Battery life and frequent charging and discharging during low solar outpu

[wazzutgm]

Hi Fox Community experts,

I recently got my fox ESS battery installed (EQ4800, ~40kwh, H3-10.0 Smart 10KW 3-phase) along with 13KW solar. The inverter is set to mostly Self-Use mode. When the solar production is low (specially in the mornings and evenings), the battery will switch between charging and discharging depending on the load I consume. For e.g. early morning, if my solar production is at 1KW, the battery will start charging, but the moment i turn on the cook top, which consumes around 2kw, the battery will switch to discharge. The moment i turn off the cook top, it switches back to charging. This cycle repeats multiple times depending on the appliances that i turn off/on (hot water, refrigerator etc.) until the solar production ramps up and produces enough power for my consumption. I do understand this behaviour since this might be expected in a self-use mode.

My question is, since the battery warranty is set to ~6000 cycles, does each of these switching between charging and discharging count as 1 cycle and reduce the expected battery life time period?

secondly, is there anyway, I could set the inverter to only discharge the battery as required, but not charge or vice versa? for e.g. in the morning, i don't want the battery to charge during low solar production, but augment the solar production as required to meet the load to avoid buying from the grid. For e.g. if the solar production is 1 kw and my load is 2kw, i want the battery to supply 1 kw. Once my load is turned off, i want the battery to stop discharging, but at the same time, not to charge from the 1kw produced from the solar, I want that to go to the grid. I have explored the forced discharge option, but that only allows me to discharge at a constant power and not dynamic as needed by my home load.

Your expert advice is highly appreciated.

[Dave Foster]

That is the normal mode of operation for Self Use with a hybrid inverter, the PV is prioritised to House Load, Battery, and any excess to export.

The charge / discharge does count towards your cycles where a cycle is full to empty and back to full.
In this case if you are taking (say) 1kW for 5 minutes that is only 83 watt/hours and with a 40kW stack it would take 480 hours like that before you would use 1 cycle - This is really how the battery is meant to be used to avoid taking (expensive) power from the grid.

If you were to set your workmode to Feed-in First the priority is House Load, Export (any excess above your inverter max AC output or an export limit if set would go to battery). In effect you would use the battery to fill in if the PV is not strong enough but the battery wouldn't charge afterwards - From what you have said I think that would better meet your requirement.

On the battery cycles, the batteries will very likely still be performing well after 6000 cycles, over time with use and ageing the capacity of the battery will gradually fall off - hopefully you should have many more years of use after that, it's just that you won't be getting the 40kWh storage.
Most manufacturers now use 'energy throughput' in their warranty as that takes into account those gradual changes in the battery capacity for each cycle and they will quote a nominal energy i.e. 70% of original that will still be maintained throughout that period of use.

[wazzutgm]

Thank you very much Dave for your detailed explanation, that clarifies a lot!