Off-Grid Solar and Battery Sizer
Size the solar array and battery bank for a remote site, camera, radio or edge server.
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How to Use It
Enter the average load in watts (for a site that runs around the clock), the peak sun hours in your worst month, how many sunless days the batteries must cover and the usable battery depth. You get a minimum array size and a battery bank size.
How This Calculator Works
The calculator runs these formulas in your browser:
- Daily energy (Wh) = average load (W) × 24
- Array (W) = daily Wh ÷ peak sun hours ÷ 0.75
- Battery (Wh) = daily Wh × days of autonomy ÷ usable depth ÷ 0.9
- Amp-hours = battery Wh ÷ system voltage (24 V or 48 V)
Default assumptions and sources
Use the worst month's peak sun hours for your exact location from NREL PVWatts. The 0.75 factor allows for heat, dust, wiring and charge-controller losses; the 0.9 covers inverter or converter losses.
Worked example
A 150 W site that runs all day needs 3,600 Wh a day. With 3.5 peak sun hours in the worst month, the array is 3,600 ÷ 3.5 ÷ 0.75 = about 1,370 W. Three days of autonomy at 80% usable depth needs 3,600 × 3 ÷ 0.8 ÷ 0.9 = 15,000 Wh, a 15 kWh bank: about 625 Ah at 24 V or 313 Ah at 48 V.
Limits
It assumes a steady load and the same sun every day of the worst month. Cold cuts battery capacity, panels lose output as they age, and loads tend to grow, so most designers add 20 to 30% margin on top.
Common Questions
Where do I find peak sun hours?
Use solar resource data for your exact location, such as NREL's PVWatts calculator, and pick the worst month, usually December or January in the U.S.
How many days of autonomy do I need?
Two to five days is common for remote monitoring. Critical sites, cloudy climates and hard-to-reach locations justify more.
Why is the array bigger than the math suggests?
The 0.75 factor covers heat, dust, wiring, charge controller and battery losses. Real systems also add margin for panel aging and load growth.