Calculate SimplyHow to use
Start with the worked example to understand the inputs, then replace every relevant value with your own figures. Use one currency and consistent units throughout. Add or remove rows where offered; irrelevant conditional fields are disabled and excluded. Select Calculate after editing. Review negative values and any “not determined” result rather than assuming every scenario must be profitable. Download a text summary or print the page for your records.
Formula and assumptions
Add every AC appliance with running watts, daily hours, quantity and total startup watts. Daily Wh is power times hours; inverter sizing uses simultaneous running power, not daily Wh. The largest-group surge option starts all units of one entered row together while other rows are already running; all-start adds every startup load. Battery Wh includes autonomy, discharge limit, inverter loss and battery discharge efficiency, then divides by system voltage for Ah. Solar power covers an average operating day at your entered sun hours and derating; it does not promise recovery after several sunless days. Confirm surge duration, battery current/BMS, temperature effects, wiring and protective equipment with an installer.
daily Wh = Σ(quantity × watts × hours); nominal battery Wh = daily Wh × autonomy / (inverter efficiency × depth of discharge × discharge efficiency); Ah = Wh / voltage
Worked example
Example only: replace rates with your own figures.
Inputs
- Nominal battery system voltage: 48 V
- Days of battery autonomy: 2
- Usable depth of discharge: 80 %
- Inverter efficiency: 90 %
- Battery discharge efficiency: 95 %
- Daily peak sun hours: 4
- Solar production derating factor: 75 %
- Inverter continuous-power headroom: 20 %
- Starting scenario: largest
| Appliance quantity | Running power per appliance | Run hours per day | Total startup watts per appliance |
|---|---|---|---|
| 1 | 100 | 8 | 300 |
- Daily AC energy: 800 Wh
- Nominal battery capacity: 2339.18 Wh
- Nominal battery capacity in amp-hours: 48.7329 Ah
- Inverter continuous rating target: 120 W
- Inverter surge rating target: 300 W
- Indicative solar array power: 311.891 W
- Continuous battery current: 2.31481 A
Frequently asked questions
Are the example rates current market prices?
No. Example inputs demonstrate arithmetic, not live prices, tax rules, salary surveys or sponsor benchmarks. Enter a dated quote, bill, manufacturer specification or verified fee schedule that applies to your situation. Compare a conservative and an optimistic scenario separately.
Why is a result not determined?
Some calculations have no meaningful value when a denominator is zero, savings are non-positive, a target cannot be reached or your data do not bracket an intersection. The tool leaves that result undetermined instead of displaying infinity or inventing a recommendation. Check the method and your inputs.
Sources
Sources explain the underlying concepts, not an endorsement of this website or its results. Method review: 20 October 2026.