on the lead acids will tell you how the total capacity changes in relation to the size of the Amp draw on the battery (the higher the Amp draw, the lower the total capacity of the battery - you can read more about the Peukert effect if wanting to know why). In other words, the 100Ah battery is only a 100Ah battery if discharged at a very specific Amp draw (and at a very specific temperature) - if you discharge it at a higher Amp rate, it actually turns into a 90 Ah battery during that use period. On the lithium batteries the C-rate will tell you generally two things. What the maximum rate of charge/discharge is that the battery internal BMS will allow before disconnecting the battery, and what the preferred charge/discharge rate is to help you get to the 10 year warranty number. The total capacity of the lithium battery does not really change much based on the rate of discharge like it does with the lead acids (it stays a 100Ah battery regardless of the Amp draw).

On 2020/07/30 at 11:14 AM, Bielie said:

Problem is the Inverter and charge controller we have is probably more suited for lead acid type batteries. So we need to understand if the inverter and charge controller will be compatible with the Pylontech batteries, and if we will get the same capacity.

basically as long as you can set the correct charge voltage, maximum charge/discharge rate and low voltage cut-off, lithium should work with an inverter/charger. I think your inverter unfortunately does not really allow for this. From what I can see the  low cut-off options are 38V, 40V and 42V. Highest Pylontech low cut-off recommended is 45V.

The solar charge controller could possibly allow for correct voltage settings (I did NOT actually check this) but you must also have the option to disable equalisation charge etc. (lithium do not need that) - so you will have to check how many settings you can change on the Outback that will meet the lithium requirement.

The Bluenova "drop-in" replacements (mentioned by @Louisvdw ) have voltage profiles that more closely fit with existing lead acid chargers etc. but price per Wh is very expensive on those (compared to something like a pylontech) and connecting them in series and/or parallel can also be bit of an issue.

If you had more fexibility in setting charge voltages etc. the lithium batteries would be an easier fit. So if looking at a possible R120K battery bill it could be a good exercise to look at total cost of replacing the inverter and charger and adding lithium to the capacity actually needed?

On 2020/07/30 at 9:32 PM, Bielie said:

Pylontech claims 10 year warranty and giving 6000 cycles @ 80% DOD, so tempted to go with that.

Last thing, some people do not realise that the 10 year warranty is to still have 70% capacity left (not 100%), you also have to send pylontech photos of how the batteries are installed to qualify for the full warranty period. You shold also confirm with your supplier that if the batteries are installed without any comms cable how that affects the warranty (I think it cuts it down to maximum 5 years). Only relevant if the warranty period is a major selling factor. Like cars, etc. you may find they still work without a warranty or service plan....

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Thank you, really appreciate the feedback. Struggling to find some good advice and the little knowledge I got is more dangerous than anything else. The "experts" that installed the current system in early 2014 was clearly not that. Approached someone now in the Mpumalanga-Badplaas area to have a look and got a quote for exactly the same batteries we can get from First National for R140k, for R190k. R50k on top. No suggestions for alternatives or even questions. So the only interest is to make a quick buck.

7 hours ago, introverter said:

4 pylontechs could be enough but only you will know for sure.

Can up it to 5 pylontechs and it will still be way below the R140k (inc VAT) that the lead acid replacement is going to cost. I will have to go and measure the exact usage again. Not permanent on the farm. Roughly something like this (wattage is a guess in some instances):

24x7: 2 green energy refrigerators (+-150w each?), security camera system (+-10w) with a vhf radio system (+-1w in standby?), electric farm fence system (+-30W), alarm system + modem (+-2w)

At night about 8 x 15W security flood lights activated by a day night switch.

In the house at night for about 3 hours: Led down lights 3W X 15 , sometimes use of 2 x Laptops, sometimes charging 2 x Cellphones

Might be missing something.

7 hours ago, introverter said:

If you have another (backup) energy source ( like a generator)

Completely off-grid, no Eskom but there is a diesel generator with a battery charger as backup. Not sure if this will still work ok if we replace the lead-acid batteries with Pylontechs.

I think the battery charger is connected via the inverter to charge the batteries but might be completely wrong.

7 hours ago, introverter said:

low cut-off options are 38V, 40V and 42V. Highest Pylontech low cut-off recommended is 45V

Yes correct that is the Inverter options. Its an old generation inverter catering for lead-acid. Will this really be a problem? I see you mentioned "BMS will only let battery discharge down to 80%", so I assume they will just switch off. Will this be bad for the batteries or Inverter? 

7 hours ago, introverter said:

The solar charge controller could possibly allow for correct voltage settings

Absorbing and Float voltage can be set in the Outback Flexmax 80 charge controller and the equalization can be disabled. But a bit apprehensive that it will not work, or we write the batteries off in a year or so.

image.png.b58ae6c0906328c4769cec6de4f11427.png

7 hours ago, introverter said:

So if looking at a possible R120K battery bill it could be a good exercise to look at total cost of replacing the inverter and charger and adding lithium to the capacity actually needed?

Maybe an option considering the R140k (inc VAT). From browsing on the forum, I saw an option from @Jaco de Jongh that looks like a good one, but not sure if I underestimate the cost or maybe missing something additional that will cost a lot, or maybe got the capacity requirements completely wrong:
EasySolar 48/5000/70-100 - 230V-MPPT 150/100 With CGX
With 5 x US3000 Pylontechs

Not sure if there is a secondhand market for the current Omnipower inverter and Flexmax charge controller.

7 hours ago, introverter said:

Last thing

We got about 6 years out of the lead-acids with the last year or so struggling along with not a lot of amp hours left. So we expect the same if we replace with lead-acid again, so anything at more or less the same price, that provides equal or better than that will be a bonus. Current batteries need a lot of maintenance, battery water, equalizing, etc. and as mentioned we are not always fulltime on the farm. The only good thing about the lead acid 2V batteries is that nobody will even try to steal them, and that they got this huge amp hour rating.

With the lead-acid we also did not want to use things like the occasional micro-wave for 10 min, or occasional quick hairdryer or using the printer. Seems the Pylontechs will be more forgiving for things like that?

Edited by Bielie

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Unfortunately I have come across very few sales people that will take effort to sell me what I need versus what they want to sell me. I would say before pricing replacement options, first as accurately as possible determine what you need peak and base power wise, add possibly a nice to have (microwave...not hairdryer 😉) - then you know minimum inverter and battery requirement. Decide how much autonomy you need/want  - then you know how much extra battery you need or to have options for a generator to help out when solar is a problem. At a glance a 8000W inverter and 1000Ah battery for your described loads/use is like shooting an impala with a 416 Rigby. Discuss with, and get a quote from someone like @Jaco de Jongh and make sure you understand what you have (on paper the existing system should cope with a microwave...). With a Victron setup you could even potentially end up being able to monitor/control your system when not on the farm via the VRM portal 🙂

In short, the pylontechs should protect themself from over discharge, ideally for battery total life span it is probably better if it does not get that low though. You could however still end up with a problem that the inverter will not start up until there is a charged battery, and the battery switched itself off...I have no idea whether this would end up requiring manual intervention like having to physically switch something on/off again..

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