Get a first-pass solar sizing estimate — panel wattage and battery bank in watt-hours and amp-hours from daily use, sun hours, autonomy and system voltage. Runs entirely in your browser — your numbers never leave this device.
| Component | Size | Basis |
|---|---|---|
| Solar array | 888.89 W | 3000 Wh ÷ (4.5 h × 0.75 derate) |
| Battery bank | 7500 Wh | 3000 Wh × 2 days ÷ 0.8 DoD |
| Battery bank | 312.5 Ah | 7500 Wh ÷ 24 V |
This is a first-pass sizing estimate, not a system design: it does not size charge controllers, inverters, cabling or protection, and it is not a code-compliance check. Have a qualified installer verify a real installation.
Off-grid sizing starts from energy, not power: how many watt-hours the loads consume in a day. The array must replace that energy during the available peak sun hours — the equivalent hours of full-strength sun your location and season deliver — after system losses, so panel watts = daily Wh ÷ (sun hours × derate). The default derate of 0.75 bundles the usual losses: inverter efficiency, cable drop, panel temperature and soiling. The battery bank is sized the other way, from storage: daily Wh multiplied by the autonomy days you want to survive without sun, grossed up by the depth of discharge you are willing to use — 0.5 for lead-acid longevity, around 0.8 for lithium — and converted to amp-hours at your system voltage.
Treat the output as a first-pass estimate for comparing options and budgets, not a system design. It does not size the charge controller or inverter (both are chosen on power and surge, not energy), cable gauges, fusing or earthing, and it uses a single sun-hours figure where a real design uses the worst month's figure for your location and panel tilt. Nothing here is a code-compliance check or an installation specification — have a qualified installer verify any system before it is built, and use the Electricity Cost Calculator to value the daily energy figure you start from.
The day's total solar energy expressed as hours of full 1,000 W/m² sun — a location receiving 4.5 kWh/m² in a day has 4.5 peak sun hours, however the daylight was actually spread. Use the figure for your worst month, not the annual average, if the system must work year-round; solar atlases and PVGIS publish it by location and tilt.
It bundles the losses between the panel's nameplate and usable stored energy: temperature (panels produce less when hot), soiling, cable losses, charge-controller and inverter efficiency. 0.75 is the standard planning default; a DC-only system with short cables can justify 0.8–0.85, while hot climates and long runs argue for 0.7. It is a fraction, so enter 0.75, not 75.
The fraction of the bank you routinely use. Lead-acid lasts longest kept to about 0.5 — the 1,000 Wh example needs a 2,000 Wh bank for that reason — while lithium iron phosphate systems commonly plan on 0.8. Deeper discharge shrinks the bank you must buy and shortens its life; the trade-off is economic, and this field is where you price it.
No — those are power devices, sized from the largest simultaneous load (and its surge) and from the array's current, not from daily energy. This page sizes the two energy components, panels and battery bank, as a first-pass estimate. Controller, inverter, cabling and protection need their own calculations and a qualified installer's sign-off.
Divide by the wattage of the panel you are buying and round up: 888.89 ÷ 400 W panels = 2.22, so 3 panels (1,200 W nameplate). Arrays are always rounded up to whole panels, and the spare headroom is useful — it covers the days that fall short of the average sun-hours figure you designed with.
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