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Solar battery sizing: convert kWh to Ah at your voltage

Size storage from appliance schedules and understand kW, kWh, Ah, voltage, DoD and efficiency.

Edited by SolarKrasibUpdated 28 September 2026Read4 min

The answer first

Ah alone cannot describe stored energy: battery-bank voltage is also needed. Nameplate kWh = V × Ah ÷ 1,000. Apply DoD and efficiency to estimate usable delivered energy. Battery and inverter kW ratings must also meet simultaneous loads.

100 Ah at different voltages

Multiplying nameplate values, 100 Ah at 12.8 V equals 1.28 kWh, while 100 Ah at 51.2 V equals 5.12 kWh. At an assumed 80% DoD and 95% discharge efficiency, the 51.2 V bank delivers approximately 3.89 kWh. These examples must be replaced with actual model specifications.

Start with loads and operating times

Sum watts × quantity × hours ÷ 1,000 for each appliance, adjusting duty cycle for cycling loads such as air conditioning. Do not substitute BTU for electrical watts or count losses twice. The appliance calculator supports minute-level schedules and overnight operation.

Enough energy does not guarantee backup

Check continuous power, starting surges, BMS/inverter compatibility and grid-isolation circuits. “Full day” in the calculator refers to one schedule under the selected sunlight, not rainy-season autonomy. Use the system simulator to explore outage behavior.

Supporting sources

  1. Victron — Battery system design ↗
  2. European Commission — PVGIS ↗
  3. U.S. DOE — Solar and Resilience Basics (general principles) ↗

General information for questions and preliminary estimates. Site and contract conditions need individual verification. International sources explain principles, not Thai law.

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