Solar Requirement Calculator
Example Data Table
| Use Case | Daily Energy | Peak Sun | Battery Voltage | Panel Size | Reserve |
|---|---|---|---|---|---|
| Small cabin | 3 kWh | 5 hours | 24 V | 400 W | 20% |
| Home backup | 8 kWh | 4.5 hours | 48 V | 450 W | 25% |
| Workshop | 12 kWh | 5.5 hours | 48 V | 550 W | 30% |
Formula Used
Daily energy: Daily Wh = Daily kWh × 1000, or Load watts × Hours × Quantity.
DC energy needed: DC Wh = Daily AC Wh ÷ Inverter efficiency.
Solar array size: Array W = DC Wh ÷ Peak sun hours ÷ System efficiency × Reserve factor.
Panel count: Panels = Ceiling(Array W ÷ Panel W).
Battery storage: Battery Wh = Daily DC Wh × Autonomy days ÷ Depth of discharge.
Battery amp hours: Battery Ah = Battery Wh ÷ Battery bank voltage.
Controller current: Controller A = Array W ÷ Battery voltage × 1.25.
Inverter surge: Surge W = Maximum AC load × Surge factor.
How To Use This Calculator
Enter your known daily kWh if you already have measured energy use.
If you do not know daily kWh, enter load watts, use hours, and quantity.
Add local peak sun hours from a solar map or site survey.
Enter realistic efficiency values for wiring, heat, controller, and inverter loss.
Choose autonomy days and discharge depth for battery backup planning.
Press Calculate to see panel size, battery size, inverter size, and controller current.
Use CSV or PDF buttons to save the same result.
Why Solar Requirement Planning Matters
Solar planning is more than matching panels to a roof. A good design starts with the load. Every fan, light, pump, charger, and appliance adds demand. The calculator converts that demand into daily watt hours. It then includes sunlight, efficiency loss, battery reserve, and inverter demand. This gives a stronger estimate than a simple panel count.
Daily Energy Comes First
The main input is daily energy use. You can enter known kilowatt hours from a bill. You can also enter load watts and hours per day. The tool uses the higher available method when the daily value is supplied. This helps users compare measured use with appliance based planning.
Panel Sizing Method
Panel wattage is based on peak sun hours. Peak sun hours are not the same as daylight hours. They represent useful full strength sunlight. Dust, wiring, heat, controller loss, and battery charging loss reduce output. The efficiency field handles these losses. The reserve margin adds extra capacity for cloudy weather and aging panels.
Battery and Inverter Planning
Batteries should not be drained fully. The depth of discharge value protects battery life. Autonomy days estimate how long the system should run without strong sun. The calculator converts stored watt hours into amp hours using battery bank voltage. This is useful for comparing 12 volt, 24 volt, and 48 volt systems.
The inverter section checks continuous load and surge load. Motors, pumps, fridges, and compressors may start with high surge current. A larger inverter can handle these short peaks better. The result still needs review by a qualified installer for code, protection devices, cable size, grounding, and safe disconnects.
Using the Results
Use the panel count as a planning number. Round up because panels are sold in fixed sizes. Use the controller current to choose a charge controller with suitable safety margin. Use battery amp hours to plan battery bank strings. Always confirm local irradiance, roof direction, shading, temperature, and electrical rules before buying equipment.
Advanced Checks
Large systems also need voltage drop checks. Long cable runs waste power and cause heating. Mounting angle affects winter production. A site with shade may need more panels or different strings. Treat every result as a design estimate.
FAQs
What is peak sun hour?
Peak sun hour means one hour of full strength solar energy. It is not total daylight. A site may have ten daylight hours but only five peak sun hours.
Why is system efficiency important?
Panels rarely deliver full rated output all day. Heat, dust, wiring loss, controller loss, and battery charging loss reduce production. Efficiency gives a more realistic estimate.
Should I use daily kWh or load watts?
Use daily kWh when you have measured energy use. Use load watts and hours when designing for listed appliances. Measured data is usually more reliable.
Why does battery depth of discharge matter?
Most batteries last longer when they are not fully drained. A lower discharge limit increases required storage but helps protect battery life.
What inverter size should I choose?
Choose an inverter above your maximum simultaneous AC load. Add reserve margin. Check surge ratings for motors, pumps, refrigerators, and compressors.
Why is the charge controller current higher?
The calculator adds a 1.25 safety factor. This gives margin for strong sun, cold panel voltage changes, and safer controller selection.
Can this replace a professional design?
No. It gives planning values. A qualified installer should confirm wiring, breakers, fuses, grounding, disconnects, roof mounting, and local electrical rules.
Why should I round panel count up?
Solar panels are sold in fixed watt sizes. Rounding up helps cover real losses, aging, cloudy periods, and small future load increases.