Black Start Capability Fronius Gen24/BYD HVM

Running 14 7kW solar/16.6kWh storage systems remotely using Fronius Gen24 inverters and BYD BatteryBox HVM batteries.

When running in backup mode (no grid power available), Fronius defers to BYD minimum SOC of 5%, at which point, the battery physically disconnects (trips built in breaker) requiring manual intervention to restore battery power. Have confirmed this behaviour. According to BYD documentation, the entire system requires the physical reset and return of grid power for the system to return to service. Have not confirmed this behaviour, as not present while grid power was not available. Therefore, to avoid the systems going offline during an extended outage, we must limit the backup circuit load. Not always possible over such a large area with multiple systems.

I have found references for both Gen24 and BYD BatteryBox stating they are capable of providing black start capability, but cannot find any documentation on how to implement it. My expectation of black start is the system can recover on it’s own after in backup mode, solar power is not available and the battery reaches a pre-defined minimum SOC, and then the solar array is illuminated.

Anyone have experience implementing black start on this configuration?

I might be wrong, but I believe you need to set the minimum battery state of charge to be higher than 5%. When the battery SOC drops to 5%, it must shut off completely, or risk allowing the voltage to drop too low, damaging the cells.

If you set the minimum battery SOC in backup mode to 10 or 15%, the breaker will not activate. It will remain idle (standby mode) and be able to wake up and start charging once enough solar power is available. You just have to ensure the backup loads are not too high or it will not be able to recharge the battery and power the loads at the same time. Recommended to switch off the main backup switch until the system has recovered and restarted.

My problem is both the installers and myself are unfamiliar with BYD settings and can find no documentation.

The Fronius Gen24 settings allow for setting minimum SOC, but, when the system enters backup mode (no grid power), the system defers to the BYD minimum SOC, which appears to be hard coded (or possibly hardwired) at 5%. I cannot find any settings in the BYD device to set a soft coded minimum SOC. Once that 5% is reached, the system cannot recover without manual reconfiguration.

This is the only mention of black start capibility in the BYD HVM Operating Manual:
" 7.5. Black Start Function
The battery system could support the black start function of compatible inverters. The ways to
trigger this function are different when the battery systems are operated with different inverters."

Hmmm, some hybrid inverters have digital outputs and controls that can be used to operate external contactors so you could disconnect the backup loads before the battery reaches 5%.
The only problem is it seems the Fronius GEN24 can only activate the digital outputs based on loads and excess PV, not battery SOC. :thinking:

I have found some more information from Fronius’s tech support. Unfortunately, the black start function in backup mode is a manual operation (reset the breaker). You cannot override this using the inverter digital outputs.

However, Fronius is working on a solution to improve this and make it fully automatic. It will be available via a firmware update, but no timeline was available as to when this will happen. I’m guessing it might be sometime this year.

Appreciate the effort and information. I have received a similar response from BYD in relation to ongoing effort with Fronius.

Until then, we have to advise the occupants to reduce loads on backup circuits in the event of a long term grid outage. Also have to be sure they are aware of procedure to reset the system.

Any chance Fronius commented on requirement for grid recovery before the system can return to service in case of a hard shutdown as a result of exceeding the 5% minimum SOC? We may have to test that. Resetting the battery breaker is simple, but not much use if we cannot use solar during the day until grid power returns.