jsmetalcraft said:
What is React Mode:
1.Power Factor
2.React Power
3.QU Wave
4.QP Wave


WrenchLight responded with:

1. Power factor sells back power at a constant power factor.
2. Reactive power sells back power at a certain percentage of reactive vs. real power.
3. QU wave changes the power factor depending on the grid voltage and the related settings V1 through V4 and Q1 through Q4. 
   This is also known as Volt-VAR mode. It's for grid stability. 
   When the grid voltage goes low, the inverter sells back power with the current lagging the voltage, also known as injecting VARs.
   When the grid voltage goes high, it absorbs VARs (current leads the voltage). This is the desired setting for most places.
4. QP wave is also known as Watt-VAR. The inverter adjusts the power factor depending on how much power the inverter is drawing or selling back.
   The settings P1, P2, P3, Q1, Q2, Q3, P1', P2', P3', Q1', Q2', and Q3' apply here.

https://diysolarforum.com/threads/megarevo-rxlna-discussion.36290/post-973350