question

I would be checking to see if the fronius grid tie is shutting down when the batteries are FULL and the grid or Gen is disconnected, if it is NOT de rating correctly then the battery voltage will rise. you need to make sure frequency shift is working correctly and that the correct assistants have been installed

It could also be that one cell in the BYD battery is going high, this can also cause a high voltage alarm

Base on around 250kWh of BYD in LV installed, we are facing lot of high voltage warning especialy in the first 10 cycles of a new set of batteries. With a AC coupled inverter we stop it at 90% of SOC and start it again under 85% of SOC because the frecency shifting id not a real time process and the BMS can generate a warning or alarm. We always keep enabled the MPPT set.

@karlheinzhaller

Not uncommon for high voltage alarms. And they sometimes do re occur especially after a deeper discharge. It settles down again.

There is a section in the manual that covers it.

On this installation we are not using a fronius inverter and instead using a Solis on the system output (metered of course). As it is grid tied we won't get frequency shifting and instead expect any surplus to flow to the grid supply which it is doing. The issue is the power is still charging at a low rate to the battery resulting in high voltage alarms. We have high voltage alarms frequently on new systems but beyond this the system shuts down in high voltage protection mode.

New batteries can be quite poorly balanced when they arrive from the factory. I have seen this with many different manufacturers. Most LiFePO batteries only enable the cell balancing right at the end of the charge cycle because the cell voltage curve is so flat for this chemistry. Normally one would simply "keep batteries charged" for a few days for the battery to balance, but since you are off grid, you probably can't do this.

Persist with the lower max voltage for a few more weeks in my opinion. Also keep an eye on the min and max cell voltages when the battery is close to 100%. You should see them start to converge. When they are within 0.02V or so, then try pushing the max pack voltage up again.