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Community Solar Storage Duration Estimator

This calculator estimates how long a battery paired with a community solar project can sustain a selected discharge power. It starts with rated energy, then accounts for usable depth of discharge, round-trip or discharge efficiency, and an operating reserve.

The result supports early storage configuration, peak-shaving, firming, and backup-duration discussions. It also reports usable energy before and after efficiency losses so users can see which assumption is limiting the discharge window.

Battery energy and discharge assumptions

kWh
kW
%
%
%
Result
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Estimated continuous discharge duration
Energy after depth-of-discharge limit—
Energy after reserve—
Delivered usable energy—
Energy-to-power ratio—

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: 8,000 kWh rated energy, 2,000 kW discharge power, 90% depth of discharge, 10% reserve, and 90% discharge efficiency.

Calculation: Delivered usable energy = 8,000 × 0.90 × 0.90 × 0.90 = 5,832 kWh. Duration = 5,832 ÷ 2,000 = 2.92 hours.

Result: 2.92 hours.

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

Is this the same as the battery’s marketed duration?

Not necessarily. Marketed duration often uses nominal energy divided by rated power, while this calculation applies operating and efficiency limits.

Should reserve be taken from rated or usable energy?

Here, reserve is applied after the depth-of-discharge limit. Keep that convention consistent when comparing scenarios.

Can discharge power exceed the battery rating?

The calculator accepts the value mathematically, but the physical system must support it. Check the inverter and battery power limits.

Does round-trip efficiency belong here?

Discharge efficiency is preferable for a discharge-only estimate. If only round-trip efficiency is known, using it directly is conservative but not exact.

How do degradation and temperature affect duration?

Both can reduce available energy and power. Represent them by lowering rated energy, usable depth, or efficiency based on project-specific data.