I have full Givenergy system with 8.2 & 9.5 Li batteries, currently I export at a reduced 2kwh instead of its limit at 3kw, my thinking is it is less harsh on the drawdown of the batteries and easier on the inverter etc.
My question is, is this thinking flawed ? does it affect the full life of the batteries and system doing this every day ? or is it totally unaffected and more than capable at full capacity ?
You no doubt paid a lot of money for your system. I think you should use it to its maximum potential.
swede rates in batteries are basically expressed as a factor of the total capacity. Its called C Rate. Givenergy has a self imposed limit of 0.5C per battery (so basically half of whatever the battery size is, gives you what Givenergy deem as a safe power level (0.5 x 8.2kWh = 4.1kW)
2 things to note - the C rates stack, so thats per battery. In your case 8.2 + 9.5 = 17.7kWh x 0.5C = 8.85kW max Charge/ discharge rate.
As you'll be aware you are more limited by your inverter than any of those values.
hoggy Thanks for that hoggy, makes sense, and good to know even at max inverter limits, it is still massively below the battery limits.
I was expecting something like this, but thought it better to simply ask now, rather than be asking at a later date why I have basically abused my system to death prematurely ;-)
swede the only time I'd possibly think about it is if I had a single 8.2/9.5 on a Gen2 or 3 that sits outside in the sun in summer.
The BMS inside at full flow (80A/4kW) does seem to run hot so I'd possibly wind it back a bit in that instance but other than that I'd leave it alone.
As for throughput - personally it's there to be used. Mines had 17MWh shoved through it to date and seems to be holding up as expected - it'll be 4yo this year.
hoggy Perfect. thanks again.
Warranty is 10MWh per kWh of capacity i believe, so the 9.5 battery is 95MWh, unlikrly to be met in the 12yr warranty.
I don't know if it counts on full charge/discharge cycles, or on charge and discharge, either way you'll be warranted for 4750 or 9500 full cycles, at 1 a day that's either 13 or 26 yrs.
My 9.5 battery is just over 1.5 months old, 48 cycles with 377kWh charge, 377kWh discharge, so either 0.4% or 0.8% or warranted life.
As an aside, I tend to charge at a reduced rate (1200-1800W) as I use the battery to collect 'clipping', or slow charge on a long sunny day over several hours.
I believe the inverter is most efficient around the 1/3 rated capacity when discharging the battery, also it's better for heat management (unless you can see a good export rate window :-) )
hoggy Mines had 17MWh shoved through it to date
Is that actual throughput or just charge?
Seems very low if its just charge - I'm just at the one year point since install and "Battery Throughput Total" is 7.1MWh (3.6 charge, 3.5 discharge).
Vestas I've only a single 6.5kWh pack (biggest they did at the time) but yes it is total throughput. I take the metric with a pinch of salt - at 1434 cycles its pretty much doing a cycle per day over 4 years (which seems pretty close to yours) - but if you multiply cycles by capacity you get an entirely different value so not that confident in either value really!
Edit: if the weather improves I may force a full 100-4% Discharge and update the long running degradation thread, not updated that in a long while.
hoggy I'm just going by the figures GivTCP pulls from the inverter - which are presumably ultimately derived from the EM115 meter?
Vestas cycles come from the battery itself and throughput can be either from the inverter or the battery but I can't remember which one of those two GivTCP Uses (if they are different from one another - one may be raw DC in/out from the battery and the other may be measured after conversion to AC (or somewhere along the way))
Edit - Didn't you stick a smart shunt on yours at one point or am I mixing that up?
hoggy Not me. We have another meter in-line with the inverter but that's all. Installer said they had to fit it as the EM115 isn't certified so isn't compliant with MCS regs.
Edit - the GivTCP "total throughput" figure matches the "Batt Total Throughput" figure on the portal in the meter section so that'll doubtless be what GE are using in terms of "fair usage", regardless of whether its actually accurate or not...
hoggy I thought battery cycles were counting an full cycle of the battery from empty to full and then back again to empty.
Mine appears to be counting each full charge or each full discharge as a cycle, so its double what I thought it should be.
e.g. yesterday, battery was fully charged on solar (cycle=109), discharged in the evening on house load and grid export (cycle=110), then recharged overnight on cheap grid (cycle=111)
Same on the night of the 9th, 2 cycles, but on the 10th just one cycle (I think the overnight rates on Sunday night weren’t great so it didn’t discharge to empty).
It is what it is I guess, it’s there to be used after all. My 5.2 battery says its done 796 cycles and 7,300kWh of throughput in 17 months (about 4.6kWh per full charge and discharge, which is a little high with 80% DoD), about 1.5 cycles a day. In winter it was sometimes doing 2 cycles a day, in summer less so.
hoggy
FYI, on the beta GivTCP (reported version 2.4.194) with my AIO I get a report of HV_Battery_Cycles of 34.6 (also seen in the bcu raw data). This is unfeasibly low. Been in operation for approx 8-9 months and works hard.
geoffreycoan yes it doesn't seem to make sense for what i interpret a cycle would be (X to Y to X again)
Mine does roughly cycle once per day so on the face of it sounds about right at 1434 cycles right now, but if I convert that to throughput (1434 x 6.5) I get pretty much half what the throughput says it has output. I'll have to look into that some more I think, never really thought to question it.
Edit, nevermind, I'm being thick today, should be 6.5x2 for a cycle - still out though just not as much as I thought (about 0.5MWh)