Input Details
Example Data Table
This example shows a simple daily load profile that can be entered into the calculator as a combined daily energy requirement.
| Appliance | Quantity | Power (W) | Hours/Day | Daily Energy (Wh) |
|---|---|---|---|---|
| LED Lights | 8 | 12 | 5 | 480 |
| Ceiling Fans | 4 | 70 | 8 | 2,240 |
| Refrigerator | 1 | 180 | 10 | 1,800 |
| Laptop | 2 | 60 | 5 | 600 |
| Wi-Fi Router | 1 | 15 | 24 | 360 |
| Water Pump | 1 | 300 | 0.2 | 60 |
| Total Daily Energy | 5,540 Wh | |||
Formula Used
1) Base daily load: Daily Load (Wh) = Daily Energy (kWh) × 1000
2) Performance ratio: Performance Ratio = (1 − Losses) × Inverter Efficiency
3) Adjusted daily load: Adjusted Load = Daily Load × (1 + Safety Margin) ÷ Performance Ratio
4) Required solar array: Array Watts = Adjusted Load ÷ Peak Sun Hours
5) Panel count: Panels = Ceiling(Array Watts ÷ Panel Wattage)
6) Battery bank energy: Battery Bank (Wh) = Daily Load × Autonomy Days ÷ DoD
7) Battery bank amp-hours: Battery Ah = Battery Bank (Wh) ÷ System Voltage
8) Inverter size: Recommended Inverter = Peak Load × (1 + Surge Margin)
9) Controller current: Controller Current ≈ Installed Array Watts ÷ System Voltage × 1.25
How to Use This Calculator
- Enter the total daily energy use in kWh for all connected loads.
- Enter the highest simultaneous load to estimate inverter size.
- Use realistic peak sun hours for your location, not daylight hours.
- Enter system losses and inverter efficiency to reflect practical performance.
- Choose the battery autonomy period and permitted depth of discharge.
- Provide panel wattage, panel area, battery voltage, and battery capacity.
- Click Calculate Requirement to view the results above the form.
- Use the CSV and PDF buttons to save your calculated summary.
Frequently Asked Questions
1) What does this calculator estimate?
It estimates required solar array wattage, recommended inverter size, battery bank capacity, controller current, panel count, array area, and projected monthly production against demand.
2) Why are peak sun hours different from daylight hours?
Peak sun hours represent equivalent full-strength solar irradiance, not total daylight. A location may have ten daylight hours but only five effective peak sun hours.
3) Should I size from average conditions or the worst month?
For reliable off-grid design, engineers often size around the weaker solar season. Average conditions can look adequate annually while still causing shortages in poor months.
4) Why include system losses and inverter efficiency?
Real systems lose energy through wiring, temperature, dust, controller conversion, and inversion. Ignoring these factors usually undersizes the system and reduces reliability.
5) How is battery quantity estimated?
The estimate uses your selected system voltage, battery voltage, battery capacity, autonomy days, and allowable discharge. It assumes identical batteries arranged into simple series and parallel strings.
6) Does this calculator work for grid-connected systems?
Yes, it can still estimate array size and production. However, battery autonomy and off-grid reserve values matter far less for a simple grid-tied installation.
7) Why should I add a safety margin?
A safety margin helps absorb future load growth, cloudy-day variability, module aging, and minor design uncertainties without immediate underperformance.
8) Is the panel count always exact?
No. Panel count is rounded up to the next whole module. Final layouts may change because of roof geometry, string voltage limits, and equipment selection.