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How deep do you draw your lithiums?


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I'm new to lithiums after recently replacing my lead acids. I have 2 x 3.5kW Pylontechs.

I'm looking for the sweet spot where I will get good battery life as well as maximum utilisation of the bank at night. I do understand the technology is new so there's no real data out there.

Currently I'm drawing down to 25% before switching to grid, but the Axpert powers itself from the batteries so this causes a further slow drop of a few %. Never goes below 20% which is my personal comfort zone limit. I'll likely modify this strategy for load shedding to leave a little more in should I need to go back to battery at 4am.

What's the feeling on this? Am I cycling too deep, or not maximising ROI?

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1 hour ago, PhilFM said:

I think you are at a good level currently, given that your panels are able to recharge completely during the day and you do not need grid power to do so

Thanks Phil. I usually don't reach 100% in the day but can easily handle all the loads even in poor weather. When it's sunny we do extra loads in the washer and pump water to keep the panels running at max to get the maximum "free" energy, or cook with the oven rather than gas. The batteries run the house to 5am in a best case scenario but more usually around 3am.

I never charge from the grid. In Cape Town we do 2.5 hours of load shedding so a cutoff of around 40% would work for me at those times and only for load shedding in the early hours. This never happens due to grid overload but can happen if they are resting the gas turbines or refilling the top dams at the pumped storage.

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Hagu13, I think you are set up nicely and as you said when there is loadshedding, you can plan for that with the needed SOC

Unfortunately for us here in rural Limpopo, infrastructure maintenance is a huge problem so it's almost always a gamble with how deep you discharge your batteries as one storm, one gust of wind, one fart in the wrong direction can mean anything from 1 to 24 hours without grid, and this happens a lot.

So I run my batteries from 2am (can probably start at midnight rather), then wait for PV to start up after 6am, charge batteries during the day, which is usually done around mid day on a good day, then we add load as needed to maximize PV and switch back to grid around 5pm.

I can extend my night hours on the batteries, but then we have no backup should something go wrong and there is a rainy day or two. Here in the Lowveld it gets seriously overcast some days, we had two weeks now with very little sunshine and lots of rain, but we do not complain as we are coming from a severe drought. Unfortunately it is under these conditions (wet/damp) that we experience most of the grid cable faults, potentially leaving you without grid for a long time.

All this said, it basically just comes down to different circumstances, there is no one correct answer for everyone and it seems you understand your needs and risks well and plan/run your system accordingly

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I also have 2x3.5 Pylons and got the attached battery performance graphs from Pylon in China.  From their own tests, seems you can run the batteries quite hard without materially reducing life expectancy.

However, I run mine down to a max DoD of 40% overnight just to allow for any load shedding early morning before the batteries have time to charge up.... I probably could reduce it further and will probably do so in future.

48V Pylontech Battery Performance 0320.pdf

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On 2020/10/26 at 6:03 PM, Delta9 said:

This video talks about this.

 

Very cool video, thanks!

But it does open a question for me. 

I have a BYD 2.54kw battery. 

Now, this thing does cell balancing and calibration when it hits 55v (100% SoC). Or 10% (not sure about voltage). I read this SOMEWHERE in either BYD or Victron manuals btw, please don't ask me for a link now it was late! 

Anyway, so now the question, if I'm not supposed to charge that up to 100% "all the time", how often is OK? Cell balancing and calibration is also important. Never mind that I can't really set upper charge limit afaik.

 

For the record, currently I'm only going down to 80%, reasoning was that I don't (yet) have enough panels to bring it back up above 90% on a heavy use day. 

Edited by demaniak
Adding actual answer to post question.
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Hi Hagu13.

I have been running Pylon us2000b(x4) + us3000b (x2) for around 20 months now and my battery bank currently reports a 98% state of health (SOH).
If this rate of degradation remains linear then after 10 years, theoretically the battery bank should retain 80 to 90% SOH.

For the 3 months of winter I drain my battery bank down to 30% state of charge (SOC).
I stop at 30% as I cannot fully charge the battery bank from PV the next day if I go any lower.
If I had more panel power I would be comfortable taking the battery bank down to 20% daily for the 3 months of winter.

During summer the battery bank typically only drops to around 60% SOC by the time the sun rises and then is back at 100% by around 12h00 on a sunny day.

Summer plot
Screenshot.thumb.png.c811f91ce2f1e07580fd9cef3aa9e3d9.png

Winter plot (24% SOC on this day and just missed getting back to 100%)

793001816_ScreenshotWinter.thumb.png.6cbe2b28406b733f7f9e988a861b4ff4.png

I run the entire house (2x geysers, pool pump, fish pond pump, cooking (no gas), air conditioning units for heating & cooling the home (30000BTU total)) off of the PV and battery storage.

 

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So... I'm having a serious look at this...

Prompted, perhaps, by the recent long spells of cloudy/rainy weather.

Even being over-panelled I have had a day or two where I don't get to 100% on my batteries. I actually had a fright at my home where the Goodwe 5048 drew the batteries down below 20% (even though I have set the app to cut off at 20%... most nights don't draw much below 50%)... even to 10% before they cut the inverter off.

I'm assuming that this is the Pylon BMS overriding the Goodwe app???

At first I was horrified. Then I started thinking... with the rate and pace of improvements on all the tech (and with graphene hybrid battery tech on the horizon) we are probably going to be replacing current Lithium tech way before 10 years in any case.

Is this something we should really be concerned about.

I have just had the experience of installing the Deye 8.8 at my office... and contrasting the ease and flexibility of that kit with what I thought was pretty sweet tech (two years ago) on the Goodwe. If I could have my way (and cash was not a consideration) I'd be ripping out the Goodwe right now and replacing with a Deye!

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3 hours ago, PaulinNorthcliff said:

I have just had the experience of installing the Deye 8.8 at my office... and contrasting the ease and flexibility of that kit with what I thought was pretty sweet tech (two years ago) on the Goodwe. If I could have my way (and cash was not a consideration) I'd be ripping out the Goodwe right now and replacing with a Deye!

Hear hear. Although my crusade against Goodwe is getting pretty old now. In any case, the Pylon's BMS will cut off at around 11% SoC (89% DoD). In fact, you can't change the DoD value above 89% in the Goodwe PV Master app. Most nights I've run my max DoD to 60% (SoC of 40%). In a few cases I've had the SoC sit at 38% in the morning. It's as if it sometimes does tap a little from the battery past the set DoD point. Running the DoD close to 89% during the night will likely result in the odd case where the Pylon BMS will cut the inverter off.

Edited by gbyleveldt
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14 hours ago, hoohloc said:

I once drew from my Pylons till my inverters tripped. Even though the batteries are ok now, I'm stuck with a battery low warning in my logs, that I can not delete. 

InkedPylontech battery low warning_LI.jpg

In my experience Growatt has the shittiest possible comms with the batteries.

When I was experimenting with a Growatt SPF5000 a couple of weeks ago (before I say the light of Deye - sorry... poor impulse control) I arrived at the office one morning to find that the batteries had switched the inverter off and when I restarted the inverter reported the batteries at 4%!!!

I had a serious sense of humour failure. In fact I don't think the Pylons BMS would allow this at all!

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On 2020/11/24 at 12:44 PM, PaulinNorthcliff said:



Even being over-panelled I have had a day or two where I don't get to 100% on my batteries. I actually had a fright at my home where the Goodwe 5048 drew the batteries down below 20% (even though I have set the app to cut off at 20%... most nights don't draw much below 50%)... even to 10% before they cut the inverter off.

 

I can only assume you must have endured a municipal power loss too?
The GoodWe (of which I am no Evangelist) has 2x battery SOC cut off limits.
The 1st cut off is for when municipal power is present.
The 2nd is for when municipal power is not present.
The 2nd automatically gets set to 10% lower than the 1st, when you set the 1st.
If you set the 2nd to some other value, you must set it after setting the 1st value.

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1 minute ago, Power Me said:

I can only assume you must have endured a municipal power loss too?
The GoodWe (of which I am no Evangelist) has 2x battery SOC cut off limits.
The 1st cut off is for when municipal power is present.
The 2nd is for when municipal power is not present.
The 2nd automatically gets set to 10% lower than the 1st, when you set the 1st.
If you set the 2nd to some other value, you must set it after setting the 1st value.

I am off grid entirely.

So, thanks, that makes sense.

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20 hours ago, gbyleveldt said:

Hear hear. Although my crusade against Goodwe is getting pretty old now. In any case, the Pylon's BMS will cut off at around 11% SoC (89% DoD). In fact, you can't change the DoD value above 89% in the Goodwe PV Master app. Most nights I've run my max DoD to 60% (SoC of 40%). In a few cases I've had the SoC sit at 38% in the morning. It's as if it sometimes does tap a little from the battery past the set DoD point. Running the DoD close to 89% during the night will likely result in the odd case where the Pylon BMS will cut the inverter off.

Note that if the cut off is set at 40% SOC then the inverter will cut off when the battery SOC falls to 39%, the battery can then self discharge (and a little power goes to the GoodWe too)  to 38% by the next morning.

 

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9 minutes ago, PaulinNorthcliff said:

I am off grid entirely.

So, thanks, that makes sense.

Cool. As you can see from my plots above, I am essentially off grid too, except I have a prepaid meter connection as backup for those prolonged overcast days and for deep cold winter days when I heat more than my PV can supply.😉

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7 hours ago, PaulinNorthcliff said:

In my experience Growatt has the shittiest possible comms with the batteries.

When I was experimenting with a Growatt SPF5000 a couple of weeks ago (before I say the light of Deye - sorry... poor impulse control) I arrived at the office one morning to find that the batteries had switched the inverter off and when I restarted the inverter reported the batteries at 4%!!!

I had a serious sense of humour failure. In fact I don't think the Pylons BMS would allow this at all!

In my case I can not blame Growatt, we had power failure in the area and it took forever for city power to have it fixed. was still using two Pylons US2000 and they lasted longer than expected. Power went off around lunch time and not sure what time it came back at night but you can see that just after mid night, my inverters tripped. That is over 10hrs of running my house on batteries and solar, solar from lunch till around 17H00 and then 7 hours of batteries only. I have added two more now, so that should last me 14 hours, should the same issue pop up again 😂

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On 2020/10/15 at 8:48 AM, Hagu13 said:

I'm new to lithiums after recently replacing my lead acids. I have 2 x 3.5kW Pylontechs.

I'm looking for the sweet spot where I will get good battery life as well as maximum utilisation of the bank at night. I do understand the technology is new so there's no real data out there.

Currently I'm drawing down to 25% before switching to grid, but the Axpert powers itself from the batteries so this causes a further slow drop of a few %. Never goes below 20% which is my personal comfort zone limit. I'll likely modify this strategy for load shedding to leave a little more in should I need to go back to battery at 4am.

What's the feeling on this? Am I cycling too deep, or not maximizing ROI?

I prefer 60% DoD (40% state of charge = SoC) if you want long life. Else 25% SoC for typical 5 year. If you want to reserve power for load shedding, I do 60% SoC for load shifting and keep 40% (i.e.: Down to 20% SoC (its occasional) for load shedding.)

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On 2020/10/15 at 8:48 AM, Hagu13 said:

I'm looking for the sweet spot where I will get good battery life

From all the articles I have read, lithium batteries are happiest between 40% and 60% state of charge. For me, I keep mine between 30% and 90% state of charge most of the time. Once a month I will go as high as 98% just to erase any memory effect. 

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