Utility Solar Storage Duration Estimator

1. Enter rated battery energy

Use the battery’s stated energy capacity in kilowatt-hours.

2. Set the discharge target

Enter the constant power level the battery must deliver.

3. Apply usable depth of discharge

Exclude the portion of capacity that operating controls do not allow you to cycle.

4. Keep an operating reserve

Reserve a share of otherwise usable energy for reliability or control needs.

5. Account for efficiency

Use discharge efficiency when available; do not double-count losses already embedded in usable-energy ratings.

6. Review duration

The result is the approximate number of hours at constant output.

Delivered usable energy = Rated energy × depth of discharge × (1 − reserve) × efficiency
Discharge duration = Delivered usable energy ÷ Discharge power

All percentages are converted to decimals. The estimate assumes constant power and does not model power limits by state of charge, temperature, auxiliary loads, degradation, or control-system restrictions.

What the result means

The duration is the modeled time the battery can maintain the entered output before reaching its operating limit.

Actual dispatch duration can be shorter when auxiliary loads and dynamic power limits are included.

Given: 200,000 kWh rated energy, 50,000 kW discharge power, 90% depth of discharge, 10% reserve, and 88% discharge efficiency.

Calculation: Delivered usable energy = 200,000 × 0.90 × 0.90 × 0.88 = 142,560 kWh. Duration = 142,560 ÷ 50,000 = 2.85 hours.

Result: 2.85 hours.

The battery can sustain the selected power for roughly that long under the simplified assumptions.