Reactive power (Q)
Also known as: VAR, Volt-Ampere Reactive
Power that oscillates between the grid and the BESS plant without transferring net energy, but is essential for voltage support and grid stability. Grid codes require BESS plants to provide reactive power capability within a specified P-Q envelope at the point of connection. Controlled by the PCS.
In energy storage
The PCS generates or absorbs reactive power independently of the battery's SoC — even a fully discharged BESS can provide voltage support. Grid codes define the required reactive power capability as a P-Q diagram at the PoC, and the PPC continuously adjusts the PCS output to maintain voltage or power factor within the specified range.