How the calculator works
Transparent math aligned with public manufacturer sizing guides (EcoFlow / Bluetti-style). Planning tool — not a lab measurement.
WattNeeds defaults: inverter efficiency η=0.90, DoD=0.90, buffer=0.15.
One-liner: nameplateWh = (whPerDay × days × 1.15) / (0.90 × 0.90).
Always re-check continuous watts and surge against the station inverter.
Steps
- Device daily energy — Wh/day if provided, else watts × hours/day.
- Sum — total Wh per day delivered to loads.
- × days of autonomy — energy needed before a reliable recharge.
- ÷ inverter efficiency — battery must supply more than the AC outlet delivers (default 0.90).
- × (1 + buffer) — planning headroom (default 15%).
- ÷ DoD — convert usable energy to nameplate Wh (default 0.90).
Combined formula
nameplateWh = (whPerDay × days × (1 + buffer)) / (dod × inverterEfficiency)
What we do not model (MVP)
- Cold-weather capacity derate or battery aging
- Solar / vehicle recharge credit (autonomy assumes no recharge)
- Inverter idle / vampire draw
Inverter continuous and surge watts are a separate check from Wh capacity — a station can have enough Wh and still fail to start a microwave.