Solar Sizing Tool

Off Grid Panel Count Calculator

Size panels from usage, losses, and sunlight. Compare wattage options, autonomy days, and safety margins. Get answers for cabins, vans, boats, farms, and backups.

Calculator inputs

The page stays in a single-column flow, while the form uses three columns on large screens, two on small screens, and one on mobile.

Total daily appliance consumption.
Use conservative seasonal sunlight.
Rated power per module.
MPPT values often sit high.
Use full-load realistic efficiency.
Useful for off-grid storage losses.
Cables, mismatch, and small drops.
Heat, dust, and real conditions.
Winter bias or cloudy season allowance.
Extra headroom for surprises.
Days the battery should cover.
How quickly you want recovery.
Typical values: 12, 24, 48.
Helps estimate bank target size.
Optional roof-fit check input.
Optional usable surface area.

Example data table

Scenario Daily Load Sun Hours Panel Watt Recommended Panels Array Wattage Battery Target
Remote cabin baseline 4,800 Wh 5.2 h 450 W 8 3,600 W 272 Ah @ 48 V
Weekend farm shed 2,600 Wh 4.8 h 410 W 6 2,460 W 196 Ah @ 24 V
Van power system 1,900 Wh 4.4 h 200 W 7 1,400 W 187 Ah @ 12 V

These examples show how panel count changes with energy use, sun availability, module size, and reserve strategy.

Formula used

1) Effective output factor
Effective Output Factor = Controller × Inverter × Battery × (1 − Wiring Loss) × (1 − Temperature Loss) × Seasonal Factor
2) Adjusted daily load
Adjusted Daily Load = Daily Load × (1 + Safety Margin)
3) Battery recovery energy per day
Battery Recovery per Day = (Daily Load × Autonomy Days ÷ Battery Efficiency) ÷ Recharge Days
4) Required daily generation
Required Daily Generation = Adjusted Daily Load + Battery Recovery per Day
5) Daily energy from one panel
Energy per Panel per Day = Panel Watt × Peak Sun Hours × Effective Output Factor
6) Recommended panel count
Recommended Panels = Ceiling(Required Daily Generation ÷ Energy per Panel per Day)
7) Battery target size
Battery Bank Wh = (Daily Load × Autonomy Days) ÷ (Usable DoD × Inverter Efficiency)
Battery Bank Ah = Battery Bank Wh ÷ System Voltage

How to use this calculator

  1. Enter your total daily energy use in watt-hours.
  2. Use conservative peak sun hours for the worst useful month.
  3. Provide the panel wattage you plan to buy.
  4. Fill in controller, inverter, battery, wiring, and temperature factors.
  5. Set a safety margin for cloudy days, growth, and uncertainty.
  6. Add autonomy and recharge days to reflect your backup strategy.
  7. Enter system voltage and usable depth of discharge for battery sizing.
  8. Press the button to view the result block above the form, then export the results as CSV or PDF.

FAQs

1) What does panel count really represent?

It is the number of modules needed to supply your adjusted daily energy target under the chosen sunlight and system-loss assumptions.

2) Why is there both a minimum count and a recommended count?

The minimum count covers raw daily load only. The recommended count adds margin and battery recovery, which better suits real off-grid operation.

3) Should I use average yearly sun hours?

For dependable off-grid design, use a conservative seasonal value instead of a flattering yearly average. It avoids under-sizing during weak solar months.

4) Why include battery efficiency in panel sizing?

Off-grid systems often charge batteries before serving loads. Battery losses mean the array must make more energy than the appliances finally consume.

5) What is a good safety margin?

Many designs use 10% to 25%, depending on weather variability, future load growth, and how much reliability you want from the array.

6) Does this calculator handle roof-fit checks?

Yes. Enter panel area and available mounting area to estimate maximum module count, area needed, and whether the surface appears sufficient.

7) Is battery autonomy always needed for panel count?

Not always. Some users size only for daily energy. This tool includes autonomy because many off-grid projects also need practical recovery planning.

8) Can this replace a full professional design?

No. It gives a strong planning estimate, but conductor sizing, controller limits, string voltage, shading, and local code checks still matter.

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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.