When I responded to this post in the "Best Inverter" thread, I missed the fact you're running a BCS.
I also run in Self-Consumption Zero-Sell mode of operation.
(For those unfamiliar with running 3 or 4 XWs in parallel, an external transfer relay replaces the functionality of the AC1 60A relays inside the XWs. You also LOSE functionality of the AC2 input and only a single external AC source can be connected, Load Shave mode is not possible, and export (sell) limiting is only possible if a WattNode is added to the configuration. AC Out (Load) side of the XWs is not used with an external contactor such as the BCS.)
You mentioned the BMS running in open loop, so I am assuming you're running the XWs in Voltage Mode and not State of Charge Mode. If the MPPTs are throttling back it has to mean that the Grid Support voltage in the XWs and the Float Voltage in the MPPTs are too close to each other.
- You can test this. If you're only getting 100W from your array and it's sunny, go into Insight, the MPPT Configuration, Advanced, and force the mode to "BULK" and apply. If you immediately see power start to flow it's just a voltage setpoint issue. (Some might suggest a workaround to this is to extend the bulk charge time to maximum to prevent float - DO NOT do that; it's not necessary to achieve the goal and your batteries will object to the abuse.)
I encourage determining the measured DC Bus voltage calibration discrepancies of and between your 3 XW Pross. Observe DC voltages at rest - no solar/inverting/charging. I would wager they are all a few millivolts off from each other, and probably don't match the BMS. Compare the reported voltages to a quality trusted meter, or in best practice to the reported voltage of your BMS. Afterall, it's the battery BMS(s) that will shut you down when thresholds are reached. Use this voltage delta to determine a voltage offset for each individual XW Pro.
Hypothetical Example:
BMS Voltage = 52.00V (This is reference)
XW Pro #1 = 51.92 V (This is 0.08V lower than reference, meaning offset desired setpoint values by -0.08V)
XW Pro #2 = 51.86 V (This is 0.14V lower than reference, meaning offset desired setpoint values by -0.14V)
XW Pro #3 = 52.06 V (This is 0.06V higher that reference, meaning offset desired setpoint values by +0.06V)
This is particularly important for Grid Support Voltage because the unit displaying the highest measured voltage in this hypothetical scenario would end up biased the most amount of load inverting. You will know these offsets are right with the inverted load is observed to randomly fluctuate and bounce between all three inverters with each one handling a 1/3 of the load on average over time.
Once the inverter voltages are balanced you should also do both MPPTs. I wrote another thread for that explaining how it helps and how to do it:
When running more than one Schneider MPPT in Voltage Battery Control Mode, I've found through trial their internal DC bus voltage calibrations can be up to a few tenths off from each other. It seems all the Schneider gear has vague calibration practices for DC voltage except for the two inverters between each other. I've gotten into a habit of using a specific voltage offset for the MPPTs to ensure balanced functionality. With the chargers especially, it's most critical when the chargers are in float and the loads on the XWs are very near the PV capacity at that moment. At that...
Pasted from your prior thread with the above question:
For reference, I run in Voltage Mode, not in State of Charge Mode. Reason being for this is that mode functionality in the XW Pro works more like a binary switch in SoC mode that the nice linear transitions that Voltage Mode provides. Already mentioned my batteries are garbage, they are Lead-Acid so consider that with these setpoints for reference:
- My Grid Support Voltage: Primary XW Pro = 51.26V, Secondary XW Pro = 51.20V. (This maintains a balance of loads between the two due to slight deviation in measured DC between them.
- My MPPT Float Voltage: MPPT 1 = 53.42V, MPPT 2 = 53.31V, MPPT 3 = 53.57V, MPPT 4 = 53.5V. (Again - Deviations between individual device measured DC voltages requires these offsets for behaviors of all four MPPTs to identically match.)
So, you can see my delta between Float and Grid Support is greater than 2.0V. It's actually 2.05V-2.37V depending on devices. With those numbers I have no Grid-sourced waste of PV when there's PV available - even in Float.