Help CenterInverters
Sizing the inverter — kVA vs kW and power factor
An inverter is always rated in kVA (apparent power), not kW (real power). For purely resistive loads (lighting, heating elements) the two are close, but for inductive loads (motors, AC units) the power factor (PF) widens the gap.
S [kVA] = P [kW] ÷ PFTypical PF 0.8 for a residential mix with motors · PF = 1.0 for pure resistive loads
S_inverter ≥ P_continuous × 1.25Minimum 25% safety margin above actual continuous power consumption
| Continuous power | Recommended inverter | Typical use |
|---|---|---|
| < 1 kW | 1.5–2 kVA | Small household, lighting + electronics |
| 1–2.5 kW | 3–3.5 kVA | Average household with a fridge |
| 2.5–4 kW | 5 kVA | Household with AC unit or pump |
| 4–6 kW | 6–8 kVA | Villa, small business |
The kVA rating on the datasheet does not account for startup peaks. A 3 kVA inverter may handle 3 kW continuous but trip on an AC unit's 900 W startup (4.5 kW peak). Always check each appliance's surge factor.
SolarDim Pro computes the required kVA from continuous power AND the highest startup peak in the appliance table, not just the sum of rated powers.
Common mistakes
- Adding up rated kW and buying an inverter of the same value in kVA
- Ignoring power factor for a household with an AC unit, pump, or motor
- Leaving no margin for future appliance additions