Solar Panel Wattage Calculator
Determine the solar system size required to cover your energy usage. Input daily consumption, sun hours, system losses, and backup needs to estimate panel count, roof area, inverter size, and battery storage.
Check your utility bill for average daily consumption.
Use solar resource maps for your location (typical range 3–6).
Accounts for inverter, temperature, wiring, and shading.
Optional: number of days you want batteries to cover without sun.
Lithium batteries typically allow 80–90% depth of discharge.
Required system size
7.06 kW
Number of panels
18
Roof area required
32.13 m²
Suggested inverter size
7.76 kW
Recommended battery capacity
37.5 kWh
Adjust based on desired time of backup and battery chemistry.
How to Use This Calculator
Gather energy usage data
Use your utility bills or energy monitor to determine average daily consumption in kilowatt-hours.
Enter site-specific solar resources
Peak sun hours reflect local climate conditions. Combine with realistic system losses to avoid oversizing.
Set battery autonomy preferences
Optional: choose how many days of backup you want and the allowable depth of discharge for your batteries.
Formula
System Size = Daily Load ÷ (Sun Hours × (1 − Losses))
Panels = System Size × 1000 ÷ Panel Wattage
Battery Capacity = Daily Load × Autonomy ÷ Depth of Discharge
Example: 30 kWh/day ÷ (5 h × 0.85) = 7.06 kW. With 400 W panels, you need 18 panels and ~32 m² of roof area.
A two-day autonomy battery with 80% depth of discharge requires 75 kWh of usable capacity.
About the Solar Panel Wattage Calculator
Properly sizing a solar PV system ensures reliable performance and avoids unnecessary costs. This calculator links household consumption to array wattage, panel count, inverter sizing, and optional battery storage in one view.
When to Use This Calculator
- Off-grid planning: Determine array and battery capacity for remote cabins.
- Grid-tied systems: Size rooftop arrays to offset a percentage of utility usage.
- Energy audits: Pair consumption data with solar design to set efficiency targets.
- Classroom demonstrations: Teach solar sizing principles in engineering or sustainability courses.
Why Use Our Calculator?
- ✅ End-to-end sizing: Links loads, panels, roof area, and batteries.
- ✅ Adaptable: Use different panel wattages or losses to fit real projects.
- ✅ Backup ready: Integrates battery autonomy calculations automatically.
- ✅ Fast iteration: Update values instantly to test energy efficiency improvements.
Common Applications
Solar installers: Provide quick pre-design estimates during client consultations.
Homeowners: Understand how usage reductions affect required system size.
NGOs: Evaluate rural electrification setups with known energy needs.
Tips for Best Results
- Improve energy efficiency first to reduce the required array size.
- Use higher losses (20–25%) for hot climates or flat roof ballast systems.
- Check battery manufacturer specs for recommended depth of discharge.
- Revisit sun hours seasonally if your location has large fluctuations.
Frequently Asked Questions
Do I need to include future load growth?
Yes. If you plan to add EV charging or electric heating, increase the daily load input to account for future consumption.
Can I use smaller panels?
Adjust the panel wattage and area constants to match the modules you intend to purchase.
Why add 10% to inverter size?
A small oversizing margin prevents clipping during peak production and accommodates future module upgrades.
How accurate is the battery calculation?
It provides a baseline. Consider battery efficiency, temperature derating, and inverter losses for detailed designs.