Separate instantaneous power from stored energy before estimating runtime.
Begin with the load record
Watts describe the rate of energy use. Watt-hours describe energy over a duration. A 100-watt load operating for five hours uses 500 Wh, which is 0.5 kWh. Duty-cycled devices need a representative average load; their nameplate maximum is not automatically their continuous consumption.
Model usable battery energy
A 1,000 Wh battery with an 85% usable conversion assumption provides 850 Wh in the simplified model. At a steady 100-watt load, that corresponds to 8.5 hours. Record what the efficiency allowance includes. Do not apply another loss factor for the same conversion stage or confuse energy capacity with maximum inverter output.
Check the peak load separately
A runtime estimate does not establish that the inverter or generator can start a motor. Compare running watts with incremental starting surge and the equipment’s surge duration rating. Adding the complete starting load to a running total can double count the portion already included. Keep each device’s operating and starting specifications in the record.
Use equipment-specific evidence
Temperature, battery age, reserve limits, conversion losses and load variation can change actual runtime. The worksheet estimates the supplied relationship; it does not design an electrical installation. Verify the relevant equipment documentation before connecting loads or choosing protective devices. Save measured consumption so later estimates can use actual operating data.
Review record
| Source | Convention | Result | Next check |
|---|---|---|---|
| Record the measured or supplied values. | State units, period and inclusions. | Retain the original calculation. | Name the person and evidence needed before use. |
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Keep the displayed formula, input units and model scope with the result. Corrections or questions can be sent through the request section on this page.
Content updated: October 11, 2026