• Battery Capacity (MWh) → How much energy is stored
• PCS/Inverter Rating (MVA) → How much power can flow at a time

Example:

• Battery = 2 MWh
• PCS = 1 MVA

So maximum charging/discharging power is about 1 MW, giving:

• 2 hours backup at full load

The inverter shares its capacity between:

• Active Power (P) → Actual charging/discharging power
• Reactive Power (Q) → Voltage & grid support

Their limit is:

P² + Q² = S²

If the inverter provides more reactive power, available active power reduces.

Example:

• 1 MW charging → 2 hours charging time
• 0.8 MW charging + 0.6 MVAr support → charging time increases to 2.5 hours

Reactive power does not consume battery energy directly. It is generated by the inverter for grid stability and voltage support.

That’s why modern BESS can:

• Store energy
• Support voltage
• Improve power factor
• Work like a STATCOM
• Support weak grids simultaneously