Off-Grid Battery Bank Sizing
Required nameplate capacity (Wh and Ah) from daily load, days of autonomy, depth-of-discharge, and round-trip efficiency.
Example
You enter
- Daily load (Wh/day) 2400
- Days of autonomy 3
- Depth-of-discharge limit (0-1; 0.5 lead-acid / 0.8 LFP) 0.5
- System DC voltage 12
- Round-trip efficiency (0-1; 0.85 lead-acid / 0.95 LFP) 0.85
- Temperature derate (0-1; 1.0 if none) 1
You get
- Usable energy required (Wh) 7200
- Nameplate capacity (Wh) 16941
- Nameplate capacity (Ah) 1412
Details, formula, and sources
Required nameplate capacity (Wh and Ah) from daily load, days of autonomy, depth-of-discharge, and round-trip efficiency, per IEEE 1013 / 1561.
usable_Wh = daily_Wh * days_autonomy; nameplate_Wh = usable_Wh / (DoD * round_trip_efficiency * temperature_derate); nameplate_Ah = nameplate_Wh / system_V.
IEEE 1013 (Sizing Lead-Acid Batteries for Stand-Alone PV Systems); IEEE 1561 (PV / Hybrid Power Systems).
standards.ieee.org for IEEE 1013 bibliographic data.
Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
Field names used by the API: daily_load_wh, days_autonomy, dod_limit, system_voltage_v, round_trip_efficiency, temperature_derate, usable_wh, nameplate_wh, nameplate_ah
- Usable depth-of-discharge about 0.50 for flooded lead-acid; about 0.80 for LFPIEEE 1013; the chemistry datasheet governs
- Round-trip efficiency about 0.85 lead-acid; about 0.95 LFPmanufacturer datasheet