Plan off-grid energy with dependable sizing guidance. Model daily demand, battery reserve, and production losses. Build resilient systems using balanced assumptions and safety margins.
| Appliance | Qty | Watts | Hours/day | Duty % | Daily Wh |
|---|---|---|---|---|---|
| LED Lights | 8 | 10 | 5 | 100 | 400 |
| Ceiling Fan | 4 | 60 | 8 | 100 | 1,920 |
| Refrigerator | 1 | 150 | 10 | 40 | 600 |
| Laptop | 2 | 65 | 6 | 100 | 780 |
| Water Pump | 1 | 750 | 0.5 | 100 | 375 |
| Total | 4,075 | ||||
With 5.5 peak sun hours, 2 autonomy days, 24 V system voltage, and the default assumptions, this example typically lands near a 1.4 to 1.7 kW array and about a 12 kWh battery bank.
1) Appliance daily energy: Daily Wh = Quantity × Watts × Hours per day × Duty cycle.
2) Adjusted daily load: Adjusted Wh/day = Daily load × Seasonal factor × Growth factor × Safety factor.
3) Required PV production: Required PV Wh/day = Adjusted daily load ÷ (Inverter efficiency × Controller efficiency × Wiring efficiency × Panel derate).
4) Solar array size: PV array watts = Required PV Wh/day ÷ Peak sun hours.
5) Battery storage: Battery Wh = (Adjusted daily load × Autonomy days) ÷ (Maximum depth of discharge × Battery efficiency × Inverter efficiency).
6) Battery amp-hours: Battery Ah = Battery Wh ÷ System voltage.
7) Inverter continuous size: Continuous inverter W = Sum of running watts × Coincidence factor × Safety factor.
8) Controller current: Controller A = (PV array watts ÷ System voltage) × 1.25.
These equations provide a practical planning estimate. Final equipment selection should still consider local climate, cable lengths, code requirements, ambient temperature, battery chemistry, and actual panel orientation.
Peak sun hours represent the equivalent number of full-sun hours received in a day. It is not daylight length. It is the solar energy intensity converted into an easy sizing value.
Seasonal factor increases energy demand or reduces expected solar harvest for difficult months. It helps avoid undersizing when winter irradiance drops or appliance use rises.
Many loads do not run continuously. Refrigerators, pumps, and compressors cycle on and off. Duty cycle converts their nameplate power into a more realistic daily energy estimate.
Depth of discharge determines how much of the battery you plan to use. Lower discharge limits improve battery life but require a larger nominal battery bank.
The inverter is sized for instantaneous power and startup surge. The solar array is sized for daily energy replacement. One handles watts now; the other handles watt-hours over time.
Coincidence factor estimates how much running power is active at the same time. It keeps inverter sizing practical when not every appliance runs simultaneously.
Yes. Adjust depth of discharge, efficiency, and battery unit details to reflect the chemistry. Lithium systems usually allow higher usable capacity and better efficiency than lead-acid banks.
No. This is a planning calculator. Final designs should confirm wire sizing, protective devices, local code, ambient temperature, panel orientation, and actual equipment datasheets.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.