What this calculator does
Solar arrays are sized from energy, not from power. This calculator turns a list of appliances and how long each runs per day into the daily energy demand in watt-hours and kilowatt-hours, which is the input every other sizing tool in this group needs.
How to use it
- Fill in watts and daily hours for each of the six rows, leaving unused rows blank.
- Refrigerators and freezers cycle, so estimate their compressor running hours rather than 24.
- The total is a daily average; multiply by 30 for a monthly estimate.
- Check the result against your utility bills, which are the best reality check available.
Governing formula
E_day = Σ (W_i × h_i) Where:
-
W_i= Rated power of appliance i [W] -
h_i= Running hours of appliance i per day [h]
Derived Equations:
E_month = E_day × 30 Worked example — Lighting, refrigeration, washing and a laptop
The figures below were produced by running this page's own engine with the example inputs (Row 1 — watts (W), Row 1 — hours per day (h), Row 2 — watts (W), Row 2 — hours per day (h), Row 3 — watts (W), Row 3 — hours per day (h), Row 4 — watts (W), Row 4 — hours per day (h), Row 5 — watts (W), Row 5 — hours per day (h), Row 6 — watts (W), Row 6 — hours per day (h)). If the calculator returns something different for the same numbers, that is a bug, not a rounding difference.
| Daily energy demand | 7440 Wh |
|---|---|
| Daily energy demand | 7.44 kWh |
| Average hours of use | 4.38 h |
| Next step | Daily energy 7.44 kWh (7440 Wh). Use this as the input to the array, battery, inverter and charge-controller sizers on this page group. |
- Lighting contributes 4,000 Wh and the refrigerator 1,200 Wh.
- The washing machine and laptop add 2,000 Wh and 240 Wh.
- The daily total is around 7.4 kWh, which is the input to the array sizer.
Assumptions & limitations
Engineering calculation. A simple energy ledger: six appliance rows of watts and daily hours. It does not include seasonal variation, duty cycles or standby loads you do not list.
- Duty cycles, variable compressor loads and standby power are not modelled — real consumption is often 10–20 % higher.
- No seasonal or weekday/weekend variation, which matters for battery sizing.
- Nameplate watts overstate real power for appliances with power factor correction.
- The schedule is fixed at six load rows by the calculation model. A larger audit must be split across separate runs, and totals from separate runs are not added together for you.
- Connected power is the sum of the listed ratings. It assumes every load runs at once, which is rarely true, and it is not a measured peak demand.
This tool supports professional engineering work; it does not replace a sealed design. Confirm every result against the applicable standard and a licensed engineer before it is built.
References & standards
- NREL PVWatts — system loss assumptions used for the derating default.
- Australian Government — off-grid solar sizing guidance.