PSOC charge levels during self consumption

richardimorserichardimorse Registered Users Posts: 98 ✭✭
What is the optimum SoC to maintain a LIFEPO4 battery at when conducting PSOC operations.
e.g. 50% allowing the battery to drop to 40% SoC and then recharging it to 60% SoC

The reason I ask is that in my country we have "Load Shedding" at random times, but likely to start at 5am, 7am, 9am or at 11am hence during a peak morning self consumption period, we may suddenly find that there was enough battery to last until 9am, but that 9am is also the time when the power utility cuts the power, so it may be wise to recharge the almost depleted battery for 30 minutes at 8:30am using utility power

Also 2nd question does anyone know what counts as a PSOC cycle vs a normal cycle, as batteries rated fo 7000 cycles can support 20,000 PSOC cycles, so estimating battery life becomes a problem, lets look at the following on a 22kW battery:

5am - start of self consumption battery level = 85% SoC
8:30am end Self consumption battery level = 25% SoC
8:30am start Inverter Charger Mains Charge for 30 mins until 33% SoC is reached
9:00am Load Shedding - system enters Island Mode and runs off the battery and solar only
During this period Solar charging takes place so power drain on the battery is not huge, however it might be a dark day
where solar output is 25% (or worse) normal yield, so then the drain on the battery is significant 
The battery fluctuates between charging and discharging depending upon clouds etc
remember between 9am and 11am, the system is still increasing solar output so PSOC charging / discharging likely
11:00am Utility Power restored battery level = 33% SoC due to solar charging

Q1 is, when preparing a system for a likely power cut and PSOC operation, what SoC is best to have the battery at in order to prolong battery life, the system can get by on a SoC of 33% and that would be the preferred level to charge the battery to (from 25% to 33%) that leaves plenty of room for the solar panels to charge the battery and enough to handle the load shedding demand from the household, is 33% SoC an optimum level for PSOC operations or is it preferable to have a higher SoC like 50%

Q2 is, lets say during the solar day, the system partially discharges the battery 3 times and partially charges the battery 3 times during this period the battery starts at 85% Soc, goes down to 25% SoC early in the morning (that would count as a Full Discharge Cycle), but during its charge cycle (lets say 9am to 5pm) it undergoes 3 PSOC charges and discharges on its way to 100% SoC at the end of the day, what is the impact of these PSOC mini cycles on the battery life, is there an equation or Rule of Thumb like 3 mini PSOC cycles = 1 normal cycle

Assume a Victron ESS is in use with both Fronius PV Inverter (AC Output Coupled) and Victron PV Charger (DC Coupled)
It is not intended to discharge too low then recharge deliberately, the scenario is just an example
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Comments

  • mike95490mike95490 Solar Expert Posts: 9,462 ✭✭✭✭✭
    If I was on grid, and had any concern about loosing the grid to either actual fires taking down transmission lines, or prophylactic shutdown to prevent a fire in bad weather, I would force the battery to 90%, and use the grid, keeping the battery full.

    I'm seeing between 30% and 90% of my normal harvest from the smoke obscuring the sun, and have had to run generator.  if you start an afternoon by selling to the grid, and it (the Grid) fails, leaving you with 40% in the battery ,  can you get thru the night comfortably???  After paying 10's of thousands for the system, I'd forgo selling $3 of electricity, to be able to make it thru the night in comfort with full batteries and the expectation of smokey conditions reducing the solar harvest.

    My town is looking at a likely FlexAlert rolling blackout Monday night, and then a PSPS shutdown Tue - Wed
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    I think Richard is somewhere down/around South Africa--So his issues is not (?) local fire issues or heat--But more of the issue with a less than robust grid at this time.

    Not sure about Richard's specific utility power issues, but as an example:

    https://af.reuters.com/article/investingNews/idAFKBN25O1XD-OZABS
    Eskom generates more than 90% of South Africa’s power but has struggled to meet demand for years because of faults at its coal-fired power stations. Some of these stations have not been properly maintained and two new ones have been hobbled by design flaws. 

    Ramaphosa has promised to break up Eskom to make it more efficient and has granted it a series of mammoth bailouts to stabilise its finances, but its problems have persisted.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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