Battery Advice

[andrew9484]

Hello,

I have a system consisting of 16 x 320W panels; 16 x 100AH Vision batteries (data sheet attached) and 2 x 5000VA Axpert inverters. I also have a victron battery monitor. I know that the 4 strings of batteries is not ideal - it is result of upgrades.

My system has been running since Feb 2017. I am 'close' to running off-grid.

I have not been having a good experience with the batteries. I replaced 3 of them a few months ago. I have now had to exchange another 4. Not a good record! And the results are still not desirable (battery monitor still showing up to 2% deviation at times).

I only discharge to about 75% on most days. I set the charge current to a max of 10A per string.

It is only a matter of time before i have more problems. the agent feels that the battery issues are as result of the charge current being too low. The newly replaced batteries will only carry  warranty from the original purchase date; meaning i will have to look at replacing all in 6 months at this rate of failure.

1) My expectation was that the lower the charge current the longer the batteries would last. Is my thinking flawed? Maybe high current is needed for some chemical process. Should i set charge current to max?

2) Should i give in now while i have 4 brand new batteries to sell off? and then replace? If so; what battery technology should i change to considering my configuration and intended use to be off grid?

Many Thanks Andrew

 

 

6FM100-X.pdf

[Sidewinder]

@andrew9484,

The quick answer, from my side, would be to ensure that your batteries are fully charged and goes into float long before the solar production subsides. Hopefully that rate is lower than the max rate of charge for your batteries.

From the life cycle graph, a 75% SOC you should get about 1300 cycles. So your not getting close to that, as they are supposed to last a lot longer than what your are experiencing.

Have a look on the BMV what is the deepest discharge and how many cycles it has reported. Also try and get the Battery Efficiency number. This will tell you how much energy your are loosing, i.e. charge 100 kWh, use 80 kWh, therefore efficiency is 80%.

Also using the Axpert to switch between Solar and Battery will damage your batteries, you need another device to control this, using the BMV, which you already have. There is plenty of threads regarding this, and the shortcomings of the Axpert.

Regarding the batteries, there would only be two recommendations: 1) Lipo / Powerwall type if you have the $$$ or 2) Trojan - the RE version, but you also need $$ and upgrade the firmware. The trojan's are still problematic, even with the new firmware, but workarounds are possible, due the the voltage limitation and lack of equalisation capability of the axpert.

Only the new Infinisolar Super 4kW addresses this.

I'm sure other will add more info to guide you to a working towards a good working system.

[andrew9484]

Hi. Thank you for the feedback. Batteries are usually fully chargedby 12h30 so still another 3-4 hours of production. Well below max charge rate of batteries.

I will look into the issue you mentioned using axpert to switch.

Any thoughts on OPZV2-490 that were also mentioned on this forum? 

 

[pilotfish]

Hi @andrew9484,

I have a very similar setup to you with 20x 310w panels, 2x Axpert MKS5 but using 24x OPzV2-490 batteries that you ask about. I have installed 3x HA02 (2 cells per terminal set) for balancing, and system monitoring via BMV-702 and ICC-win.

The system has only been running for 2 weeks, so not long enough to give a meaningful report, but midpoint deviation is 0.2% and charge efficiency is reported as 95% - both numbers that I am very happy with.

The batteries cost me about R61k (incl) from Mantech, I am happy with them so far.

[Chris Hobson]

13 hours ago, andrew9484 said:

I have not been having a good experience with the batteries. I replaced 3 of them a few months ago. I have now had to exchange another 4. Not a good record! And the results are still not desirable (battery monitor still showing up to 2% deviation at times).

Hi Andrew

I can really recommend HA 02s. If they don't work to your satisfaction I will buy them from you. @Chris-R sells them. With a 48V system you should try be under 1% deviation.

13 hours ago, andrew9484 said:

I only discharge to about 75% on most days. I set the charge current to a max of 10A per string.

I presume you mean a 75% SOC rather than a 75% DOD.  10 A per string translates to 40A - 20A per inverter. I see the charging curve is quoted at 0.25C so 25A per string.

Therefore 50A per inverter.

13 hours ago, andrew9484 said:

It is only a matter of time before i have more problems. the agent feels that the battery issues are as result of the charge current being too low. The newly replaced batteries will only carry  warranty from the original purchase date; meaning i will have to look at replacing all in 6 months at this rate of failure.

1) My expectation was that the lower the charge current the longer the batteries would last. Is my thinking flawed? Maybe high current is needed for some chemical process. Should i set charge current to max?

2) Should i give in now while i have 4 brand new batteries to sell off? and then replace? If so; what battery technology should i change to considering my configuration and intended use to be off grid?

I agree with you . Those batteries are standby batteries and not suitable for your application. Have a look at alternatives that have a 50% DOD cycle rating of at least 1200 cycles. You may have to compromise due to budget. But have a look at what is available.

[andrew9484]

Hi. thank you fro the response. Yes - 75% SOC

[ghatikar]

On 18/09/2017 at 4:56 PM, andrew9484 said:

Hello,

I have a system consisting of 16 x 320W panels; 16 x 100AH Vision batteries (data sheet attached) and 2 x 5000VA Axpert inverters. I also have a victron battery monitor. I know that the 4 strings of batteries is not ideal - it is result of upgrades.

My system has been running since Feb 2017. I am 'close' to running off-grid.

I have not been having a good experience with the batteries. I replaced 3 of them a few months ago. I have now had to exchange another 4. Not a good record! And the results are still not desirable (battery monitor still showing up to 2% deviation at times).

I only discharge to about 75% on most days. I set the charge current to a max of 10A per string.

It is only a matter of time before i have more problems. the agent feels that the battery issues are as result of the charge current being too low. The newly replaced batteries will only carry  warranty from the original purchase date; meaning i will have to look at replacing all in 6 months at this rate of failure.

1) My expectation was that the lower the charge current the longer the batteries would last. Is my thinking flawed? Maybe high current is needed for some chemical process. Should i set charge current to max?

2) Should i give in now while i have 4 brand new batteries to sell off? and then replace? If so; what battery technology should i change to considering my configuration and intended use to be off grid?

Many Thanks Andrew

 

 

6FM100-X.pdf

 

I would suggest if possible use flooded lead acid as they have much longer cycle life - may be possible to buy the 6 V 410 Ah Trojan which is perfect for your size requirement.

 

from your datahseet, it looks like the visions are designed for standby UPS and other generic application and not deep cycle solar 

I have a similar  Siz system with Sukam and Luminous mixed  ( all moderate quality Deep cycle lead Acid ) 200 AH x 8 running for past 4 years with Axpert and batteries have shown no sign of problems.  It has two 5 KVA Axperts in parallel My midpoints normally is 0.1 %  or 0 and goes to .3 %  during charging 

Few things I am doing differently than you 

 

1 charge rate C20 - 20 amps in my case - no change in temperatures

2. Do not leave them discharged  idling even for an hour  - the moment SOC is blow 70 % my generator kiks in till they are 100 % again 

3. I use a cheap  PWM morningstar charge controller  45 amps to equalize them  every 3 months - The way I do it is to disconnect the Axperts after batteries are charged  and then connect the morningstar  till it completes the equalization cycle ( typically 3-4 hours )

[andrew9484]

On 9/19/2017 at 7:38 AM, pilotfish said:

Hi @andrew9484,

I have a very similar setup to you with 20x 310w panels, 2x Axpert MKS5 but using 24x OPzV2-490 batteries that you ask about. I have installed 3x HA02 (2 cells per terminal set) for balancing, and system monitoring via BMV-702 and ICC-win.

The system has only been running for 2 weeks, so not long enough to give a meaningful report, but midpoint deviation is 0.2% and charge efficiency is reported as 95% - both numbers that I am very happy with.

The batteries cost me about R61k (incl) from Mantech, I am happy with them so far.

Hi. How are your batteries going - still all ok? Are you using as off grid system?

[pilotfish]

8 hours ago, andrew9484 said:

How are your batteries going - still all ok?

The batteries are doing a great job, performing exactly as I had hoped for now.

8 hours ago, andrew9484 said:

Are you using as off grid system?

My system only has 1 day autonomy so is not truly "off grid". I am off grid as long as the weather is decent, but If I have a cloudy day then the system will switch to grid when the batteries reach 50% SOC (normally between 8 and 10am with no PV charge). I have 2 geysers, 1 oven and 1 aircon which are grid only, but I have solar heating on the geysers and a gas hob so the grid usage is very low (around 100kWh per month, down from around 1000kWh pm before PV).

I charge my battery bank [solar only], so after switching to grid the system will remain on grid until the SOC reached 65% when it will switch back to PV mode. To be fully off grid I think I would need to have 3 days autonomy tripling the size of my battery bank, I dont see the value in that.

The battery bank is 26kWh total capacity and my average daily discharge from the batteries is 250Ah (12kWh), you can compare this to your own requirements. (Note that the OPZv2-490 is 490Ah at C10, but 540Ah at C24 which is a better approximation of my discharge rate).

The OPZv2 is a proper deep cycle battery with excellent cycle life at 50% SOC and 25"C - I have taken steps to keep within these parameters and hope to get about 8 years from my battery bank (to 80% capacity). If this dream comes true then my cost /kWh from the batteries will be around R1.50exv which is much better than all the LiPO rates that I have seen quoted.

Of the 30kWh daily consumption from the system only 12kWh is provided by batteries and 18kWh is provided directly by PV during the day, so at R1.50 x 12 / 30 = R0.60 /kWh - that is pretty good and I reckon my system will provide a decent return in the long run, but in the end this will be decided by the batteries so it is not the place to skimp on cost.

[andrew9484]

Hi. Thank you for the detailed response! I am using system in very similar way - also 1 day autonomy. And all off grid excluding Geysar, oven. Pool pump is on but i usually change over to mains if cloudy. 

At the moment I am considering the batteries that you are using and Trojans. what are your thoughts between the 2 options?

[pilotfish]

I looked at both options before buying and found the OPZv2 to be better value even before the Trojan maintenance issues are taken into account - but this relies on the OPZv2 coming close to their advertised spec.

If I had a golf cart I would definitely go with Trojans

[andrew9484]

I see in your image that you have used bars to connect batteries. Did you buy these or have them manufactured?

[Chris Hobson]

12 minutes ago, andrew9484 said:

I see in your image that you have used bars to connect batteries. Did you buy these or have them manufactured?

Those interconnects generally come with the cells.

 

[andrew9484]

Thanks Chris. Any luck with price on Trojans? I was looking at the OPzV2 as well but after some online price calculations it looks like it will be significantly more expensive option. probably better to go for the cheaper option now and then hopefully prices will drop and specs will improve by time i need to replace. 

[pilotfish]

32 minutes ago, andrew9484 said:

I see in your image that you have used bars to connect batteries.

I used a 25mm x 5mm solid copper busbar rated at 250amps that I got from ACDC. It comes as a 3m length which I cut to length and drilled as required.

Part Code: CUB025X5

The busbar is also very handy for extras like metering wires and HA-02 wires, which I have drilled into the busbar with small screws and ring lugs rather than compromise the battery terminals with additional lugs etc

[andrew9484]

Great - thank you

[pilotfish]

24 minutes ago, andrew9484 said:

I was looking at the OPzV2

The current price from Mantech for 24 x OPZv2-490 R2679.97 x 24 = R64319.28 for a 550Ah bank which is R2473/kWh. The Trojan T105RE from Re-Volt is R3100 for a 6v 225Ah battery which works out to R2296/kWh (both numbers inc vat).

The prices /kWh are very similar, so you need to look at battery specs to see which gives better value. I think the OPZv2 wins that one by a huge margin - at 200amps average consumption per night (which I believe is your approximate usage) you could expect about 3000+ cycles to 80% capacity for the OPZ, @Chris Hobson will know more but I think the Trojans will be about 1200cyc.

Bear in mind that if you go the Trojan route you will require 2x parallel strings for a 450Ah bank which is a similar capacity to your current setup. This is 48 watering points that will require regular maintenance, also you must deal with the whole "Axpert cant equalize Trojan batteries" story.

[andrew9484]

Hi Pilotfish,

thanks for the detailed breakdown. I am not keen on having parallel strings again. The OPz look good apart from the price.  I was wondering about the Trojan L16 435AH. Would work out to approx 45k based on online prices. 

The mantech price on OPz is ex VAT from what i could see.... so would be looking at R73k

 

 

[pilotfish]

You are correct about the "ex vat", I never picked that up.

I August I paid about R2250 ex vat (R61k inc vat for the bank), I guess I got lucky!