Formula Used
Appliance energy: watts × quantity × hours per day.
Design daily load: daily load × (1 + load growth percentage).
DC daily energy: design daily load ÷ inverter efficiency.
Required array watts: DC daily energy ÷ peak sun hours ÷ solar derate factor.
Panel count: required array watts ÷ panel watt rating, rounded upward.
Battery watt hours: DC daily energy × autonomy days ÷ depth of discharge ÷ battery efficiency.
Battery amp hours: battery watt hours ÷ system voltage.
Controller amps: actual array watts ÷ system voltage × controller margin.
How to Use This Calculator
First, enter appliance watts, quantity, and hours. Use real nameplate values when possible.
Second, enter manual daily watt hours only when you already know your daily energy use.
Third, choose system voltage, panel size, sun hours, and loss percentage.
Fourth, set battery reserve days, discharge limit, and battery efficiency.
Finally, press the calculate button. Review panel count, battery size, inverter rating, and controller current.
Off-Grid Solar Planning
An off-grid solar system must serve the load every day. It also needs reserve energy for cloudy weather. Good sizing starts with watt hours. Each appliance uses watts for a set time. The calculator totals those loads, adds growth, then accounts for inverter loss. This gives a safer daily energy target.
Panel Sizing
Solar panels are sized from daily energy and peak sun hours. Peak sun hours are not daylight hours. They are the usable solar energy for one average day. Losses from heat, dust, wire runs, charge control, and panel angle reduce output. A derate value makes the array more realistic. The tool divides adjusted energy by sun hours and usable output. It then rounds panels upward.
Battery Storage
Battery banks keep the system alive after sunset. They also cover cloudy days. Battery depth of discharge protects battery life. A lower discharge limit needs a larger bank. Battery efficiency also matters. Charging and discharging waste some energy. The calculator converts needed storage into watt hours and amp hours at the selected system voltage. This helps compare 12, 24, and 48 volt designs.
Inverter and Controller
The inverter must handle running load. It should also handle startup surge. Motors, pumps, and compressors can surge hard. The calculator adds a margin to the entered peak load. It estimates surge capacity from your selected factor. Charge controller current is based on array watts and battery voltage. Extra margin helps the controller stay within rating.
Using the Results
Use the panel count as a planning target. Use the battery amp hour value for bank design. Choose real parts that meet or exceed the results. Check local codes before installing wiring. Confirm roof area, shade, cable distance, and battery ventilation. For critical cabins, clinics, farms, and telecom sites, add more reserve. Recheck the design whenever loads change. A small new appliance can affect the battery and array. Conservative inputs usually produce a more dependable system.
Cost and Expansion
The calculator does not price hardware. It still supports better budgeting. Larger panels may reduce future upgrades. Higher voltage systems can reduce current. That can lower cable size. Leave space for more panels, breakers, and batteries when the site may grow later safely.
FAQs
1. What are peak sun hours?
Peak sun hours measure usable solar energy, not total daylight. A site may have ten daylight hours but only five strong solar hours for production estimates.
2. Why does the calculator use system losses?
Panels rarely produce full rated output all day. Heat, dust, wiring, controller loss, and tilt can reduce output. Loss percentage makes sizing more realistic.
3. Should I choose 12, 24, or 48 volts?
Small systems can use 12 volts. Medium systems often use 24 volts. Larger systems usually benefit from 48 volts because current is lower.
4. What does autonomy mean?
Autonomy is the number of days your battery bank should support the load without enough solar charging. More autonomy needs more battery capacity.
5. Why is depth of discharge important?
Depth of discharge controls how much stored energy you plan to use. Lower discharge improves battery life but requires a larger battery bank.
6. How should I size the inverter?
Use the highest running load and add safety margin. Also check surge loads from motors, pumps, refrigerators, and compressors before buying equipment.
7. Is the PDF download generated by the page?
Yes. The page creates a simple PDF result summary from the submitted values. It also provides a CSV file for spreadsheets.
8. Can this replace a professional design?
No. It is a planning calculator. Final wiring, protection, grounding, battery ventilation, and code checks should be reviewed by a qualified installer.