Lithium battery usage





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  1. #1
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    Default Lithium battery usage

    Hi everyone


    I have recently installed a 10kWh Revov battery, a Sunsynk inverter and 3.3kw solar panels. I am trying the get the most of the battery and solar during the day, while still having enough battery backup left for load shedding and power failures when they happen.


    I'm managing the power as follows (currently working on Voltage settings, so a bit tricky):

    • From 4:00 to 9:00 the battery discharges to approximately 80%.
    • From 9:00 to 15:00 the battery charges back up to 90% on holds at that % using solar only.
    • From 15:00 to 17:00 the battery charges back to 100% using solar only.
    • From 17:00 to about 4:00 the battery stays at 100% using grid power.



    So my questions are:

    • While the battery holds at 90% during the day it is constantly charging from solar when excess solar is available and then feeding back into the load when the SoC goes over 90%, is this good for the battery?
    • Can those small charge discharge cycles be maintained for hopefully 10 years?



    Any other advice will be appreciated.
    Thank you.

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  3. #2
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    Default Re: Lithium battery usage

    Hi Rotunda,

    Quote Originally Posted by Rotidua View Post
    So my questions are:

    • While the battery holds at 90% during the day it is constantly charging from solar when excess solar is available and then feeding back into the load when the SoC goes over 90%, is this good for the battery?
    • Can those small charge discharge cycles be maintained for hopefully 10 years?
    Sounds good, keeping the batts at 90%. Yes it is good for the batts as lithiums don't want to be kept full charged all day.
    Yes, it is good for 10 years BUT, the last thing we want, is for batts to die of old age, never used.

    Question: Can you setup the SOC on the Sunsynk that it must not use batteries below that SOC i.e. say you set a SOC of 50%, the Sunsynk will not drain the batts below that SOC.

    I'm wondering if the 90% you mention, is maybe that setting?

    Reason I'm asking is that you should set a SOC of say 50%, and let the system manage that.
    Your array will work better.
    Which means Eskom bill will be lower.
    Political Correctness
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  4. #3
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    Default Re: Lithium battery usage

    Which specific inverter do you have? I am hunting for one and this brand is new to me.

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    Default Re: Lithium battery usage

    Quote Originally Posted by the_terrible_triplett View Post
    Hi Rotunda,



    Sounds good, keeping the batts at 90%. Yes it is good for the batts as lithiums don't want to be kept full charged all day.
    Yes, it is good for 10 years BUT, the last thing we want, is for batts to die of old age, never used.

    Question: Can you setup the SOC on the Sunsynk that it must not use batteries below that SOC i.e. say you set a SOC of 50%, the Sunsynk will not drain the batts below that SOC.

    I'm wondering if the 90% you mention, is maybe that setting?

    Reason I'm asking is that you should set a SOC of say 50%, and let the system manage that.
    Your array will work better.
    Which means Eskom bill will be lower.
    The 90% is my setting, played around with the voltage settings on Sunsynk's time of use program to get the battery to stop discharging at that percentage. Reason being that the main purpose of the system is to provide full backup when Eskom goes down, which is quite often. But I see your point, maybe I'll try a lower setting for a day or two and see how it goes.

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    Default Re: Lithium battery usage

    Quote Originally Posted by bobscratchit View Post
    Which specific inverter do you have? I am hunting for one and this brand is new to me.
    It is a Sunsynk 5kw hybrid inverter. They are also branded INGE, DEYE or Sol-Ark as far as I know but all the same inside. I am quite impressed with the functionality. You can set SoC, time of day to charge/discharge, grid shaving etc.

    Ellies sells the Sunsynk brand.

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    Default Re: Lithium battery usage

    Quote Originally Posted by Rotidua View Post
    You can set SoC ...
    The 90% is my setting, played around with the voltage settings on Sunsynk's time of use program to get the battery to stop discharging at that percentage.
    Just to make sure, you set the battery volts to get the SOC you want, like i.e. setting the volts to get the 90%?


    Quote Originally Posted by Rotidua View Post
    Reason being that the main purpose of the system is to provide full backup when Eskom goes down, which is quite often. But I see your point, maybe I'll try a lower setting for a day or two and see how it goes.
    Push the limits too, see where it does not want to go, rather than having to go through it when the power is off.
    Political Correctness
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  9. #7
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    Default Re: Lithium battery usage

    Ok. I spoke to one of there technical guys that i know. His responds:

    Thank you for the message. I'll do my best to assist. Just a precursor to this message, Revov and Sunsynk integration has been completed, and should only be a firmware update required by your installer and their supplier. Please check https://revov.co.za - click on the technical tab, then scroll down to Sunsynk and expand the tab.

    https://revov.co.za/technical/

    When running the Sunsynk on voltage, the SOC is typically an assumption of what's going into and out of the battery. Generally speaking, 54.4V is full (after balancing phase of 55.4 for atleast an hour a day) *remember the BMS is top balancing, and 50V (or 49.5V) is regarded as empty (although the BMS can go as low as 48-47V under small loads).

    Relating to BMS and cycles, the BMS measures the amount of energy going into and out of the BMS. The idea is, if you use 1/3rd of the capacity today, 1/3rd tomorrow and another third the day after (and then recharge), the BMS should count that as one full cycle. If you are doing micro cycles, the BMS will count them as energy entering and leaving and then calculate the cycles based on that. Remember that installers also have access to the software so they can physically see the amount of cycles done.

    I would suggest considering the firmware update, and have communication between the two.

  10. #8
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    Default Re: Lithium battery usage

    Quote Originally Posted by bobscratchit View Post
    Which specific inverter do you have? I am hunting for one and this brand is new to me.
    It's the new kid on the block in South Africa but in the States they using them for some time know. I spoke to someone yesterday standing looking at them and looking inside it. The guys running 2 or more are going for this unit now when they replace the old expert units.
    Last edited by Gerlach; 2020/06/26 at 04:59 PM.

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    Default Re: Lithium battery usage

    Quote Originally Posted by the_terrible_triplett View Post
    Just to make sure, you set the battery volts to get the SOC you want, like i.e. setting the volts to get the 90%?
    Yes, I guess the inverter estimates the SOC, but that is what I do.

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  13. #10
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    Default Re: Lithium battery usage

    Quote Originally Posted by Gerlach View Post
    Ok. I spoke to one of there technical guys that i know. His responds:

    Thank you for the message. I'll do my best to assist. Just a precursor to this message, Revov and Sunsynk integration has been completed, and should only be a firmware update required by your installer and their supplier. Please check https://revov.co.za - click on the technical tab, then scroll down to Sunsynk and expand the tab.

    https://revov.co.za/technical/

    When running the Sunsynk on voltage, the SOC is typically an assumption of what's going into and out of the battery. Generally speaking, 54.4V is full (after balancing phase of 55.4 for atleast an hour a day) *remember the BMS is top balancing, and 50V (or 49.5V) is regarded as empty (although the BMS can go as low as 48-47V under small loads).

    Relating to BMS and cycles, the BMS measures the amount of energy going into and out of the BMS. The idea is, if you use 1/3rd of the capacity today, 1/3rd tomorrow and another third the day after (and then recharge), the BMS should count that as one full cycle. If you are doing micro cycles, the BMS will count them as energy entering and leaving and then calculate the cycles based on that. Remember that installers also have access to the software so they can physically see the amount of cycles done.

    I would suggest considering the firmware update, and have communication between the two.
    Thank you that helps a lot. I will get the installer to upgrade the firmware.

    Just a follow up question please. If I use the time of use settings, volts to 54.4 from 17:00 to 4:00 to keep the batteries full. Will the BMS then go into the balancing phase automatically during this time?

  14. #11
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    Default Re: Lithium battery usage

    Quote Originally Posted by Rotidua View Post
    Thank you that helps a lot. I will get the installer to upgrade the firmware.

    Just a follow up question please. If I use the time of use settings, volts to 54.4 from 17:00 to 4:00 to keep the batteries full. Will the BMS then go into the balancing phase automatically during this time?
    You can give Dawie a call. His number is on there web page. He will give more info how the BYD bms work on this units.

  15. #12
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    Default Re: Lithium battery usage

    The fact that you can set charge/ discharge times and the source of charge (solar, grid) makes the sunsync a very nice inverter.

    The goodwe cannot do the above, probably it's greatest downfall...BUT, the goodwe integrates seamlessly with the std battery types,so that's a plus!

    FYI, my pylontechs fluctuate between 90-100 % doc all day..in the last 4 ,months it only shows 8 cycles.
    Last edited by NewLandy; 2020/06/26 at 09:34 PM.

  16. #13
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    Default Re: Lithium battery usage

    My opinion:
    - AC only hold batteries to 30% minimum charge to get the max from your solar.
    - If loadshedding starts, you may be without power on the first day (like all your neighbours), but can then set it to 70-80% for the next days.
    - Set back to 30% if the loadshedding is gone for a few days.

    This way you get the max savings while being able to mitigate from the 2nd loadshedding in your area.

    Too many people waste and lose out on the free energy from the sun because they are afraid of experiencing ANY outage. They should then have bought batteries and an inverter only.

    If you had 24kWh+ of battery storage, you could get the best of both (backup and sun power)...
    Riaan

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    Default Re: Lithium battery usage

    Quote Originally Posted by Monkey-D View Post
    My opinion:
    - AC only hold batteries to 30% minimum charge to get the max from your solar.
    - If loadshedding starts, you may be without power on the first day (like all your neighbours), but can then set it to 70-80% for the next days.
    - Set back to 30% if the loadshedding is gone for a few days.

    This way you get the max savings while being able to mitigate from the 2nd loadshedding in your area.

    Too many people waste and lose out on the free energy from the sun because they are afraid of experiencing ANY outage. They should then have bought batteries and an inverter only.

    If you had 24kWh+ of battery storage, you could get the best of both (backup and sun power)...
    Oh... And add a schedule on your inverter to charge the batteries to 100% once a week on some evening (when the solar yield dropped). This will make sure all the Lithium cells are balanced and your SoC reading is actually right.
    Riaan

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    2019 Toyota Hilux Extracab 2.8GD6 4x4
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  19. #15
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    Default Re: Lithium battery usage

    If it wasn't for the 20 days of LS per year we would also have followed the rest of the world and fitted grid tied instead of back up/hybrid systems at a huge cost.

    Using sun as best we can is the efficiencient way using PV.

  20. #16
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    Default Re: Lithium battery usage

    We have had as much if not longer spells without power due to network faults or sub trips than loadshedding, so make that 40 days a year. One of them ran for 4 days continuous.

    We just got tired of running noisy generators.

  21. #17
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    Default Re: Lithium battery usage

    Quote Originally Posted by faniedup View Post
    We have had as much if not longer spells without power due to network faults or sub trips than loadshedding, so make that 40 days a year. One of them ran for 4 days continuous.

    We just got tired of running noisy generators.
    Yes this can be a problem in certain areas. During office hours we had only 37 hours since 25 Sep which I take as LS and no power failures . This is based on the hours we had the genny running.

    In over 20 years at home we had only 1 longish power failure and that was 30 hours when a mini sub burnt out. Overall a very good record. Over a few weeks that we got hit with cable theft at one substation after each other we were off for about 4 to 5 hours most times.
    Last edited by ekkekan; 2020/06/27 at 09:06 PM.

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