Renewable PPA Storage Duration Estimator

1. Enter usable storage energy
Use the energy capacity available for cycling, not the battery’s gross cell capacity unless they are the same.

2. Enter discharge power
Provide the maximum output power expected under the agreement or operating plan.

3. Set the reserve level
Enter the minimum state-of-charge reserve that should remain unavailable for routine discharge.

4. Apply discharge efficiency
Use the expected conversion efficiency from stored energy to delivered AC energy.

5. Review duration
The result shows how many hours rated power can be sustained under these assumptions.

Energy after reserve = Storage energy × (1 − Reserve fraction) Delivered usable energy = Energy after reserve × Discharge efficiency Duration (hours) = Delivered usable energy (MWh) ÷ Discharge power (MW)

The calculation assumes constant discharge at the entered power and no charging during the discharge interval.

What the result means

Duration indicates the continuous time the system can supply rated power before reaching the selected reserve.

Actual dispatch duration may be shorter due to degradation, temperature, auxiliary loads, inverter limits, or operating controls.

Given: 100 MWh usable storage, 25 MW discharge power, 10% reserve, and 94% discharge efficiency.

Calculation: Energy after reserve = 100 × 0.90 = 90 MWh. Delivered energy = 90 × 0.94 = 84.6 MWh. Duration = 84.6 ÷ 25 = 3.384 hours.

Result: Effective discharge duration is about 3.38 hours at 25 MW.